A novel poly(3-hydroxybutyrate)-degrading actinobacterium that was isolated from plastisphere formed on marine plastic debris

Abstract

Plastic debris surfaces in marine environments provide novel habitats for marine microbes. This type of microbial community is known as a “plastisphere”. Prior metagenomic analyses of plastispheres suggest that the surface of marine plastic debris contain plastic-degrading microbes. Here, we focus on plastisphere as a microbial source. We isolated strain OK12 from plastic bag debris collected from a beach in Japan. The strain grew on a mineral medium supplemented with poly(3-hydroxybutyrate) [P(3HB)] as the sole carbon source. Genetic and biochemical analyses demonstrated that the strain belongs to the genus Nocardioides. In addition, the average nucleotide identity value of the two genomes of the strain OK12 and Nocardioides marinisabuli DSM 18965, a marine species, was 98.3 %, above the 95 % threshold. The strain did not grow above 50 °C, and the optimum temperature for growth was 30 °C. The strain grew and degraded P(3HB) in a broad range of NaCl concentrations (0.01–2.4 M), whereas it did not grow without NaCl, suggesting that the strain is a marine species. The strain degraded the P(3HB) film at a fast rate, despite the fact that the P(3HB) degrading activity in the culture supernatant was low. The strain formed biofilms on the P(3HB) and polypropylene film surfaces. This biofilm formation may have helped the strain to degrade P(3HB).