Effect of organic complex compounds on Bacillus thermoamylovorans growth and glucose fermentation

The effect of the concentration of a mixture (1/1 [wt/wt]) of yeast extract and bioTrypcase (YE+bT) on the growth and physiology of a new species, Bac illus thermoamylovorans, a moderately thermophilic, non-spore-forming, lact ic acid-producing bacterium isolated from palm wine, was studied. At an ini tial glucose concentration of 100 mM, B. thermoamylovorans growth was limit ed when the concentration of YE+bT was lower than 5.0 g liter(-1); under th ese conditions, cellular yield reached a maximum value of 0.4 g of cells pe r g of YE+bT, Growth limitation due to deficiency in growth factors led to a significant shift in glucose metabolism towards lactate production. Lacta te constituted 27.5 and 76% of the end products of glucose fermentation in media containing YE+bT at 20.0 and 1.0 g liter(-1), respectively. This resu lt markedly differed from published data for lactic bacteria, which indicat ed that fermentative metabolism remained homolactic regardless of the conce ntration of YE. Our results showed that the ratio between cellular synthesi s and energy production increased with the concentration of YE+bT in the cu lture medium. They indicate that the industrial production of lactic acid t hrough glucose fermentation by B. thermoamylovorans can be optimized by usi ng a medium where glucose is present in excess and the organic additives ar e limiting.