Influence of clay minerals on growth and metabolic activity of Epicoccum nigrum and Stachybotrys chartarum

Abstract

The influence of montmorillonite, kaolinite and quartz on growth and metabolic activity of Epicoccum nigrum and Stachybotrys chartarum was investigated. These fungi synthesize from nonaromatic carbon sources, phenols which are polymerized to form humic acid-like substances. In both stationary and shake cultures of E. nigrum, clay minerals and quartz accelerated biomass formation, glucose consumption and nitrogen assimilation and also enhanced the efficiency of glucose utilization for cell synthesis. Montmorillonite was far more active than kaolinite and quartz, and the magnitude of the effect usually increased with increasing concentrations of montmorillonite from 0.25 to 1.0 per cent. The montmorillonite was still active when enclosed in dialysis tubing. Autolysis, indicated by a decrease of biomass, accumulation of ammonia, and an increase of pH, commenced earlier in cultures containing montmorillonite. Similar results were noted for S. chartarum in shake or shallow stationary cultures. In deep stationary cultures the addition of montmorillonite either did not affect or decrease the synthesis of cell material by S. chartarum. The decrease varied with the source of the clay and was greater at higher clay levels. The studies further suggest that the clays increase glycolysis, thereby providing greater quantities of intermediate products for cell synthesis. Depending upon the fungal species, clay-type, clay-concentration, clay-origin, and oxygen supply, growth may be decreased or inhibited.