Lactic Acid Bacteria Streptococcus Thermophilus Research Articles

Fermentation Characteristics of Fermented Milk with Streptococcus thermophilus CICC 6063 and Lactobacillus helveticus CICC 6064 and Volatile Compound Dynamic Profiles during Fermentation and Storage.

The lactic acid bacteria Streptococcus thermophilus and Lactobacillus helveticus are commonly used as starter cultures in dairy product production. This study aimed to investigate the characteristics of fermented milk using different ratios of these strains and analyze the changes in volatile compounds during fermentation and storage. A 10:1 ratio of Streptococcus thermophilus CICC 6063 to Lactobacillus helveticus CICC 6064 showed optimal fermentation time (4.2 h), viable cell count (9.64 log10 colony-forming units/mL), and sensory evaluation score (79.1 points). In total, 56 volatile compounds were identified and quantified by solid-phase microextraction and gas chromatography-mass spectrometry (SPME-GC-MS), including aldehydes, ketones, acids, alcohols, esters, and others. Among these, according to VIP analysis, 2,3-butanedione, acetoin, 2,3-pentanedione, hexanoic acid, acetic acid, acetaldehyde, and butanoic acid were identified as discriminatory volatile metabolites for distinguishing between different time points. Throughout the fermentation and storage process, the levels of 2,3-pentanedione and acetoin exhibited synergistic dynamics. These findings enhance our understanding of the chemical and molecular characteristics of milk fermented with Streptococcus thermophilus and Lactobacillus helveticus, providing a basis for improving the flavor and odor of dairy products during fermentation and storage.

Protein composition and nutritional aspects of pea protein fractions obtained by a modified isoelectric precipitation method using fermentation.

Pea albumins are promising for their nutritional, biological, and techno-functional properties. However, this fraction is usually discarded in the industry due to its low protein content compared to globulin fraction and the presence of some anti-nutritional compounds. In the present study, we used an alternative method of pea protein extraction based on alkaline solubilization/isoelectric precipitation in which the reduction of pH was achieved by lactic acid fermentation using specific starters instead of mineral acids. Hence, the main objective of this study was to examine the protein profile and the content of anti-nutritional and nutritional active compounds in pea albumin-rich fractions obtained by the isoelectric extraction method without (control) or with fermentation with different lactic acid bacteria (Streptococcus thermophilus, Lactiplantibacillus plantarum, and their co-culture). Different pea cultivars (Cartouche, Ascension, and Assas) were used here for their differences in protein profile. The results revealed a higher total nitrogen content in albumin-rich fraction for fermented samples and, in particular, for co-culture. The majority of total nitrogen was determined as non-protein (~50%), suggesting the degradation of proteins by LAB to small peptides and amino acids, which were solubilized in the soluble fraction (albumin) as confirmed by size exclusion chromatography (SEC-HPLC) analysis. Moreover, the higher antioxidant activity of fermented albumin samples was attributed to the production of small peptides during extraction. Lactic acid fermentation also resulted in a significant reduction of trypsin inhibitor activity, α-galactoside, and phytic acid content of this fraction compared to control.

Kombinasi Fermentasi Bakteri Asam Laktat dan Pemanasan Bertekanan-Pendinginan dalam Pembentukan Pati Resisten Tepung Talas Beneng (Xanthosoma undipes K. Koch)

The study aimed to determine the effect of lactic acid bacteria, fermentation time, and pressurized heating-cooling cycle on the formation of resistant starch content of beneng taro (Xanthosoma undipes K. Koch) flour. The materials used were beneng corm, isolates of lactic acid bacteria Lactobacillus casei and Streptococcus thermophilus, and MRSB media. The experimental design was randomized block design factorial with two factors: fermentation time (0, 18, and 24 hours) and pressurized-cooling heating (1, 2, and 3- cycles) in 3 replicates. The data were analyzed using analysis of variance and if necessary continued with Duncan's Multiple Range Test at a level of 95%. The tested parameters were the content of resistant starch, amylose, and amylopectin and the data were treated using variance of analysis. The results showed that the combination of L. casei and S. thermophillus produced the highest resistant starch content of 5.66%. Fermentation time of 18 and 24 hours produced resistant starch content of 4.46% and 4.51%, respectively. Autoclaving-cooling of 1-, 2-, and 3-cycle produced a similar type of resistant starch of 3.81%, 4.26%, and 4.16%, respectively. Therefore, the combination of L. casei and S. thermophillus fermented in 18 hours and 1-cycle of autoclaving-cooling is recommended to produce resistant beneng taro flour starch content.
 
 Keywords: fermentation, autoclaving-cooling, resistant starch, taro beneng, Xanthosoma undipes K. Koch

Comparative evaluation of the probiotic and antioxidant potential of indigenous Lactic Acid Bacteria

This study was undertaken to assess the probiotic and antioxidant potential of five indigenous cultures of lactic acid bacteria viz, Lactobacillus acidophilus, Lactiplantibacillus plantarum, Lacticaseibacillus rhamnosus, Lactobacillus bulgaricus and Streptococcus thermophilus. The probiotic properties in terms of acid and bile tolerance, cell surface hydrophobicity, autoaggregation, coaggregation and bile salt hydrolase activity were assessed in vitro. The DPPH assay indicated highest antioxidant activity of 45.33 per cent for Streptococcus thermophilus. All five cultures exhibited significant antioxidant potential. Lacticaseibacillus rhamnosus, Lactobacillus acidophilus and Lactiplantibacillus plantarum showed higher probiotic potential in terms of acid and bile tolerance, cell surface hydrophobicity, autoaggregation and coaggregation. None of the cultures exhibited bile salt hydrolase activity.

Influence of the exopolysaccharide Streptococcus thermophilus on the development of the Lena sturgeon

The influence of exopolysaccharide (EPS) of lactic acid bacteria Streptococcus thermophilus on the development of the Lena sturgeon when grown in an experimental aquarium was studied. It has been shown that the addition of EPS S. thermophilus to the feed of sturgeon fish contributes to an increase in the rate of growth and development of fish without adversely affecting the fish organism, and also improves the organoleptic characteristics (taste and texture) of fish meat.

Improving the sensory and rheological properties of yogurt using aqueous extract of basil (Ocimum basilicum L.)

This study aims to produce a therapeutic milk product (yogurt) to improve and treat many different digestive problems, using the lactic acid bacteria (Streptococcus thermophilus and Lactobacillus bulgaricus) supplemented with aqueous extract of the plant (basil) with three concentrations of 1%, 3% and 5% [v/v] basil, they were represented by R1, R2 and R3 treatments respectively, as well as the control [C] treatment in which the yogurt was made without any addition. The treatments were stored for 21 days at [5±1] °C. The physicochemical properties were studied, which included measurement [pH, total acidity, syneresis, viscosity, and hardness] and microbiological examinations, as well as sensory evaluation on the first day of manufacture and after 7, 14 and 21 days of cold storage. The results showed that there were no significant differences in pH values immediately after manufacturing for all treatments. As for the percentage of total acidity (TTA), it was close to immediately after manufacturing for all the different yogurt treatments, while during storage, a clear increase in their values was observed for all transactions. Results showed a significant difference in syneresis, viscosity and hardness immediately after manufacturing and during cold storage for all treatments. R1 and R2 treatments improved the viscosity, hardness and syneresis of yogurt. The R2 and R3 treatments recorded the highest numbers of starter bacteria compared to the other treatments. Also, the results showed that the superiority of R2 treatment in the sensory evaluation of the characteristics of taste, flavor, texture and general acceptance.

Co-utilization of saccharides in mixtures: Moving toward a new understanding of carbon metabolism in Streptococcus thermophilus

The lactic acid bacterium Streptococcus thermophilus is widely used in food production, notably in yogurt fermentation. It evolved under highly specific ecological conditions, resulting in its ability to efficiently metabolize lactose, the main saccharide in milk. However, when used in sweetened dairy products or plant-based products, S. thermophilus may encounter other saccharides (i.e. alone or in mixtures). To date, the bacterium's metabolic capacities in such contexts have been poorly characterized. Here, we explored saccharide utilization by 39 S. thermophilus strains. Using in silico analysis, we discovered that the identity and structure of saccharide utilization genes are conserved across strains, and we identified six saccharides that might be metabolized. Although underlying genetic variability was low, strains nonetheless displayed differences in growth when supplied with different saccharides: lactose, sucrose, fructose, and glucose.Interestingly, we found that strains preferentially used lactose and sucrose in tandem when given saccharide mixtures. Furthermore, we uncovered some main potential drivers of saccharide metabolism in S. thermophilus. Notably, the sucrose transporter ScrA is also responsible for importing glucose. Overall, this research has yielded useful findings that can help the development of new fermented foods, including plant-based products, in which sucrose may serve as a major carbon source.

Role of the Sortase A in the Release of Cell-Wall Proteinase PrtS in the Growth Medium of Streptococcus thermophilus 4F44

Growth of the lactic acid bacterium Streptococcus thermophilus in milk depends on its capacity to hydrolyze proteins of this medium through its surface proteolytic activity. Thus, strains exhibiting the cell envelope proteinase (CEP) PrtS are able to grow in milk at high cellular density. Due to its LPNTG motif, which is possibly the substrate of the sortase A (SrtA), PrtS is anchored to the cell wall in most S. thermophilus strains. Conversely, a soluble extracellular PrtS activity has been reported in the strain 4F44. It corresponds, in fact, to a certain proportion of PrtS that is not anchored to the cell wall but rather is released in the growth medium. The main difference between PrtS of strain 4F44 (PrtS4F44) and other PrtS concerns the absence of a 32-residue imperfect duplication in the prodomain of the CEP, postulated as being required for the maturation and correct subsequent anchoring of PrtS. In fact, both mature (without the prodomain at the N-terminal extremity) and immature (with the prodomain) forms are found in the soluble PrtS4F44 form along with an intact LPNTG at their C-terminal extremity. Investigations we present in this work show that (i) the imperfect duplication is not implied in PrtS maturation; (ii) the maturase PrtM is irrelevant in PrtS maturation which is probably automaturated; and (iii) SrtA allows for the PrtS anchoring in S. thermophilus but the SrtA of strain 4F44 (SrtA4F44) displays an altered activity.

Lactic Acid Bacteria (Lactobacillus bulgaricus and Streptococcus thermophillus) in Yogurt Inhibit the Growth of Escherichia coli, Salmonella typhimurium, and Shigella sp. In Vitro

Diarrhea is defecation with a frequency more often than usual (three times or more) a day (10 mL/kg/day) with a soft or liquid consistency, even in the form of water alone. Pathogenic bacteria, such as Escherichia coli, Salmonella typhimurium, and Shigella sp., play a role in many cases, to which antibiotics are prescribed as the first-line therapy. However, since antibiotic resistance cases are often found, preventive therapies are needed, such as consuming yogurt, which is produced through a fermentation process by lactic acid bacteria (LAB). This research aimed to determine the activity of lactic acid bacteria (Liactobacillus bulgaricus and Streptococcus thermophilus) in yogurt in inhibiting the growth of the pathogenic bacteria E. coli, S. typhimurium, and Shigella sp. The research applied in vitro with the liquid dilution test method and the true experimental design research method with post-test-only and control group design. The design was used to see the inhibitory effect of yogurt LAB on the growth of E. coli, S. typhimurium, and Shigell sp. to compare the effect of several different yogurt concentrations, namely 20%, 40%, 60%, and 80%. The results of the Least Significance Different analysis showed that there was a significant difference between yogurt with a concentration of 0% and that with various concentrations in inhibiting the growth of E. coli, S. typhimurium, and Shigella sp. with a p-value of <0.05. Whereas, there was no significant difference in the various concentrations of yogurt in inhibiting the growth of the three kinds of bacteria with a p-value of > 0.05.Â

STUDY OF PROPERTIES OF YOGHURTS MADE USING VIVO STARTER CULTURES

The article presents the results of experimental studies of qualitative indicators of milk and fermented milk products (yoghurts) made using VIVO starter cultures. VIVO starter cultures contain thermophilic lactic acid bacteria Streptococcus thermophilus, Lactobacillus delbrueckii ssp., Lactobacillus acidophilus and others.
 The determination of organoleptic and physico-chemical parameters of cow's milk and dairy products based on it was carried out according to generally accepted methods. During the organoleptic evaluation of milk and lactic acid products, the appearance and texture, smell, taste and color of milk were examined. Determination of active acidity was carried out in accordance with GOST 26781. Titratable acidity in degrees Turner was determined according to GOST 3624. The content of fat, protein, dry matter was determined according to GOST 2661: 2010.
 A study was made of the organoleptic characteristics of yogurts obtained by fermentation by using of VIVO starter cultures. The high activity of VIVO starter cultures was established, the products on the basis of which have a pleasant taste characteristic of these products.
 The results of physico-chemical analysis of yogurt samples obtained by using of VIVO starter cultures confirmed their compliance with DSTU 4343: 2004.
 Lactic acid products made with VIVO sourdough are functional products. It is recommended to use yogurts based on VIVO starter cultures to restore intestinal microflora, normalize digestion, strengthen immunity, and reduce the risk of colds and SARS.

Starter bacteria as producers of CLA in ripened cheese.

The profile of polyunsaturated fatty acids in cheeses obtained through fermentation by lactic acid bacteria Lactobacillus helveticus and Streptococcus thermophilus were evaluated. The milk used to make the cheeses came from cows fed with flaxseed oil and annato. The cheeses presented microbiological and physic-chemical quality with in the standards established by the legislation for Staphylococci and Listeria. With maturation, there was a reduction in the coliform values ​​for both treatments. Regarding the counts of lactic acid bacteria, these remained viable until the 30th day of maturation and the proteolytic bacteria decreased. For antioxidant capacity, the treatment containing the combination of the strains obtained high ABTS values. There was no significant difference between the treatments with respect to the color of the samples. For texture, there was a significant difference for the parameters cohesion and elasticity. No increase in CLA content was observed in the form of its two main isomers, however, the levels of polyunsaturated fatty acids were increased.

A modified reinforced clostridial medium for the isolation and enumeration of Lactobacillus delbrueckii ssp. bulgaricus in a mixed culture

In this study, we modified reinforced clostridial medium (RCM) to selectively enumerate and isolate Lactobacillus delbrueckii ssp. bulgaricus, a probiotic and important starter culture in the dairy industry. The disparity in the reported carbohydrate fermentation pattern of L. delbrueckii ssp. bulgaricus was used to develop a growth medium not only selective for L. delbrueckii ssp. bulgaricus but significantly inhibitory to the growth of other lactic acid bacteria. A recently modified RCM (mRCM) was optimized for this study by the addition of 0.5% fructose, 0.5% dextrose, 1% maltose, and 0.25% sodium pyruvate while replacing lactose as a carbohydrate source. The cell recovery and bacterial counts of L. delbrueckii ssp. bulgaricus in tested products (pure L. delbrueckii ssp. bulgaricus strains, starter culture, probiotic supplements, and yogurt) using our mRCM with sodium pyruvate (mRCM-PYR) were significantly higher than in the recently modified RCM and the common de Man, Rogosa, and Sharpe (MRS) culture medium. The growth of other lactic acid bacteria (Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus rhamnosus, and Lactobacillus reuteri) and Bifidobacteria was retarded in this modified medium compared with their growth in MRS and mRCM. This result is a significant improvement in the enumeration and differentiation of L. delbrueckii ssp. bulgaricus in mRCM-PYR compared with the results in MRS and mRCM where the high background growth of similar species interferes with the accuracy of bacterial population counts. Our results thus suggest that mRCM-PYR could be recommended as a reliable alternative growth medium for the selective enumeration and isolation of L. delbrueckii ssp. bulgaricus in a mixed culture.

Microbial and enzymatic hydrolysis of dromedary whey proteins and caseins: techno-functional, radical scavenging, antimicrobial properties and incorporation in beverage formulation

Comparative study of functional properties, radical scavenging and antimicrobial activities of dromedary whey protein and casein hydrolysates was investigated. Dromedary protein hydrolysates were prepared by treatment with digestive proteases (pepsin and pancreatin) and by the proteolytic system of two lactic acid bacteria (Streptococcus thermophilus and Lactobacillus bulgaricus). Solubility and interfacial properties like emulsifying capacity are improved after enzymatic hydrolysis of both whey protein and casein. Whereas, foam capacity and stability are more important in whey protein hydrolysates than casein hydrolysates and are widely influenced by the method of hydrolysis. All hydrolysates showed radical scavenging activities. The highest antioxidant activity is exhibited by WPHE (whey protein hydrolysated by gastro-intestinal enzymes “pepsin and pancreatin”) for DPPH (2,2-diphenyl-1-picrylhydrazyl) test and CNHE (casein hydrolysated by pepsin and pancreatin) for ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) assay. Further, whey protein hydrolysates displayed antibacterial activity and WPHE was the most effective, particularly against Escherichia coli and Staphylococcus epidermidis. Based on the results, we conclude that WPHE has great technological applicability in food ingredients, as a promising source of functional hydrolysate with antioxidant and antimicrobial activities. For this reason, WPHE was added to the dromedary milk based beverage and chemical, microbiological and sensory properties of the resulting product were investigated. Formulated beverage flavored with strawberry or banana possessed a good microbiological quality. The sensory analysis demonstrated a good acceptance mainly in taste and consistency of the beverage samples. There is only significant difference in the color of the different formulated beverages.

Characteristics of Milk Fermented by Streptococcus thermophilus MGA45-4 and the Profiles of Associated Volatile Compounds during Fermentation and Storage.

The lactic acid bacterium Streptococcus thermophilus is a major starter culture for the production of dairy products. In this study, the physiochemical characteristics of milk fermented by the MGA45-4 isolate of S. thermophilus were analyzed. Our data indicate that milk fermented using S. thermophilus MGA45-4 maintained a high viable cell count (8.86 log10 colony-forming units/mL), and a relatively high pH (4.4), viscosity (834.33 mPa·s), and water holding capacity (40.85%) during 14 days of storage. By analyzing the volatile compound profile using solid-phase microextraction and gas chromatography/mass spectrometry, we identified 73 volatile compounds in the fermented milk product, including five carboxylic acids, 21 aldehydes, 13 ketones, 16 alcohols, five esters, and 13 aromatic carbohydrates. According to the odor activity values, 11 of these volatile compounds were found to play a key role in producing the characteristic flavor of fermented milk, particularly octanal, nonanal, hexanal, 2,3-butanedione, and 1-octen-3-ol, which had the highest odor activity values among all compounds analyzed. These findings thus provide more insights in the chemical/molecular characteristics of milk fermented using S. thermophilus, which may provide a basis for improving dairy product flavor/odor during the process of fermentation and storage.

Effect of High-Pressure Processing on Quality and Microbiological Properties of a Fermented Beverage Manufactured from Sweet Whey Throughout Refrigerated Storage

The production of fermented beverages is a promising way to valorize by-products of dairy manufacturing. However, the shelf-life of these products is often limited by the post-acidification process that occurs during storage. In this work, we manufactured a fermented beverage from sweet whey by using the starter lactic acid bacteria (SLAB) Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. High-pressure processing (HPP) at 200 MPa for 10 min or 400 MPa for 1 min were applied after manufacturing. The aim of this study was to evaluate the effect of HPP on the quality of the beverage and on the behavior of the SLAB. Both high hydrostatic pressure treatments preserved flavor and texture attributes until 45 days post-HPP, without affecting chromatic parameters. Plate counts for both species were lower in HPP-treated beverages (HB) than in control beverages (CB), although treatment at 200 MPa maintained optimal amounts of total SLAB (6.6–7.9 log CFU/mL). Conversely, quantitative PCR (qPCR) and reverse transcription-qPCR (RT-qPCR) revealed that bacterial DNA or mRNA levels persisted after HPP (> 1.4 × 105 genome or cDNA copies/mL), even upon 400-MPa treatments. As a whole, this study indicated that HPP preserved the quality of the beverage until 45 days post-HPP, which is longer than the shelf-life of conventional fermented beverages obtained from milk. Moreover, our results obtained with these SLAB in a fermented dairy beverage upon HPP extend previous findings regarding the limitations of culture-dependent methods to assess microbial viability.

Preparation of Probiotic Apple Juice by Lactic Acid Fermentation

Fermentation of apple juice was done for 72 hrs by lactic acid bacteria (Lactobacillus plantarum and Streptococcus thermophilus)and physico-chemical characteristics of fermented apple juices were recorded at 0. 24, 48 and 72 hrs intervals. On the basis of highest lactic acid bacterial counts, rate of fermentation (°B/24hr), acidity, sugar utilization percentage, retention of ascorbic acid and total phenols, antioxidant activity and antimicrobial activity against pathogenic bacteria such as E. coli and S. aureus, while lowest pH, coliform, yeast and mold counts, the best treatments L. plantarum 107cfu/ml for apple fermented apple juice was selected for storage study viz. During fermentation both vitamin C and total phenols declined, while, the antioxidant activity, antimicrobial activity, viable cell counts and lactic acid bacteria counts were increased. As the antimicrobial activity increased, the counts of coliform, yeast and mold declined. During storage of selected treatment of fermented apple juice for four weeks at 4°C retained physico-chemical parameters above the value of significance. Lactic acid bacteria remained viable in prescribed number (4.76–6.00 × 106 cfu/ml), acid and bile resistance, imparted antimicrobial activity and antioxidant activity to the apple juices during storage and thus, could be called as probiotics juices. Based on the sensory evaluation (visual colour and flavours) of fermented apple juice, it was concluded that lactic acid fermentation did not influence the desirable characteristics of apple juices. So the probiotic juices were acceptable. Identification of lactic acid bacteria by biochemical test concluded that the bacteria were L. plantarum in apple juices which were inoculated in juices for fermentation, after storage apple juice were suitable for lactic acid fermentation to produce a probiotic beverage. So, this juice can serve as healthy beverage for vegetarians and lactose allergic consumers.

Influence of oregano essential oil on traditional Argentinean cheese elaboration: Effect on lactic starter cultures

The aim of this work is to study the oregano essential oil (OEO) composition from Northwestern Argentinean regions and to evaluate its effect on the lactic starter cultures. The oregano used, Origanum vulgare var hirtum, was obtained from Andalgalá, Catamarca. The essential oil presented high amounts of α-terpinene (10%), γ-terpinene (15.1%), terpinen-4-ol (15.5%) and thymol (13.0%) as the main components. No negative effect on growth or metabolic activity of lactic acid bacteria Streptococcus thermophilus CRL 728 and CRL 813, Lactobacillus delbrueckii subsp. bulgaricus CRL 656 and CRL 468, and Lactococcus lactis subsp. lactis CRL 597 up to the maximum concentration (200μg/g) assayed was observed. No differences in the organoleptic characteristics of semi-hard cheeses flavored with oregano essential oil (200μg/g) and homemade cheeses flavored with oregano leaves were found. With respect to the microbiological quality of the products, neither enterobacteria nor mold and yeast were detected during ripening in essential-oil flavored cheese compared to control cheese (enterobacteria 2×103UFC/g) and cheese flavored with oregano leaves (mold/yeast 4×104CFU/g). Our results showed that the use of oregano essential oil and lactic starter culture considerably improved cheese quality.

Identification and Analysis of a Novel Group of Bacteriophages Infecting the Lactic Acid Bacterium Streptococcus thermophilus.

We present the complete genome sequences of four members of a novel group of phages infecting Streptococcus thermophilus, designated here as the 987 group. Members of this phage group appear to have resulted from genetic exchange events, as evidenced by their "hybrid" genomic architecture, exhibiting DNA sequence relatedness to the morphogenesis modules of certain P335 group Lactococcus lactis phages and to the replication modules of S. thermophilus phages. All four identified members of the 987 phage group were shown to elicit adsorption affinity to both their cognate S. thermophilus hosts and a particular L. lactis starter strain. The receptor binding protein of one of these phages (as a representative of this novel group) was defined using an adsorption inhibition assay. The emergence of a novel phage group infecting S. thermophilus highlights the continuous need for phage monitoring and development of new phage control measures. Phage predation of S. thermophilus is an important issue for the dairy industry, where viral contamination can lead to fermentation inefficiency or complete fermentation failure. Genome information and phage-host interaction studies of S. thermophilus phages, particularly those emerging in the marketplace, are an important part of limiting the detrimental impact of these viruses in the dairy environment.

Investigation of the Activity of the Microorganisms in a Reblochon-Style Cheese by Metatranscriptomic Analysis.

The microbial communities in cheeses are composed of varying bacteria, yeasts, and molds, which contribute to the development of their typical sensory properties. In situ studies are needed to better understand their growth and activity during cheese ripening. Our objective was to investigate the activity of the microorganisms used for manufacturing a surface-ripened cheese by means of metatranscriptomic analysis. The cheeses were produced using two lactic acid bacteria (Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus), one ripening bacterium (Brevibacterium aurantiacum), and two yeasts (Debaryomyces hansenii and Geotrichum candidum). RNA was extracted from the cheese rinds and, after depletion of most ribosomal RNA, sequencing was performed using a short-read sequencing technology that generated ~75 million reads per sample. Except for B. aurantiacum, which failed to grow in the cheeses, a large number of CDS reads were generated for the inoculated species, making it possible to investigate their individual transcriptome over time. From day 5 to 35, G. candidum accounted for the largest proportion of CDS reads, suggesting that this species was the most active. Only minor changes occurred in the transcriptomes of the lactic acid bacteria. For the two yeasts, we compared the expression of genes involved in the catabolism of lactose, galactose, lactate, amino acids, and free fatty acids. During ripening, genes involved in ammonia assimilation and galactose catabolism were down-regulated in the two species. Genes involved in amino acid catabolism were up-regulated in G. candidum from day 14 to day 35, whereas in D. hansenii, they were up-regulated mainly at day 35, suggesting that this species catabolized the cheese amino acids later. In addition, after 35 days of ripening, there was a down-regulation of genes involved in the electron transport chain, suggesting a lower cellular activity. The present study has exemplified how metatranscriptomic analyses provide insight into the activity of cheese microbial communities for which reference genome sequences are available. In the future, such studies will be facilitated by the progress in DNA sequencing technologies and by the greater availability of the genome sequences of cheese microorganisms.

Draft Genome Sequence of Streptococcus thermophilus C106, a Dairy Isolate from an Artisanal Cheese Produced in the Countryside of Ireland.

The lactic acid bacterium Streptococcus thermophilus is widely used for the fermentation of dairy products. Here, we present the draft genome sequence of S. thermophilus C106 isolated from an artisanal cheese produced in the countryside of Ireland.