Alcanivorax bacteria as important polypropylene degraders in mesopelagic environments

Abstract

ABSTRACT Plastics are causing serious problems in the sea and settling even to abyssal depths. Polypropylene (PP) is the second most common plastic product and thus would constitute a large fraction of plastics in the sea. The biodegradation of PP has not been clearly shown. In this study, Alcanivorax bacteria (mainly Alcanivorax borkumensis ) were indicated to be enriched most abundantly on liquid PP and on its structurally similar branched alkane, pristane, in mesopelagic water. An Alcanivorax isolate probably of A. borkumensis showed the highest liquid PP-degrading activity among the isolates. These results indicate that Alcanivorax bacteria could be major degraders of PP in mesopelagic environments. Alcanivorax bacteria did not use liquid PP as the sole carbon and energy source. Short PP was preferentially degraded, and PP of all lengths appeared to be degraded. Liquid PP was degraded more efficiently at 10°C than at 20°C, and correspondingly, higher concentrations of another carbon source were required at 10°C. Regarding the degradation of solid PP, an initial degradation sign, oxidation, was detected, but a weight loss of at least 1% was not detected. By using this study as a model, various PP-degrading microbes would start to be clarified. IMPORTANCE PP biodegradation has not been clearly shown (it has been uncertain whether the PP structure is actually biodegraded or not). This is the first report on the obvious biodegradation of PP. At the same time, this study shows that Alcanivorax bacteria could be major degraders of PP in mesopelagic environments. Moreover, PP biodegradation has been investigated by using solid PP as the sole carbon source. However, this study shows that PP would not be used as a sole carbon and energy source. Our data thus provide very important and key knowledge for PP bioremediation.