The essential role of aggregation for the emulsifying ability of a fungal CYS-rich protein.

Biosurfactants are in demand by the global market as natural commodities suitable for incorporation into commercial products or utilization in environmental applications. Fungi are promising producers of these molecules and have garnered interest also for their metabolic capabilities in efficiently utilizing recalcitrant and complex substrates, like hydrocarbons, plastic, etc. Within this framework, biosurfactants produced by two Fusarium solani fungal strains, isolated from plastic waste-contaminated landfill soils, were analyzed. Mycelia of these fungi were grown in the presence of 5% olive oil to drive biosurfactant production. The characterization of the emulsifying and surfactant capacity of these extracts highlighted that two different components are involved. A protein was purified and identified as a CFEM (common in fungal extracellular membrane) containing domain, revealing a good propensity to stabilize emulsions only in its aggregate form. On the other hand, an unidentified cationic smaller molecule exhibits the ability to reduce surface tension. Based on the 3D structural model of the protein, a plausible mechanism for the formation of very stable aggregates, endowed with the emulsifying ability, is proposed. KEY POINTS: • Two Fusarium solani strains are analyzed for their surfactant production. • A cationic surfactant is produced, exhibiting the ability to remarkably reduce surface tension. • An identified protein reveals a good propensity to stabilize emulsions only in its aggregate form.

Production, characterization, and application of Pseudoxanthomonas taiwanensis biosurfactant: a green chemical for microbial enhanced oil recovery (MEOR).

Biosurfactants, as microbial bioproducts, have significant potential in the field of microbial enhanced oil recovery (MEOR). Biosurfactants are microbial bioproducts with the potential to reduce the interfacial tension (IFT) between crude oil and water, thus enhancing oil recovery. This study aims to investigate the production and characterization of biosurfactants and evaluate their effectiveness in increasing oil recovery. Pseudoxanthomonas taiwanensis was cultured on SMSS medium to produce biosurfactants. Crude oil was found to be the most effective carbon source for biosurfactant production. The biosurfactants exhibited comparable activity to sodium dodecyl sulfate (SDS) at a concentration of 400 ppm in reducing IFT. It was characterized as glycolipids, showing stability in emulsions at high temperatures (up to 120 °C), pH levels ranging from 3 to 9, and NaCl concentrations up to 10% (w/v). Response surface methodology revealed the optimized conditions for the most stable biosurfactants (pH 7, temperature of 40 °C, and salinity of 2%), resulting in an EI24 value of 64.45%. Experimental evaluations included sand pack column and core flooding studies, which demonstrated additional oil recovery of 36.04% and 12.92%, respectively. These results indicate the potential application of P. taiwanensis biosurfactants as sustainable and environmentally friendly approaches to enhance oil recovery in MEOR processes.

Promising Application, Efficient Production, and Genetic Basis of Mannosylerythritol Lipids.

Mannosylerythritol lipids (MELs) are a class of glycolipids that have been receiving increasing attention in recent years due to their diverse biological activities. MELs are produced by certain fungi and display a range of bioactivities, making them attractive candidates for various applications in medicine, agriculture, and biotechnology. Despite their remarkable qualities, industrial-scale production of MELs remains a challenge for fungal strains. Excellent fungal strains and fermentation processes are essential for the efficient production of MELs, so efforts have been made to improve the fermentation yield by screening high-yielding strains, optimizing fermentation conditions, and improving product purification processes. The availability of the genome sequence is pivotal for elucidating the genetic basis of fungal MEL biosynthesis. This review aims to shed light on the applications of MELs and provide insights into the genetic basis for efficient MEL production. Additionally, this review offers new perspectives on optimizing MEL production, contributing to the advancement of sustainable biosurfactant technologies.

Characterization of the surface-active exopolysaccharide produced by Halomonas sp TGOS-10: Understanding its role in the formation of marine oil snow.

In this study, we characterize the exopolymer produced by Halomonas sp. strain TGOS-10 -one of the organisms found enriched in sea surface oil slicks during the Deepwater Horizon oil spill. The polymer was produced during the early stationary phase of growth in Zobell's 2216 marine medium amended with glucose. Chemical and proton NMR analysis showed it to be a relatively monodisperse, high-molecular-mass (6,440,000 g/mol) glycoprotein composed largely of protein (46.6% of total dry weight of polymer). The monosaccharide composition of the polymer is typical to that of other marine bacterial exopolymers which are generally rich in hexoses, with the notable exception that it contained mannose (commonly found in yeast) as a major monosaccharide. The polymer was found to act as an oil dispersant based on its ability to effectively emulsify pure and complex oils into stable oil emulsions-a function we suspect to be conferred by the high protein content and high ratio of total hydrophobic nonpolar to polar amino acids (52.7:11.2) of the polymer. The polymer's chemical composition, which is akin to that of other marine exopolymers also having a high protein-to-carbohydrate (P/C) content, and which have been shown to effect the rapid and non-ionic aggregation of marine gels, appears indicative of effecting marine oil snow (MOS) formation. We previously reported the strain capable of utilising aromatic hydrocarbons when supplied as single carbon sources. However, here we did not detect biodegradation of these chemicals within a complex (surrogate Macondo) oil, suggesting that the observed enrichment of this organism during the Deepwater Horizon spill may be explained by factors related to substrate availability and competition within the complex and dynamic microbial communities that were continuously evolving during that spill.

Evaluation of surfactant-aided polycyclic aromatic hydrocarbon biodegradation by molecular docking and molecular dynamic simulation in the marine environment.

Marine oil spills directly cause polycyclic aromatic hydrocarbons (PAHs) pollution and affect marine organisms due to their toxic property. Chemical and bio-based dispersants composed of surfactants and solvents are considered effective oil spill-treating agents. Dispersants enhance oil biodegradation in the marine environment by rapidly increasing their solubility in the water column. However, the effect of dispersants, especially surfactants, on PAHs degradation by enzymes produced by microorganisms has not been studied at the molecular level. The role of the cytochrome P450 (CYP) enzyme in converting contaminants into reactive metabolites during the biodegradation process has been evidenced, but the activity in the presence of surfactants is still ambiguous. Thus, this study focused on the evaluation of the impact of chemical and bio-surfactants (i.e., Tween 80 (TWE) and Surfactin (SUC)) on the biodegradation of naphthalene (NAP), chrysene (CHR), and pyrene (PYR), the representative components of PAHs, with CYP enzyme from microalgae Parachlorella kessleri using molecular docking and molecular dynamics (MD) simulation. The molecular docking analysis revealed that PAHs bound to residues at the CYP active site through hydrophobic interactions for biodegradation. The MD simulation showed that the surfactant addition changed the enzyme conformation in the CYP-PAH complexes to provide more interactions between the enzyme and PAHs. This led to an increase in the enzyme's capability to degrade PAHs. Binding free energy (ΔG||Bind) calculations confirmed that surfactant treatment could enhance PAHs degradation by the enzyme. The SUC gave a better result on NAP and PYR biodegradation based on ΔG||Bind, while TWE facilitated the biodegradation of CHR. The research outputs could greatly facilitate evaluating the behaviors of oil spill-treating agents and oil spill response operations in the marine environment.

Surfactant-mediated bio-manufacture: A unique strategy for promoting microbial biochemicals production.

Biochemicals are widely used in the medicine and food industries and are more efficient and safer than synthetic chemicals. The amphipathic surfactants can interact with the microorganisms and embed the extracellular metabolites, which induce microbial metabolites secretion and biosynthesis, performing an attractive prospect of promoting the biochemical production. However, the commonness and differences of surfactant-mediated bio-manufacture in various fields are largely unexplored. Accordingly, this review comprehensively summarized the properties of surfactants, different application scenarios of surfactant-meditated bio-manufacture, and the mechanism of surfactants increasing metabolites production. Various biochemical productions such as pigments, amino acids, and alcohols could be enhanced using the cloud point and the micelles of surfactants. Besides, the amphiphilicity of surfactants also promoted the utilization of fermentation substrates, especially lignocellulose and waste sludge, by microorganisms, indirectly increasing the metabolites production. The increase in target metabolites production was attributed to the surfactants changing the permeability and composition of the cell membrane, hence improving the secretion ability of microorganisms. Moreover, surfactants could regulate the energy metabolism, the redox state and metabolic flow in microorganisms, which induced target metabolites synthesis. This review aimed to broaden the application fields of surfactants and provide novel insights into the production of microbial biochemicals.

Advanced surface passivation for high-sensitivity studies of biomolecular condensates.

Biomolecular condensates are cellular compartments that concentrate biomolecules without an encapsulating membrane. In recent years, significant advances have been made in the understanding of condensates through biochemical reconstitution and microscopic detection of these structures. Quantitative visualization and biochemical assays of biomolecular condensates rely on surface passivation to minimize background and artifacts due to condensate adhesion. However, the challenge of undesired interactions between condensates and glass surfaces, which can alter material properties and impair observational accuracy, remains a critical hurdle. Here, we introduce an efficient, broadly applicable, and simple passivation method employing self-assembly of the surfactant Pluronic F127 (PF127). The method greatly reduces nonspecific binding across a range of condensates systems for both phase-separated droplets and biomolecules in dilute phase. Additionally, by integrating PF127 passivation with the Biotin-NeutrAvidin system, we achieve controlled multipoint attachment of condensates to surfaces. This not only preserves condensate properties but also facilitates long-time fluorescence recovery after photobleaching imaging and high-precision single-molecule analyses. Using this method, we have explored the dynamics of polySIM molecules within polySUMO/polySIM condensates at the single-molecule level. Our observations suggest a potential heterogeneity in the distribution of available polySIM-binding sites within the condensates.

Food wastes for bioproduct production and potential strategies for high feedstock variability.

Unavoidable food wastes could be an important feedstock for industrial biotechnology, while their valorization could provide added value for the food processor. However, despite their abundance and low costs, the heterogeneous/mixed nature of these food wastes produced by food processors and consumers leads to a high degree of variability in carbon and nitrogen content, as well as specific substrates, in food waste hydrolysate. This has limited their use for bioproduct synthesis. These wastes are often instead used in anaerobic digestion and mixed microbial culture, creating a significant knowledge gap in their use for higher value biochemical production via pure and single microbial culture. To directly investigate this knowledge gap, various waste streams produced by a single food processor were enzymatically hydrolyzed and characterized, and the degree of variability with regard to substrates, carbon, and nitrogen was quantified. The impact of hydrolysate variability on the viability and performance of polyhydroxyalkanoates biopolymers production using bacteria (Cupriavidus necator) and archaea (Haloferax mediterranei) as well as sophorolipids biosurfactants production with the yeast (Starmerella bombicola) was then elucidated at laboratory-scale. After which, strategies implemented during this experimental proof-of-concept study, and beyond, for improved industrial-scale valorization which addresses the high variability of food waste hydrolysate were discussed in-depth, including media standardization and high non-selective microbial organisms growth-associated product synthesis. The insights provided would be beneficial for future endeavors aiming to utilize food wastes as feedstocks for industrial biotechnology.

Identification and Functional Characterization of a Surfactant-like Protein Region in Flagellin FliC for Stabilizing Selenium Nanoparticles and Enhancing Bioavailability.

Biogenic selenium nanoparticles (SeNPs) are the most favorable Se form for nutritional supplementation due to their high stability, low toxicity, and high activity. However, the interaction between the surface-binding proteins and their stable biogenic SeNPs, as well as their impact on the stability and bioavailability of SeNPs, remains to be understood. In vitro stabilization experiments revealed an amino acid segment (F(235-386)) in Rahnella aquatilis' flagellin FliC, with surfactant-like properties, stabilizing SeNPs under harsh conditions. FliC and F(235-386) were employed as stabilizers to synthesize SeNPs (FliC@SeNPs and F(235-386)@SeNPs), and surface chemistry analysis revealed coordination reactions between the proteins and Se atoms on the surface of SeNPs. Both FliC and F(235-386) enhanced SeNPs uptake in wheat seedlings but reduced it in bacteria and yeast. This study highlights FliC's core function in stabilizing SeNPs and enhancing their bioavailability, paving the way for agricultural and nutritional applications.

A Rare Mono-Rhamnolipid Congener Efficiently Produced by Recombinant Pseudomonas aeruginosa YM4 via the Expression of Global Transcriptional Regulator irrE.

Rhamnolipids (RLs) are widely used biosurfactants produced mainly by Pseudomonas aeruginosa and Burkholderia spp. in the form of mixtures of diverse congeners. The global transcriptional regulator gene irrE from radiation-tolerant extremophiles has been widely used as a stress-resistant element to construct robust producer strains and improve their production performance. A PrhlA-irrE cassette was constructed to express irrE genes in the Pseudomonas aeruginosa YM4 of the rhamnolipids producer strain. We found that the expression of irrE of Deinococcus radiodurans in the YM4 strain not only enhanced rhamnolipid production and the strain's tolerance to environmental stresses, but also changed the composition of the rhamnolipid products. The synthesized rhamnolipids reached a maximum titer of 26 g/L, about 17.9% higher than the original, at 48 h. The rhamnolipid production of the recombinant strain was determined to be mono-rhamnolipids congener Rha-C10-C12, accounting for 94.1% of total products. The critical micelle concentration (CMC) value of the Rha-C10-C12 products was 62.5 mg/L and the air-water surface tension decreased to 25.5 mN/m. The Rha-C10-C12 products showed better emulsifying activity on diesel oil than the original products. This is the first report on the efficient production of the rare mono-rhamnolipids congener Rha-C10-C12 and the first report that the global regulator irrE can change the components of rhamnolipid products in Pseudomonas aeruginosa.

Synthesis and characterization of iron oxide nanoparticles from Lawsonia inermis and its effect on the biodegradation of crude oil hydrocarbon.

Crude oil hydrocarbons are considered major environmental pollutants and pose a significant threat to the environment and humans due to having severe carcinogenic and mutagenic effects. Bioremediation is one of the practical and promising technology that can be applied to treat the hydrocarbon-polluted environment. In this present study, rhamnolipid biosurfactant (BS) produced by Pseudomonas aeruginosa PP4 and green synthesized iron nanoparticles (G-FeNPs) from Lawsonia inermis was used to evaluate the biodegradation efficiency (BE) of crude oil. The surface analysis of G-FeNPs was carried out by using FESEM and HRTEM to confirm the size and shape. Further, the average size of the G-FeNPs was observed around 10 nm by HRTEM analysis. The XRD and Raman spectra strongly confirm the presence of iron nanoparticles with their respective peaks. The BE (%) of mixed degradation system-V (PP4+BS+G-FeNPs) was obtained about 82%. FTIR spectrum confirms the presence of major functional constituents (C=O, -CH3, C-O, and OH) in the residual oil content. Overall, this study illustrates that integrated nano-based bioremediation could be an efficient approach for hydrocarbon-polluted environments. This study is the first attempt to evaluate the G-FeNPs with rhamnolipid biosurfactant on the biodegradation of crude oil.

Simultaneous production of biosurfactant and extracellular unspecific peroxygenases by Moesziomyces aphidis XM01 enables an efficient strategy for crude oil degradation.

Crude oil is a hazardous pollutant that poses significant and lasting harm to human health and ecosystems. In this study, Moesziomyces aphidis XM01, a biosurfactant mannosylerythritol lipids (MELs)-producing yeast, was utilized for crude oil degradation. Unlike most microorganisms relying on cytochrome P450, XM01 employed two extracellular unspecific peroxygenases, MaUPO.1 and MaUPO.2, with preference for polycyclic aromatic hydrocarbons (PAHs) and n-alkanes respectively, thus facilitating efficient crude oil degradation. The MELs produced by XM01 exhibited a significant emulsification activity of 65.9% for crude oil and were consequently supplemented in an "exogenous MELs addition" strategy to boost crude oil degradation, resulting in an optimal degradation ratio of 72.3%. Furthermore, a new and simple "pre-MELs production" strategy was implemented, achieving a maximum degradation ratio of 95.9%. During this process, the synergistic up-regulation of MaUPO.1, MaUPO.1 and the key MELs synthesis genes contributed to the efficient degradation of crude oil. Additionally, the phylogenetic and geographic distribution analysis of MaUPO.1 and MaUPO.1 revealed their wide occurrence among fungi in Basidiomycota and Ascomycota, with high transcription levels across global ocean, highlighting their important role in biodegradation of crude oil. In conclusion, M. aphidis XM01 emerges as a novel yeast for efficient and eco-friendly crude oil degradation.

Modular metabolic engineering of Bacillus amyloliquefaciens for high-level production of green biosurfactant iturin A.

As a kind of biosurfactants, iturin A has attracted people's wide attentions due to their features of biodegradability, environmentally friendly, etc.; however, high production cost limited its extensive application, and the aim of this research wants to improve iturin A production in Bacillus amyloliquefaciens. Firstly, dual promoter was applied to strengthen iturin A synthetase expression, and its yield was increased to 1.25 g/L. Subsequently, original 5'-UTRs of downstream genes (ituA, ituB, and ituC) in iturin A synthetase cluster were optimized, which significantly increased mRNA secondary stability, and iturin A yield produced by resultant strain HZ-T3 reached 2.32 g/L. Secondly, synthetic pathway of α-glucosidase inhibitor 1-deoxynojirimycin was blocked to improve substrate corn starch utilization, and iturin A yield was increased by 34.91% to 3.13 g/L. Thirdly, efficient precursor (fatty acids, Ser, and Pro) supplies were proven as the critical role in iturin A synthesis, and 5.52 g/L iturin A was attained by resultant strain, through overexpressing yngH, serC, and introducing ocD. Meanwhile, genes responsible for poly-γ-glutamic acid, extracellular polysaccharide, and surfactin syntheses were deleted, which led to a 30.98% increase of iturin A yield. Finally, lipopeptide transporters were screened, and iturin A yield was increased by 17.98% in SwrC overexpression strain, reached 8.53 g/L, which is the highest yield of iturin A ever reported. This study laid a foundation for industrial production and application development of iturin A, and provided the guidance of metabolic engineering breeding for efficient production of other metabolites synthesized by non-ribosomal peptide synthetase. KEY POINTS: • Optimizing 5'-UTR is an effective tactics to regulate synthetase cluster expression. • Blocking 1-DNJ synthesis benefited corn starch utilization and iturin A production. • The iturin A yield attained in this work was the highest yield reported so far.

The Combined Effects of Azoxystrobin and the Biosurfactant-Producing Bacillus sp. Kol B3 against the Phytopathogenic Fungus Fusarium sambucinum IM 6525.

This study aimed to evaluate how the combined presence of the synthetic fungicide azoxystrobin (AZ) and the biosurfactant-producing Bacillus sp. Kol B3 influences the growth of the phytopathogenic fungus Fusarium sambucinum IM 6525. The results showed a noticeable increase in antifungal effectiveness when biotic and abiotic agents were combined. This effect manifested across diverse parameters, including fungal growth inhibition, changes in hyphae morphology, fungal membrane permeability and levels of intracellular reactive oxygen species (ROS). In response to the presence of Fusarium and AZ in the culture, the bacteria changed the proportions of biosurfactants (surfactin and iturin) produced. The presence of both AZ and/or Fusarium resulted in an increase in iturin biosynthesis. Only in 72 h old bacterial-fungal co-culture a 20% removal of AZ was noted. In the fungal cultures (with and without the addition of the bacteria), the presence of an AZ metabolite named azoxystrobin free acid was detected in the 48th and 72nd hours of the process. The possible involvement of increased iturin and ROS content in antifungal activity of Bacillus sp. and AZ when used together are also discussed. Biosurfactants were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Microscopy techniques and biochemical assays were also used.

Hitching a Ride in the Phyllosphere: Surfactant Production of Pseudomonas spp. Causes Co-swarming of Pantoea eucalypti 299R.

Here, we demonstrate the beneficial effect of surfactant-producing pseudomonads on Pantoea eucalypti 299R. We conducted a series of experiments in environments of increasing complexity. P. eucalypti 299R (Pe299R), and Pseudomonas sp. FF1 (Pff1) or Pe299R and surfactant-production deficient Pseudomonas sp. FF1::ΔviscB (Pff1ΔviscB) were co-inoculated in broth, on swarming agar plates, and on plants. In broth, there were no differences in the growth dynamics of Pe299R when growing in the presence of Pff1 or Pff1ΔviscB. By contrast, on swarming agar plates, Pe299R was able to co-swarm with Pff1 which led to a significant increase in Pe299R biomass compared to Pe299R growing with Pff1ΔviscB or in monoculture. Finally in planta, and using the single-cell bioreporter for reproductive success (CUSPER), we found a temporally distinct beneficial effect of Pff1 on co-inoculated Pe299R subpopulations that did not occur in the presence of Pff1ΔviscB. We tested three additional surfactant-producing pseudomonads and their respective surfactant knockout mutants on PE299R on swarming agar showing similar results. This led us to propose a model for the positive effect of surfactant production during leaf colonization. Our results indicate that co-motility might be common during leaf colonization and adds yet another facet to the already manyfold roles of surfactants.

Microbial synergies drive simultaneous biodegradation of ethoxy and alkyl chains of Nonylphenol Ethoxylate in fluidized bed reactors.

The widely-used surfactant Nonylphenol Ethoxylate (NPEO) produces endocrine-disrupting compounds during biodegradation, with these byproducts being more harmful than untreated NPEO. This study investigates the effectiveness of a Fluidized Bed Reactor (FBR) in reducing the production of 4-Nonylphenol (4-NP) during the biodegradation of NPEO. Two identical FBR filled with sand were used to assess the NPEO degradation and to enhance the microbial consortia capable of breaking down the complex byproducts, ethanol and fumarate were introduced as co-substrates. Our findings demonstrate the significant potential of the FBR, especially when coupled with fumarate, for enhancing the surfactant degradation. It outperforms the efficiency achieved with ethanol as the primary electron donor, albeit with a higher rate of byproduct production. Microbial community taxonomy and metabolic prediction revealed the high abundance of Geobacter (1.51-31.71%) and Methanobacterium (1.08-13.81%) in non-conductive sand. This may hint a new metabolic interaction and expand our understanding of Direct Interspecies Electron Transfer (DIET) in bioreactors applied to micropollutants degradation. Such an intricate relationship between facultative and anaerobes working together to simultaneously biodegrade the ethoxy and alkyl chains presents a new perspective on NPEO degradation and can potentially be extended to other micropollutants.

Multiple pathways impact the swarming motility of Pseudomonas fluorescens Pf0-1.

Swarming motility in pseudomonads typically requires both a functional flagellum and the production/secretion of a biosurfactant. Published work has shown that the wild-type Pseudomonas fluorescens Pf0-1 is swarming deficient due to a point mutation in the gacA gene, which until recently was thought to inactivate rather than attenuate the Gac/Rsm pathway. As a result, little is known about the underlying mechanisms that regulate swarming motility by P. fluorescens Pf0-1. Here, we demonstrate that a ΔrsmA ΔrsmE ΔrsmI mutant, which phenotypically mimics Gac/Rsm pathway overstimulation, is proficient at swarming motility. RsmA and RsmE appear to play a key role in this regulation. Transposon mutagenesis of the ΔrsmA ΔrsmE ΔrsmI mutant identified multiple factors that impact swarming motility, including pathways involved in flagellar synthesis and biosurfactant production/secretion. We find that loss of genes linked to biosurfactant Gacamide A biosynthesis or secretion impacts swarming motility, as does loss of the alternative sigma factor FliA, which results in a defect in flagellar function. Collectively, these findings provide evidence that P. fluorescens Pf0-1 can swarm if the Gac/Rsm pathway is activated, highlight the regulatory complexity of swarming motility in this strain, and demonstrate that the cyclic lipopeptide Gacamide A is utilized as a biosurfactant for swarming motility.IMPORTANCESwarming motility is a coordinated process that allows communities of bacteria to collectively move across a surface. For P. fluorescens Pf0-1, this phenotype is notably absent in the parental strain, and to date, little is known about the regulation of swarming in this strain. Here, we identify RsmA and RsmE as key repressors of swarming motility via modulating the levels of biosurfactant production/secretion. Using transposon mutagenesis and subsequent genetic analyses, we further identify potential regulatory mechanisms of swarming motility and link Gacamide A biosynthesis and transport machinery to swarming motility.

Regulation mechanism and bioactivity characteristic of surfactin homologues with C14 and C15 fatty acid chains.

BACKGROUND: Surfactin, a green lipopeptide bio-surfactant, exhibits excellent surface, hemolytic, antibacterial, and emulsifying activities. However, a lack of clear understanding of the synthesis regulation mechanism of surfactin homologue components has hindered the customized production of surfactin products with different biological activities. RESULTS: In this study, exogenous valine and 2-methylbutyric acid supplementation significantly facilitated the production of C14-C15 surfactin proportions (up to 75% or more), with a positive correlation between the homologue proportion and fortified concentration. Subsequently, the branched-chain amino acid degradation pathway and the glutamate synthesis pathway are identified as critical pathways in regulating C14-C15 surfactin synthesis by transcriptome analysis. Overexpression of genes bkdAB and glnA resulted in a 1.4-fold and 1.3-fold increase in C14 surfactin, respectively. Finally, the C14-rich surfactin was observed to significantly enhance emulsification activity, achieving an EI24 exceeding 60% against hexadecane, while simultaneously reducing hemolytic activity. Conversely, the C15-rich surfactin demonstrated an increase in both hemolytic and antibacterial activities. CONCLUSION: This study presents the first evidence of a potential connection between surfactin homologue synthesis and the conversion of glutamate and glutamine, providing a theoretical basis for targeting the synthesis regulation and structure-activity relationships of surfactin and other lipopeptide compounds.

PAH bioremediation with Rhodococcus rhodochrous ATCC 21198: Impact of cell immobilization and surfactant use on PAH treatment and post-remediation toxicity.

Polycyclic aromatic hydrocarbons (PAHs) are prevalent environmental contaminants that are harmful to ecological and human health. Bioremediation is a promising technique for remediating PAHs in the environment, however bioremediation often results in the accumulation of toxic PAH metabolites. The objectives of this research were to demonstrate the cometabolic treatment of a mixture of PAHs by a pure bacterial culture, Rhodococcus rhodochrous ATCC 21198, and investigate PAH metabolites and toxicity. Additionally, the surfactant Tween ® 80 and cell immobilization techniques were used to enhance bioremediation. Total PAH removal ranged from 70-95% for fluorene, 44-89% for phenanthrene, 86-97% for anthracene, and 6.5-78% for pyrene. Maximum removal was achieved with immobilized cells in the presence of Tween ® 80. Investigation of PAH metabolites produced by 21198 revealed a complex mixture of hydroxylated compounds, quinones, and ring-fission products. Toxicity appeared to increase after bioremediation, manifesting as mortality and developmental effects in embryonic zebrafish. 21198's ability to rapidly transform PAHs of a variety of molecular structures and sizes suggests that 21198 can be a valuable microorganism for catalyzing PAH remediation. However, implementing further treatment processes to address toxic PAH metabolites should be pursued to help lower post-remediation toxicity in future studies.

Structure of the Bacterial Cell Envelope and Interactions with Antimicrobials: Insights from Molecular Dynamics Simulations.

Bacteria have evolved over 3 billion years, shaping our intrinsic and symbiotic coexistence with these single-celled organisms. With rising populations of drug-resistant strains, the search for novel antimicrobials is an ongoing area of research. Advances in high-performance computing platforms have led to a variety of molecular dynamics simulation strategies to study the interactions of antimicrobial molecules with different compartments of the bacterial cell envelope of both Gram-positive and Gram-negative species. In this review, we begin with a detailed description of the structural aspects of the bacterial cell envelope. Simulations concerned with the transport and associated free energy of small molecules and ions through the outer membrane, peptidoglycan, inner membrane and outer membrane porins are discussed. Since surfactants are widely used as antimicrobials, a section is devoted to the interactions of surfactants with the cell wall and inner membranes. The review ends with a discussion on antimicrobial peptides and the insights gained from the molecular simulations on the free energy of translocation. Challenges involved in developing accurate molecular models and coarse-grained strategies that provide a trade-off between atomic details with a gain in sampling time are highlighted. The need for efficient sampling strategies to obtain accurate free energies of translocation is also discussed. Molecular dynamics simulations have evolved as a powerful tool that can potentially be used to design and develop novel antimicrobials and strategies to effectively treat bacterial infections.