Cold shock proteins of Lactococcus lactis MG1363 are involved in cryoprotection and in the production of cold-induced proteins

Role of cold shock proteins B and D in Aeromonas salmonicida subsp. salmonicida physiology and virulence in lumpfish (Cyclopterus lumpus)

Cold shock proteins (Csp) are pivotal nucleic acid binding proteins known for their crucial roles in the physiology and virulence of various bacterial pathogens affecting plant, insect, and mammalian hosts. However, their significance in bacterial pathogens of teleost fish remains unexplored. Aeromonas salmonicida subsp. salmonicida (hereafter A. salmonicida) is a psychrotrophic pathogen and the causative agent of furunculosis in marine and freshwater fish. Four csp genes (cspB, cspD, cspA, and cspC) have been identified in the genome of A. salmonicida J223 (wild type). Here, we evaluated the role of DNA binding proteins, CspB and CspD, in A. salmonicida physiology and virulence in lumpfish (Cyclopterus lumpus). A. salmonicida ΔcspB, ΔcspD, and the double ΔcspBΔcspD mutants were constructed and characterized. A. salmonicida ΔcspB and ΔcspBΔcspD mutants showed a faster growth at 28°C, and reduced virulence in lumpfish. A. salmonicida ΔcspD showed a slower growth at 28°C, biofilm formation, lower survival in low temperatures and freezing conditions (-20°C, 0°C, and 4°C), deficient in lipopolysaccharide synthesis, and low virulence in lumpfish. Additionally, ΔcspBΔcspD mutants showed less survival in the presence of bile compared to the wild type. Transcriptome analysis revealed that 200, 37, and 921 genes were differentially expressed in ΔcspB, ΔcspD, and ΔcspBΔcspD, respectively. In ΔcspB and ΔcspBΔcspD virulence genes in the chromosome and virulence plasmid were downregulated. Our analysis indicates that CspB and CspD mostly act as a transcriptional activator, influencing cell division (e.g., treB), virulence factors (e.g., aexT), and ultimately virulence.

Improvement of Freeze-Dried Survival of Lactiplantibacillus plantarum Based on Cell Membrane Regulation

The cell membrane of Lactiplantibacillus plantarum is a key structure for cell survival. In this study, we aimed to improve the lyophilization resistance of L. plantarum by regulating the cell membrane structure. Unsaturated fatty acids or cell membrane-regulating substances were added during culturing to determine their effect on the composition of cell membrane fatty acids and the survival rate of the cells after freeze-drying. The results showed that Tween 80, β-carotene and melatonin increased the lyophilization survival rate of L. plantarum by 9.44, 14.53, and 18.34%, respectively. After adding a lyophilization protective agent at a concentration of 21.49% at a 1:1 ratio, a combination of Tween 80, melatonin, and β-carotene was added to regulate the cell membrane, which increased the lyophilization survival rate by 32.08–86.05%. This study proposes new research directions and ideas for improving the survival rate of probiotics for industrial production.

Draft Genome Sequence of Lactococcus lactis Subsp. cremoris WA2-67: A Promising Nisin-Producing Probiotic Strain Isolated from the Rearing Environment of a Spanish Rainbow Trout (Oncorhynchus mykiss, Walbaum) Farm

Probiotics are a viable alternative to traditional chemotherapy agents to control infectious diseases in aquaculture. In this regard, Lactococcus lactis subsp. cremoris WA2-67 has previously demonstrated several probiotic features, such as a strong antimicrobial activity against ichthyopathogens, survival in freshwater, resistance to fish bile and low pH, and hydrophobicity. The aim of this manuscript is an in silico analysis of the whole-genome sequence (WGS) of this strain to gain deeper insights into its probiotic properties and their genetic basis. Genomic DNA was purified, and libraries prepared for Illumina sequencing. After trimming and assembly, resulting contigs were subjected to bioinformatic analyses. The draft genome of L. cremoris WA2-67 consists of 30 contigs (2,573,139 bp), and a total number of 2493 coding DNA sequences (CDSs). Via in silico analysis, the bacteriocinogenic genetic clusters encoding the lantibiotic nisin Z (NisZ) and two new bacteriocins were identified, in addition to several probiotic traits, such as the production of vitamins, amino acids, adhesion/aggregation, and stress resistance factors, as well as the absence of transferable antibiotic resistance determinants and genes encoding detrimental enzymatic activities and virulence factors. These results unveil diverse beneficial properties that support the use of L. cremoris WA2-67 as a probiotic for aquaculture.

C Group-Mediated Antibiotic Stress Mimics the Cold Shock Response

A temperature downshift results in stabilized secondary structure formation in mRNA that halts translation to which Escherichia coli responds by synthesizing a set of proteins termed as cold shock proteins (Csps). To cope with the sudden temperature drop, gene expression patterns are reprogrammed to induce Csps at the cost of other proteins. Out of the nine homologous proteins in the CspA family, CspA, CspB, CspG, and CspI have major roles in protecting the cell under a cold shock. Additionally, a subset of Csps has conferred the organism an ability to adapt to various stresses along the lines of nutrient deprivation, oxidative, heat, acid, and antibiotic stresses. Stressors like C group translational inhibitors stall the translational apparatus and produce a response similar to that observed under a temperature downshift. Conditions set by the antibiotic therefore elicit a cold shock response and induce the major Csps, thereby pointing out to a common mechanism existing between the two. In the current review, we briefly describe the induction of E. coli Csps under an antibiotic stress acquired from data published previously and help establish the role of Csps in protecting the cell against the inducing agents and as a participant in the organisms' complex stress response network.

Glutamicibacter mishrai sp. nov., isolated from the coral Favia veroni from Andaman Sea

A novel aerobic marine actinobacterium (strain S5-52^T) belonging to the genus Glutamicibacter was isolated from the coral Favia veroni sampled from the Andaman Sea, India. Cells are Gram stain positive and rod shaped. The DNA G+C content was 58.7 mol%. The major quinones were MK-8 and MK-9. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, glycolipid, trimannosyldiacylglycerol, phospholipid and dimannosylglyceride. The peptidoglycan type was A4α. Strain S5-52^T showed a maximum 16S rRNA similarity of 99.36% with Glutamicibacter halophytocola DSM 101718^T. The genome of strain S5-52^T was 3.57 Mb that contains 3274 protein coding sequences (CDS). DNA-DNA similarity and ANI values between S5-52^T and the reference strains were below 70% and 95-96%, respectively. Analysis of genomic reduction events in the evolutionary path from the LUCA (last universal common ancestor) to G. mishrai LMG 29155^T and G. halophytocola DSM 101718^T exhibit a number of genes involved in amino acid metabolism, cell wall biogenesis and replication, recombination and repair mechanism that reduced in both the species. Based on phenotypic, chemotaxonomic properties and comparative genomic studies, the strain S5-52^T is considered a novel species of the genus Glutamicibacter, for which the name Glutamicibacter mishrai sp. nov. is proposed. The type strain is S5-52^T (= KCTC 39846^T = LMG 29155^T).

Quantitative Proteomic Analysis of the Response of Probiotic Putative Lactococcus lactis NCDO 2118 Strain to Different Oxygen Availability Under Temperature Variation

Lactococcus lactis is a gram positive facultative anaerobe widely used in the dairy industry and human health. L. lactis subsp. lactis NCDO 2118 is a strain that exhibits anti-inflammatory and immunomodulatory properties. In this study, we applied a label-free shotgun proteomic approach to characterize and quantify the NCDO 2118 proteome in response to variations of temperature and oxygen bioavailability, which constitute the environmental conditions found by this bacterium during its passage through the host gastro-intestinal tract and in other industrial processes. From this proteomic analysis, a total of 1,284 non-redundant proteins of NCDO 2118 were characterized, which correspond to approximately 54% of its predicted proteome. Comparative proteomic analysis identified 149 and 136 proteins in anaerobic (30°C and 37°C) and non-aerated (30°C and 37°C) conditions, respectively. Our label-free proteomic analysis quantified a total of 1,239 proteins amongst which 161 proteins were statistically differentially expressed. Main differences were observed in cellular metabolism, stress response, transcription and proteins associated to cell wall. In addition, we identified six strain-specific proteins of NCDO 2118. Altogether, the results obtained in our study will help to improve the understanding about the factors related to both physiology and adaptive processes of L. lactis NCDO 2118 under changing environmental conditions.

An intrinsically disordered domain in Polaribacter irgensii KOPRI 22228 CspB confers extraordinary freeze-tolerance

Organisms living in extremely cold environments possess mechanisms to survive low temperatures. Among the known cold-induced genes, cold-shock proteins (Csps) are the most prominent. A csp-homologous gene, cspB_Pi, has been cloned from the Arctic bacterium Polaribacter irgensii KOPRI 22228, and overexpression of this gene greatly increased the freezing tolerance of its host. This protein consists of a unique N-terminal domain and a well conserved C-terminal cold shock domain. To elucidate the detailed mechanisms involved in the extraordinary freeze-tolerance conferred by CspB_Pi, we identified the responsible domain by mutational analysis. Changes of residues in the cold shock domain that are crucial for binding RNA or single-stranded DNA did not impair the ability of the host to survive freezing stress. All domain-shuffled CspB_Pi variants containing the N-terminal domain retained the ability to confer superior freeze-tolerance. Slow electrophoretic mobility and far-UV circular dichroism spectra of the N-terminal domain suggested an intrinsically disordered structure for this region. The N-terminal domain also bound to lipid vesicles in vitro. This lipid vesicle binding characteristic is shared with other intrinsically disordered proteins, such as α-synuclein and plant dehydrins, known to confer cold-tolerance when overexpressed, suggesting a mechanism for cold-survival through membrane binding.

Genome analysis of food-processing stressful-resistant probiotic Bifidobacterium animalis subsp. lactis BF052, and its potential application in fermented soymilk

In this study, Bifidobacterium animalis subsp. lactis BF052 was demonstrated the growth capability in soymilk and could be thus supplemented as a probiotic starter that employed soymilk as one of its food vehicles. The complete genome sequence of BF052 was therefore determined to understand the genetic basis of BF052 as a technological and functional probiotic starter. The whole genome sequence of BF052 consists of a circular genome of 1938 624 bp with a G+C content of 60.50%. This research highlights relevant genes involving in its adaptive responses to industrial and/or environmental stresses and utilization of α-galacto-oligosaccharides in BF052 strain compared with other representative bifidobacterial genomes.

Monte-Carlo modeling of the central carbon metabolism of Lactococcus lactis: insights into metabolic regulation

Metabolic pathways are complex dynamic systems whose response to perturbations and environmental challenges are governed by multiple interdependencies between enzyme properties, reactions rates, and substrate levels. Understanding the dynamics arising from such a network can be greatly enhanced by the construction of a computational model that embodies the properties of the respective system. Such models aim to incorporate mechanistic details of cellular interactions to mimic the temporal behavior of the biochemical reaction system and usually require substantial knowledge of kinetic parameters to allow meaningful conclusions. Several approaches have been suggested to overcome the severe data requirements of kinetic modeling, including the use of approximative kinetics and Monte-Carlo sampling of reaction parameters. In this work, we employ a probabilistic approach to study the response of a complex metabolic system, the central metabolism of the lactic acid bacterium Lactococcus lactis, subject to perturbations and brief periods of starvation. Supplementing existing methodologies, we show that it is possible to acquire a detailed understanding of the control properties of a corresponding metabolic pathway model that is directly based on experimental observations. In particular, we delineate the role of enzymatic regulation to maintain metabolic stability and metabolic recovery after periods of starvation. It is shown that the feedforward activation of the pyruvate kinase by fructose-1,6-bisphosphate qualitatively alters the bifurcation structure of the corresponding pathway model, indicating a crucial role of enzymatic regulation to prevent metabolic collapse for low external concentrations of glucose. We argue that similar probabilistic methodologies will help our understanding of dynamic properties of small-, medium- and large-scale metabolic networks models.

Membrane fatty acid composition and fluidity are involved in the resistance to freezing of Lactobacillus buchneri R1102 and Bifidobacterium longum R0175

Determinations of membrane fatty acid composition and fluidity were used together with acidification activity and viability measurements to characterize the physiological state after freezing of Lactobacillus buchneri R1102 and Bifidobacterium longum R0175 cells harvested in the exponential and stationary growth phases. For both strains, lower membrane fluidity was achieved in cells harvested in the stationary growth phase. This change was linked to a lower unsaturated-to-saturated fatty acid ratio for both strains and a higher cyclic-to-saturated fatty acid ratio for L. buchneri R1102 alone. These membrane properties were linked to survival and to maintenance of acidification activity of the cells after freezing, which differed according to the strain and the growth phase. Survival of B. longum R0175 was increased by 10% in cells with low membrane fluidity and high relative saturated fatty acid contents, without any change in acidification activity. Acidification activity was more degraded (70 min) in L. buchneri R1102 cells displaying low membrane fluidity and high saturated and cyclic fatty acid levels. Finally, this study showed that membrane modifications induced by the growth phase differed among bacterial strains in terms of composition. By lowering membrane fluidity, these modifications could be beneficial for survival of B. longum R0175 during the freezing process but detrimental for maintenance of acidification activity of L. buchneri R1102.

UV-C pre-adaptation of Salmonella: effect on cell morphology and membrane fatty acids composition

The present study was carried out to evaluate the effects of ultraviolet radiations (UV-C) on the fatty acids composition of three serovars of Salmonella: S. typhimurium, S. hadar and S. zanzibar. Results obtained show that UV-C treatment increases significantly (P ≤ 0.05) the percentage of cyclic fatty acids. The atomic force microscopy was used to study the morphology and cell surface of irradiated strains. Results show that UV-C rays induce morphological changes and alter the bacterial cell surface (presence of grooves and irregularities).

Proteomics analysis of the Flp regulon in Lactococcus lactis subsp. cremoris

Lactococcus lactis subsp. cremoris MG1363 genome sequence was completed and encodes two flp genes flpA and flpB. Research carried out has suggested that the flpB proteins are transcriptional regulators that respond to the environmental oxygen level. A variety of flp deletion mutant strains with single and double mutation were created. Wild-type (MG1363) and its flp(-) derivatives were compared by 2DE to identify changes in protein intensity under different aerobic/anaerobic growth conditions. In total, 416 ± 20 and 444 ± 32 protein spots were quantified from anaerobic and aerobic cells, respectively, on pH 4-7 gels. Forty-five protein spots that changed were excised from 2DE gel, digested with trypsin and identified from their MALDI-TOF MS Peptide Mass Fingerprint. A variety of proteins were affected by the flp mutations and oxygen level. Some proteins were controlled by FlpA and FlpB independently and some required both FlpA and B for regulation. The identified proteins that are regulated by the Flp proteins can be grouped by biochemical function. These groups are oxidative stress, electron transfer, sugars, cell wall, ABC transporters, arginine metabolism, and pyrimidine biosynthesis pathway.

Cold shock genes cspA and cspB from Caulobacter crescentus are posttranscriptionally regulated and important for cold adaptation

Cold shock proteins (CSPs) are nucleic acid binding chaperones, first described as being induced to solve the problem of mRNA stabilization after temperature downshift. Caulobacter crescentus has four CSPs: CspA and CspB, which are cold induced, and CspC and CspD, which are induced only in stationary phase. In this work we have determined that the synthesis of both CspA and CspB reaches the maximum levels early in the acclimation phase. The deletion of cspA causes a decrease in growth at low temperature, whereas the strain with a deletion of cspB has a very subtle and transient cold-related growth phenotype. The cspA cspB double mutant has a slightly more severe phenotype than that of the cspA mutant, suggesting that although CspA may be more important to cold adaptation than CspB, both proteins have a role in this process. Gene expression analyses were carried out using cspA and cspB regulatory fusions to the lacZ reporter gene and showed that both genes are regulated at the transcriptional and posttranscriptional levels. Deletion mapping of the long 5'-untranslated region (5'-UTR) of each gene identified a common region important for cold induction, probably via translation enhancement. In contrast to what was reported for other bacteria, these cold shock genes have no regulatory regions downstream from ATG that are important for cold induction. This work shows that the importance of CspA and CspB to C. crescentus cold adaptation, mechanisms of regulation, and pattern of expression during the acclimation phase apparently differs in many aspects from what has been described so far for other bacteria.

Adaptative potential of the Lactococcus lactis IL594 strain encoded in its 7 plasmids

The extrachromosomal gene pool plays a significant role both in evolution and in the environmental adaptation of bacteria. The L. lactis subsp. lactis IL594 strain contains seven plasmids, named pIL1 to pIL7, and is the parental strain of the plasmid-free L. lactis IL1403, which is one of the best characterized lactococcal strains of LAB. Complete nucleotide sequences of pIL1 (6,382 bp), pIL2 (8,277 bp), pIL3 (19,244 bp), pIL4 (48,979), pIL5 (23,395), pIL6 (28,435 bp) and pIL7 (28,546) were established and deposited in the generally accessible database (GeneBank). Nine highly homologous repB-containing replicons, belonging to the lactococcal theta-type replicons, have been identified on the seven plasmids. Moreover, a putative region involved in conjugative plasmid mobilization was found on four plasmids, through identification of the presence of mob genes and/or oriT sequences. Detailed bioinformatic analysis of the plasmid nucleotide sequences provided new insight into the repertoire of plasmid-encoded functions in L. lactis, and indicated that plasmid genes from IL594 strain can be important for L. lactis adaptation to specific environmental conditions (e.g. genes coding for proteins involved in DNA repair or cold shock response) as well as for technological processes (e.g. genes encoding citrate and lactose utilization, oligopeptide transport, restriction-modification system). Moreover, global gene analysis indicated cooperation between plasmid- and chromosome-encoded metabolic pathways.

Rescue of a cold-sensitive mutant at low temperatures by cold shock proteins from Polaribacter irgensii KOPRI 22228

Exposure to low temperatures induces the biosynthesis of specific sets of proteins, including cold shock proteins (Csps). Since many of the specific functions of pychrophilic Csps are unknown, the roles of Csps from an Arctic bacterium, Polaribacter irgensii KOPRI 22228, were examined. The genes encoding CspA and CspC of P. irgensii were cloned in this study. Sequence analysis showed that these proteins have cold shock domains containing two RNA-binding motifs, RNP1 and RNP2. Both proteins bound oligo(dT)-cellulose resins, suggesting single-stranded nucleic acid-binding activity. When the P. irgensii Csps were overexpressed in Escherichia coli, the cold-resistance of the host was increased by more than five-fold. The P. irgensii Csps also rescued a cold-sensitive E. coli csp-quadruple deletion strain, BX04, at low temperatures. These results suggest that Csps from P. irgensii play a role in survival in polar environments.

Overexpression of cold shock protein A of Psychromonas arctica KOPRI 22215 confers cold-resistance

A polar bacterium was isolated from Arctic sea sediments and identified as Psychromonas artica, based on 16S rDNA sequence. Psychromonas artica KOPRI 22215 has an optimal growth temperature of 10 degrees C and a maximum growth temperature of 25 degrees C, suggesting this bacterium is a psychrophile. Cold shock proteins (Csps) are induced upon temperature downshift by more than 10 degrees C. Functional studies have researched mostly Csps of a mesophilic bacterium Escherichia coli, but not on those of psychrophilic bacteria. In an effort to understand the molecular mechanisms of psychrophilic bacteria that allow it withstand freezing environments, we cloned a gene encoding a cold shock protein from P. artica KOPRI 22215 (CspA(Pa)) using the conserved sequences in csp genes. The 204 bp-long ORF encoded a protein of 68 amino acids, sharing 56% homology to previously reported E. coli CspA protein. When CspA(Pa) was overexpressed in E. coli, it caused cell growth-retardation and morphological elongation. Interestingly, overexpression of CspA(Pa) drastically increased the host's cold-resistance by more than ten times, suggesting the protein aids survival in polar environments.

Synthesis of cyclopropane fatty acids in Lactobacillus helveticus and Lactobacillus sanfranciscensis and their cellular fatty acids changes following short term acid and cold stresses

An implemented GC method to separate and quantify the cell cyclopropane fatty acids lactobacillic (C19cyc11) and dehydrosterculic (C19cyc9) was used to study the adaptive response to sublethal acid and cold stresses in Lactobacillus helveticus and Lactobacillus sanfranciscensis. The comparison of the composition of cellular fatty acids of the two strains and their changes after 2 h of stress exposure under micro-aerobic and anaerobic conditions indicated that the aerobic biosynthetic pathway for unsaturated fatty acids is prevalent in L. sanfranciscensis, while the anaerobic pathway is prevalent in L. helveticus. Indeed in the latter strain, in the presence of a source of oleic acid and under micro-aerobic conditions, C18:1n11 and its post-synthetic derivative C19cyc11 accounted for overall proportion ranging from 52 to 28% of the total FAs. On the other hand L. sanfranciscensis synthesizes by aerobic pathway C18:1n9 and transforms it to C19cyc9. However in this species the cumulative level of these two FAs did not exceed 30%. The relevant proportion of dodecanoic acid in the latter species suggests that carbon chain shortening is the principal strategy of L. sanfranciscensis to modulate fluidity or chemico-physical properties of the membranes.

Activation of mRNA translation by phage protein and low temperature: the case of Lactococcus lactis abortive infection system AbiD1

Background

Abortive infection (Abi) mechanisms comprise numerous strategies developed by bacteria to avoid being killed by bacteriophage (phage). Escherichia coli Abis are considered as mediators of programmed cell death, which is induced by infecting phage. Abis were also proposed to be stress response elements, but no environmental activation signals have yet been identified. Abis are widespread in Lactococcus lactis, but regulation of their expression remains an open question. We previously showed that development of AbiD1 abortive infection against phage bIL66 depends on orf1, which is expressed in mid-infection. However, molecular basis for this activation remains unclear.

Results

In non-infected AbiD1+ cells, specific abiD1 mRNA is unstable and present in low amounts. It does not increase during abortive infection of sensitive phage. Protein synthesis directed by the abiD1 translation initiation region is also inefficient. The presence of the phage orf1 gene, but not its mutant AbiD1^R allele, strongly increases abiD1 translation efficiency. Interestingly, cell growth at low temperature also activates translation of abiD1 mRNA and consequently the AbiD1 phenotype, and occurs independently of phage infection. There is no synergism between the two abiD1 inducers. Purified Orf1 protein binds mRNAs containing a secondary structure motif, identified within the translation initiation regions of abiD1, the mid-infection phage bIL66 M-operon, and the L. lactis osmC gene.

Conclusion

Expression of the abiD1 gene and consequently AbiD1 phenotype is specifically translationally activated by the phage Orf1 protein. The loss of ability to activate translation of abiD1 mRNA determines the molecular basis for phage resistance to AbiD1. We show for the first time that temperature downshift also activates abortive infection by activation of abiD1 mRNA translation.

Extraction of RNA from cheese without prior separation of microbial cells

In situ gene expression studies are promising approaches for improving our understanding of the cheese microbial flora. This requires efficient RNA extraction methods, but studies of cheeses are scarce. The objective of the present study was to determine whether RNA samples compatible with quantitative mRNA transcript analyses can be obtained without separating the cells from the cheese matrix. In the method that we describe, the cellular processes are stopped at the very beginning of the procedure. When cheeses were produced with Lactococcus lactis LD61 as the only starter microorganism, the integrity of the purified RNA was good, even for 2-week-old cheeses that had been incubated at 30 degrees C. In addition, the RNA samples did not contain any traces of RNases, and the amount of genomic DNA was negligible. A good level of reproducibility could also be achieved. When real-time reverse transcription-PCR analyses were normalized to the total RNA concentration, the amounts of 16S and 23S rRNA transcripts were constant during the 2-week incubation period, whereas the amount of tuf mRNA transcripts decreased substantially. RNA samples obtained using the method described in this study were compared to samples obtained using the method described by Ulvé et al. (J. Appl. Microbiol., in press), which is based on separation of the cells from the cheese matrix. For most of the 29 genes investigated, the transcript abundance was the same for both types of samples. Differences were observed mainly for genes whose expression has previously been shown to be modified by heat, acid, or osmotic stresses, such as busAA and glnQ.

Cold-adapted enzymes from marine Antarctic microorganisms

The Antarctic marine environment is characterized by challenging conditions for the survival of native microorganisms. Indeed, next to the temperature effect represented by the Arrhenius law, the viscosity of the medium, which is also significantly enhanced by low temperatures, contributes to slow down reaction rates. This review analyses the different challenges and focuses on a key element of life at low temperatures: cold-adapted enzymes. The molecular characteristics of these enzymes are discussed as well as the adaptation strategies which can be inferred from the comparison of their properties and three-dimensional structures with those of their mesophilic counterparts. As these enzymes display a high specific activity at low and moderate temperatures associated with a relatively high thermosensitivity, the interest in these properties is discussed with regard to their current and possible applications in biotechnology.

Stress response of methanogenic archaea from Siberian permafrost compared with methanogens from nonpermafrost habitats

We examined the survival potential of methanogenic archaea exposed to different environmental stress conditions such as low temperature (down to -78.5 degrees C), high salinity (up to 6 M NaCl), starvation (up to 3 months), long-term freezing (up to 2 years), desiccation (up to 25 days) and oxygen exposure (up to 72 h). The experiments were conducted with methanogenic archaea from Siberian permafrost and were complemented by experiments on well-studied methanogens from nonpermafrost habitats. Our results indicate a high survival potential of a methanogenic archaeon from Siberian permafrost when exposed to the extreme conditions tested. In contrast, these stress conditions were lethal for methanogenic archaea isolated from nonpermafrost habitats. A better adaptation to stress was observed at a low temperature (4 degrees C) compared with a higher one (28 degrees C). Given the unique metabolism of methanogenic archaea in general and the long-term survival and high tolerance to extreme conditions of the methanogens investigated in this study, methanogenic archaea from permafrost should be considered as primary candidates for possible subsurface Martian life.

Identification of Lactobacillus sakei genes induced during meat fermentation and their role in survival and growth

Lactobacillus sakei is a lactic acid bacterium that is ubiquitous in the food environment and is one of the most important constituents of commercial meat starter cultures. In this study, in vivo expression technology (IVET) was applied to investigate gene expression of L. sakei 23K during meat fermentation. The IVET vector used (pEH100) contained promoterless and transcriptionally fused reporter genes mediating beta-glucuronidase activity and erythromycin resistance. A genomic library of L. sakei 23K was established, and the clones were subjected to fermentation in a raw-sausage model. Fifteen in carne-induced fusions were identified. Several genes encoded proteins which are likely to contribute to stress-related functions. One of these genes was involved in acquisition of ammonia from amino acids, and the remaining either were part of functionally unrelated pathways or encoded hypothetical proteins. The construction and use of isogenic mutants in the sausage model suggested that four genes have an impact on the performance of L. sakei during raw-sausage fermentation. Inactivation of the heat shock regulator gene ctsR resulted in increased growth, whereas knockout of the genes asnA2, LSA1065, and LSA1194 resulted in attenuated performance compared to the wild-type strain. The results of our study are the first to provide an insight into the transcriptional response of L. sakei when growing in the meat environment. In addition, this study establishes a molecular basis which allows investigation of bacterial properties that are likely to contribute to the ecological performance of the organism and to influence the final outcome of sausage fermentation.

Sequence analysis of the lactococcal plasmid pNP40: a mobile replicon for coping with environmental hazards

The conjugative lactococcal plasmid pNP40, identified in Lactococcus lactis subsp. diacetylactis DRC3, possesses a potent complement of bacteriophage resistance systems, which has stimulated its application as a fitness-improving, food-grade genetic element for industrial starter cultures. The complete sequence of this plasmid allowed the mapping of previously known functions including replication, conjugation, bacteriocin resistance, heavy metal tolerance, and bacteriophage resistance. In addition, functions for cold shock adaptation and DNA damage repair were identified, further confirming pNP40's contribution to environmental stress protection. A plasmid cointegration event appears to have been part of the evolution of pNP40, resulting in a "stockpiling" of bacteriophage resistance systems.

Environmental stress response in wine lactic acid bacteria: beyond Bacillus subtilis

Lactic acid bacteria (LAB) constitute a heterogeneous group of bacteria that are traditionally used to produce fermented foods. The industrialization of food transformations has increased the economical importance of LAB, as they play a crucial role in the development of the organoleptic and hygienic quality of fermented products. However, the strains selected for industrial purposes, should tolerate adverse conditions encountered in industrial processes, either during starter handling and storage (freeze-drying, freezing, or spray-drying) or during food processing in which abiotic stresses such as heat, cold, acidity, and high concentration of NaCl or ethanol are common. Wine LAB have to deal with several stresses including an acidic pH, a high alcoholic content, non optimal growth temperatures, and growth-inhibitory compounds such as fatty acids and tannins, originated from yeast and bacteria metabolism. Wine LAB have developed several mechanisms to escape or to tolerate wine conditions. They carry out a malolactic fermentation in this stressful environment. In addition to the regulation of the expression of specific genes, bacteria have evolved adaptive networks to face the challenges of a changing environment and to survive under conditions of stress. The so called Global Regulatory Systems control the simultaneous expression of a large number of genes in response to a variety of environmental stress factors. CIRCE sequences able to bind the HrcA repressor, sigma(B) dependent promoters and CtsR regulatory elements have been observed in several genes identified from wine LAB. Improved knowledge of regulators and a better understanding of LAB stress responses could constitute a basis of comparison with the well known model microorganisms, Escherichia coli and Bacillus subtilis. Moreover, it can provide an important insight into improving current industrial starter strains.

Cloning and characterization of a gene encoding a cold-shock protein inLactobacillus casei

One csp-like gene, called cspA, from the lactic acid bacterium Lactobacillus casei was identified by an inverse polymerase chain reaction approach based on degenerate primers. cspA encodes a protein of 66 amino acid residues, which displays at least 74% identity with Csp proteins of Lactobacillus genera. Northern blot analysis revealed that cspA is transcribed monocistronically and that its expression is induced after a temperature downshift from 37 degrees C to 20 degrees C. The transcriptional start site has been determined and is situated 98 bp upstream of the initiation codon. A cspA mutant strain was constructed and it showed reduced growth rate compared with the wild type at both optimal and low temperatures, demonstrating that CspA plays an important role in the physiology of L. casei.

Influence of cooling temperature and duration on cold adaptation of Lactobacillus acidophilus RD758

The effect of different cooling temperatures and durations on resistance to freezing and to frozen storage at -20 degrees C in Lactobacillus acidophilus RD758 was studied, by using a central composite rotatable design. A cold adaptation was observed when the cells were maintained at moderate temperature (26 degrees C) for a long time (8h) before being cooled to the final temperature of 15 degrees C. These conditions led to a low rate of loss in acidification activity during frozen storage (0.64 minday(-1)) and a high residual acidification activity after 180 days of frozen storage (1011 min). The experimental design allowed us to determine optimal cooling conditions, which were established at 28 degrees C during 8h. Adaptation to cold temperatures was related to an increase in the unsaturated to saturated fatty acid ratio and in the relative cycC19:0 fatty acid concentration. Moreover, an increased synthesis of four specific proteins was observed as an adaptive response to the optimal cooling conditions. They included the stress protein ATP-dependent ClpP and two cold induced proteins: pyruvate kinase and a putative glycoprotein endopeptidase.

Characterization of potential stress responses in ancient Siberian permafrost psychroactive bacteria

Past studies of cold-acclimated bacteria have focused primarily on organisms not capable of sub-zero growth. Siberian permafrost isolates Exiguobacterium sp. 255-15 and Psychrobacter sp. 273-4, which grow at subzero temperatures, were used to study cold-acclimated physiology. Changes in membrane composition and exopolysaccharides were defined as a function of growth at 24, 4 and -2.5 degrees C in the presence and absence of 5% NaCl. As expected, there was a decrease in fatty acid saturation and chain length at the colder temperatures and a further decrease in the degree of saturation at higher osmolarity. A shift in carbon source utilization and antibiotic resistance occurred at 4 versus 24 degrees C growth, perhaps due to changes in the membrane transport. Some carbon substrates were used uniquely at 4 degrees C and, in general, increased antibiotic sensitivity was observed at 4 degrees C. All the permafrost strains tested were resistant to long-term freezing (1 year) and were not particularly unique in their UVC tolerance. Most of the tested isolates had moderate ice nucleation activity, and particularly interesting was the fact that the Gram-positive Exiguobacterium showed some soluble ice nucleation activity. In general the features measured suggest that the Siberian organisms have adapted to the conditions of long-term freezing at least for the temperatures of the Kolyma region which are -10 to -12 degrees C where intracellular water is likely not frozen.

Cloning, molecular characterization and expression analysis of two small heat shock genes isolated from wine Lactobacillus plantarum

AIM

Understanding the molecular response to stress tolerance of wine Lactobacillus plantarum.

METHODS AND RESULTS

Two genes codifying for heat shock proteins were cloned from wine L. plantarum. The coding regions of the two heat shock genes are 420 and 444 nucleotides long, and started with an ATG codon suggesting that they were translated. The protein sequences deduced from the isolated genes have a molecular mass of 18.483 and 19.282 kDa, respectively, and were therefore named hsp18.5 and hsp19.3. The expression of small heat shock genes was analysed by RT-PCR analysis. Moreover, the 5' and 3' noncoding regions were cloned and sequenced.

CONCLUSIONS

The expression of the heat shock genes was strongly induced by heat, cold and ethanol stress. Analysis of the 5' and 3' flanking regions of hsp18.5 and hsp19.3 genes, revealed the presence of an inverted repeat sequence (TTAGCACTC-N(9)-GAGTGCTAA) homologue to the CIRCE elements found to the upstream regulatory region of heat shock operons, and an inverted sequence that could form a stem and loop structure that it is likely to function as a transcriptional terminator. Based on their structures, the genes were classified as belonging to Class I of heat shock genes according to the B. subtilis nomenclature of heat response genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Small heat shock genes isolated from wine L. plantarum might have a role in preventing damage by cold stress.

Fermentation pH and Temperature Influence the Cryotolerance of Lactobacillus acidophilus RD758

The effects of 3 fermentation temperatures (30, 37, and 42 degrees C) and 3 fermentation pH (4.5, 5, and 6) on the cryotolerance of Lactobacillus acidophilus RD758 were studied in relation to their fatty acid composition. Cryotolerance was defined as the ability of the cells to recover their acidification activity after freezing and frozen storage at -20 degrees C. Better cryotolerance was obtained in cells grown at 30 degrees C or at pH 5; these cells showed no loss in acidification activity during freezing and a low rate of loss in acidification activity during frozen storage. On the other hand, cells grown at 42 degrees C or at pH 4.5 displayed poor cryotolerance. The membrane fatty acid composition was analyzed and related to the cryotolerance using principal component analysis. The improved cryotolerance observed during the freezing step was associated with a high ratio of unsaturated to saturated fatty acids, a low C18:0 content, and high C16:0 and cyclic C19:0 relative concentrations. High resistance during frozen storage was related to a high cycC19:0 concentration. Finally, the low cryotolerance observed after fermentation at pH 4.5 was explained by a low C18:2 content.

Environmental stress responses in Lactobacillus: a review

Environmental stress responses in Lactobacillus, which have been investigated mainly by proteomics approaches, are reviewed. The physiological and molecular mechanisms of responses to heat, cold, acid, osmotic, oxygen, high pressure and starvation stresses are described. Specific examples of the repercussions of these effects in food processing are given. Molecular mechanisms of stress responses in lactobacilli and other bacteria are compared.

csp-like genes of Lactobacillus delbrueckii ssp. bulgaricus and their response to cold shock

The two csp-like genes from the lactic acid bacterium Lactobacillus delbrueckii ssp. bulgaricus were characterized and designated cspA and cspB. The gene cspA has been identified using a polymerase chain reaction (PCR)-based approach with degenerated primers and further characterized using an inverse PCR strategy. cspA encodes a protein of 65 amino acid residues which displays between 81 and 77% identity with proteins CspL and CspP of Lactobacillus plantarum. cspB has been identified as a cspA ortholog using the partial sequence of the L. bulgaricus ATCC11842. cspB encodes a protein of 69 amino acids which has 42% identity with CspA. Northern blot analyses showed that cspA is transcribed as a single gene and that its transcription increased after a temperature downshift from 42 to 25 degrees C. In contrast, cspB is part of an operon transcribed at constant level irrespective of the temperature. These results indicate that cspA encodes the only Csp-like protein of L. bulgaricus induced by a downshift of temperature.

Improved adaptation to cold-shock, stationary-phase, and freezing stresses in Lactobacillus plantarum overproducing cold-shock proteins

We have investigated the effect of overproducing each of the three cold shock proteins (CspL, CspP, and CspC) in the mesophilic lactic acid bacterium Lactobacillus plantarum NC8. CspL overproduction transiently alleviated the reduction in growth rate triggered by exposing exponentially growing cells to cold shock (8 degrees C), suggesting that CspL is involved in cold adaptation. The strain overproducing CspC resumed growth more rapidly when stationary-phase cultures were diluted into fresh medium, indicating a role in the adaptation and recovery of nutritionally deprived cells. Overproduction of CspP led to an enhanced capacity to survive freezing.