Pyrene metabolites by bacterium enhancing cell division of green alga Selenastrum capricornutum.

Collaborations between multiple microbial species are important for understanding natural clearance and ecological effects of toxic organic contaminants in the environment. However, the interactions between different species in the transformation and degradation of contaminants remain to address. In this study, the effects of pyrene and its bacterial metabolites on the algal growth (Selenastrum capricornutum) were examined. The specific growth rate of algal cells incubated with bacterial pyrene metabolites (1.18 d) was highest among all treatment, followed by the controls (1.07 d), treated with pyrene-free bacterial metabolites (1.04 d) and those treated with pyrene (0.55 d). G phase is the key growth phase for the cells to synthesize biomolecules for subsequent cell division in the cell cycle. Approximately 76.9% of the cells treated with bacterial pyrene metabolites were at the G phase and significantly lower than those with the controls (85.3%), pyrene-free bacterial metabolites (85.5%) and pyrene treatment (92.5%). Transcriptomic analysis of algae showed that the expression of 47 ribosomal unigenes was down-regulated by 5 mg L of pyrene, while 308 unigenes related to the preparation of cell division (DNA replication and protein synthesis) were up-regulated by bacterial pyrene metabolites. It indicated that basal metabolism associated with the growth and proliferation of algal cells could be significantly promoted by bacterial pyrene metabolites. Overall, this study suggests a close relationship between algae and bacteria in the transformation and ecological effects of toxic contaminants.