Utilization of L( - )-glucose by naturally occuring microorganisms

Abstract

Carbon recycle by means of physicochemically synthesized carbohydrates has been proposed. These artificial sugars can be used to generate single cell protein. However, it is not known what effects the unnatural components will have on the yield, productivity, and metabolic regulation of the or­ganisms used. We have obtained from natural populations, a number of organisms which utilize L-glucose as sole carbon source. Of the twelve organisms isolated, five are gram-negative aerobic rods, one is a gram positive coccus, two are thermophilic bacilli, three are yeasts, and one is a mycelial form. Pre­liminary taxonomy was done on these organisms. When fully adapted to growth on L-glucose, one pseudomonad grows ex­ponentially with a doubling time of 14 to 16 hours with 5 g/L L-glucose in the medium. Cell yields are about 0.46 g dry cells/g L-glucose, and cell densities as high as 2.8 g/L have been acheived in shake flasks. The ap­parent maximum growth rate is 0.0506 hr.⁻¹ and the apparent overall K[subscript m] for growth is 0.14 g/L L-glucose. However, substrate inhibition sets in at about 4.5 g/L L-glucose. L-glucose transport takes place by facilitated diffusion at V[subscript max] = 2.63 x 10⁻³ mg L-glucose/(mg cells-min) and K[subscript m]= 0.65 g/L L-glucose. The organism probably utilizes the entire L-glucose molecule. There is evidence that carbon 1 is eliminated as CO₂ and subsequently reassimilated from the medium. One or more growth factors appear to be necessary for L­ glucose utilization. They are made by the organism under good growth con­ditions and one appears to be excreted into the medium. A hypothetical mechanism of L-glucose utilization consistent with the growth kinetics is proposed. This mechanism involves a catabolic sequence with at least two limiting reactions. The first is incipient transport limitation and the second is inhibition by an intracellular metabolite derived from L-glucose.