[Deficiency in N-acetylglucosamine transport affects the sporulation process and increases the hemolytic activity of the S-layer protein in Lysinibacillus sphaericus ASB13052]. / La deficiencia en el transporte de N-acetilglucosamina en Lysinibacillus sphaericus ASB13052 afecta el proceso de esporulación e incrementa la actividad hemolítica de su S-layer.

Lysinibacillus sphaericus is a bacterium that, along with Bacillus thuringiensis var. israelensis, is considered the best biological insecticide for controlling mosquito larvae and an eco-friendly alternative to chemical insecticides. It depends on peptidic molecules such as N-acetylglucosamine to obtain carbon sources and possesses a phosphotransferase system (PTS) for their incorporation. Some strains carry S-layer proteins, whose involvement in metal retention and larvicidal activity against disease-carrying mosquitoes has been demonstrated. Alterations in the amino sugar incorporation system could affect the protein profile and functionality. Strain ASB13052 and the isogenic mutant in the ptsH gene, which is predominant in the PTS signaling pathway, were used in this study. For the first time, the presence of N-glycosylated S-layer proteins was confirmed in both strains, with a variation in their molecular weight pattern depending on the growth phase. In the exponential phase, an S-layer protein greater than 130 kDa was found in the ptsH mutant, which was absent in the wild-type strain. The mutant strain exhibited altered and incomplete low quality sporulation processes. Hemolysis analysis, associated with larvicidal activity, showed that the ptsH mutant has higher lytic efficiency, correlating with the high molecular weight protein. The results allow us to propose the potential effects that arise as a result of the absence of amino sugar transport on hemolytic activity, S-layer isoforms, and the role of N-acetylglucosamine in larvicidal activity.

An Apple and Acáchul Berry Snack Rich in Bioaccessible Antioxidants and Folic Acid: A Healthy Alternative for Prenatal Diets.

A fruit leather (apple and acáchul berry) oriented toward women of reproductive age was developed. The snack was supplemented with an ingredient composed of folic acid (FA) and whey proteins (WPI) to ensure the required vitamin intake to prevent fetal neural tube defects. In order to generate a low-calorie snack, alternative sweeteners were used (stevia and maltitol). The fruit leather composition was determined. Also, an in vitro digestion process was carried out to evaluate the bioaccessibility of compounds with antioxidant capacity (AC), total polyphenols (TPCs), total monomeric anthocyanins (ACY), and FA. The quantification of FA was conducted by a microbiological method and by HPLC. The leather contained carbohydrates (70%) and antioxidant compounds, mainly from fruits. Bioaccessibility was high for AC (50%) and TPCs (90%), and low for ACY (17%). Regarding FA, bioaccessibility was higher for WPI-FA (50%) than for FA alone (37%), suggesting that WPI effectively protected the vitamin from processing and digestion. Furthermore, the product was shown to be non-cytotoxic in a Caco-2 cell model. The developed snack is an interesting option due to its low energy intake, no added sugar, and high content of bioactive compounds. Also, the supplementation with WPI-FA improved the conservation and bioaccessibility of FA.

Surface layer proteins in species of the family Lactobacillaceae.

The S-layer or surface layer protein (SLP) is the most ancient biological envelope, highly conserved in several Bacteria and Archaea. In lactic acid bacteria (LAB), SLP is only found in species belonging to the Lactobacillaceae family, many of them considered probiotic microorganisms. New reclassification of members within the Lactobacillaceae family (International Journal of Systematic and Evolutionary Microbiology, 2020, 70, 2782) and newly sequenced genomes demands an updated revision on SLP genes and domain organization. There is growing information concerning SLP occurrence, molecular biology, biophysical properties, and applications. Here, we focus on the prediction of slp genes within the Lactobacillaceae family, and specifically, on the neat interconnection between the two different modular SLP domain organizations and the new reclassified genera. We summarize the results in a concise tabulated manner to review the present knowledge on SLPs and discuss the most relevant and updated concepts regarding SLP sequence clustering. Our assessment is based on sequence alignments considering the new genera classification and protein domain definition with post-translational modifications. We analyse the difficulties encountered to resolve the SLPs 3D structure, describing the need for structure prediction approaches and the relation between protein structure and its anchorage mechanism to the cell wall. Finally, we enumerate new SLP applications regarding heterologous display, pathogen exclusion, immunostimulation, and metal binding.

Lactic acid production using cheese whey based medium in a stirred tank reactor by a ccpA mutant of Lacticaseibacillus casei.

In lactobacilli, CcpA is known to modulate the expression of genes involved in sugar metabolism, stress response and aerobic adaptation. This study aimed to evaluate a ccpA mutant of Lacticaseibacillus casei BL23 to increase lactic acid production using cheese whey. The ccpA derivative (BL71) showed better growth than the L. casei wild-type in the whey medium. In a stirred tank reactor, at 48 h, lactate production by BL71 was eightfold higher than that by BL23. In batch fermentations, the final values reached were 44.23 g L-1 for BL71 and 27.58 g L-1 for BL23. Due to a decrease in the delay of lactate production in the mutant, lactate productivity increased from 0.17 g (L.h)-1 with BL23 to 0.80 g (L.h)-1 with BL71. We found that CcpA would play additional roles in nitrogen metabolism by the regulation of the proteolytic system. BL71 displayed higher activity of the PepX, PepQ and PrtP enzymes than BL23. Analysis of prtP expression confirmed this deregulation in BL71. Promoter analysis of the prtP gene revealed CcpA binding sites with high identity to the cre consensus sequence and the interaction of CcpA with this promoter was confirmed in vitro. We postulate that deregulation of the proteolytic system in BL71 allows a better exploitation of nitrogen resources in cheese whey, resulting in enhanced fermentation capacity. Therefore, the ccpA gene could be a good target for future technological developments aimed at effective and inexpensive lactate production from dairy industrial wastes.

Tightening Bonds in Latin America Through Phage Discovery.

Between 2015 and 2019, we hosted an International Phage Course at Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina. The 2-week full-time course was hands-on and included lectures from renowned phage biologists. Participating students were able to meet and discuss with recognized experts from around the world in a familiar setting, facilitating the establishment of scientific collaborations and the expansion of their networks. Eighty-four students from 14 Latin American countries have participated in the course, which included isolation, characterization, genome sequencing, and annotation of novel phages. We have successfully created a coursework that enabled the acquisition of new knowledge and expertise in bacteriophage biology and strengthened ties among Latin American colleagues.

Genome Sequence and Characterization of Lactobacillus casei Phage, vB_LcaM_Lbab1 Isolated from Raw Milk.

Introduction: Only a few Lactobacillus casei phages have so far been characterized. As several L. casei strains are part of probiotic formulations, bacteriophage outbreaks targeting these strains can lead to critical losses within the dairy industry. Materials and Methods: A new L. casei phage was isolated from raw milk obtained from a milking yard from the province of Buenos Aires. The phage genome was sequenced, annotated, and analyzed. Morphology was determined by electron microscopy and the host range was established. Results: Lactobacillus phage vB_LcaM_Lbab1 is a member of the Herelleviridae family and features a host range including L. casei/Lactobacillus paracasei and Lactobacillus kefiri strains. We further analyzed the baseplate proteins in silico and found putative carbohydrate binding modules that are responsible for host recognition in other Lactobacillus phages. Conclusions: A new Lactobacillus phage was isolated and characterized. The focus was made on its host recognition mechanism, pointing toward the development of future strategies to avoid deleterious infections in the dairy industry.

Strategies to display heterologous proteins on the cell surface of lactic acid bacteria using as anchor the C-terminal domain of Lactobacillus acidophilus SlpA.

The surface-layer (S-layer) protein of Lactobacillus acidophilus is a crystalline array of self-assembling subunits, non-covalently bound to the most outer cell wall envelope, which constitutes up to 20% of the total cell protein content. These attributes make S-layer proteins an excellent anchor for the development of microbial cell-surface display systems. In L. acidophilus, the S-layer is formed predominantly by the protein SlpA. We have previously shown that the C-terminal domain of SlpA is responsible for the cell wall anchorage on L. acidophilus ATCC 4356. In the present study, we evaluated the C-terminal domain of SlpA of L. acidophilus ATCC 4356 as a potential anchor domain to display functional proteins on the surface of non-genetically modified lactic acid bacteria (LAB). To this end, green fluorescent protein (GFP)-CTSlpA was firstly produced in Escherichia coli and the recombinant proteins were able to spontaneously bind to the cell wall of LAB in a binding assay. GFP was successfully displayed on the S-layer stripped surface of L. acidophilus. Both the binding stability and cell survival of L. acidophilus decorated with the recombinant protein were then studied in simulated gastrointestinal conditions. Furthermore, NaCl was tested as a safer alternative to LiCl for S-layer removal. This study presents the development of a protein delivery platform involving L. acidophilus, a microorganism generally regarded as safe, which utilizes the contiguous, non-covalently attached S-layer at the cell surface of the bacterium without introducing any genetic modification.

Exploring lectin-like activity of the S-layer protein of Lactobacillus acidophilus ATCC 4356.

The surface layer (S-layer) protein of Lactobacillus acidophilus is a crystalline array of self-assembling, proteinaceous subunits non-covalently bound to the outmost bacterial cell wall envelope and is involved in the adherence of bacteria to host cells. We have previously described that the S-layer protein of L. acidophilus possesses anti-viral and anti-bacterial properties. In this work, we extracted and purified S-layer proteins from L. acidophilus ATCC 4356 cells to study their interaction with cell wall components from prokaryotic (i.e., peptidoglycan and lipoteichoic acids) and eukaryotic origin (i.e., mucin and chitin), as well as with viruses, bacteria, yeast, and blood cells. Using chimeric S-layer fused to green fluorescent protein (GFP) from different parts of the protein, we analyzed their binding capacity. Our results show that the C-terminal part of the S-layer protein presents lectin-like activity, interacting with different glycoepitopes. We further demonstrate that lipoteichoic acid (LTA) serves as an anchor for the S-layer protein. Finally, a structure for the C-terminal part of S-layer and possible binding sites were predicted by a homology-based model.

Draft Genome Sequence of Lactobacillus helveticus ATCC 12046.

Lactobacillus helveticus is a lactic acid bacterium used traditionally in the dairy industry, especially in the manufacture of cheeses. We present here the 2,141,841-bp draft genome sequence of L. helveticus strain ATCC 12046, a potential starter strain for improving cheese production.

Proteins as Nano-Carriers for Bioactive Compounds. The Case of 7S and 11S Soy Globulins and Folic Acid Complexation.

Isolated 7S and 11S globulins obtained from defeated soy flour were complexated with folic acid (FA) in order to generate nano-carriers for this important vitamin in human nutrition. Fluorescence spectroscopy and dynamic light scattering were applied to follow the nano-complexes formation and for their characterization. Fluorescence experimental data were modeled by the Stern-Volmer and a modified double logarithm approach. The results obtained confirmed static quenching. The number of binding sites on the protein molecule was ~1. The values obtained for the binding constants suggest a high affinity between proteins and FA. Particle size distribution allowed to study the protein aggregation phenomenon induced by FA bound to the native proteins. Z-average manifested a clear trend to protein aggregation. 11S-FA nano-complexes resulted in more polydispersity. ζ-potential of FA nano-complexes did not show a remarkable change after FA complexation. The biological activity of nano-complexes loaded with FA was explored in terms of their capacity to enhance the biomass formation of Lactobacillus casei BL23. The results concerning to nano-complexes inclusion in culture media showed higher bacterial growth. Such a result was attributed to the entry of the acid by the specific receptors concomitantly by the peptide receptors. These findings have technological impact for the use of globulins-FA based nano-complexes in nutraceutical, pharmaceutical and food industries.

Influence of osmotic stress on the profile and gene expression of surface layer proteins in Lactobacillus acidophilus ATCC 4356.

In this work, we studied the role of surface layer (S-layer) proteins in the adaptation of Lactobacillus acidophilus ATCC 4356 to the osmotic stress generated by high salt. The amounts of the predominant and the auxiliary S-layer proteins SlpA and SlpX were strongly influenced by the growth phase and high-salt conditions (0.6 M NaCl). Changes in gene expression were also observed as the mRNAs of the slpA and slpX genes increased related to the growth phase and presence of high salt. A growth stage-dependent modification on the S-layer protein profile in response to NaCl was observed: while in control conditions, the auxiliary SlpX protein represented less than 10 % of the total S-layer protein, in high-salt conditions, it increased to almost 40 % in the stationary phase. The increase in S-layer protein synthesis in the stress condition could be a consequence of or a way to counteract the fragility of the cell wall, since a decrease in the cell wall thickness and envelope components (peptidoglycan layer and lipoteichoic acid content) was observed in L. acidophilus when compared to a non-S-layer-producing species such as Lactobacillus casei. Also, the stationary phase and growth in high-salt medium resulted in increased release of S-layer proteins to the supernatant medium. Overall, these findings suggest that pre-growth in high-salt conditions would result in an advantage for the probiotic nature of L. acidophilus ATCC 4356 as the increased amount and release of the S-layer might be appropriate for its antimicrobial capacity.

Draft Genome Sequence of the Probiotic Strain Lactobacillus acidophilus ATCC 4356.

We present the 1,956,699-bp draft genome sequence of Lactobacillus acidophilus strain ATCC 4356. Comparative genomic analysis revealed 99.96% similarity with L. acidophilus NCFM NC_006814.3 and 99.97% with La-14 NC_021181.2 genomes.

Contribution of S-layer proteins to the mosquitocidal activity of Lysinibacillus sphaericus.

Lysinibacillus sphaericus strains belonging the antigenic group H5a5b produce spores with larvicidal activity against larvae of Culex mosquitoes. C7, a new isolated strain, which presents similar biochemical characteristics and Bin toxins in their spores as the reference strain 2362, was, however, more active against larvae of Culex mosquitoes. The contribution of the surface layer protein (S-layer) to this behaviour was envisaged since this envelope protein has been implicated in the pathogenicity of several bacilli, and we had previously reported its association to spores. Microscopic observation by immunofluorescence detection with anti S-layer antibody in the spores confirms their attachment. S-layers and BinA and BinB toxins formed high molecular weight multimers in spores as shown by SDS-PAGE and western blot detection. Purified S-layer from both L. sphaericus C7 and 2362 strain cultures was by itself toxic against Culex sp larvae, however, that from C7 strain was also toxic against Aedes aegypti. Synergistic effect between purified S-layer and spore-crystal preparations was observed against Culex sp. and Aedes aegypti larvae. This effect was more evident with the C7 strain. In silico analyses of the S-layer sequence suggest the presence of chitin-binding and hemolytic domains. Both biochemical characteristics were detected for both S-layers strains that must justify their contribution to pathogenicity.

Osmotic stress adaptation in Lactobacillus casei BL23 leads to structural changes in the cell wall polymer lipoteichoic acid.

The probiotic Gram-positive bacterium Lactobacillus casei BL23 is naturally confronted with salt-stress habitats. It has been previously reported that growth in high-salt medium, containing 0.8 M NaCl, leads to modifications in the cell envelope of this bacterium. In this study, we report that L. casei BL23 has an increased ability to form biofilms and to bind cations in high-salt conditions. This behaviour correlated with modifications of surface properties involving teichoic acids, which are important cell wall components. We also showed that, in these high-salt conditions, L. casei BL23 produces less of the cell wall polymer lipoteichoic acid (LTA), and that this anionic polymer has a shorter mean chain length and a lower level of d-alanyl-substitution. Analysis of the transcript levels of the dltABCD operon, encoding the enzymes required for the incorporation of d-alanine into anionic polymers, showed a 16-fold reduction in mRNA levels, which is consistent with a decrease in d-alanine substitutions on LTA. Furthermore, a 13-fold reduction in the transcript levels was observed for the gene LCABL_09330 coding for a putative LTA synthase. To provide further experimental evidence that LCABL_09330 is a true LTA synthase (LtaS) in L. casei BL23, the enzymic domain was cloned and expressed in E. coli. The purified protein was able to hydrolyse the membrane lipid phosphatidylglycerol as expected for an LTA synthase enzyme, and hence LCABL_09330 was renamed LtaS. The purified enzyme showed Mn(2+)-ion dependent activity, and its activity was modulated by differences in NaCl concentration. The decrease in both ltaS transcript levels and enzyme activity observed in high-salt conditions might influence the length of the LTA backbone chain. A putative function of the modified LTA structure is discussed that is compatible with the growth under salt-stress conditions and with the overall envelope modifications taking place during this stress condition.

Metal biosorption by surface-layer proteins from Bacillus species.

Bacillus species have been involved in metal association as biosorbents, but there is not a clear understanding of this chelating property. In order to evaluate this metal chelating capacity, cultures and spores from Grampositive bacteria of species either able or unable to produce surface layer proteins (S-layers) were analyzed for their capacity of copper biosorption. Only those endowed of S-layers, like Bacillus sphaericus and B. thuringiensis, showed a significant biosorption capacity. This capacity (nearly 50%) was retained after heating of cultures, thus supporting that structural elements of the envelopes are responsible for such activity. Purified Slayers from two Bacillus sphaericus strains had the ability to biosorb copper. Copper biosorption parameters were determined for strain B. sphaericus 2362, and after analyses by means of the Langmuir model, the affinity and capacity were shown to be comparable to other bacterial biosorbents. A competitive effect of Ca2+ and Zn2+, but not of Cd2+, was also observed, thus indicating that other cations may be biosorbed by this protein. Spores that have been shown to be proficient for copper biosorption were further analyzed for the presence of Slayer content. The retention of S-layers by these spores was clearly observed, and after extensive treatment to eliminate the S-layers, the biosorption capacity of these spores was significantly reduced. For the first time, a direct correlation between S-layer protein content and metal biosorption capacity is shown. This capacity is linked to the retention of S-layer proteins attached to Bacillus spores and cells.

New method for electroporation of Lactobacillus species grown in high salt.

We here describe a new method for electroporation of Lactobacillus species, obligately homofermentative and facultatively heterofermentative, based on the cell-wall weakening resulting from growth in high-salt media. For L. casei, optimum transformation efficiency of up to 10(5) transformants per microgram of plasmid DNA was achieved following growth in the presence of 0.9 M NaCl. Plasmids of different sizes and replication origins were also similarly transformed. These competent cells could be used either directly or stored frozen, up to 1 month, for future use, with similar efficiency. This protocol was assayed with different Lactobacillus species: L. delbrueckii subsp. lactis, L. paracasei, L. plantarum and L. acidophilus, and it was found that they were transformed with similar efficiency.

Synergistic effects of the Lactobacillus acidophilus surface layer and nisin on bacterial growth.

We have previously described a murein hydrolase activity for the surface layer (S-layer) of Lactobacillus acidophilus ATCC 4356. Here we show that, in combination with nisin, this S-layer acts synergistically to inhibit the growth of pathogenic Gram-negative Salmonella enterica and potential pathogenic Gram-positive bacteria, Staphylococcus aureus and Bacillus cereus. In addition, bacteriolytic effects were observed for the Gram-positive species tested. We postulate that the S-layer enhances the access of nisin into the cell membrane by enabling it to cross the cell wall, while nisin provides the sudden ion-nonspecific dissipation of the proton motive force required to enhance the S-layer murein hydrolase activity.

Murein hydrolase activity in the surface layer of Lactobacillus acidophilus ATCC 4356.

We describe a new enzymatic functionality for the surface layer (S-layer) of Lactobacillus acidophilus ATCC 4356, namely, an endopeptidase activity against the cell wall of Salmonella enterica serovar Newport, assayed via zymograms and identified by Western blotting. Based on amino acid sequence comparisons, the hydrolase activity was predicted to be located at the C terminus. Subsequent cloning and expression of the C-terminal domain in Bacillus subtilis resulted in the functional verification of the enzymatic activity.