| Bioluminescent bacteria are phylogenetically confined to the γ-3 subgroup of the Proteobacteria, yet exhibit a diverse range of niches within the marine environment. Genera studied in this report include members of Vibrio, Photobacterium, Shewanella, and Photorhabdus. Bioluminescence is due to the functions encoded by the lux operon, an operon that bears many of the characteristics that would allow lateral transmission between bacterial strains. The luxA gene encodes the α-subunit of the bacterial luciferase enzyme: this enzyme is responsible for catalyzing a reaction that causes the release of photons. 16S rRNA and luxA sequences were compiled for 27 strains of bioluminescent bacteria. A comparison of phylogenetic results for distance, maximum likelihood and parsimony methods shows little variation in the resulting tree topology between these methods for the three datasets used. The case for the lateral transfer of lux genes is supported by the phylogenetic comparison of the topologies obtained for the luxA datasets versus the 16S rRNA dataset for Shewanella hanedaci and Photorhabdus luminescens.; ERIC, REP and RAPD fingerprinting, performed on laboratory strains of luminous marine bacteria, shows sufficient variability to distinguish between strains of a species. This technique has been applied to naturally isolated luminous bacteria to determine its usefulness in ecological studies of the various niches that can be occupied by one species of luminous bacteria. Bioluminescent strains isolated from seawater in Mexico and the Everglades, from fish guts in the Bahamas, and from light organ tissue from fish and squid have all been characterized in this study by fingerprinting methods. The degree of unique strains present in the samples has been determined to be between 25% and 63%. Fingerprinting natural isolates could thereby decrease the numbers of strains that are propagated and stored. The natural isolates were subjected to taxonomic tests, as well as colony and slot blot hybridizations using luxA as a probe, in order to assign them to a described species. Although the methodology was not definitive, most are closely allied with the Vibrio harveyi group and 16S rRNA sequence analysis of five of the strains identified four as V. campbellii and one as P. leiognathi. |
