Population Analysis of Vibrio cholerae in Aquatic Reservoirs Reveals a Novel Sister Species ( Vibrio paracholerae sp. nov.) with a History of Association with Humans

Abstract

Most efforts to understand the biology of Vibrio cholerae have focused on a single group, the pandemic-generating lineage harbouring the strains responsible for all known cholera pandemics. Consequently, little is known about the diversity of this species in its native aquatic environment. To understand the differences in the V. cholerae populations inhabiting regions with a history of cholera cases and those lacking such a history, a comparative analysis of population composition was performed. Little overlap was found in lineage compositions between those in Dhaka (cholera endemic) located in the Ganges delta, and of Falmouth (no known history of cholera), a small coastal town on the United States east coast. The most striking difference was the presence of a group of related lineages at high abundance in Dhaka which was completely absent from Falmouth. Phylogenomic analysis revealed that these lineages form a cluster at the base of the phylogeny for the V. cholerae species, sufficiently differentiated genetically and phenotypically to form a novel species. A retrospective search revealed that strains from this species have been anecdotally found from around the world and were isolated as early as 1916 from a British soldier in Egypt suffering from choleraic diarrhoea. In 1935 Gardner and Venkatraman unofficially referred to a member of this group as Vibrio paracholerae . In recognition of this earlier designation, we propose the name Vibrio paracholerae sp. nov. for this bacterium. Genomic analysis suggests a link with human populations for this novel species and substantial interaction with its better-known sister species. Importance Cholera continues to remain a major public health threat around the globe. Understanding the ecology, evolution, and environmental adaptation of the causative agent Vibrio cholerae and tracking the emergence of novel lineages with pathogenic potential are essential to combat the problem. In this study, we investigated the population dynamics of Vibrio cholerae in an inland locality which is known as endemic for cholera and compared with that of a cholera free coastal location. We found the consistent presence of the pandemic generating V. cholerae in cholera-endemic Dhaka and an exclusive presence of a lineage phylogenetically distinct from other V. cholerae . Our study suggests that this lineage represents a novel species having pathogenic potential and a human link to its environmental abundance. The possible association with human population, co-existence and interaction with toxigenic V. cholerae in the natural environment make this potential human pathogen an important subject for future studies.

Vibrio tarriae sp. nov., a novel member of the Cholerae clade isolated from across the United States

“…until recently [6,7]. As a result of some notable environmental surveillance efforts, a few closely related species have recently been found; most were initially classified as V. choleraelike bacteria in the last few decades [6,[8][9][10].…”

“…The recently described closest known sister species of V. cholerae, Vibrio paracholerae, had historically been associated with human infections and co-exists with V. cholerae in cholera endemic areas [6,16].…”

“…It is also a model system for environmental pathogens causing human disease [5]. Despite this, our understanding of the natural diversity of V. cholerae and its close relatives have been limited until recently [6, 7]. As a result of some notable environmental surveillance efforts, a few closely related species have recently been found; most were initially classified as V. cholerae -like bacteria in the last few decades [6, 8–10].…”

“…Despite this, our understanding of the natural diversity of V. cholerae and its close relatives have been limited until recently [6, 7]. As a result of some notable environmental surveillance efforts, a few closely related species have recently been found; most were initially classified as V. cholerae -like bacteria in the last few decades [6, 8–10]. In the U.S., Vibrio -related diseases are on the rise, affecting an increasing number of people coming in contact with water during recreational or professional activities [11].…”

“…In the environment, Vibrio metoecus frequently exchanges genes via horizontal gene transfer (HGT) with V. cholerae [15]. The recently described closest known sister species of V. cholerae, Vibrio paracholerae , had historically been associated with human infections and co-exists with V. cholerae in cholera endemic areas [6, 16].…”