Degradation of polyhydroxyalkanoate (PHA) drinking straws at an ocean shoreline

This study represents the first comprehensive biophysical characterization of the degradation of polyhydroxyalkanoate drinking straws in the natural marine environment. Our fifteen weekly measurements of straw mass and geometry at a Florida coastal zone resulted in several novel findings: erosion inside of the straws begins at the two ends but later dominates at the straw middle; the straw degradation rate is highly nonlinear; and straw mass loss trails bacterial growth by as much as two weeks. After hypothesizing a biological basis for straw decomposition, 16S rRNA characterization of the bacterial biofilm indicated a dynamic and unique plastisphere ‘microbiome’ with potential PHA degraders on the straws over the experimental period. The straw exterior had a more diverse, taxon-rich microbiome than the interior, likely due to the more exposed and variable environment of the exterior. Surface pitting, geometric analyses, and enhanced growth of specific bacterial taxa all point to mass loss on the straw interior being up to four times that on the straw exterior. Significant correlation to straw mass loss and high relative abundance revealed Anderseniella , Labrenzia, Limibaculum , Parasphingopyxis , and Roseovarius as possible PHA degraders, with complex biofilm dynamics. These specific taxa were identified through multiple analysis methods including a novel use of the Spearman correlation test. Our study fills in gaps left in previous studies by employing innovative analysis techniques and by focusing on temporal gradients. It is hoped that our findings will inspire review of several common, but flawed, modeling assumptions. • Erosion on interior of drinking straws is up to 4x larger than that on exterior • Specific rate of mass loss exhibits oscillations as large as 0.04 mg/(cm 2 day) • Straw mass loss trails bacterial growth on straws by up to 2 weeks • Novel bacteria growth-mass loss correlation spanned 0.73-0.98 for 5 key genera: • Anderseniella , Labrenzia, Limibaculum , Parasphingopyxis , and Roseovarius