Heat, acid and cold stresses enhance the expression of DnaK gene in Alicyclobacillus acidoterrestris

Analysis of the Probiotic Potential of Lactiplantibacillus plantarum LB1_P46 Isolated from the Mexican Fermented Pulque Beverage: A Functional and Genomic Analysis

The traditional Mexican fermented beverage pulque has been considered a healthy product for treating gastrointestinal disorders. Lactic acid bacteria (LAB) have been identified as one of the most abundant microbial groups during pulque fermentation. As traditional pulque is consumed directly from the fermentation vessel, the naturally associated LABs are ingested, reaching the consumer's small intestine alive, suggesting their potential probiotic capability. In this contribution, we assayed the probiotic potential of the strain of Lactiplantibacillus plantarum LB1_P46 isolated from pulque produced in Huitzilac, Morelos State, Mexico. The characterization included resistance to acid pH (3.5) and exposure to bile salts at 37 °C; the assay of the hemolytic activity and antibiotic resistance profiling; the functional traits of cholesterol reduction and β-galactosidase activity; and several cell surface properties, indicating that this LAB possesses probiotic properties comparable to other LAB. Additionally, this L. plantarum showed significance in in vitro antimicrobial activity against several Gram-negative and Gram-positive bacteria and in vivo preventive anti-infective capability against Salmonella in a BALB/c mouse model. Several functional traits and probiotic activities assayed were correlated with the corresponding enzymes encoded in the complete genome of the strain. The genome mining for bacteriocins led to the identification of several bacteriocins and a ribosomally synthesized and post-translationally modified peptide encoding for the plantaricin EF. Results indicated that L. plantarum LB1_P46 is a promising probiotic LAB for preparing functional non-dairy and dairy beverages.

Antibacterial mechanism of inosine against Alicyclobacillus acidoterrestris

Inosine could potentially become a novel antibacterial agent against Alicyclobacillus acidoterrestris as low doses of inosine can prevent its contamination. However, until now the antibacterial mechanism of inosine targeting A. acidoterrestris is still unknown. In this study, to unravel the mechanism of inosine against A. acidoterrestris puzzle, the effects of inosine on bacterial surface hydrophobicity, intracellular protein content, cell membrane damage extent, and permeability of the A. acidoterrestris were investigated. The results showed that inosine can effectively inhibit the growth and reproduction of A. acidoterrestris by destroying the integrity of cell membrane and increasing its permeability, causing the leakage of intracellular nutrients. Furthermore, the interaction networks of inosine target proteins were analyzed. The interaction networks further revealed that damage to bacterial cell membranes might be relevant to inosine's effect on bacterial DNA replication and cell energy metabolism through regulating nucleotide synthesis and metabolism and the activity of translation initiation factors. Finally, the antibacterial mechanism of inosine against A. acidoterrestris was proposed.

Transcriptomic and Metabolomic Profiling Uncovers Response Mechanisms of Alicyclobacillus acidoterrestris DSM 3922T to Acid Stress

Alicyclobacillus acidoterrestris, which has strong acidophilic and heat-resistant properties, can cause spoilage of pasteurized acidic juice. The current study determined the physiological performance of A. acidoterrestris under acidic stress (pH 3.0) for 1 h. Metabolomic analysis was carried out to investigate the metabolic responses of A. acidoterrestris to acid stress, and integrative analysis with transcriptome data was also performed. Acid stress inhibited the growth of A. acidoterrestris and altered its metabolic profiles. In total, 63 differential metabolites, mainly enriched in amino acid metabolism, nucleotide metabolism, and energy metabolism, were identified between acid-stressed cells and the control. Integrated transcriptomic and metabolomic analysis revealed that A. acidoterrestris maintains intracellular pH (pHi) homeostasis by enhancing amino acids decarboxylation, urea hydrolysis, and energy supply, which was verified using real-time quantitative PCR and pHi measurement. Additionally, two-component systems, ABC transporters, and unsaturated fatty acid synthesis also play crucial roles in resisting acid stress. Finally, a model of the responses of A. acidoterrestris to acid stress was proposed. IMPORTANCE Fruit juice spoilage caused by A. acidoterrestris contamination has become a major concern and challenge in the food industry, and this bacterium has been suggested as a target microbe in the design of the pasteurization process. However, the response mechanisms of A. acidoterrestris to acid stress still remain unknown. In this study, integrative transcriptomic, metabolomic, and physiological approaches were used to uncover the global responses of A. acidoterrestris to acid stress for the first time. The obtained results can provide new insights into the acid stress responses of A. acidoterrestris, which will point out future possible directions for the effective control and application of A. acidoterrestris.

Uncovering acid resistance genes in lactic acid bacteria and impact of non-viable bacteria on bacterial community during Chinese strong-flavor baijiu fermentation

Chinese strong-flavor baijiu (CSFB) brewing is a spontaneously solid-state fermentation process for approximately 60 days. Numerous microorganisms grow, die, and spark a series of metabolic reactions during fermentation. In this study, the microbial community and structure between total and viable bacteria in zaopei from the 5- and 20-year pits of CSFB are revealed by amplicon sequencing. Metagenome sequencing was applied to investigate acid resistance genes in Lactobacillus and predict carbohydrate active enzyme in zaopei. Besides, SourceTracker was conducted to expose bacterial sources. Results revealed that there was no significant difference in the bacterial community and structure between the total and viable bacteria; Lactobacillus was the most dominant bacterium in zaopei of two types of pits. Meanwhile, acid resistance genes argR, aspA, ilvE, gshA, DnaK, and cfa were genes that sustained Lactobacillus survival in the late stages of fermentation with high contents of acid and ethanol, and glycosyltransferases were identified as the predominated enzymes during the CSFB fermentation which catalyzed the process of lactic acid generation via Embden-Meyerhof-Parnas pathway and Hexose Monophosphate Pathway. Moreover, the environment contributed most bacteria to zaopei of the 5- and 20-year pits. These findings will provide a deeper understanding of the microbial community structure of viable and total bacteria and the reason for the dominance of Lactobacillus in the later stages of CSFB fermentation.

Response mechanisms to acid stress of acid-resistant bacteria and biotechnological applications in the food industry

Acid-resistant bacteria are more and more widely used in industrial production due to their unique acid-resistant properties. In order to survive in various acidic environments, acid-resistant bacteria have developed diverse protective mechanisms such as sensing acid stress and signal transduction, maintaining intracellular pH homeostasis by controlling the flow of H⁺, protecting and repairing biological macromolecules, metabolic modification, and cross-protection. Acid-resistant bacteria have broad biotechnological application prospects in the food field. The production of fermented foods with high acidity and acidophilic enzymes are the main applications of this kind of bacteria in the food industry. Their acid resistance modules can also be used to construct acid-resistant recombinant engineering strains for special purposes. However, they can also cause negative effects on foods, such as spoilage and toxicity. Herein, the aim of this paper is to summarize the research progress of molecular mechanisms against acid stress of acid-resistant bacteria. Moreover, their effects on the food industry were also discussed. It is useful to lay a foundation for broadening our understanding of the physiological metabolism of acid-resistant bacteria and better serving the food industry.

Application and potential of multifrequency ultrasound in juice industry: Comprehensive analysis of inactivation and germination of Alicyclobacillus acidoterrestris spores

The majority of acidic fruits are perishable owing to their high-water activity, which promotes microbial activity, thus exhibiting metabolic functions that cause spoilage. Along with sanitary practices, several treatments are used during processing and/or storage to inhibit the development of undesirable bacteria. To overcome the challenges caused by mild heat treatment, juice manufacturers have recently increased their involvement in developing novel non-thermal processing procedures. Ultrasonication alone or in combination with other hurdle technologies may be used to pasteurize processed fruit juices. Multifrequency ultrasound has gained popularity due to the fact that mono-frequency ultrasound has less impact on bacterial inactivation and bioactive compound enhancement of fruit juice. Here, we present and discuss the fundamental information and technological knowledge of how spoilage bacteria, specifically Alicyclobacillus acidoterrestris, assemble resistant spores and inactivate and germinate dormant spores in response to nutrient germinants and physical treatments such as heat and ultrasound. To the authors' knowledge, no prior review of ultrasonic inactivation and germination of A. acidoterrestris in fruit juice exists. Therefore, this article aims to provide a review of previously published research on the inactivation and germination of A. acidoterrestris in fruit juice by ultrasound and heat.

Endophyte-Mediated Stress Tolerance in Plants: A Sustainable Strategy to Enhance Resilience and Assist Crop Improvement

Biotic and abiotic stresses severely affect agriculture by affecting crop productivity, soil fertility, and health. These stresses may have significant financial repercussions, necessitating a practical, cost-effective, and ecologically friendly approach to lessen their negative impacts on plants. Several agrochemicals, such as fertilizers, pesticides, and insecticides, are used to improve plant health and protection; however, these chemical supplements have serious implications for human health. Plants being sessile cannot move or escape to avoid stress. Therefore, they have evolved to develop highly beneficial interactions with endophytes. The targeted use of beneficial plant endophytes and their role in combating biotic and abiotic stresses are gaining attention. Therefore, it is important to experimentally validate these interactions and determine how they affect plant fitness. This review highlights research that sheds light on how endophytes help plants tolerate biotic and abiotic stresses through plant–symbiont and plant–microbiota interactions. There is a great need to focus research efforts on this vital area to achieve a system-level understanding of plant–microbe interactions that occur naturally.

Transcriptomics and proteomics revealed the psychrotolerant and antibiotic-resistant mechanisms of strain Pseudomonas psychrophila RNC-1 capable of assimilatory nitrate reduction and aerobic denitrification

Aerobic denitrification has been proved to be profoundly affected by temperature and antibiotics, but little is known about how aerobic denitrifiers respond to temperature and antibiotic stress. In this study, the nitrate reduction performance and the intracellular metabolism by a psychrotolerant aerobic denitrifying bacteria, named Pseudomonas psychrophila RNC-1, were systematically investigated at different temperatures (10 °C, 20 °C, 30 °C) and different sulfamethoxazole (SMX) concentrations (0 mg/L, 0.1 mg/L, 0.5 mg/L, 1.0 mg/L, and 5.0 mg/L). The results showed that strain RNC-1 performed satisfactory nitrate removal at 10 °C and 20 °C, but its growth was significantly inhibited at 30 °C. Nitrate removal by strain RNC-1 was slightly promoted in the presence of 0.5 mg/L SMX, whereas it was significantly suppressed with 5.0 mg/L SMX. Nitrogen balance analysis indicated that assimilatory nitrate reduction and dissimilatory aerobic denitrification jointly dominated in the nitrate removal process of strain RNC-1, in which the inhibition effected on assimilation process was much higher than that on the aerobic denitrification process under SMX exposure. Further transcriptomics and proteomics analysis revealed that the psychrotolerant mechanism of strain RNC-1 could be attributed to the up-regulation of RNA translation, energy metabolism, ABC transporters and the over-expression of cold shock proteins, while the down-regulation of oxidative phosphorylation pathway was the primary reason for the deteriorative cell growth at 30 °C. The promotion of nitrate reduction with 0.5 mg/L SMX was related to the up-regulation of amino acid metabolism pathways, while the down-regulation of folate cycle, glycolysis/gluconeogenesis and bacterial chemotaxis pathways were responsible for the inhibition effect at 5.0 mg/L SMX. This work provides a mechanistic understanding of the metabolic adaption of strain RNC-1 under different stress, which is of significance for its application in nitrogen contaminated wastewater treatment processes.

Metagenome-assembled genomes of phytoplankton microbiomes from the Arctic and Atlantic Oceans

BACKGROUND

Phytoplankton communities significantly contribute to global biogeochemical cycles of elements and underpin marine food webs. Although their uncultured genomic diversity has been estimated by planetary-scale metagenome sequencing and subsequent reconstruction of metagenome-assembled genomes (MAGs), this approach has yet to be applied for complex phytoplankton microbiomes from polar and non-polar oceans consisting of microbial eukaryotes and their associated prokaryotes.

RESULTS

Here, we have assembled MAGs from chlorophyll a maximum layers in the surface of the Arctic and Atlantic Oceans enriched for species associations (microbiomes) with a focus on pico- and nanophytoplankton and their associated heterotrophic prokaryotes. From 679 Gbp and estimated 50 million genes in total, we recovered 143 MAGs of medium to high quality. Although there was a strict demarcation between Arctic and Atlantic MAGs, adjacent sampling stations in each ocean had 51-88% MAGs in common with most species associations between Prasinophytes and Proteobacteria. Phylogenetic placement revealed eukaryotic MAGs to be more diverse in the Arctic whereas prokaryotic MAGs were more diverse in the Atlantic Ocean. Approximately 70% of protein families were shared between Arctic and Atlantic MAGs for both prokaryotes and eukaryotes. However, eukaryotic MAGs had more protein families unique to the Arctic whereas prokaryotic MAGs had more families unique to the Atlantic.

CONCLUSION

Our study provides a genomic context to complex phytoplankton microbiomes to reveal that their community structure was likely driven by significant differences in environmental conditions between the polar Arctic and warm surface waters of the tropical and subtropical Atlantic Ocean. Video Abstract.

Integrated transcriptomic and proteomic analysis reveals the response mechanisms of Alicyclobacillus acidoterrestris to heat stress

Alicyclobacillus acidoterrestris can survive pasteurization and is implicated in pasteurized fruit juice spoilage. However, the mechanisms underlying heat responses remain largely unknown. Herein, gene transcription changes of A. acidoterrestris under heat stress were detected by transcriptome, and an integrated analysis with proteomic and physiological data was conducted. A total of 911 differentially expressed genes (DEGs) was observed. The majority of DEGs and differentially expressed proteins (DEPs) were exclusively regulated at the mRNA and protein level, respectively, whereas only 59 genes were regulated at both levels and had the same change trends. Comparative analysis of the functions of the specifically or commonly regulated DEGs and DEPs revealed that the heat resistance of A. acidoterrestris was primarily based on modulating peptidoglycan and fatty acid composition to maintain cell envelope integrity. Low energy consumption strategies were established with attenuated glycolysis, decreased ribosome de novo synthesis, and activated ribosome hibernation. Terminal oxidases, cytochrome bd and aa₃, in aerobic respiratory chain were upregulated. Meanwhile, the MarR family transcriptional regulator was upregulated, reactive oxygen species (ROS) was discovered, and the concentration of superoxide dismutase (SOD) increased, indicating that the accompanied oxidative stress was induced by high temperature. Additionally, DNA and protein damage repair systems were activated. This study provided a global perspective on the response mechanisms of A. acidoterrestris to heat stress, with implications for better detection and control of its contamination in fruit juice.

Transcriptome-Based Selection and Validation of Reference Genes for Gene Expression Analysis of Alicyclobacillus acidoterrestris Under Acid Stress

Alicyclobacillus acidoterrestris is a major concern in fruit juice industry due to its spoilage potential of acidic fruit juice. Quantifying the expression levels of functional genes by real-time quantitative polymerase chain reaction (RT-qPCR) is necessary to elucidate the response mechanisms of A. acidoterrestris to acid stress. However, appropriate reference genes (RGs) for data normalization are required to obtain reliable RT-qPCR results. In this study, eight novel candidate RGs were screened based on transcriptome datasets of A. acidoterrestris under acid stress. The expression stability of eight new RGs and commonly used RG 16s rRNA was assessed using geNorm, NormFinder, and BestKeeper algorithms. Moreover, the comprehensive analysis using the RefFinder program and the validation using target gene ctsR showed that dnaG and dnaN were the optimal multiple RGs for normalization at pH 4.0; ytvI, dnaG, and 16s rRNA at pH 3.5; icd and dnaG at pH 3.0; and ytvI, dnaG, and spoVE at pH 2.5. This study revealed for the first time that A. acidoterrestris had different suitable RGs under different acid conditions, with implications for further deciphering the acid response mechanisms of this spoilage-causing bacterium.

Mobile genetic elements mediate the mixotrophic evolution of novel Alicyclobacillus species for acid mine drainage adaptation

Alicyclobacillus species inhabit diverse environments and have adapted to broad ranges of pH and temperature. However, their adaptive evolutions remain elusive, especially regarding the role of mobile genetic elements (MGEs). Here, we characterized the distributions and functions of MGEs in Alicyclobacillus species across five environments, including acid mine drainage (AMD), beverages, hot springs, sediments, and soils. Nine Alicyclobacillus strains were isolated from AMD and possessed larger genome sizes and more genes than those from other environments. Four AMD strains evolved to be mixotrophic and fell into distinctive clusters in phylogenetic tree. Four types of MGEs including genomic island (GI), insertion sequence (IS), prophage, and integrative and conjugative element (ICE) were widely distributed in Alicyclobacillus species. Further, AMD strains did not possess CRISPR-Cas systems, but had more GI, IS, and ICE, as well as more MGE-associated genes involved in the oxidation of iron and sulfide and the resistance of heavy metal and low temperature. These findings highlight the differences in phenotypes and genotypes between strains isolated from AMD and other environments and the important role of MGEs in rapid environment niche expansions.

Expression, Rapid Purification and Functional Analysis of DnaK from Rhodococcus ruber

BACKGROUND

Heat shock proteins (HSPs) represent a group of important proteins which are produced by all kinds of organisms especially under stressful conditions. DnaK, an Hsp70 homolog in prokaryotes, has indispensable roles when microbes was confronted with stress conditions. However, few data on DnaK from Rhodococcus sp. were available in the literature. In a previous study, we reported that toluene and phenol stress gave rise to a 29.87-fold and 3.93-fold increase for the expression of DnaK from R. ruber SD3, respectively. Thus, we deduced DnaK was in correlation with the organic solvent tolerance of R. ruber SD3.

OBJECTIVE

To elucidate the role of DnaK in the organic solvent tolerance of R. ruber SD3, expression, purification and functional analysis of Dnak from R. ruber SD3 were performed in the present paper.

METHODS

In this article, DnaK from R. ruber SD3 was heterologously expressed in E. coli BL21(DE3) and purified by affinity chromatography. Functional analysis of DnaK was performed using determination of kinetics, docking, assay of chaperone activity and microbial growth.

RESULTS

The recombinant DnaK was rapidly purified by affinity chromatography with the purification fold of 1.9 and the recovery rate of 57.9%. Km, Vmax and Kcat for Dnak from R. ruber SD3 were 80.8 μM, 58.1 nmol/min and 374.3 S-1, respectively. The recombinant protein formed trimer in vitro, with the calculated molecular weight of 214 kDa. According to In-silico analysis, DnaK interacted with other molecular chaperones and some important proteins in the metabolism. The specific activity of catalase in the presence of recombinant DnaK was 1.85 times or 2.00 times that in the presence of BSA or Tris-HCl buffer after exposure to 54 °C for 1h. E. coli transformant with pET28-dnak showed higher growth than E. coli transformant with pET28 at 43°C and in the presence of phenol, respectively.

CONCLUSION

The biochemical properties and the interaction analysis of DnaK from R. ruber SD3 deepened our understanding of DnaK function. DnaK played an important role in microbial growth when R. ruber was subjected to various stress such as heating and organic solvent.

New insights into thermo-acidophilic properties of Alicyclobacillus acidoterrestris after acid adaptation

Alicyclobacillus acidoterrestris has unique thermo-acidophilic properties and is the main cause of fruit juice deterioration. Given the acidic environment and thermal treatment during juice processing, the effects of acid adaptation (pH 3.5, 3.2, and 3.0) on the resistance of A. acidoterrestris to heat (65 °C, 5 min) and acid (pH = 2.2, 1 h) stresses were investigated for the first time. The results showed that acid adaptation induced cross-protection against heat stress of A. acidoterrestris and acid tolerance response, and the extent of induced tolerance was increased with the decrease of adaptive pH values. Acid adaptation treatments did not disrupt the membrane potential stability and intracellular pH homeostasis, but reduced intracellular ATP concentration, increased cyclic fatty acids content, and changed the acquired Fourier transform infrared spectra. Transcription levels of stress-inducible (dnaK, grpE, clpP, ctsR) genes and genes related to spore formation (spo0A, ctoX) were up-regulated after acid adaptation, and spore formation was observed by scanning electron microscopy. This study revealed that the intracellular microenvironment homeostasis, expression of chaperones and proteases, and spore formation played a coordinated role in acid stress adaptive responses, with implications for applications in fruit juice processing.

Influence of Brevibacterium linens RS16 on foliage photosynthetic and volatile emission characteristics upon heat stress in Eucalyptus grandis

Heat stress induces secondary metabolic changes in plants, channeling photosynthetic carbon and energy, away from primary metabolic processes, including, growth. Use of ACC (1-aminocyclopropane-1-carboxylate) deaminase containing plant growth promoting bacteria (PGPB) in conferring heat resistance in plants and the role of PGPB, in altering net carbon assimilation, constitutive and stress volatile emissions has not been studied yet. We exposed leaves of Eucalyptus grandis inoculated and non-inoculated with PGPB Brevibacterium linens RS16 to two levels of heat stress (37 °C and 41 °C for 5 min) and quantified temporal changes in foliage photosynthetic characteristics and volatile emission rates at 0.5 h, day 1 and day 5 after the stress application. Heat stress resulted in immediate reductions in dark-adapted photosystem II (PSII) quantum yield (F_v/F_m), net assimilation rate (A), stomatal conductance to water vapor (g_s), and enhancement of stress volatile emissions, including enhanced emissions of green leaf volatiles (GLV), mono- and sesquiterpenes, light weight oxygenated volatile organic compounds (LOC), geranyl-geranyl diphosphate pathway volatiles (GGDP), saturated aldehydes, and benzenoids, with partial recovery by day 5. Changes in stress-induced volatiles were always less in leaves inoculated with B. linens RS16. However, net assimilation rate was enhanced by bacterial inoculation only in the 37 °C treatment and overall reduction of isoprene emissions was observed in bacterially-treated leaves. Principal component analysis (PCA), correlation analysis and partial least squares discriminant analysis (PLS-DA) indicated that different stress applications influenced specific volatile organic compounds. In addition, changes in the expression analysis of heat shock protein 70 gene (DnaK) gene in B. linens RS16 upon exposure to higher temperatures further indicated that B. linens RS16 has developed its own heat resistance mechanism to survive under higher temperature regimes. Taken together, this study demonstrates that foliar application of ACC deaminase containing PGPB can ameliorate heat stress effects in realistic biological settings.

Cellular metabolism network of Bacillus thuringiensis related to erythromycin stress and degradation

Erythromycin is one of the most widely used macrolide antibiotics. To present a system-level understanding of erythromycin stress and degradation, proteome, phospholipids and membrane potentials were investigated after the erythromycin degradation. Bacillus thuringiensis could effectively remove 77% and degrade 53% of 1 µM erythromycin within 24 h. The 36 up-regulated and 22 down-regulated proteins were mainly involved in spore germination, chaperone and nucleic acid binding. Up-regulated ribose-phosphate pyrophosphokinase and ribosomal proteins confirmed that the synthesis of protein, DNA and RNA were enhanced after the erythromycin degradation. The reaction network of glycolysis/gluconeogenesis was activated, whereas, the activity of spore germination was decreased. The increased synthesis of phospholipids, especially, palmitoleic acid and oleic acid, altered the membrane permeability for erythromycin transport. Ribose-phosphate pyrophosphokinase and palmitoleic acid could be biomarkers to reflect erythromycin exposure. Lipids, disease, pyruvate metabolism and citrate cycle in human cells could be the target pathways influenced by erythromycin. The findings presented novel insights to the interaction among erythromycin stress, protein interaction and metabolism network, and provided a useful protocol for investigating cellular metabolism responses under pollutant stress.

Proteome and phospholipid alteration reveal metabolic network of Bacillus thuringiensis under triclosan stress

Triclosan is a common antibacterial agent widely applied in various household and personal care products. The molecule, cell, organ and organism-level understanding of its toxicity pose to some target organisms has been investigated, whereas, the alteration of a single metabolic reaction, gene or protein cannot reflect the impact of triclosan on metabolic network. To clarify the interaction between triclosan stress and metabolism at network and system levels, phospholipid synthesis, and cellular proteome and metabolism of Bacillus thuringiensis under 1μM of triclosan stress were investigated through omics approaches. The results showed that C14:0, C16:1ω7, C16:0 and C18:2ω6 were significantly up-produced, and 19 proteins were differentially expressed. Whereas, energy supply, protein repair and the synthesis of DNA, RNA and protein were down-regulated. PyrH and Eno could be biomarkers to reflect triclosan stress. At network level, the target proteins ACOX1, AHR, CAR, CYP1A, CYP1B1, DNMT1, ENO, HSP60, HSP70, SLC5A5, TPO and UGT expressed in different species shared high sequence homology with the same function proteins found in Homo sapiens not only validated their role as biomarkers but also implied the potential impact of triclosan on the metabolic pathways and network of humans. These findings provided novel insights into the metabolic influence of triclosan at network levels, and developed an omics approach to evaluate the safety of target compound.

Heterogeneous expression of DnaK gene from Alicyclobacillus acidoterrestris improves the resistance of Escherichia coli against heat and acid stress

Alicyclobacillus acidoterrestris, an acidophilic and thermophilic bacteria, is an important microbial resource for stress resistance genes screening. In this study, DnaK gene from A. acidoterrestris was subcloned to construct the recombinant plasmid pET28a-DnaK. The successful construction of the plasmid was verified by double-enzyme digestion and sequencing analysis. The recombinant plasmid was transformed into Escherichia coli BL21 and isopropy-β-D-thiogalactoside (IPTG) was used to induce recombinant E. coli to express DnaK gene. A 70 kD fusion protein was identified by SDS-PAGE, which suggested that DnaK gene from A. acidoterrestris was successfully expressed. The recombinant and wild BL21 were treated with high temperatures of 54, 56 and 58 °C at pH values of 5.0-7.0 to compare the effects of heterogeneous expression of the DnaK gene from A. acidoterrestris on the stress resistance. The experimental results showed that survival rate of recombinant BL21-DnaK has been improved considerably under heat and acid stresses in contrast with the wild BL21, and D-values of recombinant BL21 were 14.7-72% higher than that of wild BL21, which demonstrated that heterogeneous expression of DnaK gene from A. acidoterrestris could significantly enhance the resistance of host bacteria E. coli against heat and acid stresses.

UvrA expression of Lactococcus lactis NZ9000 improve multiple stresses tolerance and fermentation of lactic acid against salt stress

Lactococcus lactis is subjected to several stressful conditions during industrial fermentation including oxidation, heating and cooling, acid, high osmolarity/dehydration and starvation. DNA lesion is a major cause of genetic instability in L. lactis that usually occurs at a low frequency, but it is greatly enhanced by environmental stresses. DNA damages produced by these environmental stresses are thought to induce DNA double-strand breaks, leading to illegitimate recombination. Nucleotide excision repair (NER) protein UvrA suppresses multiple stresses-induced illegitimate recombination. UvrA protein can survive a coincident condition of environmental harsh conditions, multiple stress factors supposedly encountered in the host and inducing UvrA in L. lactis. In this study the expression of UvrA and growth performance and viability of control strain L. lactisVector and recombinant strain L. lactisUvrA under multiple stress conditions were determined. The recombinants strain had 30.70 and 52.67% higher growth performances when subjected to acidic and osmotic stresses conditions. In addition, the L. lactisUvrA strain showed 1.85-, 1.65-, and 2.40-fold higher biomass, lactate production, and lactate productivity, compared with the corresponding values for L. lactisVector strain during the osmotic stress. Results demonstrated NER system is involved in adaptation to various stress conditions and suggested that cells with a compromised UvrA as DNA repair system have an enhanced protection behavior in L. lactis NZ9000 against DNA damage.

Roles of Hsp70s in Stress Responses of Microorganisms, Plants, and Animals

Hsp70s (heat shock protein 70s) are a class of molecular chaperones that are highly conserved and ubiquitous in organisms ranging from microorganisms to plants and humans. Most research on Hsp70s has focused on the mechanisms of their functions as molecular chaperones, but recently, studies on stress responses are coming to the forefront. Hsp70s play key roles in cellular development and protecting living organisms from environmental stresses such as heat, drought, salinity, acidity, and cold. Moreover, functions of human Hsp70s are related to diseases including neurological disorders, cancer, and virus infection. In this review, we provide an overview of the specific roles of Hsp70s in response to stress, particularly abiotic stress, in all living organisms.