Denitrifier community composition along nitrate gradient in Suquía River bed-sediment

REYNA, L.; WUNDERLIN, D. A.; GENTI-RAMONDI, S.

Córdoba

Congreso; XI Congreso Argentino de Microbiología.; 2007

ASM- Asociación Argentina de Microbiología

To understand the composition and structure of denitrifying communities along nitrate gradient (from 2 to 22 mg/L) in the Suquía River, the molecular diversity of narG gene from sediments obtained at seven stations was examined. The narG gene encoding the membrane bound nitrate reductase was selected as a functional marker for the nitrate-reducing community. The use of narG is of special interest because the phylogeny of the narG gene closely reflects the 16S ribosomal DNA phylogeny. The composition was analyzed using restriction fragment length polymorphism of narG, together with cloning and sequencing. In addition, a fingerprint of the total bacterial community was assessed by ribosomal intergenic spacer region analysis (RISA). NarG RFLP patterns show different communities at each site. A library of 19 clones of one of the DNA environmental samples was constructed. The clones were subjected to RFLP analysis and grouped based on their representative RFLP patterns. Nine different sequences were obtained with all narG clones exhibiting between 62-83 % identity at the amino acid level to those of cultivated denitrifiers and other environmental clones in the database. NarG sequences clustered into three major groups, supported by phylogenetic analyses and, all sequences amplified from environmental DNA clustered in the Gram-negative group. Preliminary analysis of narG sequences suggest that some populations are indeed distinct, although further sequencing would be required to fully characterize the highly diverse denitrifying communities at these sites. CONCLUSION: The present results reveal a degree of spatial organization of the nitrate-respiring community in terms of narG sequences correlating with a gradient of nitrate concentration.