Functional Gene and Metabolic Changes of Marine Microbial Populations Involved in Hydrocarbon Degradation Under Different Enrichment Conditions

In this study, seawater from the area of an oil extraction platform in Bohai Bay was subjected to experimental treatments with oil as the only carbon source to understand the transcriptional responses of seawater microbial populations to oil degradation treatments. Twelve enrichment conditions were used, and fluorescent in situ hybridization (FISH) along with metatranscriptomic analyses were used to understand functional changes within each treatment. RNA from the petroleum-degrading bacterial enrichments was extracted after cultivation and FISH was used to evaluate overall activity, while changes in gene expression among different culture conditions were analyzed based on eight hydrocarbon-specific gene probes and flow cytometry. Concomitantly, 1,066 metabolic pathways were identified as being expressed in the populations through RNA sequencing, metatranscriptomic analysis, and metabolic pathway enrichment analysis. The addition of oil led to the inhibition of carbohydrate metabolism and inositol phosphate metabolism, while also reducing extracellular signaling pathway transcription levels. When low- and high-nutrient conditions were compared, low-nutrient conditions inhibited taurine and hypotaurine metabolism in addition to inositol phosphate metabolism. Among oxygen-treated, carbon dioxide-treated, and air-treated conditions, oxygen-treated conditions inhibited taurine and hypotaurine metabolism but promoted galactose metabolism, while carbon dioxide-treated conditions promoted inositol phosphate metabolism. Overall, metabolic pathway expression and functional gene changes indicated that high-nutrient, oil-free, and aerobic culture conditions best promoted the growth and reproduction of marine microbial communities.