Parallel processing of substrate correlates with greater functional stability in methanogenic bioreactor communities perturbed by glucose

Parallel processing is more stable than serial processing in many areas tha t employ interconnected activities. This hypothesis was tested for microbia l community function using two quadruplicate sets of methanogenic communiti es, each set having substantially different populations. The ho communities were maintained at a mean cell residence time of 16 days and a mean glucos e loading rate of 0.34 g/liter-day in variable-volume reactors. To test sta bility to perturbation, they were subjected to an instantaneous glucose pul se that resulted in a 6.8-g/liter reactor concentration. The pattern of acc umulated products in response to the perturbation was analyzed for various measures of functional stability, including resistance, resilience, and rea ctivity for each product. A new stability parameter, "moment of amplificati on envelope," was used to compare the soluble compound stability. These par ameters indicated that the communities with predominantly parallel substrat e processing were functionally more stable in response to the perturbation than the communities with predominantly serial substrate processing. The da ta also indicated that there was good replication of function under perturb ed conditions; the degrees of replication were 0.79 and 0.83 for the two te st communities.