Meeting Abstract
31.7 Sunday, Jan. 5 09:30 The evolution of natural transformation as a mechanism of horizontal gene transfer among environmental Aeromonas species BROKAW, J. M.*; HUDDLESTON, J. R.; ZAK, J. C.; JETER, R. M.; Abilene Christian University; Abilene Christian University; Texas Tech University; Texas Tech University jmb97t@acu.edu
Aeromonas species are common inhabitants of aquatic environments and relevant as human pathogens. Their potential as pathogens may be related in part to lateral transfer of genes associated with toxin production, biofilm formation, antibiotic resistance, and other virulence determinants. Natural transformation has not been characterized in aeromonads. DNA from wild-type, prototrophic strains that had been isolated from environmental sources was used as donor DNA in transformation assays with auxotrophs as the recipients. Competence was induced in 20% nutrient broth during the stationary phase of growth. Optimal transformation assay conditions for one chosen isolate were in Tris buffer with magnesium or calcium, pH 5–8, and a saturating concentration of 0.5 μg of DNA per assay (3.3 ng of DNA μl−1) at 30 °C. Sodium was also required and could not be replaced with ammonium, potassium, or lithium. The maximal transformation frequency observed was 1.95 × 10−3 transformants (recipient cell)−1. A survey of environmental Aeromonas auxotrophic recipients (n = 37), assayed with donor DNA from other wild-type environmental aeromonads under optimal assay conditions, demonstrated that 73% were able to act as recipients, and 100% were able to act as donors to at least some other aeromonads. Three different transformation groups were identified based on each isolates’ ability to transform other strains with its DNA. The transformation groups roughly corresponded to phylogenetic groups. These results demonstrate that natural transformation is a general property of Aeromonas environmental isolates. However, a surprising result was that close relatives were far more likely to exchange DNA through transformation in a pattern reminiscent of the biological species concept in eukaryote evolution.
