Distinct Bacterial Populations Colonizing Plastic Debris in Coastal Waters of Southern California

Abstract

Microbes that attach to plastic form the so‐called plastisphere, a unique ecosystem of microbes that may impact the ocean and its inhabitants. While the microbial populations present on microplastics, tiny fragments resulting of physical and chemical breakdown of plastic debris, have been described in multiple studies, much less is known about the initial stages of bacterial colonization. This project is part of a study to evaluate the presence and diversity of bacteria colonizing floating plastic in coastal waters using metagenomic DNA sequencing and live culture experiments. We particularly focus on colonies isolated from two different sampling locations using different culture media and some of their physiological characteristics. The objective of this research is to identify bacteria colonizing ocean plastic using 16S rDNA barcoding from cultures isolated from exposed plastic. In addition, some physiological characteristics of the bacteria, such as antibiotic production and plastic degradation, is explored in parallel. Three types of floating plastic (High and low density polyethylene and polypropylene) were exposed to beach water at Doheny State Beach (Dana Point, CA) and near the Scripps Institution of Oceanography pier (La Jolla, CA). Samples were collected at different time points, in a range up to 2 months. Colonies were grown on Salt Water Agar (SWA) or Marine Agar, as well as ChromAgar Vibrio (CAV) media and characterized using 16S amplicon sequencing. Fourier Transform Infrared Spectroscopy (FTIR) was used to analyze the breakdown of plastic over time and scanning electron microscopy (SEM) to visualize the biofilms attached to plastic on day 40. No clear pattern of colonization was observed over a month period. With longer incubation times, an increase in unknown/uncultured bacteria species was noted. Antibiotic production was observed in several colonies of the genus Phaeobacter. Signs of chemical breakdown were observed as early as after 21 days of incubation.