MOLECULAR-WEIGHT DISTRIBUTION OF HYDROLYSIS PRODUCTS DURING BIODEGRADATION OF MODEL MACROMOLECULES IN SUSPENDED AND BIOFILM CULTURES .1. BOVINE SERUM-ALBUMIN

Macromolecules can comprise a significant portion of dissolved organic carbon in wastewater and affect wastewater treatability by engineered systems, but little information is available about mechanisms of macr omolecule degradation. The release of protein hydrolytic fragments was monitored during the degradation of the model protein bovine serum al bumin (BSA) in batch and continuous suspended cultures and in fixed-fi lm reactor systems. Three different inocula that represent a range of bacterial diversity were used: a protein degrading isolate, a commerci al biological oxygen demand (BOD) test inoculum (limited diversity cul ture) and a wastewater inoculum. Molecular size distributions were mon itored during degradation using membrane ultrafiltration techniques. I ntermediate-molecular-weight protein hydrolytic fragments (2000-10,000 amu) were produced and released into solution by all cultures in all reactor types investigated. In batch suspended culture reactors with i nitial BSA concentrations of 100 mg liter(-1), maximum concentrations of intermediate-molecular-weight hydrolytic fragments of 25, 10 and 6 mg liter(-1) were found, respectively, in pure, limited diversity and wastewater cultures. Since material in the 2000-10,000 amu fraction de creased as culture diversity increased, it was concluded that the invo lvement of many microbial species during protein degradation limits th e accumulation of hydrolytic fragments under conditions typical of was tewater treatment systems. These results lead to the proposal of a pro tein degradation mechanism that features cell-bound hydrolysis of prot ein and the subsequent release of hydrolytic fragments back into bulk solution. Hydrolysis and release is repeated by the same or different cells until fragments are small enough(< 1000 amu) to be directly assi milated by cells. Because the concentration of protein hydrolysis frag ments released in high-diversity wastewater inoculated reactors was lo w and they were rapidly degraded, the release of hydrolysis fragments should have little impact on overall macromolecule degradation kinetic s in domestic wastewater treatment systems. (C) 1997 Elsevier Science Ltd.