Can oil-degrading bacteria be a linker between the formation of a harmful dinoflagellate blooms and oil spills?

Abstract

The association between phytoplankton blooms and oil spills is still controversial despite numerous studies. Surprisingly, to date, there have been no studies on the effect of bacterial communities exposed to crude oil on phytoplankton growth, even though crude oil leads to variation in bacterial communities, and this variation can affect phytoplankton growth and species composition. In this study, to investigate the impact of altered bacterial communities exposed to crude oil on the growth of dinoflagellate, we exposed free-living bacteria isolated from a Prorocentrum texanum culture to crude oil (100 ppm) for a month, and then investigated the growth change in P. texanum after addition of these oil-treated bacteria. As a result, the growth rate and yield of P. texanum in bacterial treatment was clearly enhanced, compared to control. To gain more direct evidence for the role of oil-degrading bacteria in bloom formation, we isolated oil-degrading bacteria from sediment samples collected from oil-contaminated sites after the Texas City “Y” oil spill, and investigated variation in dinoflagellate growth after co-culture with single bacterial isolates. A total of seven oil-degradingbacterial cultures were established, and two bacterial cultures (C1-T3 and E1-Gal-T2) clearly enhanced the growth rate and yield of six dinoflagellate cultures axenic Amphidinium carterae and Peridinium sociale, and xenic Karenia brevis, P