Alcaligenes eutrophus CH34 is a facultative chemolithotroph with plasmid-bound resistance to heavy metals

Abstract

Alcaligenes eutrophus strain CH34, which was isolated as a bacterium resistant to cobalt, zinc, and cadmium ions, shares with A. eutrophus strain H16 the ability to grow lithoautotrophically on molecular hydrogen, to form a cytoplasmic NAD-reducing and a membrane-bound hydrogenase, and most metabolic attributes; however, it does not grow on fructose. Strain CH34 contains two plasmids, pMOL28 (163 kilobases) specifying nickel, mercury, and cobalt resistance and pMOL30 (238 kilobases) specifying zinc, cadmium, mercury, and cobalt resistance. The plasmids are self-transmissible in homologous matings, but at low frequencies. The transfer frequency was strongly increased with IncP1 plasmids RP4 and pUZ8 as helper plasmids. The phenotypes of the wild type, cured strains, and transconjugants are characterized by the following MICs (Micromolar) in strains with the indicated phenotypes: Nic+, 2.5; Nic-, 0.6; Cob+A, 5.0; Cob+B, 20.0; Cob-, less than 0.07; Zin+, 12.0; Zin-, 0.6; Cad+, 2.5; and Cad-, 0.6. Plasmid-free cells of strain CH34 are still able to grow lithoautotrophically and to form both hydrogenases, indicating that the hydrogenase genes are located on the chromosome, in contrast to the Hox structural genes of strain H16, which are located on the megaplasmid pHG1 (450 kilobases).