**2. Problems and risks of heavy metals on environment**

#### **2.1 Heavy metals pollution sources**

Firstly, pollution of environment is a huge problem in the world because of increasing of industrial activities resulting the toxic compounds which lead to contamination of soils and clean water [12]. Toxic heavy metals pollution is a wide distribution throughout world countries along with progress of different industries which chromium, copper, nickel cadmium and mercury were observed as the most common heavy metals that widespread and used causing environmental pollution [13]. Increased industrial activity and demand for heavy metals like arsenic, nickel, chrome, copper, lead, mercury, manganese, zinc cadmium and many more has recorded increasing in amounts of heavy metals at polluted wastewater [14]. Additionally, metallurgical and mining industries are generated high amounts of heavy metals in wastewaters and accumulate in soil and water. [15]. Also, agricultural activities using pesticides, fertilizers and crop preservatives which participate in releasing of heavy metals in to the environment [16].

#### **2.2 Heavy metals effects on living organisms**

Heavy metals are any inorganic metallic compound that can exert their toxicity via binding to the thiol group of the enzyme and the disulfide bond that contribute the stability of the enzyme. The metals have high affinity to the disulfide bridge between two cysteine residues in any protein compound. Heavy metals are very dangerous to living organisms especially human as certain of them cause DNA damage and their carcinogenic effects in animals and man are probably causally related to their abilities to cause mutation [17]. Also, heavy metals divided into nonessential metals (lead, cadmium, mercury and nickel) and essential metals (zinc, copper, iron and manganese). Because of their high toxicity, lead and cadmium represented the major heavy metals pollutants. Cadmium is released to ecosystem during electroplating, effluents from textile, mine tailing, tannery, leather, and galvanizing industries (cadmium batteries) [18]. Due to their high prevalence as contaminants, heavy metals have an excellent concern to environmental problems in soluble type that area unit terribly venomous to biological systems causing cancer [19]. Also, heavy metal compounds in soluble forms might be harmful for living organisms of ecosystem by entering of the food chain [16].

**87**

ing of heavy metal [14].

*Trends in Heavy Metals Tolerance and Uptake by Pseudomonas aeruginosa*

because it accumulates and increase its content in food chains [22].

tration and its resistance and tolerance mechanisms [28].

**3. Bioremediation of heavy metals by microorganisms**

In 2015, ATSDR prepared the priority list of hazardous substances and the results recorded that cadmium and lead were in the seventh position and second position, respectively. Also, The International Agency for Research on Cancer classified cadmium and cadmium compounds as a group (1) carcinogen and lead compounds as group (2) carcinogens [20]. Additionally, cadmium cause renal dysfunction especially in the proximal tubular cells which considered as the main site accumulation of cadmium. Also, cadmium cause demineralization of bone either indirectly, as a result of renal dysfunction or directly by the bones damaging. Furthermore, nickel has carcinogenic, neurotoxic, hemato-toxic, reproductive toxic, immune-toxic, genotoxic, nephrotoxic, pulmonary toxic and hepatotoxic effects [21]. On the other hand, mercury cause risks effects as neurotoxic substance

Subsequently, if plants exposure to excess copper concentrations, it generates oxidative stress causing damage to macromolecules and metabolic pathways disturbance. Also, excessive manganese accumulates in leaves and causing photosynthetic rate reduction [23]. Plants can uptake high concentration of heavy metals that present in causing adversely effect of symbiosis, the growth and consequently

In addition, chromium (hexavalent form) is the most toxic chromium species which used in some industries as leather processing. Chromium is a carcinogenic substance especially in case of the lung and enter through inhalation. Chromium toxicity comes from its potentiality to cause allergic reactions and be corrosive [25]. Furthermore, heavy metals effect on microorganisms and induced physiological and morphological changes in microbial populations [26]. When microorganisms exposed to heavy metal stress, they produce antioxidant enzymes under toxic conditions and tolerance of this stress such as some resistant bacterial strains [27]. In naturally, microbes response to toxicity of heavy metals depends on high concen-

Bioremediation meaning use of microbial metabolism to remove of pollutants. It can occur on its own and this called intrinsic bioremediation or can be done by addition of fertilizers to stimulate of microbial bioavailability inside medium and this called bio stimulation. Also, in some cases the addition of other microbial strains into medium to enhance the resident microbial population's and increase their ability to remove of heavy metals. Microorganisms that used to perform this function of bioremediation known as bio-remediators [29]. These microorganisms have developed unique resistance mechanisms which allowing to survive and remove high concentrations of heavy metals from environments [30]. Subsequently, bioremediation considered as alternative to chemical techniques by using microorganisms for biodegrading and detoxify of heavy metals from polluted soils and wasted groundwater [31].

In addition, biosorption defined as the use of biomass to remove heavy metals from environment by using microorganisms as (bacterial strains, fungal strains and algae) or plant extracts. It represents as a low-cost method and environmentally friendly for bioremediation of heavy metals and management of resource [32]. The need for an efficient and inexpensive method has interested in case of bio-sorption and bio-accumulation processes using microorganisms as profit systems for remov-

Fungal and bacterial strains have been reported to remove high concentrations of heavy metals from polluted environment using biosorption and bioaccumulation techniques [33]. Bioaccumulation is a process which involves two aspects; active

*DOI: http://dx.doi.org/10.5772/intechopen.85875*

effects on the crops yields [24].

#### *Trends in Heavy Metals Tolerance and Uptake by Pseudomonas aeruginosa DOI: http://dx.doi.org/10.5772/intechopen.85875*

*Pseudomonas aeruginosa - An Armory Within*

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].

in releasing of heavy metals in to the environment [16].

**2.2 Heavy metals effects on living organisms**

**2.1 Heavy metals pollution sources**

**2. Problems and risks of heavy metals on environment**

Firstly, pollution of environment is a huge problem in the world because of increasing of industrial activities resulting the toxic compounds which lead to contamination of soils and clean water [12]. Toxic heavy metals pollution is a wide distribution throughout world countries along with progress of different industries which chromium, copper, nickel cadmium and mercury were observed as the most common heavy metals that widespread and used causing environmental pollution [13]. Increased industrial activity and demand for heavy metals like arsenic, nickel, chrome, copper, lead, mercury, manganese, zinc cadmium and many more has recorded increasing in amounts of heavy metals at polluted wastewater [14]. Additionally, metallurgical and mining industries are generated high amounts of heavy metals in wastewaters and accumulate in soil and water. [15]. Also, agricultural activities using pesticides, fertilizers and crop preservatives which participate

Heavy metals are any inorganic metallic compound that can exert their toxicity via binding to the thiol group of the enzyme and the disulfide bond that contribute the stability of the enzyme. The metals have high affinity to the disulfide bridge between two cysteine residues in any protein compound. Heavy metals are very dangerous to living organisms especially human as certain of them cause DNA damage and their carcinogenic effects in animals and man are probably causally related to their abilities to cause mutation [17]. Also, heavy metals divided into nonessential metals (lead, cadmium, mercury and nickel) and essential metals (zinc, copper, iron and manganese). Because of their high toxicity, lead and cadmium represented the major heavy metals pollutants. Cadmium is released to ecosystem during electroplating, effluents from textile, mine tailing, tannery, leather, and galvanizing industries (cadmium batteries) [18]. Due to their high prevalence as contaminants, heavy metals have an excellent concern to environmental problems in soluble type that area unit terribly venomous to biological systems causing cancer [19]. Also, heavy metal compounds in soluble forms might be harmful for living organisms of ecosystem by entering of the food chain [16].

**86**

In 2015, ATSDR prepared the priority list of hazardous substances and the results recorded that cadmium and lead were in the seventh position and second position, respectively. Also, The International Agency for Research on Cancer classified cadmium and cadmium compounds as a group (1) carcinogen and lead compounds as group (2) carcinogens [20]. Additionally, cadmium cause renal dysfunction especially in the proximal tubular cells which considered as the main site accumulation of cadmium. Also, cadmium cause demineralization of bone either indirectly, as a result of renal dysfunction or directly by the bones damaging. Furthermore, nickel has carcinogenic, neurotoxic, hemato-toxic, reproductive toxic, immune-toxic, genotoxic, nephrotoxic, pulmonary toxic and hepatotoxic effects [21]. On the other hand, mercury cause risks effects as neurotoxic substance because it accumulates and increase its content in food chains [22].

Subsequently, if plants exposure to excess copper concentrations, it generates oxidative stress causing damage to macromolecules and metabolic pathways disturbance. Also, excessive manganese accumulates in leaves and causing photosynthetic rate reduction [23]. Plants can uptake high concentration of heavy metals that present in causing adversely effect of symbiosis, the growth and consequently effects on the crops yields [24].

In addition, chromium (hexavalent form) is the most toxic chromium species which used in some industries as leather processing. Chromium is a carcinogenic substance especially in case of the lung and enter through inhalation. Chromium toxicity comes from its potentiality to cause allergic reactions and be corrosive [25].

Furthermore, heavy metals effect on microorganisms and induced physiological and morphological changes in microbial populations [26]. When microorganisms exposed to heavy metal stress, they produce antioxidant enzymes under toxic conditions and tolerance of this stress such as some resistant bacterial strains [27]. In naturally, microbes response to toxicity of heavy metals depends on high concentration and its resistance and tolerance mechanisms [28].

## **3. Bioremediation of heavy metals by microorganisms**

Bioremediation meaning use of microbial metabolism to remove of pollutants. It can occur on its own and this called intrinsic bioremediation or can be done by addition of fertilizers to stimulate of microbial bioavailability inside medium and this called bio stimulation. Also, in some cases the addition of other microbial strains into medium to enhance the resident microbial population's and increase their ability to remove of heavy metals. Microorganisms that used to perform this function of bioremediation known as bio-remediators [29]. These microorganisms have developed unique resistance mechanisms which allowing to survive and remove high concentrations of heavy metals from environments [30]. Subsequently, bioremediation considered as alternative to chemical techniques by using microorganisms for biodegrading and detoxify of heavy metals from polluted soils and wasted groundwater [31].

In addition, biosorption defined as the use of biomass to remove heavy metals from environment by using microorganisms as (bacterial strains, fungal strains and algae) or plant extracts. It represents as a low-cost method and environmentally friendly for bioremediation of heavy metals and management of resource [32]. The need for an efficient and inexpensive method has interested in case of bio-sorption and bio-accumulation processes using microorganisms as profit systems for removing of heavy metal [14].

Fungal and bacterial strains have been reported to remove high concentrations of heavy metals from polluted environment using biosorption and bioaccumulation techniques [33]. Bioaccumulation is a process which involves two aspects; active

metal uptake and passive metal uptake and may be carried out by any living organism with the ability to withstand the toxic effects of a particular metal ion [34]. Additionally, utilization of potential microbial populations in biosorption process to transform or adsorb heavy metals either by live and dead biomass or by their products have produced to for detoxify of heavy metals forms whether in particulates or as soluble form. Negative charged of microbial cell surface as a result of the presence of different functional groups such as hydroxyl, amines, carboxylic and phenolics give microorganisms an ability for binding with different cationic heavy metals [35].

As above, microbial strains have different mechanisms for reducing the toxicity of heavy metals through its intracellular and extracellular precipitation, binding of elements to cell wall, adsorption on polysaccharides or by export via various transporters [36]. Also, in wide variety of bacterial strains especially in genus "*Pseudomonas"* resistance to heavy metals, disinfectants, antibiotics, detergents and different toxic substances were observed. *Pseudomonas* considered as one of the most indicators bacterial strains for measuring contamination in environment [37, 38].
