Microbial response to acid stress: mechanisms and applications

Guan, Ningzi; Liu, Long

doi:10.1007/s00253-019-10226-1

Cited by 305 publications

(155 citation statements)

References 157 publications

Supporting

Mentioning

147

Contrasting

Order By: Relevance

“…The acid resistance of LAB is of great importance not only for their own growth but also for the fermentation and preparation of probiotic products [ 21 ]. Several mechanisms are involved in the acid resistance regulation of LAB, including central metabolic pathways, proton pumps, changes in cell membrane composition and cell density, DNA and protein damage repair, as well as neutralization processes [ 22 , 23 ].…”

Section: Resultsmentioning

confidence: 99%

Novel probiotic lactic acid bacteria isolated from indigenous fermented foods from West Sumatera, Indonesia

et al. 2020

View full text Add to dashboard Cite

Background and Aim: Probiotics play an important role in maintaining a healthy gut and consequently promote good health. This study aimed to find novel probiotic lactic acid bacteria (LAB) from indigenous fermented foods of West Sumatera, Indonesia. Materials and Methods: This study utilized 10 LAB previously isolated from fermented buffalo milk (dadih), fermented fish (budu), and fermented cassava (tape) which have the ability to produce gamma-aminobutyric acid. The study commenced with the screening of LAB for certain properties, such as resistance to acid and bile salts, adhesion to mucosal surface, and antagonism against enteric pathogens (Escherichia coli, Salmonella Enteritidis, and Staphylococcus aureus). The promising isolates were identified through biochemical and gram staining methods. Results: All isolates in this study were potential novel probiotics. They survived at a pH level of 2.5 for 3 h (55.27-98.18%) and 6 h (50.98-84.91%). Survival in bile at a concentration of 0.3% was 39.90-58.61% and the survival rate was 28.38- 52.11% at a concentration of 0.5%. The inhibitory diameter ranged from 8.75 to 11.54 mm for E. coli, 7.02 to 13.42 mm for S. aureus, and 12.49 to 19.00 mm for S. Enteritidis. All the isolates (84.5-92%) exhibited the ability to adhere to mucosal surfaces. This study revealed that all the isolates were potential probiotics but N16 proved to be superior because it was viable at a pH level of 2 (84.91%) and it had a good survival rate in bile salts assay (55.07%). This isolate was identified as Lactobacillus spp., Gram-positive bacilli bacteria, and tested negative in both the catalase and oxidase tests. Conclusion: All the isolates in this study may be used as probiotics, with isolate N16 (Lactobacillus spp.) as the most promising novel probiotic for poultry applications based on its ability to inhibit pathogenic bacteria.

show abstract

Section: Resultsmentioning

confidence: 99%

Novel probiotic lactic acid bacteria isolated from indigenous fermented foods from West Sumatera, Indonesia

et al. 2020

View full text Add to dashboard Cite

show abstract

“…In addition, pumping H + out of the cytoplasm is another e cient way to maintain pH homeostasis [74]. F 1 F o ATP synthase (F 1 F o ATPase) can utilize the proton gradient for ATP synthesis; it can also reverse and hydrolyze ATP to pump H + out to maintain intracellular pH homeostasis [75,76].…”

Section: Resultsmentioning

confidence: 99%

Development and Characterization of Acidic-pH Tolerant Mutants of Zymomonas mobilis through Adaptation and Next Generation Sequencing based Genome Resequencing and RNA-Seq

Yang

Tang

et al. 2020

Preprint

View full text Add to dashboard Cite

Background: Acid pretreatment is a common strategy used to break down the hemicellulose component of the lignocellulosic biomass to release pentoses, and a subsequent enzymatic hydrolysis step is usually applied to release hexoses from the cellulose. The hydrolysate after pretreatment and enzymatic hydrolysis containing both hexoses and pentoses can then be used as substrates for biochemical production. However, the acid-pretreated liquor can also be directly used as the substrate for microbial fermentation, which has an acidic pH and contains inhibitory compounds generated during pretreatment. Although the natural ethanologenic bacterium Zymomonas mobilis can grow in a broad range of pH 3.5~7.5, cell growth and ethanol fermentation are still affected under acidic-pH conditions below pH 4.0. Results: In this study, adaptive laboratory evolution (ALE) strategy was applied to adapt Z. mobilis under acidic-pH conditions. Two mutant strains named 3.6M and 3.5M with enhanced acidic-pH tolerance were selected and confirmed, of which 3.5M grew better than ZM4 but worse than 3.6M in acidic-pH conditions that is served as a reference strain between 3.6M and ZM4 to help unravel the acidic-pH tolerance mechanism. Mutant strains 3.5M and 3.6M exhibited 50~130% enhancement on growth rate, 4~9 h reduction on fermentation time to consume glucose, and 20~63% improvement on ethanol productivity than wild-type ZM4 at pH 3.8. Next-generation sequencing (NGS)-based whole genome resequencing (WGR) and RNA-Seq technologies were applied to unravel the acidic-pH tolerance mechanism of mutant strains. WGR result indicated that compared to wild-type ZM4, 3.5M and 3.6M have seven and five single nucleotide polymorphisms (SNPs) respectively, among which four are shared in common. Additionally, RNA-Seq result showed that the upregulation of genes involved in glycolysis and the downregulation of flagellar and mobility related genes would help generate and redistribute cellular energy to resist acidic pH while keeping normal biological processes in Z. mobilis. Moreover, genes involved in RND efflux pump, ATP-binding cassette (ABC) transporter, proton consumption, and alkaline metabolite production were significantly upregulated in mutants under the acidic-pH condition compared with ZM4, which could help maintain the pH homeostasis in mutant strains for acidic-pH resistance. Furthermore, our results demonstrated that in mutant 3.6M, genes encoding F1F0 ATPase to pump excess protons out of cells were upregulated under pH 3.8 compared to pH 6.2. This difference might help mutant 3.6M manage acidic conditions better than ZM4 and 3.5M. A few gene targets were then selected for genetics study to explore their role on acidic-pH tolerance, and our results demonstrated that the expression of two operons in the shuttle plasmids, ZMO0956-ZMO0958 encoding cytochrome bc1 complex and ZMO1428-ZMO1432 encoding RND efflux pump, could help Z. mobilis tolerate acidic-pH conditions. Conclusion: An acidic-pH tolerant mutant 3.6M obtained through this study can be used for commercial bioethanol production under acidic fermentation conditions. In addition, the molecular mechanism of acidic-pH tolerance of Z. mobilis was further proposed, which can facilitate future research on rational design of synthetic microorganisms with enhanced tolerance against acidic-pH conditions. Moreover, the strategy developed in this study combining approaches of ALE, genome resequencing, RNA-Seq, and classical genetics study for mutant evolution and characterization can be applied in other industrial microorganisms.

show abstract

“…Recently, it was suggested that the reactions with ozone and HO q 2 /O q − 2 might represent major sinks (∼ 50 % and ∼ 20 %, respectively) of catechol in the aqueous phase (Hoffmann et al, 2018). However, the only available rate constant for the ozone reaction was derived at pH = 1.5 by Gurol and Nekouinaini (1984), who postulate that at higher pH (∼ 5-6), the reaction with q OH likely dominates the overall loss. Therefore, in our base case simulations, we limit the reactions of phenol and catechol to the reactions with q OH and NO q 3 radicals.…”

Section: Chemical and Biological Processesmentioning

confidence: 99%

Biodegradation of phenol and catechol in cloud water: comparison to chemical oxidation in the atmospheric multiphase system

et al. 2020

View full text Add to dashboard Cite

Abstract. The sinks of hydrocarbons in the atmosphere are usually described by oxidation reactions in the gas and aqueous (cloud) phases. Previous lab studies suggest that in addition to chemical processes, biodegradation by bacteria might also contribute to the loss of organics in clouds; however, due to the lack of comprehensive data sets on such biodegradation processes, they are not commonly included in atmospheric models. In the current study, we measured the biodegradation rates of phenol and catechol, which are known pollutants, by one of the most active strains selected during our previous screening in clouds (Rhodococcus enclensis). For catechol, biodegradation is about 10 times faster than for phenol. The experimentally derived biodegradation rates are included in a multiphase box model to compare the chemical loss rates of phenol and catechol in both the gas and aqueous phases to their biodegradation rate in the aqueous phase under atmospheric conditions. Model results show that the degradation rates in the aqueous phase by chemical and biological processes for both compounds are similar to each other. During day time, biodegradation of catechol is even predicted to exceed the chemical activity in the aqueous phase and to represent a significant sink (17 %) of total catechol in the atmospheric multiphase system. In general, our results suggest that atmospheric multiphase models may be incomplete for highly soluble organics as biodegradation may represent an unrecognized efficient loss of such organics in cloud water.

show abstract

Microbial response to acid stress: mechanisms and applications

Cited by 305 publications

References 157 publications

Novel probiotic lactic acid bacteria isolated from indigenous fermented foods from West Sumatera, Indonesia

Novel probiotic lactic acid bacteria isolated from indigenous fermented foods from West Sumatera, Indonesia

Development and Characterization of Acidic-pH Tolerant Mutants of Zymomonas mobilis through Adaptation and Next Generation Sequencing based Genome Resequencing and RNA-Seq

Biodegradation of phenol and catechol in cloud water: comparison to chemical oxidation in the atmospheric multiphase system

Contact Info

Product

Resources

About