Recent advancements in the production of rhamnolipid biosurfactants by Pseudomonas aeruginosa.

Rhamnolipid (RL) biosurfactant which is produced by Pseudomonas species is one of the most effective surface-active agents investigated in the literature. Over the years, many efforts have been made and an array of techniques has been developed for the isolation of RL produced strains as well as RL homolog characterization. Reports show that RL productivity by the best-known producer, Pseudomonas aeruginosa, is very diverse, from less than 1 gr/l to more than 200 g L-1. There are some major parameters that can affect RL productivity. These are culture conditions, medium composition, the mode of operation (batch, fed-batch and continuous), bioengineering/gene manipulation and finally extraction methods. The present paper seeks to provide a comprehensive overview on the production of rhamnolipid biosurfactant by different species of Pseudomonas bacteria. In addition, we have extensively reviewed their potential for possible future applications.

Overproduction of rhamnolipid by fed-batch cultivation of Pseudomonas aeruginosa in a lab-scale fermenter under tight DO control.

Rhamnolipids are one of the most well-known classes of biosurfactants having wide applications in various industries due to low toxicity, high biodegradability, and environmentally friendly. Dissolved oxygen (DO) concentration has the crucial effect on rhamnolipids production, particularly through fed-batch cultivation. In this study, the effect of different levels of DO concentrations on rhamnolipid production by Pseudomonas aeruginosa in both batch and fed-batch fermentation was investigated in a lab-scale fermenter under precise DO control. A maximal rhamnolipid production of 22.5 g/l was obtained at a DO concentration of 40% in batch fermentation. In order to achieve the high rhamnolipid production, a fed-batch operation under tight DO control of 40% was conducted. As a result, the overall rhamnolipid production and productivity reached to 240 g/l and 0.9 (g/l h), corresponding to a 10.7 and 4.8-fold improvement compared to the batch experiments. The high level of rhamnolipid production via the fed-batch cultivation can be attributed to both DO concentration and the feeding strategy. This achievement is promising for the production of rhamnolipid in industrial scale.

Physicochemical characterization and optimization of glycolipid biosurfactant production by a native strain of Pseudomonas aeruginosa HAK01 and its performance evaluation for the MEOR process.

In this study, a glycolipid type of biosurfactant (BS) was produced, its characteristics were evaluated and several flooding tests were conducted in a micromodel to investigate its potential for enhancing oil recovery. A rhamnolipid BS producer strain was identified as a bacterium belonging to the genus Pseudomonas aeruginosa. This BS showed good stability at temperatures of 40-121 °C, pH values of 3-10 and salinity up to 10% (w/v) NaCl which is important in Microbial Enhanced Oil Recovery (MEOR). The rhamnolipid decreased the surface tension of water from 72 to 28.1 mN m-1 with a critical micelle concentration of 120 ppm. Thin layer chromatography, FTIR spectroscopy, 1H-NMR and 13C-NMR spectroscopy revealed the glycolipid structure of the BS. Response surface methodology was applied to optimize BS production. Several micromodel flooding tests were conducted to study the capability of the produced rhamnolipid in enhanced oil recovery for the first time. An oil recovery factor of 43% was obtained at 120 ppm of BS solution whereas the recovery factor obtained for water flooding was 16%. Contact angle measurements showed that BS solutions altered the wettability of a glass surface from oil wet to a strongly water wet state. Also the results illustrated that all BS solutions were impressive in microbial enhanced oil recovery (MEOR) and using the produced BS a considerable amount of trapped oil can be extracted due to interfacial tension reduction, wettability alteration towards water wet conditions and improving the mobility ratio.

Overproduction of lipopeptide biosurfactant by Aneurinibacillus thermoaerophilus HAK01 in various fed-batch modes under thermophilic conditions.

An efficient lipopeptide biosurfactant (BS) producer, Aneurinibacillus thermoaerophilus HAK01, was isolated from municipal landfill sites. The strain was able to produce about 4.9 g L-1 lipopeptide at a thermophilic temperature of 45 °C. After optimization of culture component concentrations using the response surface method, the main focus is to find the most appropriate fed-batch strategy to enhance lipopeptide production by the HAK01 strain. For this purpose, four fed-batch strategies including (a) pH-stat mode, (b) constant feeding rate strategy, (c) DO-stat mode, and (d) combined feeding strategy were designed. The production of BS was increased systematically from 4.9 g L-1 in batch mode to 5.9, 7.1, 8.8 and 11.2 g L-1 in each fed-batch mode, respectively. While poor results were obtained in the pH-stat mode, the DO-stat mode showed excellent results in the production of BS. The results of the study confirmed the importance of operational mode, oxygen supply and the kind of feeding strategy in BS production.

Biosurfactants from probiotic bacteria: A review.

Among microorganisms, bacteria are the main group of biosurfactant-producing organisms. Different types of bacteria including Pseudomonas sp., Acinetobacter sp., Bacillus sp., and Arthrobacter sp. are among the most commonly studied bacteria in the realm of scientific research. However, due to the pathogenic nature of the producing organisms, the application of these compounds is restricted, therefore, not suitable for use in food-related industries. Given that probiotic bacteria impact human health, applying probiotics as nonpathogenic and safe organisms have gained much attention for the production of biosurfactants in recent years. Most biosurfactants obtained from probiotic bacteria are related to a number of lactic acid bacteria (LAB). These types of biosurfactants are classified based on their structures as protein-carbohydrate complexes, lipids, or fatty acids. The present paper seeks to provide comprehensive and useful information about the production of various kinds of biosurfactants by different probiotic bacteria. In addition, we have extensively reviewed their potential for possible future applications.

Vitamin B12 biosynthesis over waste frying sunflower oil as a cost effective and renewable substrate.

Statistical experimental designs were used to develop a medium based on waste frying sunflower oil (WFO) and other nutrient sources for production of vitamin B12 (VB12) by Propionibacterium freudenreichii subsp. freudenreichii PTCC 1674. The production of acetic acid and propionic acid were also evaluated using the same microorganism. The amount of WFO in the media was initially optimized. The amount of 4 % w/v of oil found to be an appropriate amount for production of VB12. A Plackett Burman design was then employed to identify nutrients that have significant effect on the production of VB12 in the WFO media. Dimethylbenzimidazolyl (DMB), cobalt chloride, ferrous sulfate, and calcium chloride were the most important compounds. The level optimization of nutrients as the significant factors was finally performed using response surface methodology based on a central composite design. The model predicted that a medium containing 35.56 mg/L DMB, 14.69 mg/L CoCl2.6H2O, 5.82 mg/L FeSO4.7H2O, and 11.41 mg/L CaCl2.2H2O gives the maximum VB12 production of 2.60 mg/L. The optimized medium provides a final concentration of vitamin 170 % higher than that by the original medium. This study offers valuable insights on a cost-effective carbon source for industrial production of food-grade VB12.

Lipid production and mixotrophic growth features of cyanobacterial strains isolated from various aquatic sites.

The present study was conducted to determine the potential of five cyanobacteria strains isolated from aquatic zones to induce lipid production. The phylogenetic affiliation of the isolates was determined by 16S rRNA gene sequencing. Amongst the isolates, an efficient cyanobacterium, Synechococcus sp. HS01 showing maximal biomass and lipid productivity, was selected for further studies. In order to compare lipid productivity, the HS01 strain was grown in different media to screen potential significant culture ingredients and to evaluate mixotrophic cultivation. Mixotrophic cultivation of the strain using ostrich oil as a carbon source resulted in the best lipid productivity. GC analysis of fatty acid methyl esters of the selected cyanobacterial strain grown in media supplemented with ostrich oil showed a high content of C16 (palmitoleic acid and palmitic acid) and C18 (linoleic acid, oleic acid and linolenic acid) fatty acids of 42.7 and 42.8 %, respectively. Transmission electron micrographs showed that the HS01 cells exhibited an elongated rod-shaped appearance, either isolated, paired, linearly connected or in small clusters. According to initial experiments, ostrich oil, NaNO3 and NaCl were recognized as potential essential nutrients and selected for optimization of media with the goal of maximizing lipid productivity. A culture optimization technique using the response surface method demonstrated a maximum lipid productivity of 56.5 mg l(-1) day(-1). This value was 2.82-fold higher than that for the control, and was achieved in medium containing 1.12 g l(-1) NaNO3, 1 % (v/v) ostrich oil and 0.09 % (w/v) NaCl.

Lactobacillus crustorum KH: novel prospective probiotic strain isolated from Iranian traditional dairy products.

In recent years, exploring novel probiotic strains for therapeutic intervention has been raised due to the significant increase in market demand. This study aimed to investigate the certain probiotic properties of 15 Lactobacillus isolates from Iranian traditional dairy products. Among them, a novel potential probiotic strain was isolated and identified as Lactobacillus crustorum. The characteristics of potential probiotics were examined in terms of resistance to acidity, bile, and salinity as well as antibiotic tolerance and antibacterial activity. L. crustorum KH has shown tolerance property to bile (0.3 % w), acidity (pH 2-9), and salinity (1-5 % NaCl) and strong antibacterial activity against tested enteropathogens by well-diffusion assay. Furthermore, in vivo study and histological assays were performed to study whether live and heat-killed cells of L. crustorum KH are able to protect against the challenge of Escherichia coli O157:H7 in the gastrointestinal tract of mice used as an experimental model. Therefore, heat-killed and live cells of L. crustorum KH were inoculated by gavage to different groups of 4-6-week-old female BALB/c mice in doses of 10(8) colony-forming unit (CFU)/dose. Thereafter, these mice were challenged with E. coli O157:H7 also inoculated in the gastrointestinal tract (GIT) of the animals. The results showed that heat-killed cells of L. crustorum KH exert a protective effect against E. coli O157:H7 colonization at different degrees, being lower than that produced by viable cells.

Newly antibacterial and antiadhesive lipopeptide biosurfactant secreted by a probiotic strain, Propionibacterium freudenreichii.

A lipopeptide biosurfactant production from a probiotic type strain of Propionibacterium freudenreichii subsp. freudenreichii is being reported here for the first time. This biosurfactant is able to reduce the surface tension of water from 72 to 38 mN/m with an increase of the biosurfactant concentration up to critical micelle concentration value of 1.59 mg/ml. The production of the biosurfactant was found to be much higher in medium containing sunflower oil compared to the glucose-containing medium. The maximum emulsifying activity (E24 = 72 %) was attained with used frying sunflower oil, while kerosene and starch had the lowest emulsifying activity. Biosurfactant production seems to be parallel to cell growth. The produced biosurfactant was relatively thermo-stable and no appreciable changes in biosurfactant activity occurred at temperature ranges of 25-85 °C. The analysis of the extracted biosurfactant by thin layer chromatography, infrared spectroscopy, and (1)H and (13)CNMR spectroscopy revealed the chemical nature of the biosurfactant as lipopeptide. Produced lipopeptide was evaluated for its antimicrobial and antiadhesive activity and showed significant antimicrobial and antiadhesive action against a wide range of pathogenic bacteria and fungi. A total growth inhibition was observed over Rhodococcus erythropolis, while the best result of antiadhesion was obtained against Pseudomonas aeruginosa.

Distinctive protein expression patterns of the strain Brevundimonas sp. ZF12 isolated from the aqueous zone containing high levels of radiation to cadmium-induced stress.

In the current study, different protein expression profiles in a strain Brevundimonas sp. ZF12, isolated from the aqueous zone containing high levels of radiation, were characterized following exposure to cadmium (II) using a proteomic strategy. In order to gain a deeper understanding of the cellular events that allow this strain to survive and undergo cadmium adaptation and sorption, the strain was tested under three experimental conditions of 5, 10 and 30 ppm cadmium (II) ions stress. Two-dimensional polyacrylamide gel electrophoresis and mass spectrometry were used to identify the differentially expressed proteins under cadmium (II) stress. 20 differentially expressed spots were successfully identified by MS/MS analysis. These proteins are involved in DNA repair and protection, amino acid metabolism, nucleotide metabolism, energy homeostasis, oxidative stress response, redox homeostasis, protein folding and heat-shock response. The results obviously indicate that the ZF12 strain tends to endure the cadmium (II) stress conditions by modification in many aspects of its cellular physiology and metabolism.

First report of a lipopeptide biosurfactant from thermophilic bacterium Aneurinibacillus thermoaerophilus MK01 newly isolated from municipal landfill site.

A biosurfactant-producing thermophile was isolated from the Kahrizak landfill of Tehran and identified as a bacterium belonging to the genus Aneurinibacillus. A thermostable lipopeptide-type biosurfactant was purified from the culture medium of this bacterium and showed stability in the temperature range of 20-90 °C and pH range of 5-10. The produced biosurfactant could reduce the surface tension of water from 72 to 43 mN/m with a CMC of 1.21 mg/mL. The strain growing at a temperature of 45 °C produces a substantial amount of 5 g/L of biosurfactant in the medium supplemented with sunflower oil as the sole carbon source. Response surface methodology was employed to optimize the biosurfactant production using sunflower oil, sodium nitrate, and yeast extract as variables. The optimization resulted in 6.75 g/L biosurfactant production, i.e., 35% improved as compared to the unoptimized condition. Thin-layer chromatography, FTIR spectroscopy, 1H-NMR spectroscopy, and biochemical composition analysis confirmed the lipopeptide structure of the biosurfactant.