Potential role of oil-degrading bacteria in the formation of a harmful dinoflagellate blooms after oil spills

Abstract

There have been no studies on effect of altered bacterial communities due to crude oil exposure on phytoplankton growth, even though crude oil leads to change in bacterial communities, and this change can affect phytoplankton growth and community composition. Thus, we examined effect of change in bacterial communities due to oil exposure on dinoflagellate growth. For this study, free-living bacteria isolated from a Prorocentrum texanum culture were exposed to crude oil for a month, and the growth change in P. texanum after co-culture with oil-treated bacteria was investigated. Interestingly, the growth rate and yield of P. texanum in bacterial treatment was clearly enhanced. To gain more direct evidence, we investigated variation in dinoflagellates growth after co-culture with oil-degrading bacterial isolates from oil spilled soil after the Texas City "Y" oil spill. Two bacterial isolates (C1-T3 and E1-Gal-T2) clearly enhanced the growth rate and yield of six different dinoflagellates, including axenic cultures (Amphidinium carterae and Peridinium sociale). Lastly, to determine whether or not these isolates can enhance dinoflagellate growth by releasing nutrients, nutrient-limited medium was prepared by removing each one of the components (nitrogen, phosphorous, trace metals or vitamins), and the two bacterial isolates were inoculated into each nutrient limited media, containing A. carterae and Pe. sociale. These bacterial isolates enhanced the growth rate and yield of the two dinoflagellates, regardless of any nutrient-limited media. Together with these findings, oil-degrading bacteria may enhance the growth of dinoflagellates and this growth-enhancing activity may not be derived from nutrients released from the bacteria