Numeric abundance, identity and pH preferences of methanotrophic Gammaproteobacteria (type I methanotrophs) inhabiting the northern acidic wetlands were studied. The rates of methane oxidation by peat samples from six-wetlands of European Northern Russia (pH 3.9-4.7) varied from 0.04 to 0.60 µg CH4 g(-1) peat h(-1). The number of cells revealed by hybridization with fluorochrome-labeled probes M84 + M705 specific for type I methanotrophs was 0.05-2.16 x 10(5) cells g(-1) dry peat, i.e. 0.4-12.5% of the total number of methanotrophs and 0.004-0.39% of the total number of bacteria. Analysis of the fragments of the pmoA gene encoding particulate methane monooxygenase revealed predominance of the genus Methylocystis (92% of the clones) in the studied sample of acidic peat, while the proportion of the pmoA sequences of type I methanotrophs was insignificant (8%). PCR amplification of the 16S rRNA gene fragments of type I methanotrophs with TypeIF-Type IR primers had low specificity, since only three sequences out of 53 analyzed belonged to methanotrophs and exhibited 93-99% similarity to those of Methylovulum, Methylomonas, and Methylobacter species. Isolates of type I methanotrophs obtained from peat (strains SH10 and 83A5) were identified as members of the species Methylomonaspaludis and Methylovulum miyakonense, respectively. Only Methylomonaspaludum SH10 was capable of growth in acidic media (pH range for growth 3.8-7.2 with the optimum at pH 5.8-6.2), while Methylovulum miyakonense 83A5 exhibited the typical growth characteristics of neutrophilic methanotrophs (pH range for growth 5.5-8.0 with the optimum at pH 6.5-7.5).
The community composition of N2 -fixing microorganisms (diazotrophs) was investigated in copepods (primarily Acartia spp.) in parallel to that of seawater in coastal waters off Denmark (Øresund) and New England, USA. The unicellular cyanobacterial diazotroph UCYN-A was detected from seawater and full-gut copepods, suggesting that the new N contributed by UCYN-A is directly transferred to higher trophic levels in these waters. Deltaproteobacterial and Cluster 3 nifH sequences were detected in > 1 µm seawater particles and full-gut copepods, suggesting that they associate with copepods primarily via feeding. The dominant communities in starved copepods were Vibrio spp. and related Gammaproteobacteria, suggesting they represent the most permanent diazotroph associations in the copepods. N2 fixation rates were up to 3.02 pmol N copepod(-1) day(-1). Although at a typical copepod density in estuarine waters, these volumetric rates are low; considering the small size of a copepod, these mesozooplanktonic crustaceans may serve as hotspots of N2 fixation, at 12.9-71.9 µmol N dm(-3) copepod biomass day(-1). Taken together, diazotroph associations range from more permanent attachments to copepod feeding on some groups. Similar diazotroph groups detected on the eastern and western Atlantic Ocean suggest that these associations are a general phenomenon and play a role in the coastal N cycles.