How do bacteria sense and respond to low temperature?

Impact of chlorhexidine digluconate and temperature on curli production in Escherichia coli-consequence on its adhesion ability

Chlorhexidine-Digluconate (CHX-Dg) is a biocide widely used as disinfectant or antiseptic in clinical and domestic fields. It is often found in the formulation of solutions to treat superficial wounds. Nevertheless, few studies have focused on its effects on Escherichia coli while this bacterium is commonly involved in mixed infections. Therefore, the impact of CHX-Dg and temperature on E. coli was investigated; particularly the curli production. In accordance with bibliographic data, the curli production decreased when the temperature of the culture was shift from 30 °C to 37 °C. The bacterial adhesion to abiotic surfaces was also reduced. Surprisingly, the curli production at 37 °C was maintained in presence of antiseptic and the bacterial adhesion was improved at a very low concentration (1 µg ml^-1) of CHX-Dg. Complementary investigations with a cpxR mutant demonstrated that the CpxA/R-TCS (Two-Component System) is involved in the temperature-dependent control of the curli expression. Indeed, the curli production was not altered by the growth temperature in the mutant. Otherwise, no relationship between CHX-Dg and the Cpx-TCS was shown. A subsequent proteomic investigation revealed the alteration of the production of 44 periplasmic and outer membrane proteins in presence of CHX-Dg. These proteins are involved in the transport of small molecules, the envelope integrity, the stress response as well as the protein folding.

Variation with depth of the abundance, diversity and pigmentation of culturable bacteria in a deep ice core from the Yuzhufeng Glacier, Tibetan Plateau

It has been suggested that the cryosphere is a new biome uniquely dominated by microorganisms, although the ecological characteristics of these cold-adapted bacteria are not well understood. We investigated the vertical variation with depth of the proportion of pigmented bacteria recovered from an ice core drilled in the Yuzhufeng Glacier, Tibetan Plateau. A total of 25,449 colonies were obtained from 1250 ice core sections. Colonies grew on only one-third of the inoculated Petri dishes, indicating that although the ice core harbored abundant culturable bacteria, bacteria could not be isolated from every section. Four phyla and 19 genera were obtained; Proteobacteria formed the dominant cluster, followed by Actinobacteria, Bacteroidetes and Firmicutes. The proportion of pigmented bacteria increased with depth from 79 to 95% and yellow-colored colonies predominated throughout the ice core, making up 47% of all the colonies. Pigments including α- and β-carotene, diatoxanthin, peridinin, zea/lutein, butanoyloxy, fucoxanthin and fucoxanthin were detected in representative colonies with α-carotene being the dominant carotenoid. To the best of our knowledge, this is the highest resolution study of culturable bacteria in a deep ice core reported to date.

How does temperature influences the development of lactococcosis? Transcriptomic and immunoproteomic in vitro approaches

Lactococcus garvieae is the aetiological agent of lactococcosis, a haemorrhagic septicaemia that affects marine and freshwater fish, with special incidence and economic relevance in farmed rainbow trout. Water temperature is one of the most important predisposing factors in the development of lactococcosis outbreaks. Lactococcosis in trout usually occur when water temperatures rise to about 18 °C, while fish carriers remain asymptomatic at temperatures below 13 °C. The aim of this work was to analyse the differences in the complete transcriptome response of L. garvieae grown at 18 °C and at 13 °C and to identify the immunogenic proteins expressed by this bacterium at 18 °C. Our results show that water temperature influences the expression of L. garvieae genes involved in the lysis of part of the bacterial cell population and in the cold response bacterial adaptation. Moreover, the surface immunogenic protein profile at 18 °C suggests an important role of the lysozyme-like enzyme, WxL surface proteins and some putative moonlighting proteins (proteins with more than one function, usually associated with different cellular locations) as virulence factors in L. garvieae. The results of this study could provide insights into the understanding of the virulence mechanisms of L. garvieae in fish.

Impact of temperature on Marinobacter hydrocarbonoclasticus SP17 morphology and biofilm structure during growth on alkanes

Alkanes are widespread pollutants found in soil, freshwater and marine environments. Marinobacter hydrocarbonoclasticus (Mh) strain SP17 is a marine bacterium able to use many hydrophobic organic compounds, including alkanes, through the production of biofilms that allow their poor solubility to be overcome. This study pointed out that temperature is an environmental factor that strongly affects the biofilm formation and morphology of Mh on the model alkanes, hexadecane and paraffin. We showed that Mh biofilm formation and accumulation of intracytoplasmic inclusions are higher on solid alkanes (hexadecane at 10 °C and paraffin at 10 °C and 30 °C) than on liquid alkane (hexadecane at 30 °C) or soluble substrate (lactate at both temperatures). We also found that Mh produces more extracellular polymeric substances at 30 °C than at 10 °C on alkanes and none on lactate. We observed that bacterial length is significantly higher at 10 °C than at 30 °C on lactate and hexadecane. On paraffin, at 30 °C, the cell morphology is markedly altered by large rounded or irregularly shaped cytoplasmic inclusions. Altogether, the results showed that Mh is able to adapt and use alkanes as a carbon source, even at low temperature.

Comparative genomic analysis reveals the environmental impacts on two Arcticibacter strains including sixteen Sphingobacteriaceae species

How the genomic diversity of species is driven by geographical isolation and environmental factors are not well understood for cold environments. Here, the environmental stress responses of two phylogenetically close Arcticibacter strains, A. eurypsychrophilus MJ9-5 and A. svalbardensis MN12-7, isolated from a Tibetan Plateau glacier and Svalbard soil, were analyzed. The comparative genomic analysis was performed with sixteen other related Sphingobacteriaceae species. Analyses of the relationships between growth temperature and genome composition, cold and heat shock genes showed that genomic adaption characteristics were more obvious when the strains were grouped by their upper limit in growth temperature, rather than by their minimal or optimal growth temperatures for Sphingobacteriaceae species. The very divergent genetic distance of genome fractions assigned to the functions of ‘secondary metabolism’, ‘dormancy and sporulation’ and ‘metabolism of aromatic compounds’ indicated the heterogeneous evolution of genes under different environmental pressures of the Sphingobacteriaceae species. The greatest differences between strains MJ9-5 and MN12-7 occurred in the genes devoted to the CRISPRs, osmotic adaption and metabolism of monosaccharides, nitrogen and aromatic compounds. These distinctions corresponded to two different environmental pressures, salinity and nutritional level, in the glacier ice and Svalbard soil environments.

Adaptations of archaeal and bacterial membranes to variations in temperature, pH and pressure

The cytoplasmic membrane of a prokaryotic cell consists of a lipid bilayer or a monolayer that shields the cellular content from the environment. In addition, the membrane contains proteins that are responsible for transport of proteins and metabolites as well as for signalling and energy transduction. Maintenance of the functionality of the membrane during changing environmental conditions relies on the cell's potential to rapidly adjust the lipid composition of its membrane. Despite the fundamental chemical differences between bacterial ester lipids and archaeal ether lipids, both types are functional under a wide range of environmental conditions. We here provide an overview of archaeal and bacterial strategies of changing the lipid compositions of their membranes. Some molecular adjustments are unique for archaea or bacteria, whereas others are shared between the two domains. Strikingly, shared adjustments were predominantly observed near the growth boundaries of bacteria. Here, we demonstrate that the presence of membrane spanning ether-lipids and methyl branches shows a striking relationship with the growth boundaries of archaea and bacteria.

First high quality draft genome sequence of a plant growth promoting and cold active enzyme producing psychrotrophic Arthrobacter agilis strain L77

Arthrobacter agilis strain L77, is a plant growth promoting and cold active hydrolytic enzymes producing psychrotrophic bacterium, isolated from Pangong Lake, a subglacial lake in north western Himalayas, India. Genome analysis revealed metabolic versatility with genes involved in metabolism and cold shock adaptation, utilization and biosynthesis of diverse structural and storage polysaccharides such as plant based carbon polymers. The genome of Arthrobacter agilis strain L77 consists of 3,608,439 bp (3.60 Mb) of a circular chromosome. The genome comprises of 3316 protein coding genes and 74 RNA genes, 725 hypothetical proteins, 25 pseudo-genes and 1404 unique genes.

Proteomic analysis of Mortierella isabellina M6-22 during cold stress

We aimed to gain a better understanding of cold adaption in Mortierella isabellina M6-22 by using proteomics approaches. The temperature range and optimal temperature for M6-22 growth were investigated, and composition changes in fatty acids were analyzed. Accompanied with the 2-D gel electrophoresis, MALDI-TOF/TOF-MS analysis was conducted to characterize alterations in protein profiling in M6-22 cultured at 30 °C for 24 h and 15 °C for another 24 h when compared with those cultured at 30 °C for 48 h. Gene Ontology (GO) cluster analysis was finally conducted for successfully identified proteins. M6-22 cells could grow well at temperatures ranging from 15 to 30 °C. As temperature decreased from 30 to 15 °C, LA and GLA significantly increased from 11.63 to 17.85 % and from 9.12 to 13.19 %, respectively, while oleic acid significantly decreased from 47.25 to 36.53 %. Proteomics analyses revealed 111 differentially expressed protein spots, among which 5 unique proteins (A38, A40, A47, A49 and A58), 29 up-regulated proteins and 10 down-regulated proteins were identified by MALDI-TOF/TOF-MS. GO enrichment analysis demonstrated that these proteins mainly involved in glycolytic pathway (A34 and A50), electron transport (A28), ATP production (A35 and B39) and protein modification (A38). A total of 44 differentially expressed proteins have been successfully identified in M. isabellina M6-22 cultured at 15 °C. These proteins may play important roles in cold adaption via regulation of ATP synthesis, activation of cold-adaptive proteins, degradation of needless protein, accumulation of PUFAs, etc.

Ethanol adaptation induces direct protection and cross-protection against freezing stress in Salmonella enterica serovar Enteritidis

AIMS

Salmonella enterica serovar Enteritidis (Salm. Enteritidis) encounters mild ethanol stress during its life cycle. However, adaptation to a stressful condition may affect bacterial resistance to subsequent stresses. Hence, this work was undertaken to investigate the influences of ethanol adaptation on stress tolerance of Salm. Enteritidis.

METHODS AND RESULTS

Salmonella Enteritidis was subjected to different ethanol adaptation treatments (2·5-10% ethanol for 1 h). Cellular morphology and tolerance to subsequent environmental stresses (15% ethanol, -20°C, 4°C, 50°C and 10% NaCl) were evaluated. It was found that 10% was the maximum ethanol concentration that allowed growth of the target bacteria. Ethanol adaptation did not cause cell-surface damage in Salm. Enteritidis as revealed by membrane permeability measurements and electron micrograph analysis. Salmonella Enteritidis adapted with 2·5-10% ethanol displayed an enhanced resistance to a 15%-ethanol challenge compared with an unchallenged control. The maximum ethanol resistance was observed when ethanol concentration used for ethanol adaptation was increased to 5·0%. Additionally, pre-adaptation to 5·0% ethanol cross-protected Salm. Enteritidis against -20°C, but not against 4°C, 50°C or 10% NaCl.

CONCLUSIONS

Ethanol adaptation provided Salm. Enteritidis direct protection from a high level ethanol challenge and cross-protection from freezing, but not other stresses tested (low temperature, high salinity or high temperature).

SIGNIFICANCE AND IMPACT OF THE STUDY

The results are valuable in developing adequate and efficient control measures for Salm. Enteritidis in foods.

New Antimicrobially Amended Media for Improved Nonpoint Source Bacterial Pollution Treatment

Nonpoint source pollution (NPS) such as stormwater runoff may introduce high loads of bacteria, impairing surface water bodies. The existing filter materials in stormwater best management practices (BMP) are typically not designed to inactivate bacteria. Herein, novel filtration media were extensively tested for microbial load reduction in stormwater runoff. Red cedar wood chips (RC) were amended with different loadings of either 3-(trihydroxysilyl) propyldimethyloctadecyl ammonium chloride (TPA) or silver nanoparticles (AgNP). Under batch conditions at 25 °C, log10 removal values (LRV) up to 3.71 ± 0.38 (mean ± standard error) for TPA-RC and 2.25 ± 1.00 for AgNP-RC were achieved for Escherichia coli (E. coli), whereas unmodified RC achieved less than 0.5 LRV. Similar trends were observed at 17.5 °C, however at low temperature (10 °C) no statistically significant difference in E. coli inactivation between modified and unmodified RC was detected. Inactivation kinetic studies show that TPA-RC has higher inactivation rate constants compared to AgNP-RC. Under dynamic flow conditions a mass balance approach indicates that even after remobilization up to 99.8% of E. coli removal using 9 mg/g TPA-RC compared to 64.8% for unmodified RC. This study demonstrates that RC wood chips amended with antimicrobial compounds show promising applications as filtration material for the reduction of microbiological contamination load in stormwater runoff.

Investigation of Reference Genes in Vibrio parahaemolyticus for Gene Expression Analysis Using Quantitative RT-PCR

Vibrio parahaemolyticus is a significant human pathogen capable of causing foodborne gastroenteritis associated with the consumption of contaminated raw or undercooked seafood. Quantitative RT-PCR (qRT-PCR) is a useful tool for studying gene expression in V. parahaemolyticus to characterize its virulence factors and understand the effect of environmental conditions on its pathogenicity. However, there is not a stable gene in V. parahaemolyticus that has been identified for use as a reference gene for qRT-PCR. This study evaluated the stability of 6 reference genes (16S rRNA, recA, rpoS, pvsA, pvuA, and gapdh) in 5 V. parahaemolyticus strains (O3:K6-clinical strain-tdh⁺, ATCC33846-tdh⁺, ATCC33847-tdh⁺, ATCC17802-trh⁺, and F13-environmental strain-tdh⁺) cultured at 4 different temperatures (15, 25, 37 and 42°C). Stability values were calculated using GeNorm, NormFinder, BestKeeper, and Delta CT algorithms. The results indicated that recA was the most stably expressed gene in the V. parahaemolyticus strains cultured at different temperatures. This study examined multiple V. parahaemolyticus strains and growth temperatures, hence the finding provided stronger evidence that recA can be used as a reference gene for gene expression studies in V. parahaemolyticus.

Even a Chronic Mild Hyperglycemia Affects Membrane Fluidity and Lipoperoxidation in Placental Mitochondria in Wistar Rats

It is known the deleterious effects of diabetes on embryos, but the effects of diabetes on placenta and its mitochondria are still not well known. In this work we generated a mild hyperglycemia model in female wistar rats by intraperitoneal injection of streptozotocin in 48 hours-old rats. The sexual maturity onset of the female rats was delayed around 6–7 weeks and at 16 weeks-old they were mated, and sacrificed at day 19th of pregnancy. In placental total tissue and isolated mitochondria, the fatty acids composition was analyzed by gas chromatography, and lipoperoxidation was measured by thiobarbituric acid reactive substances. Membrane fluidity in mitochondria was measured with the excimer forming probe dipyrenylpropane and mitochondrial function was measured with a Clark-type electrode. The results show that even a chronic mild hyperglycemia increases lipoperoxidation and decreases mitochondrial function in placenta. Simultaneously, placental fatty acids metabolism in total tissue is modified but in a different way than in placental mitochondria. Whereas the chronic mild hyperglycemia induced a decrease in unsaturated to saturated fatty acids ratio (U/S) in placental total tissue, the ratio increased in placental mitochondria. The measurements of membrane fluidity showed that fluidity of placenta mitochondrial membranes increased with hyperglycemia, showing consistency with the fatty acids composition through the U/S index. The thermotropic characteristics of mitochondrial membranes were changed, showing lower transition temperature and activation energies. All of these data together demonstrate that even a chronic mild hyperglycemia during pregnancy of early reproductive Wistar rats, generates an increment of lipoperoxidation, an increase of placental mitochondrial membrane fluidity apparently derived from changes in fatty acids composition and consequently, mitochondrial malfunction.

Cis and trans unsaturated phosphatidylcholine bilayers: A molecular dynamics simulation study

Trans unsaturated lipids are uncommon in nature. In the human diet, they occur as natural products of ruminal bacteria or from industrial food processing like hydrogenation of vegetable oils. Consumption of trans unsaturated lipids has been shown to have a negative influence on human health; in particular, the risk of cardiovascular disease is higher when the amount of trans unsaturated lipids in the diet is elevated. In this study, we first performed quantum mechanical calculations to specifically and accurately parameterize cis and trans mono-unsaturated lipids and subsequently validated the newly derived parameter set. Then, we carried out molecular dynamics (MD) simulations of lipid bilayers composed of cis or trans unsaturated lipids with and without cholesterol. Our results show that trans mono-unsaturated chains are more flexible than cis mono-unsaturated chains due to lower barriers for rotation around the single bonds next to the trans double bond than those next to the cis double bond. In effect, interactions between cholesterol and trans unsaturated chains are stronger than cis unsaturated chains, which results in a higher ordering effect of cholesterol in trans unsaturated bilayers.

Temperature-dependent expression of virulence genes in fish-pathogenic bacteria

Virulence gene expression in pathogenic bacteria is modulated by environmental parameters. A key factor in this expression is temperature. Its effect on virulence gene expression in bacteria infecting warm-blooded hosts is well documented. Transcription of virulence genes in these bacteria is induced upon a shift from low environmental to a higher host temperature (37°C). Interestingly, host temperatures usually correspond to the optimum for growth of these pathogenic bacteria. On the contrary, in ectothermic hosts such as fish, molluscs, and amphibians, infection processes generally occur at a temperature lower than that for the optimal growth of the bacteria. Therefore, regulation of virulence gene expression in response to temperature shift has to be modulated in a different way to that which is found in bacteria infecting warm-blooded hosts. The current understanding of virulence gene expression and its regulation in response to temperature in fish-pathogenic bacteria is limited, but constant extension of our knowledge base is essential to enable a rational approach to the problem of the bacterial fish diseases affecting the aquaculture industry. This is an interesting issue and progress needs to be made in order to diminish the economic losses caused by these diseases. The intention of this review is, for the first time, to compile the scattered results existing in the field in order to lay the groundwork for future research. This article is an overview of those relevant virulence genes that are expressed at temperatures lower than that for optimal bacterial growth in different fish-pathogenic bacteria as well as the principal mechanisms that could be involved in their regulation.

Microarray transcriptional profiling of Arctic Mesorhizobium strain N33 at low temperature provides insights into cold adaption strategies

Background

Arctic Mesorhizobium strain N33 was isolated from nodules of the legume Oxytropis arctobia in Canada’s eastern Arctic. This symbiotic bacterium can grow at temperatures ranging from 0 to 30 °C, fix nitrogen at 10 °C, and is one of the best known cold-adapted rhizobia. Despite the economic potential of this bacterium for northern regions, the key molecular mechanisms of its cold adaptation remain poorly understood.

Results

Using a microarray printed with 5760 Arctic Mesorhizobium genomic clones, we performed a partial transcriptome analysis of strain N33 grown under eight different temperature conditions, including both sustained and transient cold treatments, compared with cells grown at room temperature. Cells treated under constant (4 and 10 °C) low temperatures expressed a prominent number of induced genes distinct from cells treated to short-term cold-exposure (<60 min), but exhibited an intermediate expression profile when exposed to a prolonged cold exposure (240 min). The most prominent up-regulated genes encode proteins involved in metabolite transport, transcription regulation, protein turnover, oxidoreductase activity, cryoprotection (mannitol, polyamines), fatty acid metabolism, and membrane fluidity. The main categories of genes affected in N33 during cold treatment are sugar transport and protein translocation, lipid biosynthesis, and NADH oxidoreductase (quinone) activity. Some genes were significantly down-regulated and classified in secretion, energy production and conversion, amino acid transport, cell motility, cell envelope and outer membrane biogenesis functions. This might suggest growth cessation or reduction, which is an important strategy to adjust cellular function and save energy under cold stress conditions.

Conclusion

Our analysis revealed a complex series of changes associated with cold exposure adaptation and constant growth at low temperatures. Moreover, it highlighted some of the strategies and different physiological states that Mesorhizobium strain N33 has developed to adapt to the cold environment of the Canadian high Arctic and has revealed candidate genes potentially involved in cold adaptation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1611-4) contains supplementary material, which is available to authorized users.

Metagenomic analysis reveals adaptations to a cold-adapted lifestyle in a low-temperature acid mine drainage stream

An acid mine drainage (pH 2.5-2.7) stream biofilm situated 250 m below ground in the low-temperature (6-10°C) Kristineberg mine, northern Sweden, contained a microbial community equipped for growth at low temperature and acidic pH. Metagenomic sequencing of the biofilm and planktonic fractions identified the most abundant microorganism to be similar to the psychrotolerant acidophile, Acidithiobacillus ferrivorans. In addition, metagenome contigs were most similar to other Acidithiobacillus species, an Acidobacteria-like species, and a Gallionellaceae-like species. Analyses of the metagenomes indicated functional characteristics previously characterized as related to growth at low temperature including cold-shock proteins, several pathways for the production of compatible solutes and an anti-freeze protein. In addition, genes were predicted to encode functions related to pH homeostasis and metal resistance related to growth in the acidic metal-containing mine water. Metagenome analyses identified microorganisms capable of nitrogen fixation and exhibiting a primarily autotrophic lifestyle driven by the oxidation of the ferrous iron and inorganic sulfur compounds contained in the sulfidic mine waters. The study identified a low diversity of abundant microorganisms adapted to a low-temperature acidic environment as well as identifying some of the strategies the microorganisms employ to grow in this extreme environment.

Cold signal transduction and its interplay with phytohormones during cold acclimation

Cold stress is a major environmental factor that affects plant growth, development, productivity and distribution. In higher plants, the known major cold signaling pathway is the C-repeat (CRT)-binding factor/dehydration-responsive element (DRE) binding factor (CBF/DREB)-mediated transcriptional regulatory cascade, which is essential for the induction of a set of cold responsive (COR) genes. Recent studies indicate that various plant hormones are also involved in responses to cold stress. This review summarizes recent progress in cold signaling and our understanding of phytohormone signaling in the regulation of plant responses to cold stress.

The effect of cold stress on the proteome of the marine bacterium Pseudomonas fluorescens BA3SM1 and its ability to cope with metal excess

This study examined the effect of cold stress on the proteome and metal tolerance of Pseudomonas fluorescens BA3SM1, a marine strain isolated from tidal flat sediments. When cold stress (+10 °C for 36 h) was applied before moderate metal stress (0.4 mM Cd, 0.6 mM Cd, 1.5 mM Zn, and 1.5 mM Cu), growth disturbances induced by metal, in comparison with respective controls, were reduced for Cd and Zn while they were pronounced for Cu. This marine strain was able to respond to cold stress through a number of changes in protein regulation. Analysis of the predicted differentially expressed protein functions demonstrated that some mechanisms developed under cold stress were similar to those developed in response to Cd, Zn, and Cu. Therefore, pre-cold stress could help this strain to better counteract toxicity of moderate concentrations of some metals. P. fluorescens BA3SM1 was able to remove up to 404.3 mg Cd/g dry weight, 172.5 mg Zn/g dry weight, and 11.3 mg Cu/g dry weight and its metal biosorption ability seemed to be related to the bacterial growth phase. Thus, P. fluorescens BA3SM1 appears as a promising agent for bioremediation processes, even at low temperatures.

Features of pseudomonads growing at low temperatures: another facet of their versatility

Pseudomonads are a diverse and ecologically successful group of γ-proteobacteria present in many environments (terrestrial, freshwater and marine), either free living or associated with plants or animals. Their success is at least partly based on their ability to grow over a wide range of temperatures, their capacity to withstand different kinds of stress and their great metabolic versatility. Although the optimal growth temperature of pseudomonads is usually close to 25–30°C, many strains can also grow between 5°C and 10°C, and some of them even close to 0°C. Such low temperatures strongly affect the physicochemical properties of macromolecules, forcing cells to evolve traits that optimize growth and help them withstand cold-induced stresses such as increased levels of reactive oxygen species, reduced membrane fluidity and enzyme activity, cold-induced protein denaturation and the greater stability of DNA and RNA secondary structures. This review gathers the information available on the strategies used by pseudomonads to adapt to low temperature growth, and briefly describes some of the biotechnological applications that might benefit from cold-adapted bacterial strains and enzymes, e.g., biotransformation or bioremediation processes to be performed at low temperatures.

Incorporation of exogenous fatty acids protects Enterococcus faecalis from membrane-damaging agents

Enterococcus faecalis is a commensal bacterium of the mammalian intestine that can persist in soil and aquatic systems and can be a nosocomial pathogen to humans. It employs multiple stress adaptation strategies in order to survive such a wide range of environments. Within this study, we sought to elucidate whether membrane fatty acid composition changes are an important component for stress adaptation. We noted that E. faecalis OG1RF was capable of changing its membrane composition depending upon growth phase and temperature. The organism also readily incorporated fatty acids from bile, serum, and medium supplemented with individual fatty acids, often dramatically changing the membrane composition such that a single fatty acid was predominant. Growth in either low levels of bile or specific individual fatty acids was found to protect the organism from membrane challenges such as high bile exposure. In particular, we observed that when grown in low levels of bile, serum, or the host-derived fatty acids oleic acid and linoleic acid, E. faecalis was better able to survive the antibiotic daptomycin. Interestingly, the degree of membrane saturation did not appear to be important for protection from the stressors examined here; instead, it appears that a specific fatty acid or combination of fatty acids is critical for stress resistance.

Trehalose enhancing microbial electrolysis cell for hydrogen generation in low temperature (0 °C)

This work explored the feasibility of a method combining physical (sonication and base) and biological (partial fermentation) processes for sludge treatment and the effects of trehalose on the hydrogen generation of microbial electrolysis cell at 0 °C. The results demonstrated that the above pretreatment method was favorable, which promoted organics decomposing into lower molecular weight matter. The promotion of trehalose for MEC efficiency was obvious and the optimal concentration of trehalose was 50 mmol/L. With this concentration, the highest hydrogen recovery rate was 0.25 m(3)-H₂/-m(3)-reactor per day. Coulomb efficiency and energy recovery efficiency were 46.4% and 203%, respectively. Further, the consumption order of mixed substances was VFAs>proteins>carbohydrates. For microorganism community, SEM photographs illustrated that the selectivity of environmental temperature for the species of anode bacteria was strong and denaturing gradient gel electrophoresis indicated that Microbacterium and Proteobacteria were the two main species and Proteobacteria may be one of the species that produced electrons.

Bacterial ice crystal controlling proteins

Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions.

Cryotolerance strategies of Pseudomonads isolated from the rhizosphere of Himalayan plants

The cold stress biology of psychrotrophic Pseudomonas strains isolated from the rhizosphere of Himalayan plants have been explored to evaluate their cryotolerance characteristcs. Pseudomonas strains were examined for stress metabolites, viz., exopolysaccharide (EPS) production, intracellular sugar, polyols and amino acid content, ice nucleation activity, and their freezing survival at -10 and -40°C, respectively. High freezing survival was observed for the Pseudomonas strains that were grown at 4°C prior to their freezing at -10 or -40°C. Increased EPS production was noticed when Pseudomonas strains were grown at lower temperatures, i.e., 4 and 15°C, in comparison with their optimal growth temperature of 28°C. All Pseudomonas strains showed low level of type-III class ice nucleation activity at -10°C after 96 h. Considerable differences were noticed in accumulated contents of various intracellular sugars, polyols, amino acids for all Pseudomonas strains when they grown at two different temperatures, i.e., 4 and 28°C, respectively. The unusual complement of stress protectants especially, raffinose, cysteine and aspartic acid that accumulated in the bacterial cells at low temperature was novel and intriguing finding of this study. The finding that raffinose is a key metabolite accumulated at low temperature is an exciting discovery, and to the best of our information this is first report ever signifying its role in bacterial cold tolerance.

Global transcriptome analysis of Lactococcus garvieae strains in response to temperature

Lactococcus garvieae is an important fish and an opportunistic human pathogen. The genomic sequences of several L. garvieae strains have been recently published, opening the possibility of global studies on the biology of this pathogen. In this study, a whole genome DNA microarray of two strains of L. garvieae was designed and validated. This DNA microarray was used to investigate the effects of growth temperature (18°C and 37°C) on the transcriptome of two clinical strains of L. garvieae that were isolated from fish (Lg8831) and from a human case of septicemia (Lg21881). The transcriptome profiles evidenced a strain-specific response to temperature, which was more evident at 18°C. Among the most significant findings, Lg8831 was found to up-regulate at 18°C several genes encoding different cold-shock and cold-induced proteins involved in an efficient adaptive response of this strain to low-temperature conditions. Another relevant result was the description, for the first time, of respiratory metabolism in L. garvieae, whose gene expression regulation was temperature-dependent in Lg21881. This study provides new insights about how environmental factors such as temperature can affect L. garvieae gene expression. These data could improve our understanding of the regulatory networks and adaptive biology of this important pathogen.

Site-specific acylation changes in the lipid A of Escherichia coli lpxL mutants grown at high temperatures

LPS is a major component of the outer membrane of Gram-negative bacteria. The lipid A region of LPS mediates stimulation of the immune system. In E. coli, the gene (formerly htrB) codes for a late lauroyltransferase (LpxL) in lipid A biosynthesis. E. coli lpxL mutants have been described previously with impaired growth above 33°C in rich media. However, we were able to grow lpxL mutants at 30°C, 37°C and 42°C, and investigate their lipid A moieties to gain insight into changes and regulatory effects in lipid A biosynthesis. Multiple-stage mass spectrometry was used to decipher unusual lipid A structures produced by lpxL mutant bacteria at high temperatures that rescue the temperature-sensitive phenotype. At 37°C and 42°C, E. coli lpxL mutants appear to activate different acyltransferases or biosynthetic pathways that generate atypical penta- and hexaacyl lipid A structures by incorporating longer fatty acids, such as a secondary palmitoleic acid (2'-O-position, distal) and a secondary palmitic acid (2-O-position, proximal) respectively. However, we observed no changes in these structures through various growth curve stages. This study indicates that E. coli (lpxL) lipid A biosynthesis, and specifically the 'late' acylation of lipid A, is temperature dependent, thus suggesting a highly regulated process.

Sea ice microorganisms: environmental constraints and extracellular responses

Inherent to sea ice, like other high latitude environments, is the strong seasonality driven by changes in insolation throughout the year. Sea-ice organisms are exposed to shifting, sometimes limiting, conditions of temperature and salinity. An array of adaptations to survive these and other challenges has been acquired by those organisms that inhabit the ice. One key adaptive response is the production of extracellular polymeric substances (EPS), which play multiple roles in the entrapment, retention and survival of microorganisms in sea ice. In this concept paper we consider two main areas of sea-ice microbiology: the physico-chemical properties that define sea ice as a microbial habitat, imparting particular advantages and limits; and extracellular responses elicited in microbial inhabitants as they exploit or survive these conditions. Emphasis is placed on protective strategies used in the face of fluctuating and extreme environmental conditions in sea ice. Gaps in knowledge and testable hypotheses are identified for future research.

The polar lipids of Clostridium psychrophilum, an anaerobic psychrophile

We have examined the polar lipids of Clostridium psychrophilum, a recently characterized psychrophilic Clostridium isolated from an Antarctic microbial mat. Lipids were extracted from cells grown near the optimal growth temperature (+5°C) and at -5°C, and analyzed by two-dimensional thin layer chromatography and liquid chromatography coupled with mass spectrometry. The major phospholipids of this species are: cardiolipin, phosphatidylethanolamine, and phosphatidylglycerol. Phosphatidylserine and lyso-phosphatidylethanolamine were found as minor components. The most abundant glycolipids are a monoglycosyldiradylglycerol (MGDRG) and a diglycosyldiradylglycerol (DGDRG). The latter was only seen in cells grown at -5°C. An ethanolamine-phosphate derivative of N-acetylglucosaminyldiradylglycerol was seen in cells grown at -5°C and an ethanolamine-phosphate derivative of MGDRG was found in cells grown at +5°C. All lipids were present in both the all acyl and plasmalogen (alk-1'-enyl acyl) forms with the exception of PS and MGDRG, which were predominantly in the diacyl form. The significance of lipid changes at the two growth temperatures is discussed.

The microbial diversity of Polar environments is a fertile ground for bioprospecting

The term bioprospecting has been adopted for systematic searches in nature for new bioactive compounds, genes, proteins, microorganisms and other products with potential for commercial use. Much effort has been focused on microorganisms able to thrive under harsh conditions, including the Polar environments. Both the lipid and protein cellular building blocks of Polar microorganisms are shaped by their adaptation to the permanently low temperatures. In addition, strongly differing environments, such as permafrost, glaciers and sea ice, have contributed to additional functional diversity. Emerging massive-parallel sequencing technologies have revealed the existence of a huge, hitherto unseen diversity of low-abundance phylotypes--the rare biosphere--even in the Polar environments. This realization has further strengthened the need to employ cultivation-independent approaches, including metagenomics and single-cell genomic sequencing, to get comprehensive access to the genetic diversity of microbial communities for bioprospecting purposes. In this review, we present an updated snapshot of recent findings on the molecular basis for adaptation to the cold and the phylogenetic diversities of different Polar environments. Novel approaches in bioprospecting are presented and we conclude by showing recent bioprospecting outcomes in terms of new molecules patented or applied by some biotech companies.

Lipids of plant membrane rafts

Lipids tend to organize in mono or bilayer phases in a hydrophilic environment. While they have long been thought to be incapable of coherent lateral segregation, it is now clear that spontaneous assembly of these compounds can confer microdomain organization beyond spontaneous fluidity. Membrane raft microdomains have the ability to influence spatiotemporal organization of protein complexes, thereby allowing regulation of cellular processes. In this review, we aim at summarizing briefly: (i) the history of raft discovery in animals and plants, (ii) the main findings about structural and signalling plant lipids involved in raft segregation, (iii) imaging of plant membrane domains, and their biochemical purification through detergent-insoluble membranes, as well as the existing debate on the topic. We also discuss the potential involvement of rafts in the regulation of plant physiological processes, and further discuss the prospects of future research into plant membrane rafts.

Context-dependent symbioses and their potential roles in wildlife diseases

It is well known in ecology, evolution and medicine that both the nature (commensal, parasitic and mutualistic) and outcome (symbiont fitness, survival) of symbiotic interactions are often context-dependent. Less is known about the importance of context-dependence in symbioses involved in wildlife disease. We review variable symbioses, and use the amphibian disease chytridiomycosis to demonstrate how understanding context-dependence can improve the understanding and management of wildlife diseases. In chytridiomycosis, the host-pathogen interaction is context-dependent; it is strongly affected by environmental temperature. Skin bacteria can also modify the interaction; some bacteria reduce amphibians' susceptibility to chytridiomycosis. Augmentation of protective microbes is being considered as a possible management tool, but informed application of bioaugmentation requires understanding of how the interactions between host, beneficial bacteria and pathogen depend upon environmental context. The community-level response of the amphibian skin microbiota to environmental conditions may explain the relatively narrow range of environmental conditions in which past declines have occurred. Environmental context affects virulence and the protection provided by mutualists in other host-pathogen systems, including threatened bats and corals. Increased focus on context-dependence in interactions between wildlife and their symbionts is likely to be crucial to the future investigation and management of emerging diseases of wildlife.

Inactivation of a low temperature-induced RNA helicase in Synechocystis sp. PCC 6803: physiological and morphological consequences

Inactivation of the DEAD box RNA helicase, crhR, has dramatic effects on the physiology and morphology of the photosynthetic cyanobacterium, Synechocystis sp. PCC 6803. These effects are observed at both normal growth temperature (30°C) and under cold stress (20°C), indicating that CrhR performs crucial function(s) at all temperatures. A major physiological effect is the rapid cessation of photosynthesis upon temperature downshift from 30 to 20°C. This defect does not originate from an inability to transport or accumulate inorganic carbon or a deficiency in photosynthetic capacity as the mutant has sufficient electron transport and enzymatic capacity to sustain photosynthesis at 30°C and inorganic carbon (Ci) accumulation at 20°C. Oxygen consumption in the presence of methyl viologen indicated that while electron transport capacity is sufficient to accumulate Ci, the mutant does not possess sufficient activity to sustain carbon fixation at maximal rates. These defects are correlated with severely impaired cell growth and decreased viability, cell size and DNA content at low temperature. The ΔcrhR mutant also progressively accumulates structural abnormalities at low temperature that cannot be attributed solely to reactive oxygen species (ROS)-induced photooxidative damage, suggesting that they are manifestations of pre-existing defects that are amplified over time. The data indicate that the observed physiological and morphological effects are intimately related to crhR mutation, implying that the lack of CrhR RNA unwinding/annealing activity results in the inability to execute one or more vital steps in photosynthesis that are required at all temperatures but are crucial at low temperature.

Differential expression of membrane proteins helps Antarctic Pseudomonas syringae to acclimatize upon temperature variations

Antarctic bacteria are adapted to the extremely low temperature. The transcriptional and translational machineries of these bacteria are adapted to the sub-zero degrees of temperature. Studies directed towards identifying the changes in the protein profiles during changes in the growth temperatures of an Antarctic bacterium Pseudomonas syringae Lz4W may help in understanding the molecular basis of cold adaptation. In this study, subcellular fractionation methods of proteins were used for the enrichment and identification of proteins including low abundance proteins. The membrane proteins of the bacterium P. syringae Lz4W were prepared employing sucrose density gradient method. The proteins were separated through 2D gel-electrophoresis with the pH ranges 3-10, 4-7 and 5-8 using the detergent, amidosulfobetaine (ASB-14). The proteins separated on the 1D SDS PAGE and 2D gels were identified with the help of LC-ESI MS/MS and MALDI TOF TOF using bioinformatic programs MASCOT and SEQUEST. Since the genome sequence of P. syringae Lz4W is not available, the proteins are identified by using the genome database of the Pseudomonas sp. available at NCBI. The present studies focus on identifying temperature dependent expression of proteins by employing LC-MS/MS method and the functional significance of these proteins is discussed.

A temporal-omic study of Propionibacterium freudenreichii CIRM-BIA1 adaptation strategies in conditions mimicking cheese ripening in the cold

Propionibacterium freudenreichii is used as a ripening culture in Swiss cheese manufacture. It grows when cheeses are ripened in a warm room (about 24°C). Cheeses with an acceptable eye formation level are transferred to a cold room (about 4°C), inducing a marked slowdown of propionic fermentation, but P. freudenreichii remains active in the cold. To investigate the P. freudenreichii strategies of adaptation and survival in the cold, we performed the first global gene expression profile for this species. The time-course transcriptomic response of P. freudenreichii CIRM-BIA1(T) strain was analyzed at five times of incubation, during growth at 30°C then for 9 days at 4°C, under conditions preventing nutrient starvation. Gene expression was also confirmed by RT-qPCR for 28 genes. In addition, proteomic experiments were carried out and the main metabolites were quantified. Microarray analysis revealed that 565 genes (25% of the protein-coding sequences of P. freudenreichii genome) were differentially expressed during transition from 30°C to 4°C (P<0.05 and |fold change|>1). At 4°C, a general slowing down was observed for genes implicated in the cell machinery. On the contrary, P. freudenreichii CIRM-BIA1(T) strain over-expressed genes involved in lactate, alanine and serine conversion to pyruvate, in gluconeogenesis, and in glycogen synthesis. Interestingly, the expression of different genes involved in the formation of important cheese flavor compounds, remained unchanged at 4°C. This could explain the contribution of P. freudenreichii to cheese ripening even in the cold. In conclusion, P. freudenreichii remains metabolically active at 4°C and induces pathways to maintain its long-term survival.

Bacterial gene expression at low temperatures

Under suboptimal environmental conditions such as low temperatures, many bacteria have an extended lag phase, altered cell structures, and composition such as a less fluid (more rigid) and leaky cytoplasmic membrane. As a result, cells may die, enter into a starvation mode of metabolism or a physiologically viable but non-culturable (VBNC) state. In the latter state, the amount of gene expression per cell is virtually undetectable. In this article, gene expression under (suboptimal) low temperature conditions in non-psychrophilic environmental bacteria is examined. The pros and cons of some of the molecular methodologies for gene expression analysis are also discussed.

Eicosapentaenoic acid plays a role in stabilizing dynamic membrane structure in the deep-sea piezophile Shewanella violacea: a study employing high-pressure time-resolved fluorescence anisotropy measurement

Shewanella violacea DSS12 is a psychrophilic piezophile that optimally grows at 30MPa. It contains a substantial amount of eicosapentaenoic acid (EPA) in the membrane. Despite evidence linking increased fatty acid unsaturation and bacterial growth under high pressure, little is known of how the physicochemical properties of the membrane are modulated by unsaturated fatty acids in vivo. By means of the newly developed system performing time-resolved fluorescence anisotropy measurement under high pressure (HP-TRFAM), we demonstrate that the membrane of S. violacea is highly ordered at 0.1MPa and 10°C with the order parameter S of 0.9, and the rotational diffusion coefficient D(w) of 5.4μs(-1) for 1-[4-(trimethylamino)pheny]-6-phenyl-1,3,5-hexatriene in the membrane. Deletion of pfaA encoding the omega-3 polyunsaturated fatty acid synthase caused disorder of the membrane and enhanced the rotational motion of acyl chains, in concert with a 2-fold increase in the palmitoleic acid level. While the wild-type membrane was unperturbed over a wide range of pressures with respect to relatively small effects of pressure on S and D(w), the ΔpfaA membrane was disturbed judging from the degree of increased S and decreased D(w). These results suggest that EPA prevents the membrane from becoming hyperfluid and maintains membrane stability against significant changes in pressure. Our results counter the generally accepted concept that greater fluidity is a membrane characteristic of microorganisms that inhabit cold, high-pressure environments. We suggest that retaining a certain level of membrane physical properties under high pressure is more important than conferring membrane fluidity alone.