Heavy metal tolerance of filamentous fungi from the sediments of Visayas State University wastewater pond

Abstract

The ability to tolerate high concentrations of heavy metals is one important characteristic of organisms that can be used for bioremediation. In this study, the heavy metal tolerance of filamentous fungi isolated from the VSU wastewater settlement pond was investigated. Specifically, the research was done to determine the Cd, Cu, Fe and Zn in the sediments of the pond, isolate and identify filamentous fungi from these sediments, identify the most tolerant isolate, and determine the minimum inhibitory concentration of heavy metals to the identified isolate. Isolation of filamentous fungi from a composite of eight sediment samples was done through serial dilution and plating using Potato Dextrose Agar (PDA). Isolates were then purified using Sabouraud Dextrose Agar (SDA). Colony and microscopic characteristics of the isolates were used to identify the isolates to genus level only. The tolerance of the isolates to Cd, Cu, Fe, and Zn were then compared through analysis of their tolerance index based on the colony extension radius. The Minimum Inhibitory Concentrations (MIC) of these heavy metals were obtained for the isolate with the highest tolerance index. The Cd, Cu, Fe, and Zn contents of the composite sediment sample were <0.0002mg kg-1, 0.0203mg kg-1, 7.419mg kg-1, and 0.106mg kg-1, respectively. Three filamentous fungi were successfully isolated from the sediments and were identified as Rhizopus sp., Mucor sp. and Trichoderma sp. Among these isolates, Rhizopus sp. was the most tolerant to all the heavy metals tested. Average range of MIC values of Cd, Cu, Fe and Zn to Rhizopus sp. were determined at 5mM<MIC≤6.5mM, 10mM<MIC≤15mM, 30mM≤MIC≤35mM, and 25mM<MIC≤30mM, respectively. These results showed that the Rhizopus sp. isolated is the most potential candidate in bioremediating heavy metal contaminated areas.