Complex dynamics of adaptation in a nonaxenic Microcystis culture - 2. Computer simulation of dinitrophenol effects

A hypothesis was modeled to account for complex 20-day dynamics in a cultur e of blue-green algae Microcystis and heterotrophic bacteria exposed to 2,4 -dinitrophenol (DNP), In trials with little or no added DNP, a limiting fac tor (light or CO2) may cause algal density to fluctuate after 14 days of in crease. Such factors may be unimportant at levels of DNP that restrict phot osynthesis, Bacterial growth may be limited by organic substrate, and bacte ria may be more resistant to DNP than blue-green algae, Hence, at intermedi ate levels of DNP, substrate provided by increased algal death stimulates b acterial growth more than DNP retards it, causing a bacterial peak. Sorptio n of DNP to cells may cause the DNP decline. Greater growth and slower DNP decline in experiments with preexposed organisms indicate lower DNP sorptio n affinity in preexposed cells. Bacterial assimilation of DNP-containing su bstrate may cause the reappearance of DNP, The model reproduced the fluctua tion in algal density after growth was limited and better growth and lower DNP decline with preexposed organisms, Reappearance of DNP occurred, but wa s not obvious. Bacterial dynamics were least well reproduced. Changes in ba cterial constants most affected output. Despite model inadequacies, probabl e aspects of toxicant action in nature have been revealed. Ecological relat ionships among populations of different species and genetic differences amo ng individuals may have led to lower than expected toxicity, adaptation, an d even growth stimulation, Responses of single species tested in isolation may be inadequate to predict toxicant impact, (C) 2001 Academic Press.