Diversity of nitrogen-fixing bacteria in cyanobacterial mats

Abstract

The structure of the microbial community and the diversity of the functional gene for dinitrogenase reductase and its transcripts were investigated by analyzing >1400 16S rRNA gene and nifH sequences from two microbial mats situated in the intertidal zone of the Dutch barrier island Schiermonnikoog. Although both microbial mat communities were dominated by Cyanobacteria, they differed with respect to the composition of the total bacterial community. Proteobacteria-related sequences were retrieved as the second most abundant group higher up in the littoral (Station I), whereas Bacteroidetes were the second most abundant group at the low water mark (Station II). The diazotrophic (nitrogen-fixing) communities at both stations were also different, but had more operational taxonomic units in common than the total bacterial community. Denaturing gradient gel electrophoresis also revealed differences in the total bacterial and diazotrophic community in two consecutive years. Analysis of the expression of nifH at Station I showed a discrepancy between the present and the active diazotrophic community. Transcript abundances of the different diazotrophs changed over a 24-h cycle and were dominated by cyanobacterial lineages in the daytime, while Gammaproteobacteria peaked at night. These variations might be responsible for the pattern in nitrogenase activity observed in these mats.

Planktonic and benthic cyanobacteria of European brackish waters: a perspective on estuaries and brackish seas

“…Recently, it was shown in a New Zealand estuary that water temperature and flow can influence benthic cyanobacterium proliferation (Heath et al, 2010). The success of mat-building cyanobacteria might be due to two main factors: (i) N 2 fixation, which is another advantageous characteristic of cyanobacteria in mat environments, commonly described as nutrient-poor and nitrogen-depleted; and (ii) their ability to adapt to the wide environmental fluctuations experienced by mats (Badger et al, 2006;Severin et al, 2010). Up to now, no work on these aspects has been published for European brackish waters.…”

Identification of a novel cyanobacterial group as active diazotrophs in a coastal microbial mat using NanoSIMS analysis

“…More recently, the nifH gene has been used as a phylogenetic and functional marker for N 2 fixation and allows investigating the phylogenetic distribution of the genetic potential for N 2 fixation in complex microbial communities. Surveys of nifH in microbial mats suggested that heterotrophic bacteria might also have an important role in microbial mat N 2 fixation in addition to cyanobacteria (Zehr et al, 1995;Steppe et al, 1996;Zehr et al, 2003;Omoregie et al, 2004a;Severin et al, 2010;Severin and Stal, 2010b). Analysis and quantification of nifH transcripts have helped to identify the fraction of diazotrophs actively expressing this essential gene for N 2 fixation and has given insights into gene-expression dynamics in the environment (Omoregie et al, 2004b;Moisander et al, 2006;Severin and Stal, 2010a).…”

Environment-Dependent Distribution of the Sediment nifH -Harboring Microbiota in the Northern South China Sea

“…Deep-sea sediments constitute the largest fraction of the Earth's surface and a vast portion of these sediments are anoxic and thus suitable habitat for microbial N 2 fixation (19); however, marine diazotrophic microbes have been studied mostly in oligotrophic surface waters (see reference 20 and references therein) and certain shallow-water benthic systems, such as salt marshes, mangroves, microbial mats and other coastal environments (21)(22)(23)(24)(25)(26). Rarely conducted investigations of the N 2 fixation microbial communities of deep-sea waters and hydrothermal vent fluids have discovered diverse and novel nifH gene sequences (12,13).…”