Experimental and Computational Approaches to Studying Chemotaxis of Vibrio spp. to Biotic and Abiotic Substrates, including Plastic Marine Debris.

Supervisors: Linda Amaral-Zettler (NIOZ), Tracy J. Mincer (Florida Atlantic University).
Plastic marine debris (PMD) is quickly becoming ubiquitous to the world’s oceans. While plastic pollution is undoubtably a major problem, it is inadvertently becoming a novel and unique ecosystem for many marine bacteria. Recruitment to PMD, colonization, and biofilm formation have been observed in various bacterial species, including the genus Vibrio (Zettler et al. 2013). Various species of Vibrio are equipped with highly sensitive chemosensory pathways, allowing them to sense changes in environmental signal gradients and respond appropriately (Ringaard et al. 2018). It is speculated that a signal could be released from plastic debris that has entered the ocean, initiating the chemosensory pathway and subsequent cascade of metabolic pathways. In this study, various tools were used to assess the chemosensory pathway of fifteen Vibrio isolates collected from different microbiomes in the open ocean, including those found on PMD particles as well as biotic substrates. A chemotaxis assay was developed to test for chemotaxis towards plastic dissolved organic matter from three plastic polymers. Seven of the fifteen isolates showed a significant chemotactic response to polypropylene and nylon. Comparative genomics showed enrichment, inter-gene homogeneity, and orthology in genes related to pathogenesis, biofilm formation, motility, and chemotaxis among various isolates. Pangenomic analysis highlighted various important gene clusters shared between the fifteen isolates that promote a wide array of chemotactic responses. Whole genome comparisons revealed a phylogenetic relationships based on average nucleotide identity (ANI) percentage, genome completeness of assembled isolate genomes, and maximum likelihood trees of the main chemotaxis genes. Whole genome alignments were compared visually based on phylogeny. These visualizations highlighted large quantities of conserved nucleotide residues. Bioinformatic analysis of methyl-accepting chemotaxis proteins (MCPs) showed diverse ligand binding domains, significant nucleotide variation, and potential hydrophobic ligand binding residues that could indicate a ligand binding domain for hydrocarbons released from PMD. We demonstrated that these Vibrio isolates possess a large array of chemotaxis and chemotaxis-related genes, particularly genes associated chemosensory of gradients. We hypothesize that a diverse set of chemosensory genes allow Vibrio spp. to acutely sense changes in their environment, such as hydrocarbon products released from PMD, facilitating colonization of biotic and abiotic substrate.