Microbiome analysis of polyhydroxybutyrate degradation in laboratory-scale cultivation using seawater

Polyhydroxybutyrate (PHB) has attracted attention as a representative polymer compound for biodegradable plastics produced by microorganisms. Since information on the dynamics of PHB released into the environment is limited and there are likely to be many PHB-degrading bacteria that have not been isolated, it is necessary to identify microorganisms responsible for PHB degradation based on metagenomic information. In this study, we estimated the biodegradability of PHB powder using seawater collected from 15 sites in the near shore around Japan, using oxygen consumption as an indicator in laboratory-scale cultivation. The results of 16S rRNA gene-based microbial community analysis indicate that the significant positive correlation between the alpha diversity indexes of the microbial community in seawater prior to incubation and the biodegradation rate of PHB. Several operational taxonomic units (OTUs) having a significant positive correlation between their abundance and PHB degradation rates were observed. Then, we analyzed gene expression pattern over incubation time using a seawater sample using metagenomic and metatranscriptomic approaches. Several PHB/PHA depolymerase genes were found in recovered metagenomic bins, and the expression of these genes changed with increasing biodegradation rates. These findings can contribute to expand the knowledge on the degradation of biodegradable plastics by complex marine microbial ecosystem.