Xylose and Glucose Utilization by Bacteroides xylanolyticus X5-1 Cells Grown in Batch and Continuous Culture

Abstract

During cultivation on a mixture of xylose and glucose, Bacteroides xylanolyticus X5-1 showed neither diauxic growth nor a substrate preference. Xylose-limited continuous-culture cells were able to consume xylose and glucose both as single substrates and as mixed substrates without any lag phase. When glucose was the growth-limiting substrate, the microorganism was unable to consume xylose. However, in the presence of a small amount of glucose or pyruvate, xylose was utilized after a short lag phase. In glucose-limited cells, xylose isomerase was present at low activity but xylulose kinase activity could not be detected. On addition of a mixture of xylose and glucose, xylose isomerase was induced immediately and xylulose kinase was induced after about 30 min. The induction of the two enzymes was sensitive to chloramphenicol, showing de novo synthesis. Xylose uptake in glucose-grown cells was very low, but the uptake rate could be increased when incubated with a xylose-glucose mixture. The increase in the uptake rate was not affected by chloramphenicol, indicating that a constitutive uptake system had to be activated. The inability of B. xylanolyticus X5-1 cells undergoing glucose-limited continuous culture to induce the xylose catabolic pathway after the addition of only xylose probably was caused by energy limitation.

Simultaneous Growth on Citrate Reduces the Effects of Iron Limitation during Toluene Degradation in Pseudomonas

“…The effects of the presence of alternative growth substrates in an environment during the degradation of an aromatic hydrocarbon can be important for the kinetics of biodegradation of these compounds. The results above show that simultaneous use of two carbon sources under carbonlimited growth in continuous cultures as also observed for several other carbon sources [3,8,14,17] (for a review see [15]), proceeds with high efficiency in the case of the harmful hydrocarbon toluene and the readily degradable carbon source citrate. The effect of the addition of a second carbon source on the degradation of harmful hydrocarbons has been reported previously [14,16], but did not include data on the effect of additional limitations, e.g., iron limitation, on substrate utilization.…”

“…Plant species and growth conditions determine the composition of root exudates, which, among many other compounds, can contain organic acids such as acetate and lactate [9] and amino acids such as glutamate and aspartate [30]. The presence of multiple carbon and energy sources may result in catabolite repression or simultaneous use of these compounds [3] (for an overview see [8,15]). An example of catabolite repression was found in Pseudomonas putida mt2 in which expression of the toluene degradation pathway was inhibited by the presence of succinate [5].…”

Xylose anaerobic conversion by open-mixed cultures

“…The yield of catabolic products is higher for xylose, which would suggest a higher generation of ATP ( Y ATP/S ); however, the biomass yield is in fact higher when glucose is the substrate ( Y X/S ). This difference has also been observed in studies conducted with pure bacterial cultures, where the biomass yield on the catabolic ATP yield estimated ( Y ATP/S ) is significantly higher for glucose than for xylose (Biesterveld et al 1994 ; Heyndrickx et al 1991 ; Ounine et al 1985 ). Furthermore, in solvent-producing bacteria, not only growth is inhibited but also the xylose uptake is affected by the solvents (Ounine et al 1985 ; Qureshi et al 2006 ).…”

“…The differences between the pentose phosphate pathway (PPP) and the phosphoketolase pathway (PKP) are indicated. The reactions indicated with ( a ) and ( b ), ( c ) and ( d ) are alternative pathways for the same product, depending mainly on the type of microorganism (Biesterveld et al 1994 ; Tanaka et al 2002 ) …”