ECOHAB: Doucette_G- Algicidal bacteria and the regulation of Karenia brevis blooms in the Gulf of Mexico from 1998-11-16 to 1999-09-29 (NODC Accession 0000542)

Interactions between bacteria and species of harmful and/or toxic algae are potentially important factors affecting both the population dynamics and toxicity of these algae. Recent reports of bacteria lethal to certain harmful algal bloom (HAB) species, coupled with a rapidly evolving interest in attempting to minimize the adverse effects of HABs through various prevention, control, and mitigation strategies, has focused attention on defining the role of algicidal bacteria in bloom termination. The aim of the present study was to determine if algicidal bacteria active against Karenia brevis, a dinoflagellate responsible for frequent and protracted red tides in the Gulf of Mexico, are present in the waters of the west Florida shelf. To date we have detected one algicidal bacterium from samples obtained during ECOHAB-Florida cruises and we are continuing this effort. A taxon-specific 16S rRNA probe was developed for a previously isolated algicidal strain, 41-DBG2, and we have begun to screen water samples for its presence using fluorescent in-situ hybridization. In addition, we have employed denaturing gradient gel electrophoresis (DGGE) to characterize the diversity of the ambient microbial assemblages and to visualize the band characteristic of strain 41-DBG2. This band can then be analyzed further by excising and sequencing. Our screening results to date have yielded negative results on all but one of the field samples tested, which was positive with the rRNA probe. These largely negative findings may not be unexpected due to the marked temporal and spatial separation of the original algicidal bacterial isolation and the water samples being screened. Future efforts will focus on isolating algicidal bacteria from the same bloom event as the samples for screening are obtained, thereby increasing the likelihood of detecting algicidal strains and permitting a more effective analysis of their population dynamics.

Purpose: This project dealing with the potential role of algicidal bacteria in regulating K. brevis bloom dynamics is a targeted ECOHAB proposal, the field portion of which is being conducted through a collaborative working relationship with the ECOHAB-Florida regional project. The present dataset reflects results from analyses of samples collected during the ECOHAB-Florida process cruises identified below. The primary use of these samples has been two-fold: first to screen water samples for the presence of a previously identified algicidal bacterium, strain 41-DBG2, using fluorescent in-situ hybridization of a taxon-specific rRNA probe as well as analysis by denaturing gradient gel electrophoresis (DGGE); and, second, to continue attempts at isolating and identifying algicidal bacteria indigenous to the waters of the west Florida shelf.