Effect of Nickel on Growth of some Actinomycetes Isolated from Three Caves in Saudi Arabia

Abstract

Soil contamination with heavy metals become severe problems and cause several disorders in humans like anaemia, cancer, kidney failure, and Alzheimer’s. Using microorganisms to eliminate contamination of the environment is an efficient process. The aim of this study was to isolate actinomycetes with abilities to remove the harmful heavy metals. Different samples were collected from Mossy, Hotel and Reda caves which were located approximately 200 km of Riyadh region for actinomycetes isolation on starch nitrate agar medium. All isolates were screened for heavy metal resistance by adding different concentrations of nickel (II) chloride (10- 200 mg/l) to the medium to determine the minimum inhibitory concentration (MIC). MICs of a mixture of nickel and copper were determined for each strain. The most resistant actinomycetes was isolate NM20 at 200 mg/l which were morphologically and physiologically characterized. Phylogenetic analysis by sequencing the 16S rRNA genes for the selected strains was performed. The isolate NM20 was identified as Streptomyces sp. NM20. The effect nickel concentration on growth of the isolate NM20 was determined by the dry weights which were reduced by increasing the tested metal concentration. The factors affecting the growth and nickel removal process such as temperature, pH, and addition of yeast extract and incubation time were studied and removal percentage of nickel was calculated after measuring the remaining concentration using inductively couple plasma (ICPE-9000). The high removal of nickel was at 25°C, pH 9, and 0.3 g/l of yeast extract and at 7 days of incubation period.