Abstract
Pollution of the environment by copper(II) exerts numerous adverse impacts on soils, microorganisms, plants, animals and humans. Assessing these impacts on microorganisms is essential as they are potential agents of bioremediation to purify the ecosystem. The aim of this study was to investigate the tolerance of Streptomyces species obtained from historically contaminated soils to copper (II) toxicity. Soil samples were collected from farms around sewage sludge dump sites (tests) and where there were no dumps (control). Standard microbiological methods were used to isolate, characterize and identify the three best copper tolerant species. Also, the impact on Streptomyces growth characteristics such as radial growth (R2), index of growth (GI) and percentage inhibition of radial growth (PIRG) by copper (II) was examined. Results obtained indicated that; the minimum inhibitory concentration of copper (II) for some of the Streptomyces isolates was 600 mg/l. However, three isolates; SW2B, SW7A and SW7B had MIC of 3000 mg/l and were selected for further investigations. Increasing metal concentration from 100 mg/l to 2000 mg/l reduced R2 from 40.2 to 4.0 and GI from 0.77 to 0.08, corresponding to 69.48 % increase in PIRG for SW2B. For isolate SW7A, R2 and GI decreased from 33.7 to 3.8 and from 0.67 to 0.08 respectively as copper (II) concentration increased from 100 mg/l to 2000 mg/l, giving 59.33 % increase in PIRG. The highest increase in PIRG (88.04 %) was obtained for SW7B, corresponding to a decrease of R2 and GI from 39.2 to 5.2 and 0.77 to 0.10 respectively. Molecular method was used to identify the isolates as Streptomyces chartreusis (SW2B), Streptomyces aureoverticillatus (SW7A) and Streptomyces subrutilus (SW7B).
Highlights
Heavy metal pollution poses significant threat to health as some heavy metals possess well documented toxic, mutagenic and carcinogenic properties [1,2,3]
Streptomyces are of major interest because of their documented capabilities to thrive in metal polluted environment by producing a wide range of exo-polymeric substances and metal ion chelators known as siderophores, which confer protection against adverse effects of heavy metals [11]. This primary aim of this study is to investigate the tolerance of Streptomyces species from heavy metal polluted sites to Cu(II) toxicity
Samples were randomly taken from seventeen (17) different sampling points at depth ranging from 0-10cm and taken to the Microbiology lab, University of Nigeria Nsukka immediately where they were air dried for four days and sieved with 2mm mesh sieve before carrying out microbiological analysis
Summary
Heavy metal pollution poses significant threat to health as some heavy metals possess well documented toxic, mutagenic and carcinogenic properties [1,2,3]. The European Environmental Agency [4] gave the annual estimate of heavy metals release from all sources worldwide to be around (in metric tons) 22,000 of cadmium (Cd); 939,000 of copper (Cu); 783,000 of lead (Pb); 1,350,000 of zinc (Zn); 7,000,000 and 19,300,000 metric tons ferro-chromium (FeCr) and chromites (Cr2FeO4) respectively. According to Oves et al [5], heavy metal pollutions are mainly results of Corresponding author: Ifunanya R. Akaniro Department of Microbiology, Faculty of Biological Sciences, University of Nigeria, Nsukka. Anthropogenic activities such as chemical wastes from industrial activities and agricultural effluents (such as fertilizer, herbicides and pesticide), combustion of fossil fuels and mining activities
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