Novel Aerobic Methylotrophic Isolates from the Soda Lakes of the Southern Transbaikal Region

Twenty-one bacterial associations isolated from the soda lakes of the southern Transbaikal region were found to be able to actively grow at pH 9–10 on methanol as the source of carbon and energy. Two alkalitolerant facultatively methylotrophic strains, Bur 3 and Bur 5, were obtained in pure cultures. Both strains represent gram-negative, nonmotile, bean-shaped, encapsulated cells that reproduce by binary fission. The strains are able to grow at temperatures ranging from 6 to 42°C, with an optimum growth temperature of 25–29°C (strain Bur 3) and 35–37°C (strain Bur 5) and at pH between 6.5 and 9.5, with an optimum pH value of 8.0–8.5. At pH 9.0, strain Bur 3 exhibits an increased content of phosphatidylglycerol and a decreased content of phosphatidylethanolamine. Strains Bur 3 and Bur 5 are similar in the G+C content of their DNAs (66.2 and 65.5 mol %, respectively) and in the type of the dominant ubiquinone (Q ₁₀). Unlike Bur 5, strain Bur 3 is able to grow autotrophically in an atmosphere of CO₂+ O₂+ H₂. The strains oxidize, by the respective dehydrogenases, methanol to CO₂, which is assimilated by the ribulose bisphosphate pathway. Ammonium ions are assimilated in the glutamate cycle and by the reductive amination of -ketoglutarate. The strains are highly homologous to each other (92%) and are much less homologous (at a level of 28–35%) to representatives of the genus Ancylobacter, A. aquaticusATCC 25396^Tand A. vacuolatumDSM 1277. Based on the results obtained, both strains are assigned to a new species, Ancylobacter natronumsp. nov.     

Microbial cycling of iron and sulfur in sediments of acidic and pH-neutral mining lakes in Lusatia (Brandenburg, Germany)

A vast number of lakes developed in the abandoned opencast lignite mines of Lusatia (East Germany) contain acidic waters (mmolSm^–2a^–). Potential Fe(III) reduction measured by the accumulation of Fe(II) during anoxic incubation yielded similar rates in both types of sediments, however, the responses towards the supplementation of Fe(III) and organic carbon were different. Sulfate reduction rates estimated with ³⁵S-radiotracer were much lower in the slightly acidic sediment than in the pH-neutral sediment (156 v.s. 738mmolSO₄ ^2–m^–2a^–1). However, sulfate reduction rates were increased by the addition of organic carbon. Severe limitation of sulfate-reducing bacteria under acidic conditions was also reflected by low most probable numbers (MPN). High MPN of acidophilic iron- and sulfur-oxidizing bacteria in acidic sediments indicated a high reoxidation potential. The results show that potentials for reductive processes are present in acidic sediments and that these are determined mainly by the availability of oxidants and organic matter.     

Accelerated molecular evolution in halophilic crustaceans

In contrast to the stable ionic composition of the oceans, inland waters show striking diversity, possessing salt concentrations varying from I mM to 5 M. Although species diversity is highest in fresh water, some lineages have colonized hypersaline environments where they encounter elevated levels of both ultraviolet (UV) radiation and osmotic stress. This study compares rates of evolution in halophilic and freshwater taxa for two groups of microcrustaceans, anostracans and daphniids, from Australia and North America. The results establish that halophilic species show consistent rate acceleration, involving elevated levels of both insertion/deletion events and of nucleotide substitutions. The elevated pace of molecular evolution does not appear to be linked to selection or to other agents that are known to influence the supply rate of mutations, such as UV exposure, generation length, or shifts in metabolic rate. However, variance in ionic strength, which is known to have potent effects on DNA-protein interactions as well as on the structural properties of DNA and proteins, might account for the lowered fidelity of DNA replication in life from hypersaline settings. Regardless of its cause, the consistent rate acceleration in halophiles suggests that past efforts to employ sequence divergences to date events, such as the age of asexual lineages in Artemia, have resulted in serious overestimates. More generally, the results indicate that coordinated shifts in rates of molecular evolution may occur in lineages exposed to extreme environmental conditions.     

Phytoplankton of the extremely acidic mining lakes of Lusatia (Germany) with pH ≤3

Most of the flooded, open-cast lignite mining lakes of Lusatia (Germany) impacted by the oxidation of iron sulphides (pyrite and marcasite) are extremely acidic. Of 32 lakes regularly studied from 1995 to 1998, 14 have a pH <3 (median pH 2.3–2.9). These lakes are typically buffered by high concentrations of Fe (III) and have high conductivity (1000–5000 S cm^–1). Concentrations of dissolved inorganic carbon (DIC) and phosphorus are typically extremely low. These factors result in a very different environment for algae than found in neutral and acid-rain impacted lakes. The planktonic algal flora is generally dominated by flagellates belonging to genera of Chlorophyta (Chlamydomonas), Heterokontophyta of the class Chrysophyceae (Ochromonas, Chromulina), Cryptophyta (Cyathomonas) and Euglenophyta (Lepocinclis, Euglena mutabilis). Near-spherical non-motile Chlorophyta (Nanochlorum sp.), Heterokontophyta of the class Bacillariophyceae (Eunotia exigua, Nitzschia), Dinophyta (Gymnodinium, Peridinium umbonatum), other Chlorophyta (Scourfieldia cordiformis) and Cryptophyta (Rhodomonas minuta) are also found.     

Short-term variations in the abundance and cell volume of bacterioplankton in an artificial tropical lake

Circadian and spatial fluctuations in bacterioplankton abundance and cell volume were examined, for the first time, in the Municipal Lake located in the down town area of Yaoundé (Capital of Cameroon, Central Africa, ca 3° 52′ N, 11° 31′ E). Bacterial cell volumes (range, 0.05 to 0.2 μm3) were consistent with those reported for other aquatic systems while bacterial densities (0.8 to 2 × 108 cells ml-1) were among the highest values reported in pelagic systems. These variables and chlorophyll a and dissolved oxygen concentrations within a single depth-zone varied from 13 to 61%, while water temperature fluctuated only from 2 to 6%. Spatial fluctuations of physical-chemical and biological variables were generally higher during the day-time than during the night-time. A significant diel variation was provided for bacterial cell volume in the surface waters where synchronized cell division was occurring during the night. The measured bacterial abundances in this study were 4 to 17 fold higher than values known from other lakes of similar trophic status, and both cell abundance and volume were not correlated with chlorophyll. We conclude that this was due to the dependence of bacterial populations to different sources of allochthonous substrates, including untreated sewage from the major influents of the lake, resuspension of benthic material, and substrate releasing from macrophytes which are prevalent in the littoral zone of the lake. This revised version was published online in September 2006 with corrections to the Cover Date.     

Predictors of Seasonal Oxygen Levels in Small Florida Lakes: The Importance of Color

This study examines the relationship of profundal oxygen concentrations in 55 shallow Florida lakes to humic color, trophic state, and lake size during different seasons. The data set represented a broad range of color and trophic state. The percent saturation of dissolved oxygen remained relatively constant during the fall (mean 78.4%), winter (mean 81.3%), and spring (mean 82.5%), but declined markedly during summer (mean 65.2%). Chlorophyll a concentrations were highest during the winter (mean 2.52 mg m^–3) and lowest during the fall (mean 1.17 mg m^–3), while color peaked during the fall (mean 30.1 mg Pt l^–1) and was lowest during the summer (mean 12.7 mg Pt l^–1). The relative importance of lake size, chlorophyll a, and color in explaining variation in percent oxygen saturation was examined using multiple regression. Percent oxygen saturation was negatively correlated with color during the winter, spring, and summer, and positively correlated with lake size in the winter and spring. However, percent oxygen saturation showed no relationship with chlorophyll a during any season. These results suggest that colored Florida lakes are naturally oxygen depleted and that profundal oxygen values have little relationship to lake trophic state. This revised version was published online in July 2006 with corrections to the Cover Date.     

Community structures of ammonia‐oxidising archaea and bacteria in high‐altitude lakes on the Tibetan Plateau

1. Community structures of planktonic ammonia‐oxidising archaea (AOA) and bacteria (AOB) were investigated for five high‐altitude Tibetan lakes, which could be classified as freshwater, oligosaline or mesosaline, to develop a general view of the AOA and AOB in lakes on the Tibetan Plateau. 2. Based on PCR screening of the ammonia monooxygenase α‐subunit (amoA) gene, AOA were present in 14 out of 17 samples, whereas AOB were detected in only four samples. Phylogenetic analyses indicated that the AOB communities were dominated by a unique monophylogenetic lineage within Nitrosomonas, which may represent a novel cluster of AOB. AOA, on the other hand, were distinct among lakes with different salinities. 3. Multivariate statistical analyses indicated a heterogeneous distribution of the AOA communities among lakes largely caused by lake salinity, whereas the uniform chemical properties within lakes and their geographical isolation may favour relatively homogeneous AOA communities within lakes. 4. Our results suggest a wide occurrence of AOA in Tibetan lakes and provide the first evidence of salinity‐related differentiation of AOA community composition as well as potential geographical isolation of AOA in inland aquatic environments.