Individual-based approach to modeling hyphal growth of a biocontrol fungus in soil.

ABSTRACT Fungi in soil perform beneficial roles that include biological control of soilborne plant pathogens. However, relatively little predictive information is available about the growth and activity of fungal hyphae in soil habitats. A stochastic computer simulation model ("Fungmod") was developed to predict hyphal growth of the biocontrol fungus Trichoderma harzianum ThzID1 in soil. The model simulates a fungal colony as a population of spatially referenced hyphal segments, and is individual-based, in that records of spatial location and branching hierarchy are maintained for individual hyphal nodes. In this way, the entire spatial structure of the fungal colony (hyphal network) can be explicitly reconstructed at any point in time. Also, the soil habitat is modeled as a population of spatially referenced 1-mm(3) soil cells, allowing for the simulation of a spatially heterogeneous environment. Initial hyphal growth parameters were derived from previously published results, and the model was tested against new data derived from image analysis of hyphal biomass accumulation in soil. The ability to predict fungal growth in natural habitats will help to improve the predictability of successful myco-parasitic events in biological control systems.

Stress-Induced Production of Biofilm in the Hyperthermophile Archaeoglobus fulgidus.

Archaeoglobus fulgidus, an anaerobic marine hyperthermophile, forms a biofilm in response to environmental stresses. The biofilm is a heterogeneous, morphologically variable structure containing protein, polysaccharide, and metals. Production of the biofilm can be induced by nonphysiological extremes of pH and temperature, by high concentrations of metals, and by addition of antibiotics, xenobiotics, or oxygen. Cells within the biofilm show an increased tolerance to otherwise toxic environmental conditions. Metals sequestered within the biofilm stimulate growth of A. fulgidus cells in metal-depleted medium. These data suggest that cells may produce biofilm as a mechanism for concentrating cells and attaching to surfaces, as a protective barrier, and as a reserve nutrient. Because similar biofilms are formed by Archaeoglobus profundus, Methanococcus jannaschii, and Methanobacterium thermoautotrophicum, biofilm formation might be a common stress response mechanism among the archaea.