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Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) is a microaerophylic anaerobe, which is widely used in the production of yogurt, cheese, and other fermented dairy products. L. bulgaricus and its partner Streptococcus thermophilus were used as starter cultures of yogurt in the world for thousands of years. In our previous study, L. bulgaricus LDB-C1 was obtained from traditional fermented milk, and possessed some characteristics like high exopolysaccharide yield and good fermentation performance. The analysis of its CRISPR–Cas system, antibiotic resistance, virulence factors, and mobile elements, was performed to reveal the stability of the strain LDB-C1. It was found that LDB-C1 contains a plenty of spacers in the CRISPR region, indicating it might have better performance against the infection of phages and plasmids. Furthermore, the acquired or transmittable antibiotic resistance/virulence factor genes were absent in the tested L. bulgaricus strain LDB-C1. [ABSTRACT FROM AUTHOR]

Clustered regularly interspaced short palindromic repeats (CRISPR) consists of a series of regular repeat-spacer sequences. It can not only act as a natural immune system in most prokaryotes, but also be utilized as the tool of newly developed genome modification and evolutionary researches. Streptococcus thermophilus is an important model organism for the study and application of CRISPR systems. In present study, the occurrence and diversity of CRISPR–Cas systems in the genomes of S. thermophilus were investigated including 4 new sequenced strains CS5, CS9, CS18, CS20, and other 23 strains downloaded from NCBI website. 66 CRISPR/Cas systems were identified among these 27 strains and could divided into four subsystems according to the arrangement of Cas proteins, notably I-E, II-A, II-C and III-A. Overall, 26 type II-C systems, 18 type II-A systems, 13 type III-A systems, 9 type I-E systems were identified. It was mentioned that CS20 contained two type II-C systems which had not been identified in the other 26 S. thermophilus strains. Overall, 1,080 spacers were analyzed and blasted. Sequence identity searches of spacers implied that most spacers derived from partial sequences of exogenous DNA, including various bacteriophages and plasmids. Of note, a large number of novel spacers were found in this study, indicating the unique phage environment they have undergone, especially CS20 strain. In addition, the analysis of the cas1 and cas9 genes revealed the genetic relationship among CRISPR–Cas system in these strains. Furthermore, the analysis of CRISPR spacers also indicated protospacer adjacent motif (PAM) sequences. Summary of PAM sequences could lay the foundations for the application of S. thermophilus CRISPR–Cas system. Our results suggested CS5 and CS18 can be used as model strains in the research of CRISPR–Cas system, and CS20 might have greater application potential in gene editing. [ABSTRACT FROM AUTHOR]

Lactobacillus delbrueckii subsp. bulgaricus is currently one of the most valuable lactic acid bacteria (LAB) and widely used in global dairy industry. The acid tolerance and adaptation ability of LAB is the key point of their survival and proliferation during fermentation process and in gastrointestinal tract of human body. Two component system (TCS) is one of the most important mechanisms to allow bacteria to sense and respond to changes of environmental conditions. TCS typically consists of a histidine protein kinase (HPK) and a corresponding response regulator (RR). Our previous study indicated a TCS (JN675228/JN675229) was involved in acid adaptation in L. bulgaricus. To reveal the role of JN675228 (HPK1)/JN675229 (RR1) in acid adaptation, the target genes of JN675228 (HPK1)/JN675229 (RR1) were identified by means of a proteomic approach complemented with transcription data in the present study. The results indicated that HPK1/RR1 regulated the acid adaptation ability of bacteria by means of many pathways, including the proton pump related protein, classical stress shock proteins, carbohydrate metabolism, nucleotide biosynthesis, DNA repair, transcription and translation, peptide transport and degradation, and cell wall biosynthesis, etc. To our knowledge, this is the first report with the effect of acid adaptation-related TCS HPK1/RR1 on its target genes. This study will offer experimental basis for clarifying the acid adaptation regulation mechanism of L. bulgaricus, and provide a theoretical basis for this bacterium in industry application. [ABSTRACT FROM AUTHOR]

Lactic acid bacteria (LAB) can take advantage of fermentable carbohydrates to produce lactic acid. They are proverbially applied in industry, agricultural production, animal husbandry, food enterprise, pharmaceutical engineering and some other important fields, which are closely related to human life. For performing the probiotic functions, LAB have to face the low pH environment of the gastrointestinal tract. Therefore, acid resistance of LAB is of great importance not only for their own growth, but also for fermentation and preparation of probiotic products. Recent research studies on acid resistance mechanisms of LAB are mainly focused on neutralization process, biofilm and cell density, proton pump, protection of macromolecules, pre-adaptation and cross-protection, and effect of solutes. In this context, biotechnological strategies such as synthetic biology, genome shuffling, high pressure homogenization and adaptive laboratory evolution were also used to improve the acid resistance of LAB to respond to constantly changing low pH environment. [ABSTRACT FROM AUTHOR]

Streptococcus thermophilus is the most important thermophilic dairy starter, and is widely used in the dairy industry. Streptococcus thermophilus exopolysaccharides received wide attention over recent decades, because they can improve the properties of the dairy product and confer beneficial health effects. The understanding of the regulatory and biosynthetic mechanisms of EPS will improve the EPS biosynthesis, increase the productivity of EPSs, and develop EPSs with desirable properties. The structure of EPSs is the focus of this study. Revealing the structure-function relationship can lead to increase the knowledge base and from there to increased research of EPS. The EPS yield is a key limiting factor in the research and utilization of EPS. In the present review, biosynthetic pathways and genetics of S. thermophilus EPSs were described and reviewed. At the same time, functional properties and applications of EPS, and strategies for enhancement of EPS production are discussed. [ABSTRACT FROM AUTHOR]

Streptococcusthermophilus is one of the economically most representatives of lactic acid bacteria, which is widely used as a starter to produce fermented milk products. In this study, 22 S. thermophilus strains were isolated from 26 fermented milk samples. Most isolates showed the ability to ferment a broad range of carbohydrates. Interestingly, eight strains are galactose positive, which is a desirable property in various industrial dairy fermentations. Four different nucleotide sequences were found in the galR-galK intergenic regions. The 16S-23S intergenic spacer region sequences of most isolates were determined as ITS-St-II type, which are related with protease positive and fast acidification. CS18 presented excellent technological performances, and showed potential as a promising starter candidate. To gain a comprehensive view of stress response mechanisms of strains, the distribution of all the two-component systems (TCSs) in strains were investigated. TCS analysis indicated that the nucleotide sequence of TCSs have obvious differences in different strains. And the strains with the special nucleotide sequences of TCS have distinctive traits. Therefore, it was speculated that there is a certain connection between the traits’ difference and the TCS difference of strains. [ABSTRACT FROM AUTHOR]