MATHEMATICAL SIMULATION OF THE INTERACTIONS AMONG CYANOBACTERIA, PURPLE SULFUR BACTERIA AND CHEMOTROPIC SULFUR BACTERIA IN MICROBIAL MAT COMMUNITIES

A deterministic one-dimensional reaction diffusion model was construct ed to simulate benthic stratification patterns and population dynamics of cyanobacteria, purple and colorless sulfur bacteria as found in ma rine microbial mats. The model involves the major biogeochemical proce sses of the sulfur cycle and includes growth metabolism and their kine tic parameters as described from laboratory experimentation. Hence, th e metabolic production and consumption processes are coupled to popula tion growth. The model is used to calculate benthic oxygen, sulfide an d light profiles and to infer spatial relationships and interactions a mong the different populations. Furthermore, the model is used to expl ore the effect of different abiotic and biotic environmental parameter s on the community structure. A strikingly clear pattern emerged of th e interaction between purple and colorless sulfur bacteria: either col orless sulfur bacteria dominate or a coexistence is found of colorless and purple sulfur bacteria. The model predicts that purple sulfur bac teria only proliferate when the studied environmental parameters surpa ss well-defined threshold levels. However, once the appropriate condit ions do occur, the purple sulfur bacteria are extremely successful as their biomass outweighs that of colorless sulfur bacteria by a factor of up to 17. The typical stratification pattern predicted closely rese mbles the often described bilayer communities which comprise a layer o f purple sulfur bacteria below a cyanobacterial top-layer; colorless s ulfur bacteria are predicted to sandwich in between both layers. The p rofiles of oxygen and sulfide shift on a diel basis similarly as obser ved in real systems.