Abundance and Genetic Diversity of nifli Gene Sequences in Anthropogenically Affected Brazilian Mangrove Sediments.

Although mangroves represent ecosystems of global importance, the genetic diversity and abundance of functional genes that are key to their functioning scarcely have been explored. Here, we present a survey based on the nifli gene across transects of sediments of two mangrove systems located along the coast line of Säo Paulo state (Brazil) which differed by degree of disturbance, i.e., an oil-spill-affected and an unaffected mangrove. The diazotrophic communities were assessed by denaturing gradient gel electrophoresis (DGGE), quantitative PCR (qPCR), and clone libraries. The nifli gene abundance was similar across the two mangrove sediment systems, as evidenced by qPCR. However, the nifli-based PCR-DGGE profiles revealed clear differences between the mangroves. Moreover, shifts in the nifli gene diversities were noted along the land-sea transect within the previously oiled mangrove. The nifli gene diversity depicted the presence of nitrogen-fixing bacteria affiliated with a wide range of taxa, encompassing members oi the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Firmicutes, and also a group of anaerobic sulfate-reducing bacteria. We also detected a unique mangrove-specific cluster of sequences denoted Mgv-nifli. Our results indicate that nitrogen-fixing bacterial guilds can be partially endemic to mangroves, and these communities are modulated by oil contamination, which has important implications for conservation strategies. [ABSTRACT FROM AUTHOR]