LOCATION OF PROTEIN AND POLYSACCHARIDE HYDROLYTIC ACTIVITY IN SUSPENDED AND BIOFILM WASTE-WATER CULTURES

Macromolecular compounds such as proteins and polysaccharides can comp rise a significant portion of dissolved organic carbon in wastewater, but limited information is available on how these compounds are degrad ed in biological wastewater treatment systems. Bacteria cannot assimil ate intact macromolecules but must first hydrolyze them to monomers or small oligomers. Whether this hydrolysis occurs in contact with cells or by enzymes released into bulk solution is critical to an understan ding of macromolecule metabolism. This study used the fluorescent mode l substrate analogs L-leucine-7-amido-4-methylcoumarin . HCl (Leu-MCA) and 4-methylumbelliferyl-alpha-glucoside (MUF-alpha-glc) to determine the location of leucine aminopeptidase and alpha-glucosidase activity in wastewater inoculated biofilm and suspended cultures and in trickl ing filter effluent. In biofilm cultures, no more than 3% of total hyd rolytic activity was located in the cell-free bulk solution. Similar r esults were obtained in suspended culture where 97% of leucine aminope ptidase and 93% of alpha-glucosidase activity occurred in contact with cells. In trickling filter effluent, hydrolysis was also predominantl y cell-associated. Hydrolysis rates were at least five times higher in contact with cells and sloughed biofilm pieces than in cell-free solu tion. When considered with the results of other experiments demonstrat ing that hydrolytic fragments of proteins and polysaccharides accumula te in bulk solution during macromolecule degradation, these experiment s support a generalized mechanism for macromolecule degradation that f eatures cell-associated hydrolysis followed by the release of hydrolyt ic fragments back into bulk solution. This cell-associated hydrolysis and release is repeated until hydrolytic fragments are small enough to be assimilated by cells. Use of this macromolecule degradation mechan ism can help refine wastewater treatment models so that they can more accurately predict the performance of bioreactors treating complex was tewaters. (C) 1998 Elsevier Science Ltd. All rights reserved.