This Article Full Text Full Text (PDF) Other Versions of this Article: AEM.02191-07v1 74/9/2595    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Mayali, X. Articles by Azam, F. PubMed PubMed Citation Articles by Mayali, X. Articles by Azam, F. Agricola Articles by Mayali, X. Articles by Azam, F.

Cultivation and Ecosystem Role of a Marine Roseobacter Clade-Affiliated Cluster Bacterium

Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0202

Received 26 September 2007/ Accepted 29 February 2008

Isolation and cultivation are a crucial step in elucidating the physiology, biogeochemistry, and ecosystem role of microorganisms. Many abundant marine bacteria, including the widespread Roseobacter clade-affiliated (RCA) cluster group, have not been cultured with traditional methods. Using novel techniques of cocultivation with algal cultures, we have accomplished successful isolation and propagation of a strain of the RCA cluster. Our experiments revealed that, in addition to growing on alga-excreted organic matter, additions of washed bacterial cells led to significant biomass decrease of dinoflagellate cultures as measured by in vivo fluorescence. Bacterial filtrate did not adversely affect the algal cultures, suggesting attachment-mediated activity. Using an RCA cluster-specific rRNA probe, we documented increasing attachment of these algicidal bacteria during a dinoflagellate bloom, with a maximum of 70% of the algal cells colonized just prior to bloom termination. Cross-correlation analyses between algal abundances and RCA bacterial colonization were statistically significant, in agreement with predator-prey models suggesting that RCA cluster bacteria caused algal bloom decline. Further investigation of molecular databases revealed that RCA cluster bacteria were numerically abundant during algal blooms sampled worldwide. Our findings suggest that the widespread RCA cluster bacteria may exert significant control over phytoplankton biomass and community structure in the oceans. We also suggest that coculture with phytoplankton may be a useful strategy to isolate and successfully grow previously uncultured but ecologically abundant marine heterotrophs.

Published ahead of print on 7 March 2008.