PHYLOGENETIC RELATIONSHIPS AND FUNCTIONAL GENES: DISTRIBUTION OF A MANGANESE-OXIDIZING GENE (MNXG) IN BACILLUS SPECIES

The oxidation and reduction of metals in the environment affects their chemical behavior, bioavailability, and cycling. Many members of the Domain Bacteria are known to possess genes responsible for the oxidation or reduction of specific metals. Select species within the group Bacillus possess a functional gene (mnxG) that codes for a putative Mn(II)-oxidizing enzyme. This gene has been found in Bacillus sp. isolated from a variety of natural environments, including recently cultivated Bacillus sp. from the deep subsurface at Henderson Mine, CO. The Henderson Molybdenum Mine, Empire, Colorado accesses mineral deposits in a Tertiary intrusion into the Precambrian Silver Plume Granite. At 7025', ~3000' below the surface, manganese oxide minerals were detected on the walls of the mine and high levels of soluble Mn(II) were measured in the waters draining from mine boreholes. Investigations into the microbial communities present in the minerals and water resulted in the isolation of ten organisms most closely related to members of the genus Bacillus or Paenibacillus. The isolates were interrogated for possession of the mnxG gene; presence of the gene was detected in only one isolate. A phylogenetic study was subsequently undertaken to determine if a correlation exists between 16S rRNA sequences and the presence or absence of the gene. 16S rRNA and mnxG gene sequences of known mnxG-positive and mnxG-negative Bacillus species and the Henderson Mine isolates were used to build phylogenetic trees that relate the species to one another. A correlation between the 16S rRNA sequences and the presence or absence of the mnxG gene is evident from the analyses. Character mapping experiments reveal that random mutations alone cannot explain the observed data. Additionally, a complex pattern of distribution of the gene throughout the Bacillus species was observed. Bayesian analyses and character mapping indicate that, while both gains and losses of the gene occurred within the group of Bacilli studied, the occurrence of a loss of mnxG is more probable than a gain of mnxG. The relationships between organisms and patterns of mnxG distribution can be explained by phylogenetic inheritance, lateral gene transfer, and genomic remodeling through gene loss.