Community structure of sediment bacteria in the Everglades freshwater marsh, fringing mangrove forest, and Florida Bay seagrass meadows were described based on polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) patterns of 16S rRNA gene fragments and by sequencing analysis of DGGE bands. The DGGE patterns were correlated with the environmental variables by means of canonical correspondence analysis. There was no significant trend in the Shannon-Weiner index among the sediment samples along the salinity gradient. However, cluster analysis based on DGGE patterns revealed that the bacterial community structure differed according to sites. Not only were these salinity/vegetation regions distinct but the sediment bacteria communities were consistently different along the gradient from freshwater marsh, mangrove forest, eastern-central Florida Bay, and western Florida Bay. Actinobacteria- and Bacteroidetes/Chlorobi-like DNA sequences were amplified throughout all sampling sites. More Chloroflexi and members of candidate division WS3 were found in freshwater marsh and mangrove forest sites than in seagrass sites. The appearance of candidate division OP8-like DNA sequences in mangrove sites distinguished these communities from those of freshwater marsh. The seagrass sites were characterized by reduced presence of bands belonging to Chloroflexi with increased presence of those bands related to Cyanobacteria, gamma-Proteobacteria, Spirochetes, and Planctomycetes. This included the sulfate-reducing bacteria, which are prevalent in marine environments. Clearly, bacterial communities in the sediment were different along the gradient, which can be explained mainly by the differences in salinity and total phosphorus.

UV radiation induced DNA damage (inferred from cyclobutane pyrimidine dimers, CPDs) in native marine virus communities was examined at 12 locations along a latitudinal transect from 41°S to 3°N in the southeastern Pacific Ocean. Surface waters were collected prior to sunrise each day and placed in UV transparent incubators kept at in situ seawater temperatures. A replicate treatment was prefiltered through a 0.2 µm filter to remove microbial host cells. Both treatments were exposed to ambient solar radiation until approximately 1 h before sunset. At the end of the day, the virus fraction was collected from each sample by filtration and concentration. DNA damage was determined in each fraction and compared to DNA damage in pre-dawn samples as well as DNA dosimeters exposed to an entire solar day's influence. CPDs in dosimeters and integrated solar irradiance were very highly correlated, as was DNA damage in the pre-sunrise virus community and latitude. A reduction in host cell abundance resulted in no consistent pattern or change in the CPD induction of virus particles, suggesting minimal host mediated repair in this natural virus community. The low daily induction of damage in virus incubations combined with the high residual damage suggests that the sunrise damage levels were the result of DNA damage accumulation over numerous days, indicating a long residence time for virus particles in surface waters in this region.KEY WORDS: Virus · DNA damage · Cyclobutane pyrimidine dimers · Southeastern Pacific Ocean · Marine microbiology Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 31: [1][2][3][4][5][6][7][8] 2003 viral infectivity in surface waters (Suttle & Chen 1992, Wommack et al. 1996, Noble & Fuhrman 1997, Garza & Suttle 1998, Wilhelm et al. 1998a, 2002. In fact, measured destruction rates of viral infectivity are so high that scientists had been left with a paradox concerning their existence: while estimates of UV-mediated destruction predicted viral clearance rates that should sterilize the water column on a daily basis, high titers of infectious viral particles continued to persist in these environments (Suttle et al. 1993). This problem was partially resolved by the realization that some UVmediated damage (as inferred from the formation of cyclobutane pyrimidine dimers, CPDs) could be repaired on a daily scale by host-cell-mediated repair mechanisms (Weinbauer et al. 1997).Early attempts to understand the persistence of viruses under significant UV pressures suggested that the temporal and spatial distribution of viral production, in consideration of water column mixing, were important (Murray & Jackson 1993). In part, the depth-dependent decay of viral infectivity (relative to the destruction of viral particles; Wommack et al. 1996) suggested an imbalance. If viral particles were destroyed at a lower rate than viral infectivity was lost from a community, and production of viral infectivity was a direct result of new viral particles, then the oce...

To address questions regarding the potential impact of elevated total phosphorus (TP) inputs (due to relaxed regulations of TP loading), a series of TP enrichment experiments were conducted at pelagic stations in the 3 hydrologically distinct basins of Lake Erie. Results of nutrient assimilation measurements and assays for nutrient bioavailability suggest that the chemical speciation, and not concentration, of nitrogenous compounds may influence phytoplankton community structure; this in turn may lead to the selective proliferation of cyanobacteria in the eastern basin of the lake. Assays with cyanobacterial bioluminescent reporter systems for P and N availability as well as N tot :P tot assimilation ratios from on-deck incubation experiments support this work. Considered in the context of a microbial food web relative to a grazing food web, the results imply that alterations in current TP loading controls may lead to alterations in the phytoplankton community structure in the different basins of the Lake Erie system. KEY WORDS: Nutrient loading · Lake Erie · Microbial process · Bioluminescent reportersResale or republication not permitted without written consent of the publisher

We investigated the effects of sunlight on bacterial 3 H-leucine (Leu) and 3

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 m(2) 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.

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