Abundance and Multilocus Sequence Analysis of Vibrio Bacteria Associated with Diseased Elkhorn Coral (Acropora palmata) of the Florida Keys

Abstract

The critically endangered elkhorn coral, Acropora palmata, is affected by white pox disease (WPX) throughout the Florida Reef Tract and wider Caribbean. The bacterium Serratia marcescens was previously identified as one etiologic agent of WPX, but is no longer consistently detected in contemporary outbreaks. It is now believed that multiple etiologic agents cause WPX; however, to date, no other potential pathogens have been thoroughly investigated. This study examined the association of Vibrio bacteria with WPX occurrence from August 2012--2014 at Looe Key Reef in the Florida Keys, USA. The concentration of cultivable Vibrio was consistently greater in WPX samples compared to healthy samples. The relative abundance of Vibrio bacteria to total bacteria was four times higher in samples from WPX lesions compared to adjacent apparently healthy regions of diseased corals based on quantitative PCR (qPCR). Multilocus sequence analysis (MLSA) was used to assess the diversity of 69 Vibrio isolates collected from diseased and apparently healthy A. palmata colonies and the surrounding seawater. Vibrio species with known pathogenicity to corals were detected in both apparently healthy and diseased samples. While the causative agent(s) of contemporary WPX outbreaks remain elusive, our results suggest that Vibrio may be part of a non-specific heterotrophic bacterial bloom rather than acting as primary pathogens. This study highlights the need for highly resolved temporal sampling in situ to further elucidate the role of Vibrio during WPX onset and progression.