title: Persistence of bacterial proteolytic enzymes in lake ecosystems.
abstract: This study analyzes proteolytic enzyme persistence and the role of dead (or metabolically inactive) aquatic bacteria in organic matter cycling. Samples from four lakes of different trophic status were used. Irrespective of the trophic status of the examined lakes, bacterial aminopeptidases remained active even 72 h after the death of the bacteria that produced them. The total pool of proteolytic enzymes in natural lake water samples was also stable. We found that the rates of amino acid enzymatic release from proteinaceous matter added to preserved lake water sample were constant for at least 96 h (r(2)  = 0.99, n = 17, P ≤ 0.0001, V(max)  = 84.6 nM h(-1) ). We also observed that proteases built into bacterial cell debris fragments remained active for a long time, even after the total destruction of cells. Moreover, during 24 h of incubation time, about 20% of these enzymatically active fragments adsorbed onto natural seston particles, becoming a part of the 'attached enzymes system' that is regarded as the 'hot-spot' of protein degradation in aquatic ecosystems.
authors.affiliation: Department of Microbial Ecology, Institute of Botany, University of Warsaw, Warsaw, Poland.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Kiersztyn
authors.forename: Waldemar
authors.initials: W
authors.lastname: Siuda
authors.forename: Ryszard J
authors.initials: RJ
authors.lastname: Chróst
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D001419:Bacteria / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D001426:Bacterial Proteins / Q000032:analysis / Q000378:metabolism*; D017753:Ecosystem; D060106:Lakes / Q000737:chemistry / Q000382:microbiology*; D007931:Leucyl Aminopeptidase / Q000032:analysis / Q000378:metabolism; D010447:Peptide Hydrolases / Q000032:analysis / Q000378:metabolism*; D059748:Proteolysis
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D010447:Peptide Hydrolases; D007931:Leucyl Aminopeptidase