Influence of zinc on bacterial populations and their proteolytic enzyme activities in freshwater environments: a cross-site comparison

Abstract

Temporal responses of indigenous bacterial populations and proteolytic enzyme (i.e., aminopeptidase) activities in the bacterioplankton assemblages from 3 separate freshwater environments were examined after exposure to various zinc (Zn) concentrations under controlled microcosm conditions. Zn concentrations (ranging from 0 to 10 μmol/L) were added to water samples collected from the Kalamazoo River, Rice Creek, and Huron River and examined for bacterial abundance and aminopeptidase activities at various time intervals over a 48 h incubation period in the dark. The results showed that the Zn concentrations did not significantly influence total bacterial counts directly; however, aminopeptidase activities varied significantly to increasing zinc treatments over time. Also, analysis of variance and linear regression analyses revealed significant positive relationships between bacterial numbers and their hydrolytic enzyme activities, suggesting that both probably co-vary with increasing Zn concentrations in aquatic systems. The results from this study serve as additional evidence of the ecological role of Zn as an extracellular peptidase cofactor on the dynamics of bacterial assemblages in aquatic environments.

Effects of iron and copper treatments on the bacterioplankton assemblages from surface waters along the north branch of the Kalamazoo River, Michigan, USA

“…The similarity in bacterial abundance to the different metal concentrations, but with significant changes over the study period, is further indicative of tolerance by the exposed bacterial populations within the assemblages to the metal treatments. These observation corroborates earlier similar studies that have also reported high metal tolerance over time by indigenous bacterial assemblages in aquatic environments . For instance, Kim et al reported that the addition of copper slightly stimulated bacterial growth in the microlayers as compared to subsurface water in their study.…”

“…Similarly Appenzeller et al reported an increase in total cells of Escherichia coli in the presence of iron under controlled conditions and attributed this change over time to iron utilization, which eventually promoted the growth and culturability of the cells. A previous study also designed to examine the effects of increasing Zn concentrations on bacterial assemblages from the Kalamazoo River reported similar tolerance to Zn exposure as currently observed in this study to both Fe and Cu treatments . These results are not at all surprising, given that bacterial adaptation to heavy metals can be expected, especially in metal contaminated environments .…”

“…This present study was designed to examine the effects of increasing concentrations of Fe and Cu on the indigenous bacterial populations within the bacterioplankton assemblages as well as on the hydrolytic enzyme activities of aminopeptidase in surface waters collected from the north branch of the Kalamazoo River in Michigan, USA. This serves as a followup to a previous study that examined the effects of Zn concentrations on the bacterioplankton assemblages within the same river among two other freshwater environments studied using similar approaches [22]. While the results from this past study revealed no significant direct influence by Zn concentrations on total bacterial abundance, significant increases in aminopeptidase activities were observed over time within the same bacterioplankton assemblages, directly indicating concurrent increase in metabolic activities.…”

“…Heterotrophic bacterial populations are known to produce wide-array of proteolytic enzymes in order to effectively hydrolyze and assimilate various high molecular weight organic materials in their immediate milieus [18]. Leucine aminopeptidase was targeted in this study because of its ecological importance relative to the high hydrolytic rate by bacterial assemblages, and hence predominant coverage in similar previous studies [19,20,22,23,25,[38][39][40][41]. The pronounced effects by both Fe and Cu to aminopeptidase activities in this study agree with other similar studies that have also documented high activities of the enzyme in polluted environments [19,42].…”

Pb and Zn contamination as rate-regulation agents on decomposition of two emergent macrophytes: a systemic approach

“…Considering that the number of heterotrophic bacteria, the presence of Zn up to 0.7 mg L -1 in freshwater environment presented positive relationships between bacterial numbers and their hydrolytic enzyme activities (Rasmussen & Olapade, 2016). An inhibitory effect on glucose mineralization rates as response by microbial activities in water samples was observed as increasing concentrations of Zn (Romero et al, 1999).…”