Autotropic CO2 fixation in Pseudomonas sp. strain HD-1

Abstract

Pseudomonas sp. strain HD-1, was reported to grow autotrophically on H2-CO, by Morikawa and Imanaka (1993). However, there is no report on the mechanism of CO, fixation this strain. In our study the strain was cultivated autotrophically. The result shows no significant growth of the strain under autotrophic condition. In further study the enzyme involved in autotrophic growth was induced by inoculating heterotrophically grown cells in a complete inorganic medium in the presence of H2-CO,. Cell-free extract was prepared from the induced cells by sonicatioa, then the activities of the key enzymes of autotrophic CO, fixation pathways in the cell-free extract were investigated. The activities of the key enzymes of the reductive citric acid cycle (ATP:Citrate lyase) and acetyl-CoA pathway (Carbon monoxide dehydrogenase) could not be detected. In contrast, the activity of the key enzyme of the reductive pentose phosphate cycle (Ribuiose-1,s- Bisphosphate CarboxylaselOxygenase; RubisCO) was detected. The activity was in the range of 0.94 to 5.32 nmol min" mg protein-'. The data implies that the strain assimilates CO, autotrophically via reduced pentose phosphate cycle.