Molecular analyses of the diversity in marine bacterioplankton assemblages along the coastline of the northeastern Gulf of Mexico.

Bacterial community diversity in marine bacterioplankton assemblages were examined in 3 coastal locations along the northeastern Gulf of Mexico (GOM) using 16S rRNA gene libraries and fluorescence in situ hybridization approaches. The majority of the sequences (30%-60%) were similar to the 16S rRNA gene sequences of unknown bacteria; however, the operational taxonomic units from members of the Cyanobacteria, Proteobacteria, and Bacteroidetes were also present at the 3 GOM sites. Overall, sequence diversity was more similar between the Gulf sites of Carrabelle and Ochlockonee than between either of the Gulf sites and Apalachicola Bay. Fluorescence in situ hybridization analyses revealed the quantitative predominance of members of the Alphaproteobacteria subclass and the Cytophaga-Flavobacterium cluster within the bacterioplankton assemblages. In general, the study further reveals the presence of many bacterial taxa that have been previously found to be dominant in coastal marine environments. Differences observed in the representation of the various bacterial phylogenetic groups among the GOM coastal sites could be partly attributed to dynamic variations in several site-specific conditions, including intermittent tidal events, nutrient availability, and anthropogenic influences.

Diverse responses to UV-B radiation and repair mechanisms of bacteria isolated from high-altitude aquatic environments.

Acinetobacter johnsonii A2 isolated from the natural community of Laguna Azul (Andean Mountains at 4,560 m above sea level), Serratia marcescens MF42, Pseudomonas sp. strain MF8 isolated from the planktonic community, and Cytophaga sp. strain MF7 isolated from the benthic community from Laguna Pozuelos (Andean Puna at 3,600 m above sea level) were subjected to UV-B (3,931 J m-2) irradiation. In addition, a marine Pseudomonas putida strain, 2IDINH, and a second Acinetobacter johnsonii strain, ATCC 17909, were used as external controls. Resistance to UV-B and kinetic rates of light-dependent (UV-A [315 to 400 nm] and cool white light [400 to 700 nm]) and -independent reactivation following exposure were determined by measuring the survival (expressed as CFU) and accumulation of cyclobutane pyrimidine dimers (CPD). Significant differences in survival after UV-B irradiation were observed: Acinetobacter johnsonii A2, 48%; Acinetobacter johnsonii ATCC 17909, 20%; Pseudomonas sp. strain MF8, 40%; marine Pseudomonas putida strain 2IDINH, 12%; Cytophaga sp. strain MF7, 20%; and Serratia marcescens, 21%. Most bacteria exhibited little DNA damage (between 40 and 80 CPD/Mb), except for the benthic isolate Cytophaga sp. strain MF7 (400 CPD/Mb) and Acinetobacter johnsonii ATCC 17909 (160 CPD/Mb). The recovery strategies through dark and light repair were different in all strains. The most efficient in recovering were both Acinetobacter johnsonii A2 and Cytophaga sp. strain MF7; Serratia marcescens MF42 showed intermediate recovery, and in both Pseudomonas strains, recovery was essentially zero. The UV-B responses and recovery abilities of the different bacteria were consistent with the irradiation levels in their native environment.

Identification and characterization of potentially algal-lytic marine bacteria strongly associated with the toxic dinoflagellate Alexandrium catenella.

The toxic dinoflagellate Alexandrium catenella isolated from fjords in Southern Chile produces several analogues of saxitoxin and has been associated with outbreaks of paralytic shellfish poisoning. Three bacterial strains, which remained in close association with this dinoflagellate in culture, were isolated by inoculating the dinoflagellate onto marine agar. The phenotypically different cultivable bacterial colonies were purified. Their genetic identification was done by polymerase chain reaction amplification of the 16S rRNA genes. Partial sequence analysis suggested that the most probable affiliations were to two bacterial phyla: Proteobacteria and the Cytophaga group. The molecular identification was complemented by morphological data and biochemical profiling. The three bacterial species, when grown separately from phytoplankton cells in high-nutrient media, released algal-lytic compounds together with aminopeptidase, lipase, glucosaminidase, and alkaline phosphatase. When the same bacteria, free of organic nutrients, were added back to the algal culture they displayed no detrimental effects on the dinoflagellate cells and recovered their symbiotic characteristics. This observation is consistent with phylogenetic analysis that reveals that these bacteria correspond to species distinct from other bacterial strains previously classified as algicidal bacteria. Thus, bacterial-derived lytic activities are expressed only in the presence of high-nutrient culture media and it is likely that in situ environmental conditions may modulate their expression.