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John W. Foster – One of the best experts on this subject based on the ideXlab platform.
A Low pH-Inducible, PhoPQ-Dependent Acid Tolerance Response Protects Salmonella typhimurium against Inorganic Acid StressJournal of bacteriology, 1998Co-Authors: Bradley L. Bearson, Lee Wilson, John W. FosterAbstract:
The Acid Tolerance response enables Salmonella typhimurium to survive exposures to potentially lethal Acidic environments. The Acid stress imposed in a typical assay for Acid Tolerance (log-phase cells in minimal glucose medium) was shown to comprise both inorganic (i.e., low pH) and organic Acid components. A gene previously determined to affect Acid Tolerance, atbR, was identified as pgi, the gene encoding phosphoglucoisomerase. Mutations in pgi were shown to increase Acid Tolerance by preventing the synthesis of organic Acids. Protocols designed to separate the stresses of inorganic from organic Acids revealed that the regulators sigma38 (RpoS), Fur, and Ada have major effects on Tolerance to organic Acid stress but only minor effects on inorganic Acid stress. In contrast, the two-component regulatory system PhoP (identified as Acid shock protein ASP29) and PhoQ proved to be important for Tolerance to inorganic [corrected] Acid stress but had little effect against organic Acid stress. PhoP mutants also failed to induce four ASPs, confirming a role for this regulator in Acid Tolerance. Acid shock induction of PhoP appears to occur at the transcriptional level and requires the PhoPQ system. Furthermore, induction by Acid occurs even in the presence of high concentrations of magnesium, the ion known to be sensed by PhoQ. These results suggest that PhoQ can sense both Mg2+ and pH. Since phoP mutants are avirulent, the low pH activation of this system has important implications concerning the pathogenesis of S. typhimurium. The involvement of four regulators, two of which are implicated in virulence, underscores the complexity of the Acid Tolerance stress response and further suggests that features of Acid Tolerance and virulence are interwoven.
Internal pH crisis, lysine decarboxylase and the Acid Tolerance response of Salmonella typhimuriumMolecular microbiology, 1996Co-Authors: Yong Keun Park, Bradley L. Bearson, Seong Ho Bang, Iel Soo Bang, John W. FosterAbstract:
Salmonella typhimurium possesses an adaptive response to Acid that increases survival during exposure to extremely low pH values. The Acid Tolerance response (ATR) includes both log-phase and stationary-phase systems. The log-phase ATR appears to require two components for maximum Acid Tolerance, namely an inducible pH homeostasis system, and a series of Acid-shock proteins. We have discovered one of what appears to be a series of inducible exigency pH homeostasis systems that contribute to Acid Tolerance in extreme Acid environments. The low pH-inducible lysine decarboxylase was shown to contribute significantly to pH homeostasis in environments as low as pH 3.0. Under the conditions tested, both lysine decarboxylase and sigma s-dependent Acid-shock proteins were required for Acid Tolerance but only lysine decarboxylase contributed to pH homeostasis. The cadBA operon encoding lysine decarboxylase and a lysine/cadaverine antiporter were cloned from S. typhimurium and were found to be 79% homologous to the cadBA operon from Escherichia coli. The results suggest that S. typhimurium has a variety of means of fulfilling the pH homeostasis requirement of the ATR in the form of inducible amino Acid decarboxylases.
Adaptive Acid Tolerance response (ATR) in Aeromonas hydrophila.Microbiology, 1994Co-Authors: Kevin L. Karem, John W. Foster, Asim K. BejAbstract:
Aeromonas hydrophila, a gastrointestinal pathogen of humans, was shown to exhibit a significant adaptive Acid Tolerance response (ATR) capable of protecting cells from severe Acid at a pH of 3.5. The ATR was induced by exposure to a relatively mild pH level of 5.0 for 20 min. Adaptation required protein synthesis since treatment with chloramphenicol during adaptation to pH 5.0 prevented the development of Acid Tolerance. The adaptation to Acid environment was found to be a non-transient phenomenon. Also, iron was not required for Acid adaptation in A. hydrophila. Two-dimensional protein analyses revealed an increased production of 28 proteins and decreased synthesis of 10 following pH shifts from 7.2 to 5.0. The mild pH treatment must act as a signal to A. hydrophila to adapt and survive in Acid environments by producing ‘protective’ proteins. The adaptation and survival of this pathogen in low pH may provide valuable information about its ability to withstand Acid environments in nature and in the human gastrointestinal tract.
Xiaoyang Pang – One of the best experts on this subject based on the ideXlab platform.
Whole-genome sequencing and genomic-based Acid Tolerance mechanisms of Lactobacillus delbrueckii subsp. bulgaricus LJJ.Applied microbiology and biotechnology, 2020Co-Authors: Li Weixun, Lan Yang, Wenlong Nan, Shuwen Zhang, Obaroakpo Joy Ujiroghene, Xiaoyang PangAbstract:
The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus), a widely used probiotic, is majorly affected by its Acid Tolerance. Here, we conducted whole-genome sequencing of the high Acid-tolerant L. bulgaricus LJJ stored in the laboratory. Compared with the whole genome of low Acid-tolerant strain L. bulgaricus ATCC11842, the results show that 16 candidate Acid-tolerant genes may be involved in the regulation of the Acid Tolerance of L. bulgaricus LJJ. Association analysis of candidate Acid-tolerant genes and Acid-tolerant traits of different L. bulgaricus strains revealed that the three genes dapA, dapH, and lysC are the main reasons for the strong Acid Tolerance of L. bulgaricus LJJ. The results of real-time quantitative PCR (RT-qPCR) supported this conclusion. KEGG pathway analysis showed that these three Acid-tolerant genes are involved in the synthesis of lysine; the synthesis of lysine may confer L. bulgaricus LJJ strong Acid Tolerance. This study successfully revealed the Acid Tolerance mechanism of L. bulgaricus LJJ and provides a theoretical basis for the subsequent selection of strains with high Acid Tolerance for improved probiotic functions. • Three genes are identified as Acid-tolerant genes, respectively, lysC, dapA, and dapH. • LysC and dapA are the major key genes in the synthesis of lysine. • The synthesis of lysine may confer L. bulgaricus LJJ strong Acid Tolerance.
Whole-genome sequencing and genomic-based Acid Tolerance mechanisms of Lactobacillus delbrueckii subsp. bulgaricus LJJ, 2019Co-Authors: Xiaoyang Pang, Lan Yang, Shuwen Zhang, Obaroakpo Joy Ujiroghene, Cai ZhangAbstract:
Abstract Background: The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp. Bulgaricus ( L. d. bulgaricus ), a widely used probiotic, is majorly affected by its Acid Tolerance. In this study, a genome-wide sequence of a highly Acid-tolerant L. d. bulgaricus LJJ was supposed to be determined, and we expect to find out the Acid Tolerance mechanism of L. d. bulgaricus LJJ by comparative genomics. Results: Functional annotation and pathways of differential genes were determined using bioinformatics. The results in our study showed that the three genes dapA , dapH and lysC identified are implicated in the high Acid Tolerance of LJJ strain. Thus, they are potentially important as Acid-tolerant genes of LJJ strain. Conclusions: This study successfully revealed the Acid Tolerance mechanism of LJJ. Based on the previous research of LJJ in our laboratory, the successful analysis of the Acid-tolerant mechanism of L. d. bulgaricus will further lay the foundation for the subsequent breeding of high Acid-tolerant strains and greatly enhance their probiotic functions. Keywords: Lactobacillus delbrueckii subsp. Bulgaricus ; Acid-tolerant mechanism; comparative genomics; dapA ; dapH ; LysC
Gunnel Svensäter – One of the best experts on this subject based on the ideXlab platform.
Acid Tolerance properties of dental biofilms in vivo.BMC microbiology, 2017Co-Authors: Anna Senneby, Julia R. Davies, Gunnel Svensäter, Jessica NeilandsAbstract:
The ecological plaque hypothesis explains caries development as the result of the enrichment of Acid tolerant bacteria in dental biofilms in response to prolonged periods of low pH. Acid production by an Acid tolerant microflora causes demineralisation of tooth enamel and thus, individuals with a greater proportion of Acid tolerant bacteria would be expected to be more prone to caries development. Biofilm Acid Tolerance could therefore be a possible biomarker for caries prediction. However, little is known about the stability of biofilm Acid Tolerance over time in vivo or the distribution throughout the oral cavity. Therefore the aim of this study was to assess intra-individual differences in biofilm Acid–Tolerance between different tooth surfaces and inter-individual variation as well as stability of Acid Tolerance over time. The majority of the adolescents showed low scores for biofilm Acid Tolerance. In 14 of 20 individuals no differences were seen between the three tooth sites examined. In the remaining six, Acid–Tolerance at the premolar site differed from one of the other sites. At 51 of 60 tooth sites, Acid–Tolerance at baseline was unchanged after 1 month. However, Acid Tolerance values changed over a 1-year period in 50% of the individuals. Biofilm Acid Tolerance showed short-term stability and low variation between different sites in the same individual suggesting that the Acid Tolerance could be a promising biological biomarker candidate for caries prediction. Further evaluation is however needed and prospective clinical trials are called for to evaluate the diagnostic accuracy.
Fluoride-supplemented milk inhibits Acid Tolerance in root caries biofilmsCaries research, 2012Co-Authors: Jessica Neilands, Lars G. Petersson, David Beighton, Gunnel SvensäterAbstract:
In this study we investigated the effect of fluoride on plaque Acid Tolerance. The test group consumed 200 ml of milk supplemented with 5 mg F/l as NaF once a day, the milk control group drank 200 ml of unsupplemented milk, and the no-milk control group did not consume milk in this manner. Plaque samples were taken at baseline and after 15 months. The proportion of Acid-tolerant bacteria in plaque was estimated using LIVE/DEAD® BacLight™ staining after exposure to pH 3.5 for 2 h. The fluoride group showed a statistically significant decrease in plaque Acid Tolerance compared to baseline. This study shows that daily intake of fluoride in milk reduces plaque Acid Tolerance.
Acid Tolerance of Biofilm Cells of Streptococcus mutansApplied and environmental microbiology, 2007Co-Authors: Jessica Welin-neilands, Gunnel SvensäterAbstract:
Streptococcus mutans, a member of the dental plaque community, has been shown to be involved in the carious process. Cells of S. mutans induce an Acid Tolerance response (ATR) when exposed to sublethal pH values that enhances their survival at a lower pH. Mature biofilm cells are more resistant to Acid stress than planktonic cells. We were interested in studying the Acid Tolerance and ATR-inducing ability of newly adhered biofilm cells of S. mutans. All experiments were carried out using flow-cell systems, with Acid Tolerance tested by exposing 3-h biofilm cells to pH 3.0 for 2 h and counting the number of survivors by plating on blood agar. Acid adaptability experiments were conducted by exposing biofilm cells to pH 5.5 for 3 h and then lowering the pH to 3.5 for 30 min. The viability of the cells was assessed by staining the cells with LIVE/DEAD BacLight viability stain. Three-hour biofilm cells of three different strains of S. mutans were between 820- and 70,000-fold more Acid tolerant than corresponding planktonic cells. These strains also induced an ATR that enhanced the viability at pH 3.5. The presence of fluoride (0.5 M) inhibited the induction of an ATR, with 77% fewer viable cells at pH 3.5 as a consequence. Our data suggest that adhesion to a surface is an important step in the development of Acid Tolerance in biofilm cells and that different strains of S. mutans possess different degrees of Acid Tolerance and ability to induce an ATR.