Diversity of Streptococcus thermophilus in bacteriocin production; inhibitory spectrum and occurrence of thermophilin genes

Draft genome sequences of eight strains isolated from homemade yogurts and cheeses from Bulgaria

Here, we report draft genome sequences of eight strains isolated from naturally processed, homemade dairy foods or human milk in Bulgaria; strains Lactobacillus gasseri AM-LG-29, Lactiplantibacillus plantarum AM-LP-81, Lactobacillus helveticus AM-LH-32, Lactobacillus delbrueckii subsp. bulgaricus AM-LB-13, Streptococcus thermophilus AM-ST-89, Lactobacillus acidophilus AM-LA-19, Bifidobacterium longum AM-BL-55, and Lacticaseibacillus rhamnosus AM-LR-51.

Enhancing the microbial dynamics, volatile profile, and ripening efficiency of white brined cheese using Lactiplantibacillus plantarum L33 as a probiotic co-culture

Lactiplantibacillus plantarum L33 was used as a co-culture in the production of white brined cheese. The study compared control samples (without co-culture) and those including the co-culture at 1, 15 and 30 days of ripening, assessing various factors such as pH, moisture content, protein and fat levels, proteolysis intensity, organic acids, aromatic compounds, bacterial dynamics, hardness, and sensory evaluations. The results indicated that the cheese samples containing Lpb. plantarum L33 exhibited a higher moisture content (15 %) and lower hardness (11 %) compared to the control sample, while fat and protein levels remained consistent across both samples. Moreover, the co-culture sample had higher levels of lactic acid, acetic acid, and aromatic compounds such as acetone and diacetyl. Analysis of bacterial dynamics revealed that the presence of co-culture and storage time significantly enhanced the relative abundance of bacteria in the samples containing the co-culture, with the highest relative abundance found for Streptococcus salivarius subsp. thermophilus (107.27), followed by Lpb. plantarum L33 (25.51), Lactococcus lactis subsp. lactis (7.46), and Lactococcus lactis subsp. cremoris (0.74). The co-culture sample also received favorable sensory scores for overall acceptance. The findings suggest that a strain with moderate proteolytic activity can effectively reduce the ripening time of cheese by enhancing proteolysis intensity, thereby accelerating the production of aromatic compounds.

BlpU is a broad-spectrum bacteriocin in Streptococcus thermophilus

Streptococcus thermophilus strain B59671 naturally produces thermophilin 110, a broad-spectrum bacteriocin encoded within the bacteriocin-like peptide (blp) gene cluster, and thermophilin 13 from a separate chromosomal locus. Analysis of the blp gene cluster revealed two genes, blpU and blpK, as potentially encoding bacteriocins. Deletion of blpK from the B59671 chromosome did not result in a loss of antimicrobial activity against either S. thermophilus ST113 or Pediococcus acidilactici F. A deletion mutant of blpU could not be generated in B59671, but the mature BlpU peptide obtained through overexpression in E. coli BL21 or chemical synthesis inhibited the growth of S. thermophilus strains, Streptococcus mutans UA159, P. acidilactici F, and Listeria innocua GV9 L-S, evidencing as a broad-spectrum bacteriocin that does not require modification for activity. This study also showed that the transcription of blpU was approximately 16-fold higher in B59671 than in an induced culture of S. thermophilus LMD-9, which produces a blp-encoded bacteriocin. The increased expression of BlpU in B59671 may explain the unique antimicrobial spectrum associated with this strain. Additionally, it was shown that a blpC deletion mutant of B59671, which prevents expression of BlpU and BlpK, inhibited the growth of other S. thermophilus strains and Bacillus cereus, suggesting that thermophilin 13 produced by B59671 possessed both intra- and interspecies antimicrobial activity. While this study confirmed that BlpU can function as an independent antimicrobial peptide, further studies are required to determine if BlpK can function independently as a broad-spectrum antimicrobial.

Improvement of Urolithin A Yield by In Vitro Cofermentation of Streptococcus thermophilus FUA329 with Human Gut Microbiota from Different Urolithin Metabotypes

Streptococcus thermophilus FUA329 converts ellagic acid (EA) to urolithin A (Uro-A), which is not autonomously converted by the gut microbiota to produce highly bioavailable and multibiologically active Uro-A in urolithin metabotype 0 (UM-0) populations. We consider that Streptococcus thermophilus FUA329 has the potential to be developed as a probiotic. Therefore, we utilized S. thermophilus FUA329 for in vitro cofermentation with gut microbiota. The results revealed that strain FUA329 increased the production of EA-converted Uro-A during in vitro cofermentation with the human gut microbiota of different urolithin metabotypes (UMs), with a significant increase in the production of Uro-A in the experimental group of UM-0. In addition, changes in the in vitro cofermentation microbial community were determined using high-throughput sequencing. Strain FUA329 modulated the structure and composition of the gut microbiota in different UMs, thereby significantly increasing the abundance of beneficial microbiota in the gut microbiota while decreasing the abundance of harmful microbiota. Of greatest interest was the significant increase in the abundance of Actinobacteria phylum after the cofermentation of strain FUA329 with UM-0 gut microbiota, which might be related to the significant increase in the production of Uro-A.

Safety assessment, whole genome sequence, and metabolome analysis of Streptococcus thermophilus CICC 20372 for bone cement fermentation

Bone is a kind of meat processing by-product with high nutritional value but low in calorie, which is a typical food in China and parts of East Asian countries. Microbial fermentation by lactic acid bacteria showed remarkable advantages to increase the absorption of nutrients from bone cement by human body. Streptococcus thermophilus CICC 20372 is proven to be a good starter for bone cement fermentation. No genes encoding virulence traits or virulence factors were found in the genome of S. thermophilus CICC 20372 by a thorough genomic analysis. Its notable absence of antibiotic resistance further solidifies the safety. Furthermore, the genomic analysis identified four types of gene clusters responsible for the synthesis of antimicrobial metabolites. A comparative metabolomic analysis was performed by cultivating the strain in bone cement at 37 °C for 72 h, with the culture in de Man, Rogosa, and Sharpe (MRS) medium as control. Metabolome analysis results highlighted the upregulation of pathways involved in 2-oxocarboxylic acid metabolism, ATP-binding cassette (ABC) transporters, amino acid synthesis, and nucleotide metabolism during bone cement fermentation. S. thermophilus CICC 20372 produces several metabolites with health-promoting function during bone cement fermentation, including indole-3-lactic acid, which is demonstrated ameliorative effects on intestinal inflammation, tumor growth, and gut dysbiosis. In addition, lots of nucleotide and organic acids were accumulated at higher levels, which enriched the fermented bone cement with a variety of nutrients. Collectively, these features endow S. thermophilus CICC 20372 a great potential strain for bone food processing.

Compositional Variations between Adult and Infant Skin Microbiome: An Update

Human skin and its commensal microbiome form the first layer of protection to the outside world. A dynamic microbial ecosystem of bacteria, fungi and viruses, with the potential to respond to external insult, the skin microbiome has been shown to evolve over the life course with an alteration in taxonomic composition responding to altered microenvironmental conditions on human skin. This work sought to investigate the taxonomic, diversity and functional differences between infant and adult leg skin microbiomes. A 16S rRNA gene-based metataxonomic analysis revealed significant differences between the infant and adult skin groups, highlighting differential microbiome profiles at both the genus and species level. Diversity analysis reveals differences in the overall community structure and associated differential predicted functional profiles between the infant and adult skin microbiome suggest differing metabolic processes are present between the groups. These data add to the available information on the dynamic nature of skin microbiome during the life course and highlight the predicted differential microbial metabolic process that exists on infant and adult skin, which may have an impact on the future design and use of cosmetic products that are produced to work in consort with the skin microbiome.

Metagenome-mining indicates an association between bacteriocin presence and strain diversity in the infant gut

BACKGROUND

Our knowledge about the ecological role of bacterial antimicrobial peptides (bacteriocins) in the human gut is limited, particularly in relation to their role in the diversification of the gut microbiota during early life. The aim of this paper was therefore to address associations between bacteriocins and bacterial diversity in the human gut microbiota. To investigate this, we did an extensive screening of 2564 healthy human gut metagenomes for the presence of predicted bacteriocin-encoding genes, comparing bacteriocin gene presence to strain diversity and age.

RESULTS

We found that the abundance of bacteriocin genes was significantly higher in infant-like metagenomes (< 2 years) compared to adult-like metagenomes (2-107 years). By comparing infant-like metagenomes with and without a given bacteriocin, we found that bacteriocin presence was associated with increased strain diversities.

CONCLUSIONS

Our findings indicate that bacteriocins may play a role in the strain diversification during the infant gut microbiota establishment.

Co-carriage of Staphylococcus aureus and Streptococcus pneumoniae among children younger than 2 years of age in a rural population in Pakistan

Objectives

Staphylococcus aureus and Streptococcus pneumoniae are common colonizers of the human nasopharynx. In this study, we describe S. aureus nasopharyngeal carriage and evaluate its association with S. pneumoniae carriage post-10-valent pneumococcal conjugate vaccine (PCV10) introduction in Pakistan.

Methods

A serial cross-sectional study was undertaken from 2014 to 2018, children <2 years were randomly selected, and nasopharyngeal swabs were collected using standard WHO guidelines. S. aureus and S. pneumoniae isolates were identified using standard methods and tested for antimicrobial susceptibility by the standard Kirby-Bauer disk-diffusion method as per Clinical & Laboratory Standards Institute (CLSI) recommendations. Regression analysis was used to determine predictors associated with S. aureus carriage.

Results

We enrolled 3140 children. S. aureus carriage prevalence was 5.6% (176/3140), and 50.1% (81/176) of the isolates were methicillin-resistant S. aureus (MRSA). S. aureus carriage was higher in the absence of pneumococcus compared to isolates in which pneumococcus was present (7.5% vs 5.0%). S. aureus carriage was negatively associated with pneumococcal carriage, being in 3rd and 4th year of enrollment, and vaccination with two and three PCV10 doses, in addition, fast breathing, ≥2 outpatients visits, and rainy season were positively associated. The following resistance rates were observed: 98.9% for penicillin, 74.4% for fusidic acid, and 23.3% for gentamicin, 10.2% for erythromycin, and 8.5% for cotrimoxazole. All isolates were susceptible to amikacin.

Conclusions

Overall S. aureus carriage prevalence was low, PCV10 vaccine was protective against the carriage. The proportion of MRSA carriage and antimicrobial resistance was high in this community warranting continuous monitoring for invasive infections.

The genomic basis of the Streptococcus thermophilus health-promoting properties

Background

Streptococcus thermophilus is a Gram-positive bacterium widely used as starter in the dairy industry as well as in many traditional fermented products. In addition to its technological importance, it has also gained interest in recent years as beneficial bacterium due to human health-promoting functionalities. The objective of this study was to inventory the main health-promoting properties of S. thermophilus and to study their intra-species diversity at the genomic and genetic level within a collection of representative strains.

Results

In this study various health-related functions were analyzed at the genome level from 79 genome sequences of strains isolated over a long time period from diverse products and different geographic locations. While some functions are widely conserved among isolates (e.g., degradation of lactose, folate production) suggesting their central physiological and ecological role for the species, others including the tagatose-6-phosphate pathway involved in the catabolism of galactose, and the production of bioactive peptides and gamma-aminobutyric acid are strain-specific. Most of these strain-specific health-promoting properties seems to have been acquired via horizontal gene transfer events. The genetic basis for the phenotypic diversity between strains for some health related traits have also been investigated. For instance, substitutions in the galK promoter region correlate with the ability of some strains to catabolize galactose via the Leloir pathway. Finally, the low occurrence in S. thermophilus genomes of genes coding for biogenic amine production and antibiotic resistance is also a contributing factor to its safety status.

Conclusions

The natural intra-species diversity of S. thermophilus, therefore, represents an interesting source for innovation in the field of fermented products enriched for healthy components that can be exploited to improve human health. A better knowledge of the health-promoting properties and their genomic and genetic diversity within the species may facilitate the selection and application of strains for specific biotechnological and human health-promoting purpose. Moreover, by pointing out that a substantial part of its functional potential still defies us, our work opens the way to uncover additional health-related functions through the intra-species diversity exploration of S. thermophilus by comparative genomics approaches.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08459-y.

Pressure and Temperature Combined With Microbial Supernatant Effectively Inactivate Bacillus subtilis Spores

Spores from the Bacillus species pose a challenge to the food industry because of their ubiquitous nature and extreme resistance. Accumulated evidence indicates that it is effective to induce spore germination homogenously before killing them. However, it is difficult to obtain and apply exogenous germination factors, which will affect food composition. Therefore, this study screened endogenous germinants from microorganisms by assessing the effect of Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae, Lactiplantibacillus plantarum, and Streptococcus thermophilus cultures (cell-free) on B. subtilis spore germination. The results showed that the supernatants from these five microorganisms induced spore germination instead of sediments. Moreover, the supernatants of E. coli, B. subtilis, and S. cerevisiae exhibited higher germination rates than L. plantarum and S. thermophilus, and the induction effects were concentration-dependent. Furthermore, plate counting confirmed that the microbial supernatants induced the lowest spore germination ratio on strains B. subtilis FB85 [germination receptors (GRs) mutant] but not strains B. subtilis PB705 (PrkC mutant). In addition, B. subtilis and S. cerevisiae supernatants, combined with pressure and temperature, were effective in spore inactivation. The findings suggested that microbial supernatants may include agents that induce spore germination and may be used for spore inactivation.

Microbial Interactions within the Cheese Ecosystem and Their Application to Improve Quality and Safety

The cheese microbiota comprises a consortium of prokaryotic, eukaryotic and viral populations, among which lactic acid bacteria (LAB) are majority components with a prominent role during manufacturing and ripening. The assortment, numbers and proportions of LAB and other microbial biotypes making up the microbiota of cheese are affected by a range of biotic and abiotic factors. Cooperative and competitive interactions between distinct members of the microbiota may occur, with rheological, organoleptic and safety implications for ripened cheese. However, the mechanistic details of these interactions, and their functional consequences, are largely unknown. Acquiring such knowledge is important if we are to predict when fermentations will be successful and understand the causes of technological failures. The experimental use of "synthetic" microbial communities might help throw light on the dynamics of different cheese microbiota components and the interplay between them. Although synthetic communities cannot reproduce entirely the natural microbial diversity in cheese, they could help reveal basic principles governing the interactions between microbial types and perhaps allow multi-species microbial communities to be developed as functional starters. By occupying the whole ecosystem taxonomically and functionally, microbiota-based cultures might be expected to be more resilient and efficient than conventional starters in the development of unique sensorial properties.

Dietary supplementation with multi-strain formula of probiotics modulates inflammatory and immunological markers in apical periodontitis

Objective

The aim of this study was to evaluate whether probiotics multi-strain formula affects the development of apical periodontitis (AP) induced in rats.

Methodology

16 Wistar rats were divided in two groups (n=8): rats with AP fed with regular diet (Control-C (CG)); rats with AP, fed with regular diet and supplemented with multi-strain formula (one billion colony-forming units (CFU)): GNC Probiotic Complex (PCG) ( Lactobacillus acidophilus, Lactobacillus salivaris, Lactobacillus plantarum, Lactobacillus rhamnosus, Bifidobacterium bifidum, Bifidobacterium animalis subs. lactis and Streptococcus thermofilus ). AP was induced in the upper and lower first molars by dental pulp exposure to the oral environment. PCG was administered orally through gavage for 30 days during the AP development. After this period the animals were euthanized and the mandibles were removed and processed for histologic analysis, and immunochemical assays for interleukin (IL)-6, IL-10, IL-1β, RANKL, OPG, and TRAP. The Mann–Whitney U test and Student’s t test were performed (P<.05).

Results

The CG showed more intense inflammatory infiltrate than the PCG group (P<.05). IL-1β, IL 6 and RANKL decreased in the PCG group compared with CG (P<.05). The IL-10 level increased in the PCG group (P<.05). The OPG level was similar in both groups (P>.05). The number of mature osteoclasts (TRAP-positive multinucleated cells) was lower in PCG group when compared to the CG (P<.05).

Conclusion

Probiotic Complex modulates inflammation and bone resorption in apical periodontitis.

Genomic and in vitro properties of the dairy Streptococcus thermophilus SMQ-301 strain against selected pathogens

Cumulative studies have suggested that probiotic bacterial strains could be an effective alternative in inhibiting conditions caused by foodborne and vaginal pathogens. The use of genomic techniques is becoming highly useful in understanding the potential of these beneficial microorganisms. This study presents some genomic and in vitro properties of the Streptococcus thermophilus SMQ-301 strain against foodborne and vaginal pathogens (Staphylococcus aureus, Escherichia coli, and Gardnerella vaginalis) to validate its use in dairy food formulations. Genomic analyses include bacteriocin production, stress response systems, antioxidant capability, and RAST-based functional annotation. In vitro investigations focused on the antimicrobial effects of the S. thermophilus SMQ-301 cell-free solution (CFS) against the selected pathogens after enzymatic actions and pH treatments, assessment of cytotoxic effects using murine RAW264.7 cells, and assessment of organic acid production levels using supplementary carbon sources. The results show that the S. thermophilus SMQ-301 genome possesses essential pathways for stress management, antioxidant activities, and bacteriocin production. For the first time, the bacteriocin-producing peptides of S. thermophilus SMQ-301 are reported, which gives an insight into its inhibitory potential. In vitro, the CFS of S. thermophilus SMQ-301 had significant (P < 0.05) antimicrobial effects on the selected pathogens, with S. aureus ATCC25923 being the most resistant. All antimicrobial activities of the CFS against the selected pathogens were eliminated at pH 6.5 and 7.0. S. thermophilus SMQ-301 CFS yielded the highest lactic (25.58 ± 0.24 mg mL-1) and acetic (5.53 ± 0.12 mg mL-1) acid production levels, with 1% fructooligosaccharide (P < 0.05). The S. thermophilus SMQ-301 strain also lowered murine RAW264.7 cell activities from 101.77% (control) to 80.16% (T5 - RAW264.7 cells + 1 × 109 CFU mL-1 cells) (P < 0.05). This study showed that although the S. thermophilus SMQ-301 strain had excellent genomic characteristics, the in vitro effects varied markedly against all three pathogens. In all, the S. thermophilus SMQ-301 strain has promising applications as a potential probiotic in the food and allied industries.

High-quality genome sequence assembly of R.A73 Enterococcus faecium isolated from freshwater fish mucus

BACKGROUND

Whole-genome sequencing using high throughput technologies has revolutionized and speeded up the scientific investigation of bacterial genetics, biochemistry, and molecular biology. Lactic acid bacteria (LABs) have been extensively used in fermentation and more recently as probiotics in food products that promote health. Genome sequencing and functional genomics investigations of LABs varieties provide rapid and important information about their diversity and their evolution, revealing a significant molecular basis. This study investigated the whole genome sequences of the Enterococcus faecium strain (HG937697), isolated from the mucus of freshwater fish in Tunisian dams. Genomic DNA was extracted using the Quick-GDNA kit and sequenced using the Illumina HiSeq2500 system. Sequences quality assessment was performed using FastQC software. The complete genome annotation was carried out with the Rapid Annotation using Subsystem Technology (RAST) web server then NCBI PGAAP.

RESULTS

The Enterococcus faecium R.A73 assembled in 28 contigs consisting of 2,935,283 bps. The genome annotation revealed 2884 genes in total including 2834 coding sequences and 50 RNAs containing 3 rRNAs (one rRNA 16 s, one rRNA 23 s and one rRNA 5 s) and 47 tRNAs. Twenty-two genes implicated in bacteriocin production are identified within the Enterococcus faecium R.A73 strain.

CONCLUSION

Data obtained provide insights to further investigate the effective strategy for testing this Enterococcus faecium R.A73 strain in the industrial manufacturing process. Studying their metabolism with bioinformatics tools represents the future challenge and contribution to improving the utilization of the multi-purpose bacteria in food.

Draft Genome Sequence of Streptococcus thermophilus Strain CBC-S77, Isolated from Homemade Dairy Foods in Bulgaria

Here, we report the draft genome sequence of Streptococcus thermophilus strain CBC-S77. The strain was originally isolated from naturally processed, homemade dairy foods in West Rhode Mountain, Bulgaria. The genome was assembled in 148 contigs with a total length of 1,707,130 bp, with 1,563 coding genes and a GC content of 39.11%.

Here, we report the draft genome sequence of Streptococcus thermophilus strain CBC-S77. The strain was originally isolated from naturally processed, homemade dairy foods in West Rhode Mountain, Bulgaria. The genome was assembled in 148 contigs with a total length of 1,707,130 bp, with 1,563 coding genes and a GC content of 39.11%.

Complete Genome Sequences of Bacteriocin-Producing Streptococcus thermophilus Strains ST106 and ST109

Streptococcus thermophilus strains ST106 and ST109 produce broad-spectrum bacteriocins encoded within a bacteriocin-like peptide (blp) gene cluster. This study reports the complete genome sequences for both strains, with the ST109 chromosome containing 1,788,866 nucleotides (nt) and 1,572 predicted genes, and ST106 having 1,856,083 nt and 1,601 predicted genes.

Streptococcus thermophilus strains ST106 and ST109 produce broad-spectrum bacteriocins encoded within a bacteriocin-like peptide (blp) gene cluster. This study reports the complete genome sequences for both strains, with the ST109 chromosome containing 1,788,866 nucleotides (nt) and 1,572 predicted genes, and ST106 having 1,856,083 nt and 1,601 predicted genes.

Complete Genome Sequence of Streptococcus thermophilus Strain B59671, Which Naturally Produces the Broad-Spectrum Bacteriocin Thermophilin 110

Streptococcus thermophilus strain B59671 is a Gram-positive lactic acid bacterium that naturally produces a broad-spectrum bacteriocin, thermophilin 110, and is capable of producing gamma-aminobutyric acid (GABA). The complete genome sequence for this strain contains 1,821,173 nucleotides, 1,936 predicted genes, and an average G+C content of 39.1%.

The complete genome sequence of the yogurt isolate Streptococcus thermophilus ACA-DC 2

Streptococcus thermophilus ACA-DC 2 is a newly sequenced strain isolated from traditional Greek yogurt. Among the 14 fully sequenced strains of S. thermophilus currently deposited in the NCBI database, the ACA-DC 2 strain has the smallest chromosome, containing 1,731,838 bp. The annotation of its genome revealed the presence of 1,850 genes, including 1,556 protein-coding genes, 70 RNA genes and 224 potential pseudogenes. A large number of pseudogenes were identified. This was also accompanied by the absence of pathogenic features suggesting evolution of strain ACA-DC 2 through genome decay processes, most probably due to adaptation to the milk ecosystem. Analysis revealed the existence of one complete lactose-galactose operon, several proteolytic enzymes, one exopolysaccharide cluster, stress response genes and four putative antimicrobial peptides. Interestingly, one CRISPR-cas system and one orphan CRISPR, both carrying only one spacer, were predicted indicating low activity or inactivation of the cas proteins. Nevertheless, four putative restriction-modification systems were determined that may compensate any deficiencies of the CRISPR-cas system. Furthermore, whole genome phylogeny indicated three distinct clades within S. thermophilus. Comparative analysis among selected strains representative for each clade, including strain ACA-DC 2, revealed a high degree of conservation at the genomic scale, but also strain specific regions. Unique genes and genomic islands of strain ACA-DC 2 contained a number of genes potentially acquired through horizontal gene transfer events, that could be related to important technological properties for dairy starters. Our study suggests genomic traits in strain ACA-DC 2 compatible to the production of dairy fermented foods.

New Insights into Various Production Characteristics of Streptococcus thermophilus Strains

Streptococcus thermophilus is one of the most valuable homo-fermentative lactic acid bacteria, which, for a long time, has been widely used as a starter for the production of fermented dairy products. The key production characteristics of S. thermophilus, for example the production of extracellular polysaccharide, proteolytic enzymes and flavor substances as well as acidifying capacity etc., have an important effect on the quality of dairy products. The acidification capacity of the strains determines the manufacturing time and quality of dairy products. It depends on the sugar utilization ability of strains. The production of extracellular polysaccharide is beneficial for improving the texture of dairy products. Flavor substances increase the acceptability of dairy products. The proteolytic activity of the strain influences not only the absorption of the nitrogen source, but also the formation of flavor substances. Different strains have obvious differences in production characteristics via long-time evolution and adaptation to environment. Gaining new strains with novel and desirable characteristics is an important long-term goal for researchers and the fermenting industry. The understanding of the potential molecular mechanisms behind important characteristics of different strains will promote the screening and breeding of excellent strains. In this paper, key technological and functional properties of different S. thermophilus strains are discussed, including sugar metabolism, proteolytic system and amino acid metabolism, and polysaccharide and flavor substance biosynthesis. At the same time, diversity of genomes and plasmids of S. thermophilus are presented. Advances in research on key production characteristics and molecular levels of S. thermophilus will increase understanding of molecular mechanisms of different strains with different important characteristics, and improve the industrialization control level for fermented foods.

Bacteriocin production by Streptococcus thermophilus in complex growth media

OBJECTIVE

To test if the production of bacteriocins by Streptococcus thermophilus is influenced when grown in various complex media commonly used for the culturing of lactic acid bacteria.

RESULTS

Forty-one strains of S. thermophilus were screened for the production of bacteriocins in tryptone/yeast extract/lactose (TYL), M17-lactose (M17L), M17-glucose (M17G) and MRS media. Two strains, ST144 and ST145, were identified as novel bacteriocin producers, with constitutive production observed only in M17G. Strains ST110, ST114 and ST134 constitutively produced bacteriocins in all growth media but ST114 required growth in MRS for its antimicrobial activity to persist in a 24 h culture. The addition of a synthetic quorum sensing peptide (BlpC) induced bacteriocin production by ST106 in all media tested; and by ST118 in TYL and M17L. Strain ST109, which constitutively produced a bacteriocin in TYL and M17 broths, required BlpC induction when grown in MRS. Real-time PCR analysis showed that the natural expression of blpC in ST109 was lower when grown in MRS, suggesting that something in medium interfered with the blp quorum sensing system.

CONCLUSION

As the choice of growth medium influences both bacteriocin production and peptide stability, several types of production media should be tested when screening for novel bacteriocin-producing strains of S. thermophilus.

Polymorphism of the phosphoserine phosphatase gene in Streptococcus thermophilus and its potential use for typing and monitoring of population diversity

The phosphoserine phosphatase gene (serB) of Streptococcus thermophilus is the most polymorphic gene among those used in Multilocus Sequence Typing schemes for this species and has been used for both genotyping of isolates and for evaluation of population diversity. However, the information on the potential of this gene as a marker for diversity in S. thermophilus species is still fragmentary. In this study, we evaluated serB nucleotide polymorphism and its potential impact on protein structure using data from traditional sequencing. In addition we evaluated the ability of serB targeted high-throughput sequencing in studying the diversity of S. thermophilus populations in cheese and starter cultures. Data based on traditional cultivation based techniques and sequencing provided evidence that the distribution of serB alleles varies significantly in some environments (commercial starter cultures, traditional starter cultures, cheese). Mutations had relatively little impact on predicted protein structure and were not found in domains that are predicted to be important for its functionality. Cultivation independent, serB targeted high-throughput sequencing provided evidence for significantly different alleles distribution in different cheese types and detected fluctuations in alleles abundance in a mixed strain starter reproduced by backslopping. Notwithstanding some shortcomings of this method that are discussed here, the cultivation independent approach appears to be more sensitive than cultivation based approaches based on isolation and traditional sequencing.

Streptococcus thermophilus, an emerging and promising tool for heterologous expression: Advantages and future trends

Streptococcus thermophilus is the second most used bacterium in dairy industry. It is daily consumed by millions of people through the worldwide consumption of yogurts, cheeses and fermented milks. S. thermophilus presents many features that make it a good candidate for the production of heterologous proteins. First, its ability to be naturally transformable allows obtaining swiftly and easily recombinant strains using various genetic tools available. Second, its Generally Recognised As Safe status and its ability to produce beneficial molecules or to liberate bioactive peptides from milk proteins open up the way for the development of new functional foods to maintain health and well-being of consumers. Finally, its ability to survive the intestinal passage and to be metabolically active in gastrointestinal tract allows considering S. thermophilus as a potential tool for delivering various biological molecules to the gastrointestinal tract. The aim of this review is therefore to take stock of various genetic tools which can be employed in S. thermophilus to produce heterologous proteins and to highlight the advantages and future trends of use of this bacterium as a heterologous expression host.