Direct measurement of carbon substrate oxidation and incorporation patterns in RuMP-type methylotrophs: Chemostatic cultures of Methylomonas L3

A technique using C-14 isotope tracers to probe the branching of carbon flow in methylotrophic bacteria has been devised and applied to continuous steady-state cultures. Methylomonas L3, a strain which utilizes the KDPG/TA variant of the ribulose monophosphate cycle for carbon fixation, was employed in the experimental studies. The actual in vivo rates of substrate-carbon incorporation into biomass, both direct and via CO(2), and of the two carbon oxidation schemes were determined in three different steady-state cultures. The results show that the carbon substrate is oxidized predominantly via formate (the linear oxidation scheme), and that the cyclic scheme of oxidation is minimally, if at all, utilized. The carbon incorporation and oxidation patterns appear to vary considerably with the dilution rate and the inoculum history. The experimental accuracy of the new technique is discussed in detail.