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.
Actinomycetes; Heavy Metal; Resistant; Contamination; MIC; Streptomyces
Although heavy metals are naturally occurring elements that are found throughout the earth’s crust, most environmental contamination and human exposure result from anthropogenic activities such as mining and smelting operations, industrial production and use, and domestic and agricultural use of metals and metal-containing compounds [1,2]. Environmental contamination can also occur through metal corrosion, atmospheric deposition, soil erosion of metal ions and leaching of heavy metals, sediment re-suspension and metal evaporation from water resources to soil and ground water . It has been reported that natural phenomena such as weathering and volcanic eruptions also lead to heavy metal pollution [4-6].
It has been reported that metals such as cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se) and zinc (Zn) are essential nutrients that are required for various biochemical and physiological functions. Inadequate supply of these micro-nutrients results in a variety of deficiency diseases or syndromes . The presence of toxic metals in soil can severely inhibit the biodegradation of organic contaminants .
Ni is a trace element for bacteria, serving as an essential component of enzymes such as ureases, hydrogenases, CO dehydrogenases, and enzymes in the metabolism of strictly anaerobic bacteria .
Heavy metal contamination of soil may pose risks and hazards to humans and the ecosystem through direct ingestion or contact with contaminated soil, the food chain (soil-plant-human or soil-plant animal, human), drinking of contaminated ground water, reduction in food quality (safety and marketability) via phytotoxicity, reduction in land usability for agricultural production causing food insecurity, and land tenure problems [10,11].