Surprisingly high substrate specificities observed in complex biofilms

The behavior of microorganisms in natural ecosystems (e.g. biofilms) differs significantly from laboratory studies. In nature microorganisms experience alternating periods of surplus nutrients, nutrient-limitation, and starvation. Literature data suggests that to survive and compete successfully, microorganisms can regulate their metabolism expressing wide range of uptake and catabolic systems. However, ecophysiological studies of natural biofilms indicate that bacteria are very specialized in their choice of substrate, so even minor changes in substrate composition can affect the community composition by selection for different specialized species.
We hypothesized that bacteria growing in natural environment express strongly conserved substrate specificity which is independent on short-term (few hours) variations in growth conditions.
In this study, biofilm from Aalborg wastewater treatment plant was used to investigate the cell-specific in situ substrate uptake pattern of different bacteria. Different substrates were tested by combination of Microautoradiography and Fluorescence in situ Hybridization. Conditions applied (different substrate concentrations, starvation, induction with specific substrates, multiple substrates) mimicked the conditions encountered in the natural environment. All results were consistent with the hypothesis presented. Substrate uptake pattern expressed by probe-targeted bacterial groups did not change irrespectively to the conditions applied under in situ conditions.
We concluded that bacteria living in natural environment, represented here by wastewater treatment plant microbial community, are strongly specialized in the uptake of organic substrates; fluctuating conditions, often encountered in natural environment, do not influence the profile of substrate uptake of these specialized species but may change community composition by affecting growth rates of individual species.