Aims: To select an autotrophic arsenic(III)-oxidizing population, named CASO1, and to evaluate the performance of the selected bacteria in reactors. Methods and Results: An As(III)-containing medium without organic substrate was used to select CASO1 from a mining environment. As(III) oxidation was studied under batch and continuous conditions. The main organisms present in CASO1 were identified with molecular biology tools. CASO1 exhibited significant As(III)-oxidizing activity between pH 3 and 8. The optimum temperature was 25°C. As(III) oxidation was still observed in the presence of 1000 mg l )1 As(III). In continuous culture mode, the As(III) oxidation rate reached 160 mg l )1 h )1 . The CASO1 consortium contains at least two organisms -strain b3, which is phylogenetically close to Ralstonia picketii, and strain b6, which is related to the genus Thiomonas. The divergence in 16S rDNA sequences between b6 and the closest related organism was 5AE9%, suggesting that b6 may be a new species. Conclusions: High As(III)-oxidizing activity can be obtained without organic nutrient supply, using a bacterial population from a mining environment. Significance and Impact of the Study: The biological oxidation of arsenite by the CASO1 population is of particular interest for decontamination of arsenic-contaminated waste or groundwater.
Nitrate and its reduced forms produced during denitrification, nitrite and nitrous oxide, were studied for their influence on methane production from acetate by Methanosarcina mazei. While 0.18 mM nitrite and 0.8% nitrous oxide in the gas phase completely suppressed methane production, 71.4 mM nitrate resulted in only 83.3% inhibition. Co‐culture experiments showed that M. mazei growing with 15 mM nitrate produced methane from acetate until the denitrifying bacterium Pseudomonas stutzeri was inoculated and nitrate denitrification began. The presence of nitrous oxide in the gas phase after cessation of denitrification activity by P. stutzeri in co‐cultures flasks prevented M. mazei resuming methane production. Nitrous oxide, instead of dinitrogen, was the end product of denitrification by P. stutzeri either in pure cultures or in co‐cultures with M. mazei, probably because of the highly reduced culture conditions that were used. This study strongly suggests that acetate‐dependent methane production by M. mazei was inhibited by reduced nitrogen forms produced during bacterial nitrate denitrification, rather than by competition for acetate between denitrifying and methanogenic bacteria. These results are consistent with previous studies with H2/CO2 methanogens.
Transcription of the heat shock gene grpE was studied in two different morphologic stages of the archaeon Methanosarcina mazei S-6 that differ in resistance to physical and chemical traumas: single cells and packets. While single cells are directly exposed to environmental changes, such as temperature elevations, cells in packets are surrounded by intercellular and peripheral material that keeps them together in a globular structure which can reach several millimeters in diameter. grpE transcript levels determined by Northern (RNA) blotting peaked after a 15-min heat shock in single cells. In contrast, the highest transcript levels in packets were observed after the longest heat shock tested, 60 min. The same response profiles were demonstrated by primer extension experiments and S1 nuclease analysis. A comparison of the grpE response to heat shock with those of dnaK and dnaJ showed that the grpE transcript level was the most increased, closely followed by that of the dnaK transcript, with that of the dnaJ gene being the least augmented. Transcription of grpE started at the same site under normal and heat shock temperatures, and the transcript was consistently ϳ700 bases long. Codon usage patterns revealed that the three archaeal genes use most codons and have the same codon preference for 61% of the amino acids.A gene encoding a GrpE homolog has recently been cloned from the genome of the archaeon Methanosarcina mazei S-6 and sequenced (6). It is the first example of a grpE heat shock gene found within the domain Archaea. The Archaea are organisms phylogenetically distinct from Bacteria (eubacteria) and Eucarya (eucaryotes) (41). However, Archaea resemble eucaryotes in several molecular biological features more than they resemble bacteria and are closer to eucaryotes than bacteria (15,28,30,31,41). A case in point is gene regulation, since there are data indicating that Archaea use a transcription regulation machinery similar to that of eucaryotes (10,24,28,33). Whether this is the case also for archaeal heat shock genes has not been established. To address this question, it is necessary to first determine the expression pattern of the known archaeal heat shock genes and then proceed to analyze the regulation mechanisms at the molecular level.Among the Archaea, M. mazei is particularly interesting because it is one of a small group of organisms, the methanosarcinae (22,23), that undergo a growth cycle with morphologic conversions (3,25,32,42). The cycle includes a unicellular form or stage, named single cells, and two multicellular forms, called lamina and packets. The latter are globular structures with zonal heterogeneity and intercellular connective material that extends the outer surface of the packets and wraps the cells together. This connective material is composed chiefly of a heteropolysaccharide (14, 16) which confers to the packets resistance to traumas of various types: mechanical, physical (e.g., heat), and chemical (unpublished observations). This resistance is in contrast to the relative fragilit...
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