The CasKR Two-Component System Is Required for the Growth of Mesophilic and Psychrotolerant Bacillus cereus Strains at Low Temperatures

The different strains of Bacillus cereus can grow at temperatures covering a very diverse range. Some B. cereus strains can grow in chilled food and consequently cause food poisoning. We have identified a new sensor/regulator mechanism involved in low-temperature B. cereus growth. Construction of a mutant of this two-component system enabled us to show that this system, called CasKR, is required for growth at the minimal temperature (T_min). CasKR was also involved in optimal cold growth above T_min and in cell survival below T_min. Microscopic observation showed that CasKR plays a key role in cell shape during cold growth. Introducing the casKR genes in a ΔcasKR mutant restored its ability to grow at T_min. Although it was first identified in the ATCC 14579 model strain, this mechanism has been conserved in most strains of the B. cereus group. We show that the role of CasKR in cold growth is similar in other B. cereus sensu lato strains with different growth temperature ranges, including psychrotolerant strains.     

Root Growth and Carbohydrate Metabolism at Low Temperatures

A study of carbohydrate metabolism in the roots of pea and maizeshows that the differing ability of these two species to growat low temperatures is associated with the maintenance of adequatesugar supplies to the root tip. In the maize root reducing theambient temperature to 2 °C causes a sharp and continuingfall in the soluble sugar content of the growing tip. A similartreatment with pea roots causes only a temporary reduction insugar content lasting no more than 24 h. The fall in root sugarsin maize is accompanied by a reduction in respiration rate andthe cessation of growth. During the periods of sugar shortagecaused by low temperatures both respiration and growth can bestimulated in root tips by a supply of exogenous glucose. Pearoots also show an additional ability to adapt to low temperaturesby lowering the K^m value for invertase after pretreatment ata low temperature. This effect is not seen in maize.     

The Biology and Osmoadaptation of Haloalkaliphilic Methanotrophs

There is increasing evidence for the presence and activity of methanotrophic bacteria in saline and alkaline aquatic environments located in different ecogeographical regions. Alkalitolerant halophilic and alkaliphilic halotolerant methanotrophs of type I were found to be able to utilize methane and methanol, to oxidize ammonium ions, and to transform various organic compounds in a wide range of water salinities (up to 12% NaCl) and pH values (from 5 to 11). The ecophysiological importance of methanotrophs in microbial communities inhabiting saline and alkaline aquatic environments is due to their involvement in the global cycles of methane and major bioelements (C, N, and S). Specific cyto- and biochemical properties of haloalkaliphilic methanotrophs—the synthesis of osmoprotectants (ectoine, 5-oxoproline, and sucrose), the accumulation of potassium ions, the formation of glycoprotein S-layers on the outer surface of their cell walls, and the modification of the chemical composition of their membranes—allow them to adapt to highly saline and alkaline habitats. Due to their specific properties, haloalkaliphilic methanotrophs may be of use in modern biotechnology.     

New Thermophilic Methanotrophs of the Genus Methylocaldum

Two pure cultures of obligate methanotrophs, strains H-11 and O-12, growing in the temperature range from 30 to 61°C with a optimum at 55°C were isolated from samples of silage and manure. Based on the results of analysis of the 16S rRNA genes and genes of membrane-bound methane monooxygenase, as well as on phenotypic properties, the isolates were assigned to the genus Methylocaldum. Significant temperature-dependent variations in morphology and phospholipid and fatty acid composition were revealed. Both strains assimilated methane carbon via the ribulose monophosphate, serine, and ribulose bisphosphate pathways. The activity of hexulosephosphate synthase was independent of the cultivation temperature; however, the activities of hydroxypyruvate reductase and ribulose bisphosphate carboxylase were higher in cells grown at 55°C than in cells grown at 37°C, indicating the important roles of the serine and ribulose bisphosphate pathways in the thermoadaptation of the strains under study. NH₄ ⁺ assimilation occurred through reductive amination of -ketoglutarate and via the glutamate cycle. The relationship between the physiological and biochemical peculiarities of the isolates and their thermophilic nature is discussed.     

Growth of Bacteria Degrading Naphthalene and Salicylate at Low Temperatures

A total of 58 bacterial strains degrading naphthalene and salicylate were isolated from soil samples polluted with oil products, collected in different regions of Russia during winter and summer. The isolates were assessed for their ability to grow at low temperatures (4, 8, and 15°C); bacteria growing at 4°C in the presence of naphthalene or salicylate accounted for 65 and 53%, respectively, of the strains isolated. The strains differed in the temperature dependence of their growth rates. It was demonstrated that the type of expression of the Nah⁺ phenotype at low temperatures depended on the combination of host bacterium and plasmid.     

Differentiation of Pathogenic and Saprophytic Leptospires I. Growth at Low Temperatures

The minimal growth temperature of the pathogenic leptospires is between 13 and 15 C. The saprophytic leptospires have a minimal growth temperature between 5 and 10 C, or approximately 5 C below that of the pathogens. The capability of the saprophytic leptospires to grow at temperatures below those which allow the growth of the pathogenic leptospires provides a simple method of discrimination. With an inoculum yielding approximately 8 x 10(7) cells per ml in the test medium and an incubation temperature of 13 C, the saprophytic leptospires were easily differentiated from the pathogenic leptospires. All 13 saprophytic leptospires tested grew in the 10% rabbit serum medium at 13 C, whereas none of the 20 pathogens grew during the 30-day incubation period.     

Collection of marine microalgae at the A. V. Zhirmunsky institute of marine biology

This article presents information about a special collection of marine microalgae at the Institute of Marine Biology (Far East Branch of the Russian Academy of Sciences). A list of microalgae currently maintained in the collection is given, and the main directions of the work with them are identified.     

Modifications to Thylakoid Composition during Development of Maize Leaves at Low Growth Temperatures

The effects of reductions in growth temperature on the development of thylakoids of maize (Zea mays var LG11) leaves are examined. Thylakoids isolated from mesophyll cells of leaves grown at 17° and 14°C, compared with 25°C, exhibited a decreased accumulation of many polypeptides, which was accompanied by a loss of activity of photosystems (PS) I and II. Probing the polypeptide profiles with a range of antibodies specific for thylakoid proteins demonstrated that a number of polypeptides encoded by the chloroplast genome failed to accumulate at low temperatures. Although thylakoid protein synthesis was reduced severely at 14°C compared with 25°C, major synthesis of both chloroplast and nuclear encoded polypeptides was detected. It is suggested that the lack of accumulation of some thylakoid proteins at low temperatures may be due to an inability to stabilize the proteins in the membranes. A number of thylakoid polypeptides were found to appear as the growth temperature was decreased. Analyses of pigments and polypeptides demonstrated that decreases in the photosystem reaction center core complexes occur relative to the light harvesting complex associated with PS II at reduced growth temperatures. Differential effects on the development of PSI and PSII were also observed, with PSII activity being preferentially reduced. Reductions in PSII content and activity occurred in parallel with decreases in the quantum yield and light-saturated rate of CO₂ assimilation. Fractionation of thylakoid pigment-protein complexes showed that the ratio of monomeric:oligomeric form of the light harvesting complex associated with PSII increased at low growth temperature, which is consistent with a chill-induced modification of thylakoid organization. Many, but not all, of the characteristic changes in thylakoid protein metabolism, which were observed when leaves were grown at low temperatures in controlled environments, were identified in leaves of a field maize crop during the early growing season when low temperatures were experienced by the crop. Chill-induced perturbations of thylakoid development can occur in the field in temperate regions and may have implications for the photosynthetic productivity of the crop.     

Two-Component-System Histidine Kinases Involved in Growth of Listeria monocytogenes EGD-e at Low Temperatures

Two-component systems (TCSs) aid bacteria in adapting to a wide variety of stress conditions. While the role of TCS response regulators in the cold tolerance of the psychrotrophic foodborne pathogen Listeria monocytogenes has been demonstrated previously, no comprehensive studies showing the role of TCS histidine kinases of L. monocytogenes at low temperature have been performed. We compared the expression levels of each histidine kinase-encoding gene of L. monocytogenes EGD-e in logarithmic growth phase at 3°C and 37°C, as well as the expression levels 30 min, 3 h, and 7 h after cold shock at 5°C and preceding cold shock (at 37°C). We constructed a deletion mutation in each TCS histidine kinase gene, monitored the growth of the EGD-e wild-type and mutant strains at 3°C and 37°C, and measured the minimum growth temperature of each strain. Two genes, yycG and lisK, proved significant in regard to induced relative expression levels under cold conditions and cold-sensitive mutant phenotypes. Moreover, the ΔresE mutant showed a lower growth rate than that of wild-type EGD-e at 3°C. Eleven other genes showed upregulated gene expression but revealed no cold-sensitive phenotypes. The results show that the histidine kinases encoded by yycG and lisK are important for the growth and adaptation of L. monocytogenes EGD-e at low temperature.     

Saponification of Methylated Mucosubstances at Low Temperatures

A fresh 1% solution of KOH in 70% ethanol in 2 hr at 2-4 C restores basophilia to methylated acid mucosubstances satisfactorily without detaching or damaging tissue sections. A 0.5% solution of Ba(OH)₂ under the same conditions gives results nearly as good, but NaOH and KMnO₄ are unsatisfactory.     

Accumulation of Free Proline at Low Temperatures

The accumulation of free proline in the first leaves of barley, Hordeum distichum L., and wheat, Triticum aestivum L., in response to a range of low temperatures was examined with 10-day-old plants. In barley (cv. Prior) no proline accumulated at 8°C or above, but in wheat (cv. Gabo) proline accumulated at 12°C and lower temperatures. In barley, the first leaf survived for 29 days following transfer to 5°C and continued to accumulate proline throughout this period. In contrast, the first leaves of plants maintained at 20°C survived for 13 days only and accumulated no proline. Proline accumulation at low temperature was shown to be light-dependent, both in intact plants and excised leaf sections, and the light requirement could not be replaced by supplying leaf segments with precursors of proline. Proline accumulation in response to water stress was not light-dependent at 20°C but was at 5°C. Inter-specific and intra-specific variation in the extent of accumulation in response to low temperature was also examined. Considerable variation was encountered but there was no clear relationship with geographical distribution or chilling sensitivity for the species and no correlation with accumulation in response to water stress in the cultivars of barley examined.     

High-Rate Anaerobic Treatment of Wastewater at Low Temperatures

Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8°C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids⁻¹ day⁻¹, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40°C.     

Microbiological Oxidation of Ferrous Iron at Low Temperatures

Acidophilic iron-oxidizing bacteria were enriched from mine water samples with ferrous sulfate as the substrate at incubation temperatures in the range of 4 to 46°C. After several subcultures at each test temperature except 46°C, which was prohibitive to growth, the rates of iron oxidation were determined in batch cultures. The results yielded linear rates in a semilogarithmic scale. The rate constants of iron oxidation by growing cultures were fitted into the Arrhenius equation, which displayed linearity in the 4 to 28°C range and yielded an activation energy value of 83 ± 3 kJ/mol.