Abundance and Genetic Diversity ofnifHGene Sequences in Anthropogenically Affected Brazilian Mangrove Sediments

Abstract

ABSTRACTAlthough 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 thenifHgene across transects of sediments of two mangrove systems located along the coast line of São 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. ThenifHgene abundance was similar across the two mangrove sediment systems, as evidenced by qPCR. However, thenifH-based PCR-DGGE profiles revealed clear differences between the mangroves. Moreover, shifts in thenifHgene diversities were noted along the land-sea transect within the previously oiled mangrove. ThenifHgene diversity depicted the presence of nitrogen-fixing bacteria affiliated with a wide range of taxa, encompassing members of theAlphaproteobacteria,Betaproteobacteria,Gammaproteobacteria,Firmicutes, and also a group of anaerobic sulfate-reducing bacteria. We also detected a unique mangrove-specific cluster of sequences denoted Mgv-nifH. 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.