Responses of phytoplankton and its satellite bacteria to exogenous ethanol

The response of phytoplankton and its satellite bacteria to various concentrations (0.01%-10% v/v) of ethanol is studied. To elucidate the effect of ethanol, single-strains of phytoplankton (SSP) culture, pure strains of satellite bacteria isolated from nonaxenic SSP cultures, and Escherichia coli were screened. Results indicate that ethanol could promote the growth and photosynthetic efficiency (F-v/F-m) of SSP at 0.01% and the growth of satellite bacteria at 0.01%-1%. Nevertheless, ethanol inhibited the growth and F-v/F-m of SSP at 0.1%-1%, and killed bacteria and SSP at 10% concentration. Further investigation on a satellite bacterium (Mameliella alba) revealed that ethanol promotes growth by serving as a growth stimulant rather than a metabolic carbon source. The 16S rRNA gene amplicon indicated that all nonaxenic SSP cultures harbor distinct satellite bacteria communities where the SSP culture of Skeletonema costatum, Phaeodactylum tricornutum, and Dunaliella bardawil were dominated by bacteria genera of Marivita (similar to 80%), Dinoroseobacter (similar to 47%), and Halomonas (similar to 87%), respectively, indicating that every SSP cultures have their own distinct satellite bacterial community. The bacteria family Rhodobacteraceae was dominant in the two marine diatoms, whereas Halomonadaceae was dominant in the saline green microalga. Compared to their respective controls, the supply of 0.5% ethanol to SSP cultures promoted the growth of the satellite bacteria but did not cause a significant difference in species composition of satellite bacteria. Therefore, a low concentration of ethanol can promote the growth of bacteria in a non-selective way. This study enriched our knowledge about the effect of ethanol on aquatic microbes and provided a baseline for basic and applied biotechnological research in the aquatic environment in the future.

Automated summary

The study investigates the response of phytoplankton and its satellite bacteria to different concentrations of ethanol. It found that low concentrations of ethanol promote growth, while high concentrations inhibit growth. Further analysis revealed that ethanol stimulates bacterial growth by serving as a growth stimulant rather than a carbon source.