Naturally occurring genetic transfer of hydrogen-oxidizing ability between strains of Alcaligenes eutrophus

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Abstract
Mutants defective in chemolithoautotrophic growth (Aut-) were isolated from A. eutrophus strains H16, N9A, G27 and TF93. Spontaneous Aut- mutants were obtained only with strain TF93. Mutants of the other strains were selected after conventional mutagenesis or treatment with mitomycin. Most of the mutants, including the spontaneous Aut- strains, lacked hydrogenase [EC 1.12.1.2] activity (Hox-) but possessed the ability to fix CO2 (Cfx+). Agar mating of A. eutrophus H16 with Hox- mutants of the various strains resulted in transconjugants which had recovered the ability to grow autotrophically and to express activity of hydrogenase as examined by enzymatic and immunochemical analysis. Transfer of hydrogen-oxidizing ability occurred in the absence of a mobilizing plasmid such as RP4. The transfer frequency was particularly high (.apprx. 10-2/donor) when the spontaneous Hox- mutants of strain TF93 were used as recipients. These strains proved to be plasmid free; donors, transconjugants and the mutagen-treated Hox- mutants contained a large plasmid (MW, 270 .+-. 10 .times. 106) revealed by agarose gel electrophoresis. A. eutrophus H16 apparently harbors a self-transmissible plasmid, designated pHG1, which carries information for hydrogen-oxidizing ability.