THE RELATIONSHIP BETWEEN ELECTRON-TRANSPORT ACTIVITY AS MEASURED BY CTC REDUCTION AND CO2 PRODUCTION IN MIXED MICROBIAL COMMUNITIES

CTC (5-cyano-2,3-ditolyl tetrazolium chloride) is a redox indicator th at facilitates the detection of microbial electron transport activity due to the fluorescence and water insolubility of the reduced CTC-form azan (CTF). The goal of this work was to establish the relationship be tween the CTC response (both the numbers of CTF-containing cells and t he fluorescence intensity of CTF per cell) and respiration in mixed mi crobial communities. To obtain CTF-containing cell numbers over a rang e of respiration rates, aerobic bioreactors with on-line CO2 monitorin g were batch fed ground wheal at slow, intermediate, and fast retentio n limes. Samples were taken before and after feeding, and throughout s tarvation cycles. Each sample was treated with 25 mM CTC, and either s upplemented with 10% R2A, or left unsupplemented. CTF-containing cell numbers showed a weak and inconsistent response to transient pulses in respiration, and decreased during long-term starvation at all three r etention times. The degree of starvation within the microbial communit y could be estimated using the ratio of supplemented to unsupplemented CTF-containing cell population. Total fluorescence intensity per cell was consistently higher at peaks of CO2 production, but did not decre ase as dramatically as total cell numbers did in response to starvatio n. The results indicate the importance of concurrent examination of bo th the numbers and total fluorescence intensity of CTF-containing cell s.