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Changes in Sediment Bacterial Community in Response to Long-Term Nutrient Enrichment in a Subtropical Seagrass-Dominated Estuary

Author:
Guevara, Rafael, Ikenaga, Makoto, Dean, Amanda L., Pisani, Cristina, Boyer, Joseph N.
Source:
Microbial ecology 2014 v.68 no.3 pp. 427-440
ISSN:
0095-3628
Subject:
Cytophagales, Desulfobulbaceae, Ectothiorhodospiraceae, Spirochaetales, bacterial communities, community structure, denaturing gradient gel electrophoresis, environmental factors, estuaries, marine sediments, molecular cloning, nucleotide sequences, organic matter, phylogeny, ribosomal RNA, seagrasses, Florida, Gulf of Mexico
Abstract:
Florida Bay exhibits a natural gradient of strong P limitation in the east which shifts to weak P or even N limitation at the western boundary. This nutrient gradient greatly affects seagrass abundance and productivity across the bay. We assessed the effects of N and P additions on sediment bacterial community structure in relation to the existing nutrient gradient in Florida Bay. Sediment samples from 24 permanent 0.25 m² plots in each of six sites across Florida Bay were fertilized with granular N and P in a factorial design for 26 months. Sediment bacterial community structure was analyzed using PCR-denaturing gradient gel electrophoresis (DGGE) analysis of 16S ribosomal RNA (rRNA) genes and a cloning strategy from DGGE bands. The phylogenetic positions of 16S rRNA sequences mostly fell into common members found in marine sediments such as sulfate-reducing Deltaproteobacteria, Gammaproteobacteria, Spirochaetes, and Bacteriodetes. Twenty-eight common DGGE bands were found in all sediment samples; however, some DGGE bands were only found or were better represented in eastern sites. Bacterial community diversity (Shannon-Weiner index) showed similar values throughout all sediment samples. The N treatment had no effect on the bacterial community structures across the bay. Conversely, the addition of P significantly influenced the bacterial community structure at all but the most western site, where P is least limiting due to inputs from the Gulf of Mexico. P additions enhanced DGGE band sequences related to Cytophagales, Ectothiorhodospiraceae, and Desulfobulbaceae, suggesting a shift toward bacterial communities with increased capability to degrade polymeric organic matter. In addition, a band related to Deferribacteres was enhanced in eastern sites. Thus, indigenous environmental conditions were the primary determining factors controlling the bacterial communities, while the addition of P was a secondary determining factor. This P-induced change in community composition tended to be proportional to the amount of P limitation obviated by the nutrient additions.
Agid:
815410