**1. Introduction**

Heavy metals are wide distribution elements in environment have a high density, atomic weight and multiple applications in different fields [1]. Heavy metal pollution causes environmental problems to human, animal, plant and ecosystem [2]. This pollution resulted in accumulation of different heavy metals in to soil and water. Different heavy metals such as copper, cadmium, nickel, lead, chrome and mercury, etc. released into natural sources and recorded high accumulation then have toxic effects on human health and biological system [3].

To remove of this heavy metals, there are different biotechnological methods were done such as bio-mineralization, bio-sorption, phyto-stabilization, hyperaccumulation, bio-stimulation, rhizo-remediation, myco-remediation, cyanoremediation and geno-remediation [4].

In nature, microorganisms play a potential role for a recycling and degradation of accumulated heavy metals which decrease their toxicity. This microorganisms as fungi, bacteria and algae were recognized [5]. Also, bioremediation of heavy metals by microorganisms is an economic and effective strategy because of its high efficiency, low cost and eco-friendly nature. Additionally, microbial bioremediation is done by interaction of microbe-metal for accumulation and detoxification of heavy metals [6].

Subsequently, some of bacterial strains can remove heavy metals from polluted soils as *Pseudomonas* sp., *Arthrobacter* sp., *Alcaligenes* sp., *Corynebacterium* sp., *Bacillus* sp., *Flavobacterium* sp., *Mycobacterium* sp., *Azotobacter* sp., *Rhodococcus* sp. and *Methanogens* [7]. Bacterial strains have different mechanisms to adapt and remove of heavy metals from polluted environments [8]. Different mechanisms are responsible for adapted of bacterial strains to grow at high concentrations from heavy metal. Also, mechanisms include accumulation and uptake, sorption of metal, enzymatic reduction or oxidation and extracellular precipitation. Additionally, metal tolerance was done by molecular mechanisms by having resistant genes [9]. Heavy metals resistant bacterial strains able to grow under exposing to high concentrations and have potentiality in bioremediation of high content of heavy metals in soils [10]. Finally, *Pseudomonas aeruginosa* tolerated and removal the highest dose of heavy this metals as compared with different bacterial strains [11].
