Supercooling ability in two populations of the land snail Helix pomatia (Gastropoda: Helicidae) and ice-nucleating activity of gut bacteria

The land snail Helix pomatia (Gastropoda: Helicidae) is widely distributed in Northern and Central Europe where it may experience subzero temperatures during winter months. Its supercooling ability was studied in two populations of H. pomatia. One population originated from Southern Sweden (Gotaland) and the other from Central France (Auvergne). In the experimental design, they were acclimated, over 2 weeks, to artificial winter conditions (hibernation, T=5 degrees C). The Swedish snails showed a rather limited supercooling ability (temperature of crystallization, T(c)=-6.4+/-0.8 degrees C), significantly greater, however, than the supercooling capacity of the population from France (T(c)=-4.6+/-1.4 degrees C). In artificial spring conditions (3 months of hibernation followed by a progressive acclimation, over 2 weeks, to activity at T=20 degrees C), both populations exhibited a similar high T(c) (-2.0+/-1.0 degrees C). The lower T(c) of hibernating Swedish snails could be due to a greater loss of body water, accompanied by a higher concentration of solutes in the hemolymph. In both populations, the variation in hemolymph osmolality measured between hibernating (250-270 mOsm kg(-1)) and active (165-215 mOsm kg(-1)) snails may be explained by the variation in body water mass and did not suggest the production of colligative cryoprotectants. Moreover, the three bacterial strains, Buttiauxella sp., Kluyvera sp., and Tatumella sp. (Enterobacteriaceae) which were isolated from fed snails, but absent in starved snails, did not show any ice-nucleating activity at temperatures higher than -9 degrees C. Only the strain Kluyvera sp. initiated nucleation at -9 degrees C. This strain, therefore, is a weak, also termed a Type III or Class C ice-nucleating active bacterium, but with no influence on the supercooling ability of individual snails. In summary, fluctuations in body water mass of hibernating snail populations, triggering changes in osmolyte concentration, rather than the presence of endogenous ice-nucleating-active bacteria, accounts for fluctuations in their T(c).     

Relationships between macroalgal biomass and microbiological quality of water in a phytotreatment pond

The microbiological quality of wastewater in phytotreatment ponds with foliose macroalgae can be influenced by biofilm formation on thallus surface. This hypothesis was tested with an in situ experiment which was carried out in a pond with Ulva spp. receiving wastewater from a land based fish farm at Piombino (Italy). The total bacterial load (TBL) was determined in the inflowing and outflowing waters and a multifactorial design was employed to investigate the effect of different macroalgal biomass. Microbiological analysis revealed a high TBL in the water column (18.4 ± 7.4 × 10⁸ cells ml⁻¹). TBL of inlet water was significantly correlated with quantity and quality of particulate organic matter (POM) of inflowing water, whereas no correlation was found between TBL and POM in the outlet water. A significant decrease in the POM concentration was detected within macroalgal ponds, due to the mechanical action of thalli which favoured POM sedimentation. Nevertheless, great TBLs were found in the outlet water. These findings suggest that TBL probably depended upon macroalgae. Indeed high bacterial density was found on macroalgal thallus surface (~10⁸ cells cm²). Furthermore, high plate counts of faecal bacteria (faecal enterococci) were determined on thallus surface (~ 40 CFU cm²) and outlet water (11 886 ± 3984 CFU 100 ml⁻¹) supporting the evidence that macroalgae negatively affect the microbiological quality of treated water. Bacterial activities in terms of exoenzymatic rates and secondary production were two folds higher in the water within macroalgal beds, than in the open water. These preliminary results suggest that high macroalgal biomass represents a ‚hot spot’ of bacterial density and activity that may affect microbiological quality of the treated water. Bacterial control of inlet water and management of macroalgal biomass through periodic removal are essential for a more efficient treatment of wastewater in phytotreatment ponds.     

Bacterioplankton Abundance and Activity in a Small Hypertrophic Stratified Lake

Bacterioplankton abundance and production were followed during one decade (1991–2001) in the hypertrophic and steeply stratified small Lake Verevi (Estonia). The lake is generally dimictic. However, a partly meromictic status could be formed in specific meteorological conditions as occurred in springs of 2000 and 2001. The abundance of bacteria in Lake Verevi is highly variable (0.70 to 22 × 10⁶ cells ml⁻¹) and generally the highest in anoxic hypolimnetic water. In 2000–2001, the bacterial abundance in the hypolimnion increased probably due to meromixis. During a productive season, heterotrophic bacteria were able to consume about 10–40% of primary production in the epilimnion. Our study showed that bacterioplankton in the epilimnion was top-down controlled by predators, while in metalimnion bacteria were dependent on energy and carbon sources (bottom-up regulated). Below the thermocline hypolimnetic bacteria mineralized organic matter what led to the depletion of oxygen and created anoxic hypolimnion where rich mineral nutrient and sulphide concentrations coexisted with high bacterial numbers.     

Cold-active DnaK of an Antarctic psychrotroph Shewanella sp. Ac10 supporting the growth of dnaK-null mutant of Escherichia coli at cold temperatures

Shewanella sp. Ac10 is a psychrotrophic bacterium isolated from the Antarctica that actively grows at such low temperatures as 0°C. Immunoblot analyses showed that a heat-shock protein DnaK is inducibly formed by the bacterium at 24°C, which is much lower than the temperatures causing heat shock in mesophiles such as Escherichia coli. We found that the Shewanella DnaK (SheDnaK) shows much higher ATPase activity at low temperatures than the DnaK of E. coli (EcoDnaK): a characteristic of a cold-active enzyme. The recombinant SheDnaK gene supported neither the growth of a dnaK-null mutant of E. coli at 43°C nor phage propagation at an even lower temperature, 30°C. However, the recombinant SheDnaK gene enabled the E. coli mutant to grow at 15°C. This is the first report of a DnaK supporting the growth of a dnaK-null mutant at low temperatures.     

Enhancing the growth of Vicia faba plants by microbial inoculation to improve their phytoremediation potential for oily desert areas

Two experiments were conducted to investigate the effect of inoculating Vicia faba plants (broad beens) raised in clean and oily sand with nodule-forming rhizobia and plant-growth-promoting rhizobacteria (PGPR) on growth of these plants in sand and to test whether this can improve the phytoremediation potential of this crop for oily desert areas. It was found that crude oil in sand at concentrations < 1.0% (w/w) enhanced the plant heights, their fresh and dry weights, the total nodule weights per plant, and the nitrogen contents of shoots and fruits. Similar enhancing effects were recorded when roots of the young plants were inoculated with nodule bacteria alone, PGPR alone, or a mixture of one strain of nodule bacteria and one of the PGPR. Such plant growth effects were associated with a better phytoremediation potential of V. faba plants for oily sand. The total numbers of oil-utilizing bacteria increased in the rhizosphere and more hydrocarbons were eliminated in sand close to the roots. The nodule bacteria tested were two strains of Rhizobium leguminosarum and the PGPR were Pseudomonas aeruginosa and Serratia liquefaciens. The four strains were found to use crude oil, n-octadecane, and phenanthrene as sole sources of carbon and energy. It was concluded that coinoculation of V. faba plant roots in oily sand with nodule bacteria and PGPR enhances the phytoremediation potential of this plant for oily desert sand through improving plant growth and nitrogen fixation.     

On-line monitoring of CO2 production in Lactococcus lactis during physiological pH decrease using membrane inlet mass spectrometry with dynamic pH calibration

Monitoring CO2 production in systems, where pH is changing with time is hampered by the chemical behavior and pH-dependent volatility of this compound. In this article, we present the first method where the concentration and production rate of dissolved CO2 can be monitored directly, continuously, and quantitatively under conditions where pH changes rapidly ( approximately 2 units in 15 min). The method corrects membrane inlet mass spectrometry (MIMS) measurements of CO2 for pH dependency using on-line pH analysis and an experimentally established calibration model. It is valid within the pH range of 3.5 to 7, despite pH-dependent calibration constants that vary in a non-linear fashion with more than a factor of 3 in this interval. The method made it possible to determine the carbon dioxide production during Lactococcus lactis fermentations, where pH drops up to 3 units during the fermentation. The accuracy was approximately 5%. We used the method to investigate the effect of initial extracellular pH on carbon dioxide production during anarobic glucose fermentation by non-growing Lactocoocus lactis and demonstrated that the carbon dioxide production rate increases considerably, when the initial pH was increased from 6 to 6.8.     

Structure of the O-specific polysaccharide from Shewanella japonica type strain KMM 3299T containing the rare amino sugar Fuc4NAc

An acidic O-specific polysaccharide (PS) of the agar-digesting bacterium Shewanella japonica with the type strain KMM 3299(T) was obtained by mild acid hydrolysis of the lipopolysaccharide. The polysaccharide was studied by component analysis, methylation analysis, (1)H and (13)C NMR spectroscopy, including 2D NMR experiments. The PS was determined to have the following structure involving three unusual amino sugars:     

Structure of an acidic polysaccharide from the marine bacterium Pseudoalteromonas aliena type strain KMM 3562T containing two residues of L-serine in the repeating unit

The structure of an acidic polysaccharide from Pseudoalteromonas aliena type strain KMM 3562(T) has been elucidated. The polysaccharide was studied by component analysis, (1)H and (13)C NMR spectroscopy, including 2D NMR experiments. A (1)H, (13)C band-selective constant-time heteronuclear multiple-bond connectivity experiment was used to determine amide linkages, between serine and uronic acid (UA) residues, via (3)J(H,C) correlations between Ser-alphaH and UA-C-6. It was found that the polysaccharide consists of pentasaccharide repeating units with the following structure: [carbohydrate structure]; see text.     

The O-chain structure from the LPS of marine halophilic bacterium Pseudoalteromonas carrageenovora-type strain IAM 12662T

The O-chain polysaccharide of the lipopolysaccharide from the halophilic marine bacterium Pseudoalteromonas carrageenovora IAM 12662T was characterized. The structure was studied by means of chemical analysis and 2D NMR spectroscopy of the de-O-acylated lipopolysaccharide and shown to be the following:Col is colitose, 3,6-di-deoxy-L-xylo-hexose.     

Structural characterisation of a highly branched exopolysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB2074

Lactobacillus delbrueckii subsp. bulgaricus NCFB2074 when grown in skimmed milk secretes a highly branched exopolysaccharide. The exopolysaccharide has a heptasaccharide repeat unit and is composed of glucose and galactose in the molar ratio 3:4. Using chemical techniques and 1D and 2D NMR spectroscopy the polysaccharide has been shown to possess the following repeat unit structure: [carbohydrate structure: see text].