The Role of Glucose in the pH Regulation of Germ-tube Formation in Candida albicans

Abstract

It has been reported that Candida albicans can form germ-tubes only in the narrow pH range of 6-8, and that by changing only the pH one can regulate germ-tube formation. We found that the pH minimum for germ-tube formation could be dramatically lowered by eliminating the glucose present in many induction solutions. Lee's medium lacking glucose, ethanol, N-acetyl-D-glucosamine, and proline induced germ-tubes at pH values as low as 3 under most conditions. The presence of as little as 1 mM-glucose in these induction solutions was sufficient to cause the cells to grow either as yeasts with multiple buds or as pseudohyphae when the pH was 3.7. However, when C. albicans was grown in any of the above induction solutions (with the exception of ethanol), containing 200 mM-glucose buffered at pH 5.8, not only were germ-tubes formed, but their rate of formation and length were also increased. Preincubation of the cells in a solution buffered at pH 3.7 and containing 200 mM-glucose, before exposure to induction solutions lacking glucose at pH 3.7 or at pH 5.8, did not inhibit germ-tube formation. Likewise, addition of glucose after 45 min exposure to an induction solution was without effect. Theophylline and dibutyryl cAMP did not counteract the action of glucose. Other sugars which suppressed germ-tube formation at low pH were fructose, galactose, mannose, xylose, gluconic acid and the nonmetabolizable sugar 3-O-methylglucose. These results indicate that pH does not directly regulate dimorphism in C. albicans, and that glucose or its metabolites may play an important role.

Yeast-mycelial dimorphism of haploid and diploid strains of Ustilago maydis

“…High concentrations of glucose reduced mycelial development whereas succinate induced the formation of long, slender filaments. It has been reported that glucose and related sugars repress filamentous growth of C. albicans at acid pH (Pollack & Hashimoto, 1987), and it is known that mycelial growth of Yarrowia lipolytica is induced only by acetate and N-acetylglucosamine, and is repressed by glucose (Rodriguez & Dominguez, 1984).…”

Influence of Na+ and anions on the dimorphic transition of Candida albicans

“…The specific growth rate ( p ) for yeast cells at pH 5.5 and 27 "C was calculated as p = (In OD -In OD,)/t-to (Harvey, 1973), where OD, and O D were the optical densities at times to (4 h) and t (6 h), respectively. Germ tube formation was examined using an improved Neubauer haemocytometer ; the morphological criteria of Pollack & Hashimoto (1987) were adopted whereby a germ tube was defined as a projection of at least 2pm, lacking a constriction at its base. Percentage formation of germ tubes was estimated by sampling approximately 80-100 cells.…”

“…Both 200 m M NaCl and sodium gluconate treatments were significantly different at the 99% confidence level to the sorbitol control. The relatively low control germ tube formation rates could be a consequence of the high (55 mM) glucose concentration (Pollack & Hashimoto, 1987).…”

Rapid differentiation of Candida albicans from other Candida species using its unique germ tube formation at 39° C

“…In vitro, a germ tube can be induced from the yeast cell and developed into the mycelial form. This morphological transition can be induced by changes in a variety of environmental factors, including ambient pH (Pollack, 1987), nutritional status (Barlow et al, 1974;Bruatto et al, 1993;Casanova et al, 1997;Mattia et al, 1982) and temperature (Odds, 1985). However, the mechanism whereby these factors induce germ tube formation in C. albicans is virtually unknown.…”