Abstract
Aeromonas veronii biovar sobria, Aeromonas veronii biovar veronii, and Aeromonas allosaccharophila are a closely related group of organisms, the Aeromonas veronii Group, that inhabit a wide range of host animals as a symbiont or pathogen. In this study, the ability of various strains to colonize the medicinal leech as a model for beneficial symbiosis and to kill wax worm larvae as a model for virulence was determined. Isolates cultured from the leech out-competed other strains in the leech model, while most strains were virulent in the wax worms. Three housekeeping genes, recA, dnaJ and gyrB, the gene encoding chitinase, chiA, and four loci associated with the type three secretion system, ascV, ascFG, aexT, and aexU were sequenced. The phylogenetic reconstruction failed to produce one consensus tree that was compatible with most of the individual genes. The Approximately Unbiased test and the Genetic Algorithm for Recombination Detection both provided further support for differing evolutionary histories among this group of genes. Two contrasting tests detected recombination within aexU, ascFG, ascV, dnaJ, and gyrB but not in aexT or chiA. Quartet decomposition analysis indicated a complex recent evolutionary history for these strains with a high frequency of horizontal gene transfer between several but not among all strains. In this study we demonstrate that at least for some strains, horizontal gene transfer occurs at a sufficient frequency to blur the signal from vertically inherited genes, despite strains being adapted to distinct niches. Simply increasing the number of genes included in the analysis is unlikely to overcome this challenge in organisms that occupy multiple niches and can exchange DNA between strains specialized to different niches. Instead, the detection of genes critical in the adaptation to specific niches may help to reveal the physiological specialization of these strains.
Highlights
Over 150 years after Darwin published the Origin of Species [1], the mechanisms by which organismal lineages separate and diverge remain an intensely studied problem in evolutionary biology
Microbiologists often assume that these processes are more complicated in archaea and bacteria because species or ecotype boundaries are distorted due to genes transferred between divergent organisms [2], and very different mechanisms that can contribute to the cohesion of groups of organisms [3]
Source of Isolation sputum of drowning victim blood human feces under eye wound feces feces blood feces finger wound feces duck foot wound leech (Hirudo verbana) leech (H. verbana) leech (H. verbana) leech (H. verbana) leech (H. verbana) leech (Hirudo orientalis) leech (H. orientalis) eel evaluated the capacity of these isolates to establish beneficial and pathogenic associations by assessing their ability to colonize the digestive tract of the medicinal leech and kill G. mellonella, respectively
Summary
Over 150 years after Darwin published the Origin of Species [1], the mechanisms by which organismal lineages separate and diverge remain an intensely studied problem in evolutionary biology. Motivating our study was the hypothesis that the genes important for interaction with the host, e.g., those encoding the T3SS and in particular the effector proteins, which are translocated across the eukaryotic cell membrane and into the host cell cytoplasm [7], might be driving divergence, similar to the genes determining beak morphology in Darwin’s finches. Under this hypothesis we expect that the T3SS system genes should more closely reflect ecological niche, whereas housekeeping genes continue to be exchanged between organisms adapted to different niches. A group of related organisms that inhabits a variety of niches would be ideal to test the importance of the T3SS in driving diversity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
