Research Express@NCKU - Articles Digest

Competition between two populations tends to eliminate one of the populations from their common habitat, when competition is focused on a single resource and when the populations do not otherwise interact. It is known that two microbial species competing for a single rate-limiting nutrient cannot grow together in a chemostat under steady-state operation, but eventually the species with the lower specific growth rate at the particular operating conditions will become extinct (Fredrickson and Stephanopoulos, 1981, Science, 213(28), 972-979). However, a number of factors mitigate the severity of competition and thus competitors often coexist. One example is in the case where the specific growth rate functions of the two species are such that for certain values of the nutrient concentration the first species grows faster than the second, and for other values of the nutrient concentration the second species is the one growing faster (Sommer, 1999, Nature, 402, 366-367; Huisman and Weissing, 1999, Nature, 402, 366-367). This specific topic is not only a particular interesting question of microbiologists and scientists, but also an important issue to biochemical and environmental engineers when they apply bioreactors that enrich more than two microorganisms for production of chemicals or removal of contaminants. In a series of study (Whang et al., 2002, 2006, 2007), we observed and identified environmental and operational factors that determine competition between two populations, polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating non-poly-P organisms (GAOs), in bioreactors designed for enhanced biological phosphorus removal (EBPR) from wastewater and the resultant stability of EBPR due to competition was elucidated.