Microbial Growth on C 1 Compounds 1 . ISOLATION AND CHARACTERIZATION OF PSEUDOMONAS

It has long been known that some non-photosynthetic micro-organisms can grow on organic C, compounds as their sole source of energy and carbon. The means whereby such organisms grow has been the subject of speculation. It has been suggested (Bhat & Barker, 1948; van Niel, 1954) that they might couple the energy of oxidation of the organic substrate to the reduction of carbon dioxide and the synthesis therefrom of all cell constituents. This would then be a variant of chemosynthetic autotrophy in which the organic compound would merely play a role similar to the inorganic electron donor. The occurrence of this autotrophic type of metabolism has been established by Quayle & Keech (1959a, b) in Pseudomonas oxalaticus grown on formate as sole carbon and energy source. In this organism, the cellular carbon is incorporated as carbon dioxide by the ribulose diphosphate cycle of carbon dioxide fixation (Bassham et al. 1954). More data are needed before the extent of occurrence of this cycle in general microbial growth on organic C, compounds can be assessed. It might be expected, especially with a C, substrate more reduced than formate, that the reduction level of the organic substrate might be conserved by at least some assimilation of carbon as reduced C, units, rather than synthesis of all cell material from carbon dioxide. Evidence has been obtained which indicates that such a heterotrophic type of metabolism operates during growth of Pseudomonas methanica on methane (Leadbetter & Foster, 1958) and Pseudomonas PRL-W4 on methanol (Kaneda & Roxburgh, 1959 a, b, c). Few details of the process are known. For use in investigation of this problem, an organism has been isolated which grows rapidly on methylamine, methanol, formate, or a wide range of other compounds, in an otherwise mineral medium. Its isolation and characteristics are described in this paper. A preliminary account of part of this work has been presented (Quayle & Peel, 1960).