Regulation and butanol inhibition of D-xylose and D-glucose uptake in Clostridium acetobutylicum

Abstract

Clostridium acetobutylicum exhibited diauxie growth in the presence of mixtures of glucose and xylose. Both glucose-and xylose-grown cells had a glucose uptake activity. On the other hand, growth on xylose was associated with the induction of a xylose permease activity, which was repressed by glucose in xylose-induced cells. The rate of sugar uptake with increasing sugar concentrations showed saturation kinetics with an apparent Km of 1.25 x 10-5 M for glucose and 5 x 10-3 M for xylose. Concomitant with the production of solvents, the activities of the glucose and xylose transport systems decreased. Among the main products of fermentation, butanol was shown to be a potent inhibitor of the growth of the organism and of the rate of sugar uptake as well as of sugar incorporation into cell materials. These inhibitory effects of butanol were more pronounced in xylose-grown cells than in glucose-grown cells. Butanol completely inhibited growth at a concentration of 14 g/liter for cultures growing on glucose and 8 g/liter for cultures growing on xylose. Concentrations of 7 and 10.5 g/liter of butanol caused a 50% inhibition of the xylose and glucose incorporations into cell materials. These inhibitory levels of butanol were found in typical glucose or xylose fermentation.

Note: Sucrose transport and metabolism in Clostridium beijerinckii NCIMB 8052

“…The sucrose PTS was absent in both xylose and fructose grown cells, indicating that the system is inducible by its substrate. It remains possible that fructose may also repress the sucrose PTS (in fact we have preliminary evidence that this may indeed be the case), but it is very unlikely that the absence of sucrose PTS activity in xylose cells is a result of repression, as this is not a favoured substrate in this organism (Ounine et al 1985). Work in this laboratory has confirmed that mannitol and glucitol are also transported by inducible PTS transport mechanisms in Cl.…”

Diauxic growth of Clostridium thermosaccharolyticum on glucose and xylose

“…However, in our assays using resting cells glucose did not inhibit xylose accumulation, and the mechanism by which glucose acts remains to be determined. A similar inhibition of xylose metabolism by glucose, involving repression of the xylose permease, has been observed in C. acetobutylicum [14] but the mechanisms responsible were not investigated.…”

Factors affecting utilization of carbohydrates by clostridia

“…The glucose PTS is constitutive, being found in cells grown on a variety of sugars, including fructose, galactose, maltose, sucrose, lactose, mannitol and glucitol (unpublished results). On the other hand, xylose transport in C. acetobutylicum is inducible [41], as are transport and metabolic activities for glucitol, mannitol and galactose (unpublished results). In C. thermocellum, glucose transport and metabolism was induced by glucose [27,50], while growth on fructose or mannitol led to induction of synthesis of a fructose PTS and fructose-l-P kinase, or a mannitol PTS and mannitol-l-P dehydrogenase, respectively [25].…”

“…There are no examples of PTS-mediated pentose accumulation in bacteria, and thus pentoses are unlikely to be PTS substrates in clostridia. However, while xylose has been shown to be fermented by many clostridia, and in some cases transport has been assayed [41,42], there have been no detailed studies relating to the mechanism of uptake.…”

“…acetobutylicum and C. thermosaccharolyticum exhibit a classical diauxic growth when presented with a mixture of glucose and xylose; after metabolism of the available glucose, there is a lag period during which the xylose metabolic system is synthesised [41,42]. In the case of C. thermosaccharolyticum, xylose was shown to induce three activities (xylose transport, xylose isomerase and xylulokinase), and their coordinate induction by xylose and repression by glucose is consistent with the corresponding genes being arranged in an operon, similar to other bacteria [53][54][55].…”