Previous work has shown that high glucose concentrations (between 20 and 80 g/l) cause a reduction in the X. dendrorhous growth rate; the low
carotenoid production may be associated with that inhibition . However, our results indicate that, at least under the conditions tested, glucose can induce an important increase in biomass. Thus, the inhibition of carotenoid biosynthesis reported here cannot be explained by a reduction in growth rate. Another possibility is that the inhibition of pigment production is a consequence of the cell growth promoted by glucose, in contrast with the lack of growth observed in the control culture. However, the experiments were designed to evaluate the effect of glucose and ethanol over a short period of time after the addition of the carbon source (only during the first six #this website randurls[1|1|,|CHEM1|]# hours). In most cases, the maximum effect on carotenogenic gene expression was observed between 2 and 4 h after the treatment; during this time, biomass variations were very low. In addition, X. dendrorhous exhibited very poor growth in other carbon sources, such as galactose, sorbose and succinate, registering a growth level equivalent to the control condition (data not shown), preventing Fosbretabulin molecular weight these
carbon sources from being used as a “”growing”" control. It is well known that glucose has a global effect on cell metabolism, causing induction of genes related to glycolysis and fermentative metabolism and thereby repressing many of the genes involved in secondary metabolism and the use of alternative carbon sources . The
induction of the PDC gene and repression of the invertase-coding gene INV (data not shown) in response to glucose addition suggests that this phenomenon may also occur in X. dendrorhous. Therefore, the inhibition of pigment synthesis in response new to glucose may also be a consequence of inhibition of the components of respiratory metabolism, which control the availability of substrates for the carotenogenesis pathway. However, in contrast to glucose, non-fermentable carbon sources generally cause an increase in the synthesis of pigments in X. dendrorhous [12, 13]. Accordingly, our results indicate that the addition of ethanol causes an increase in the total amount of carotenoids 24 h after treatment. Strikingly, even when there was an increase in the biomass, ethanol induced de novo synthesis of pigments, as evidenced by an increase in the relative amounts of intermediate carotenoids in the pathway. These results agree with a previous report by Gu and coworkers, in which the addition of ethanol at different stages of growth caused an increase in the total amount of carotenoids . The authors proposed two mechanisms by which ethanol induced the biosynthesis of pigments.