Quantifying mold biomass on gypsum board: comparison of ergosterol and beta-N-acetylhexosaminidase as mold biomass parameters.

Two mold species, Stachybotrys chartarum and Aspergillus versicolor, were inoculated onto agar overlaid with cellophane, allowing determination of a direct measurement of biomass density by weighing. Biomass density, ergosterol content, and beta-N-acetylhexosaminidase (3.2.1.52) activity were monitored from inoculation to stationary phase. Regression analysis showed a good linear correlation to biomass density for both ergosterol content and beta-N-acetylhexosaminidase activity. The same two mold species were inoculated onto wallpapered gypsum board, from which a direct biomass measurement was not possible. Growth was measured as an increase in ergosterol content and beta-N-acetylhexosaminidase activity. A good linear correlation was seen between ergosterol content and beta-N-acetylhexosaminidase activity. From the experiments performed on agar medium, conversion factors (CFs) for estimating biomass density from ergosterol content and beta-N-acetylhexosaminidase activity were determined. The CFs were used to estimate the biomass density of the molds grown on gypsum board. The biomass densities estimated from ergosterol content and beta-N-acetylhexosaminidase activity data gave similar results, showing significantly slower growth and lower stationary-phase biomass density on gypsum board than on agar.

The use of fluorogenic substrates to measure fungal presence and activity in soil.

Our objective was to determine if 4-methylumbelliferyl-labelled enzyme substrates could be used to detect and quantify specific components of chitinase and cellulase activities as specific indicators of the presence and activity of fungal biomass. The fluorogenic substrates 4-methylumbelliferyl (MUF) N-acetyl-beta-D-glucosaminide and MUF beta-D-lactoside were used for the detection and quantification of beta-N-acetylglucosaminidase (EC 3.2.1.30) (NAGase) and endo 1,4-beta-glucanase (EC 3.2.1.4)/cellobiohydrolase (EC 3.2.1.91) (CELase), respectively. Culture screenings on solid media showed a widespread ability to produce NAGase among a taxonomically diverse selection of fungi on media with and without added chitin. NAGase activity was expressed only in a limited number of bacteria and on media supplemented with chitin. The CELase activity was observed only in a limited number of fungi and bacteria. Bacterial CELase activity was expressed on agar media containing a cellulose-derived substrate. In soil samples, NAGase activity was significantly correlated with estimates of fungal biomass, based on the content of two fungus-specific indicator molecules, 18:2 omega 6 phospholipid fatty acid (PLFA) and ergosterol. CELase activity was significantly correlated with the PLFA-based estimate of fungal biomass in the soil, but no correlation was found with ergosterol-based estimates of fungal biomass.

Comparison of biomass dry weights and radial growth rates of fungal colonies on media solidified with different gelling compounds.

Penicillium commune, Aureobasidium pullulans, and Paecilomyces farinosus were grown on two different media solidified with agar, Pluronic F-127, Carrageenan X-4910, or Carrageenan X-4910 overlaid with cellophane. Growth on Carrageenan X-4910 was generally the same as that on agar, as was the visual appearance of the colonies, e.g., the pigmentation. The Carrageenan X-4910 gels had a melting point, depending on the medium, of 41 to 46(deg)C, and the dry weights of the colonies were readily determined at 60(deg)C. To determine the dry weights of the colonies grown on agar plates, the gels were boiled for 10 min to melt the agar. Comparison of these two procedures showed that the boiling procedure resulted in a 22% reduction of the biomass dry weight. Cellophane membranes did not affect the radial growth rate profoundly. The biomass density was almost halved for P. commune and P. farinosus grown with membranes, whereas the presence of the membrane did not affect the biomass density of A. pullulans. The biomass densities of the colonies grown on Pluronic F-127 were significantly reduced, while in most cases, the radial growth rates of colonies grown on Pluronic F-127 were significantly higher than those obtained on agar or Carrageenan X-4910. Furthermore, the morphology of the leading hyphae was altered, and the hyphal growth unit length was more than twice that obtained on agar and Carrageenan X-4910. Carrageenan X-4910 is a valuable gelling compound for the study of the growth of fungi, as the biomass dry weight is readily determined and growth is similar to that obtained on agar gels.

Influence of Zn2+ on yeast-mycelium dimorphism and exopolysaccharide production by the fungus Aureobasidium pullulans grown in a defined medium in continuous culture.

The yeast-mycelium dimorphism of Aureobasidium pullulans was studied in continuous culture in a defined medium. At a constant dilution rate (0.08 h-1) the morphological status of the culture could be controlled by the input concentration of Zn2+. As the input concentration of Zn2+ was increased (in intervals from 0 to 7.6 microM) the culture shifted from a zinc-limited to a carbon-limited state. In this interval the culture gradually passed through three growth regimes based on morphology and concentration of exopolysaccharide and biomass. The first growth regime was found when the input concentration of Zn2+ was kept below 0.45 microM. Growth in this regime was zinc-limited and more than 90% of the biomass was in the yeast growth form. An increase in the input concentration of Zn2+ in this growth regime led to a proportional increase in both the biomass and the concentration of exopolysaccharide. When the input concentration of Zn2+ was varied between 0.45 microM and 0.80 microM a second growth regime could be detected where simultaneous limitations in two nutrients were recognized. Although the carbon source (glucose) was exhausted an increase in the input concentration of Zn2+ led to a proportional increase in the steady-state biomass concentration. The increase in biomass concentration was at the expense of exopolysaccharide production, which gradually decreased. The culture, still being primarily limited by Zn2+, remained in the yeast growth form. In a third growth regime (input concentration of Zn2+ above 0.80 microM) no increase in the steady-state biomass was seen when the input concentration of Zn2+ was increased.(ABSTRACT TRUNCATED AT 250 WORDS)