Inhibitors of protein phosphorylation including the retinoblastoma protein induce germination of Candida albicans.

It has been previously shown that the induction of germination in Candida albicans occurs following its cessation of growth as a yeast. Similarly, mammalian cells undergo a differentiation process that is preceded by a growth cessation associated with a hypophosphorylation of proteins of the retinoblastoma gene family. It is postulated that a similar type of mechanism may be operative in C. albicans and protein phosphorylation inhibitors: forskolin (stimulates cyclic adenosine monophosphate production), okadaic acid (phosphatase inhibitor) and D-erythro-sphingosine (retinoblastoma protein phosphorylation inhibitor) have been used to further strengthen this hypothesis. Okadaic acid (1-1000 nM) and D-erythro-sphingosine (100 microM) significantly inhibited the growth of yeast cells of C. albicans. D-Erythro-sphingosine at 1000 microM was candidicidal. Forskolin did not significantly affect growth. Exponentially grown C. albicans pretreated with forskolin (10 microM), okadaic acid (1000 nM) or D-erythro-sphingosine (100 microM) readily germinated. In comparison, when these inhibitors were incorporated in the same medium, germination of exponentially grown cells did not occur. These results suggest that protein dephosphorylation may be necessary at an early stage of the yeast-hyphae transition in C. albicans.

Activation of blood clotting factors by microbial proteinases.

There are very few reports on the involvement of bacterial proteinases on the blood clotting system using both human plasma and purified clotting factors. We studied whether microbial proteinases from the opportunistic pathogens Candida albicans, Pseudomonas aeruginosa and Serratia marcescens activate the blood clotting cascade by using normal human plasma, human plasmas deficient in clotting factor XII or X, and also by using purified clotting factors XII, X and prothrombin. All proteinases tested activated either clotting factor XII or prothrombin in vitro, thus resulting in generation of thrombin. Clotting factor X was converted to the active form (Xa) by both Candida and Pseudomonas proteinases, but not by Serratia proteinase. These results suggest that peripheral and systemic blood circulation may be impaired by activation of the blood clotting cascade by microbial infections, especially in septic patients, which would enhance disseminated intravascular coagulation and multi-organ failure.

The relationship between cyclic adenosine 3',5'-monophosphate and morphology in exponential phase Candida albicans.

The relationship between changes in cyclic AMP content and germ tube formation in exponential phase Candida albicans was investigated using two simple media containing glucose plus ammonium chloride, or N-acetyl-D-glucosamine (GlcNAc). The glucose medium did not promote germ tube formation unless the cells were starved before inoculation, whereas the GlcNAc medium promoted germ tube formation in both non-starved and starved cells. The cyclic AMP content of exponential phase cells, non-starved cells and starved cells was 0.21, 0.34 and 0.64 pmol mg-1 dry wt, respectively. In glucose medium, cyclic AMP content in both non-starved cells and starved cells increased for a period of 60 min after inoculation, but then decreased for a further 120 min. The cyclic AMP content of non-starved cells and starved cells was 0.16 and 0.29 pmol mg-1 dry wt, respectively, after 180 min. The maximum percentage of non-starved cells with germ tubes was around 20%. Starved cells with germ tubes were observed after 40 min and reached a maximum (around 90%) after 140 min. The number of germ tubes remained constant for the next 40 min. In GlcNAc medium, the cyclic AMP content of both non-starved cells and starved cells showed a tendency to increase for 180 min. The content of non-starved cells and starved cells was 2.02 and 1.75 pmol mg-1 dry wt, respectively, after 180 min. Germ tube formation in non-starved cells started after 70 min, reached around 80% after 150 min, and remained stable for the next 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Starvation and germ tube formation in the exponential phase Candida albicans.

Two chemically defined media were developed for the induction of germ tubes in exponential phase cells of Candida albicans. One medium was N-acetyl-D-glucosamine medium which is composed of L-thiazolidine-4-carboxylic acid, L-proline, NaHCO3, sodium acetate, NaH2PO4 and N-acetyl-D-glucosamine. The other one was glucose medium in which N-acetyl-D-glucosamine is exchanged for glucose plus NH4Cl in N-acetyl-D-glucosamine medium. In these media, a high percentage of germ tube forming cells was obtained without a temperature shift. However, starvation of the cells in water at 37 degrees C was a necessary pretreatment to consistently obtain a high percentage of germ tube forming cells. The effect of starvation was remarkable in glucose medium, the percentages of germ tube forming cells among the normal cells and starved cells were 20 and 80, respectively. As for intracellular changes during starvation, a decrease in adenosine triphosphate concentration and an increase in adenosine 3',5'-cyclic monophosphate concentration were observed.