Effect of starvation length upon microbial activity in a biomass recycle reactor

The kinetics of substrate degradation and bacterial growth was determined in a microbial community from a biomass recycle reactor that had been deprived of substrate feed for 0–32 days. Starvation caused changes in bacterial numbers, community composition, and physiological state. Substrate starvation for less than 1 day resulted in modest (less than threefold) changes in endogenous respiration rate, ATP content, and biomass level. During a starvation period of 32 days, there were substantial changes in microbial community composition, as assessed by denaturing gradient gel electrophoresis (DGGE) fingerprinting of PCR amplicons of a portion of the 16S rDNA or by phospholipid fatty acid (PLFA) analysis. When the starved communities were stimulated with organic nutrients, the growth kinetics was a function of the length of the starvation period. For starvation periods of 2–8 days prior to nutrient addition, there was a phase of suboptimal exponential growth (S-phase) in which the exponential growth rate was about 30% of the ultimate unrestricted growth rate. S-phase lasted for 2–8 h and then unrestricted growth occurred at rates of 0.3–0.4 h⁻¹. At starvation times of 12 and 20 days, a lag phase preceded S-phase and the unrestricted growth phase.