Characterization of marine bacterial flora in the presence of natural rubber and isolation of poly(cis-1,4-isoprene)-utilizing marine bacterium

• Marine bacteria degrade natural and synthetic isoprene rubber. • Bacteroidia and Alphaproteobacteria dominate during isoprene rubber degradation. • Nitratireductor sp. strain A3 thought to metabolize poly( cis -1,4-isoprene) into low molecular weight oligo-isoprenoids with aldehyde or carboxylic acid groups. • It was found that the rubber degradation pathway of marine bacteria is similar to that of soil bacteria. Poly( cis -1,4-isoprene), a primary component of natural rubber and used in synthetic isoprene rubber, is widely utilized in industrial applications. However, its disposal through incineration and landfilling poses environmental challenges, while its accumulation in marine ecosystems raises concerns about potential ecological impacts. In this study, marine bacteria with the potential to utilize poly( cis -1,4-isoprene) were isolated from marine environments along the Okinawa coast and evaluated. Using enrichment cultures supplemented with synthetic isoprene rubber, the shift of bacterial communities was analyzed using metagenomic analysis. Our results showed that Bacteroidia and Alphaproteobacteria predominated at different incubation stages. Nitratireductor sp. strain A3 was isolated from agar plates containing natural rubber as the carbon source. This strain is considered to be involved in the cleavage of poly( cis -1,4-isoprene) into low molecular-weight compounds and in its utilization, as previously reported for isoprene rubber-utilizing soil bacteria. The cleaved products were found to contain oligo-isoprenoids with aldehydes or carboxylic acids. Our findings suggest that poly( cis -1,4-isoprene) is metabolized in marine environments through pathways similar to those reported for soil bacteria. Future genome sequencing studies will help elucidate the molecular mechanisms underlying isoprene rubber degradation in marine ecosystems.