When proliferating cells exhaust nutrients, they enter into a stationary phase, adapting to this stress with adjustments in metabolism and gene expression. We have examined cellular RNA content as C. albicans planktonic cells progress into stationary phase. When grown in minimal medium in suspension culture the degradation was observed beginning at day 2 of the 11 day observation. In rich medium the onset of degradation was delayed about 1 day (beginning day 3) and progressively declined over the 13 days examined. In minimal and rich medium 28S and 18S rRNA bands became undetectable by day 5 and 9 respectively. When biofilm was grown on acrylic pieces in a 35 mm polystyrene dish in rich medium for similar time periods as that of planktonic cells, three cell populations were observed: biofilm, and two planktonic populations -a floating population of yeast cells and hyphae, and settled yeasts cells. RNA integrity was observed at 3 and 6 days when degradation had been observed in the planktonic suspension culture. Both planktonic populations showed loss of RNA integrity that appeared more extensive in the floating population. RNA degradation was not apparent even at 6 days in the biofilm. Biofilm organisms develop reduced susceptibility to some antifungal drugs. The apparent lack of response or delayed response to RNA degradation of biofilm organisms raises the notion that a biofilm may be a protected environment. The community structure may serve to accumulate nutrients and thus postpone nutrient limitation stress or perhaps develop other mechanisms to deflect stresses in the environment and thus maintain a more homeostatic environment.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)