Groups of microorganisms

The use of living organisms, including microorganisms, algae, fungi, and higher plants, for the degradation or assimilation of xenobiotic composts, aiming to the environmental decontamination, is an approach known as bioremediation (Baneijee et al. 2018). Such organisms are capable of transforming pollutants and such transformation may be the degradation of organic molecules that hold toxic properties or complexation of composts that contain heavy metals. Among the organic molecules, the most common is perhaps the petroleum-related molecules, whereas heavy metals are also of high importance in terms of contamination. Tluee main groups of microorganisms are widely used in bioremediation: bacteria, fungi, and algae (Biswas et al. 2015).

Bacteria

The degradation of toxic substances by bacteria present in the soil depends on the presence of several metabolizing enzymes for their growth, thus being able to remedy the chemical compounds, and reduce the concentrations present in the environment, making such substances less toxic (Williams and Inweregbu 2019).

Table 5. A succinct list of species of bacteria and the correspondent contaminant focused to be metabolized.

Genera/species

Contaminants

Pseudomonas spp., specially: Pseudomonas aeruginosa and Pseudomonas fluorescens

The Pseudomonas spp. are mostly environmental saprotrophs. They usually degrade aliphatic and aromatic hydrocarbons. P. fluorescens can be used for bioremediation of crude oil contaminated soil; P. aeruginosa can be used to remove or detoxify the heavy metals in most contaminated sites (Williams and Inweregbu 2019).

Rhodococcus wratislaviensis

Egorova et al. (2017) found a good performance of this species of bacteria for remediating soils contaminated by organochlonne compounds (DDT). The obtained final concentrations were permissible according to legislation.

Sphingomonas paucimobilis

In general, most of the species of this genera are of special interest for degrading PAH (Polycyclic aromatic hydrocarbons) - contaminated soils. They are especially adapted to degrade PAHs with moderately high bioavailability, for example, phenanthrene (Zhou et al. 2016). The species S. paucimobilis was noticeably efficient for degrading the PAH naphthalene in waters when combined with surfactant products (San Miguel Amanz et al. 2009).

Escherichia coli

In environmental water samples using a temperature-controlled, Wang et al. (2019) found dual-functionality (biodetection and bioremediation) of copper ions by the cells of such species.

Bacteria with the ability to biodegrade petroleum hydrocarbons can be found in polluted areas or even in areas that have not had prior contact with hydrocarbons (Zhou et al. 2016, Egorova et al.

2017). However, it is easier to find them in already impacted environments because the pollutants provide assistance in the selection of strains with the ability to degrade these compounds. In Table 5, we find a brief list with some bacteria species with the correspondent product that such species usually degrades.

Algae

Due to the feature to be photosynthetic organisms, algae are the primary producers of biomass which have been the nutritional foundation of a large variety of live forms reliant on algae as the primary source of food. Such organisms also play a crucial role in foraging minerals and molecules from the (contaminated) environment, which will favor humans and the ecosystems, frequently removing them from the contaminants by means of degradation (Vidyashankar and Ravishankar 2016).

Although algae can be efficient in remediating contaminated soils by pesticides (Biwas et al. 2015), this group of organisms is famous for its ability to remediate contaminated soils with some kinds of heavy metals, such as titanium, lead, magnesium, zinc, cadmium, strontium, copper, mercury, nickel and cobalt (Ibuot et al. 2019). Algal systems, especially the cyanobacteria, are not only valuable in treating the waste, but also making a variety of suitable products from the biomass that are generated by such organisms (Vijayakumar and Manoharan 2012).

The culture of photosynthetic microorganisms, including algae, is an option in biological processes that have been shown that microorganisms that inhabit saline or hypersaline environments (halophilic) have a high ability of bioremediation, since they may be used as catalyst in various processes where extreme situations are of vital importance to efficiently repair a polluted environment. In the process of bioremediation of water, algae use their photosynthetic abilities, permitting them to convert sunlight energy into biomass, and then absorb nutrients such as nitrogen and phosphorus which are responsible for the process of eutrophication (Ramirez et al. 2017, Ibuot et al. 2019).

Microalgae, when consoxted with bacteria and fungi, also have the capability to remove metals such as iron, aluminum, manganese, magnesium, and zinc from wastewater (Ramirez et al. 2018). Mechanisms of absoiption and adsoiption are commonly used by algae species to eliminate nutrients, hearty metals (dependent on the species) and other mineralized products from wastewater (Bwapwa et al. 2017). When absorbed, a substance is soaked by the absorbent substance or organism and

Table 6. A succinct list of species of bacteria and the correspondent contaminant focused to be metabolized.

Genera/species

Contaminant

Chlorella vulgaris

By means of a microbial consortium of a bacteria species (Pseudomona putida) and C. vulgaris (a common single-cell microalgae (green colored) that endures a variety of heavy metals and metalloids), Awasthi et al. (2018) reported an improvement in the growth of such microorganisms and reduction of arsenic-induced oxidative stress in nee, as well as an improvement of the level of nutntious elements in rice.

Pinnularia obscura

In very acidic environments, they have the ability to constitute biofilms (i.e., biological communities with a high degree of organization, where bactena form structured, coordinated and functional communities). Such biofilms may be utilized to degrade diverse pollutants in the degraded environments, as well as in engineered systems.

Spirulina platensis

This species of algae uses the absorbency mechanism to remove chromium (Fernandez et al. 2018).

Westietlopsis protifica

It can be used both for in situ and off site works of remediation. This species was successfully employed in experiments that removed color and some nutrients from effluents (Yijayakumar and Manoharan 2012).

when a substance is adsorpted, the substance is only retained on the adsorbing surface, without being incorporated into the volume or body of the other (Caumette et al. 2015). Table 6 illustrates some examples of algae and their potentialities.

Fungi

Fungi represent a very important promising group of agents for biodegradation. As example, some species are depicted in Table 7. The capacity of fungi, both yeasts and molds, to transform a wide variety of dangerous chemical materials have attracted the researchers and engineers to use them in bioremediation (Kumar 2017, Vishnoi and Dixit 2019).

Fungi have the capability to mineralize xenobiotic composites to C02 and H20 by means of their non-specific ligninolytic and highly oxidative enzyme apparatus, which also influences the degradation and decolorization of a varied range of dyes (Biswas et al. 2015). Fungi show the capacity to absorb a substantial amount of metals in their cell wall, or also by extracellular polysaccharide slime (Das et al. 2009).

Table 7. A succinct list of species of bacteria and the correspondent contaminant focused to be metabolized.

Genera/species

Contaminant

Gloeophyllum trabeum

They are able to eliminate the pesticide DDT m contaminated soils and can be used directly for the degradation of DDT m soil without any other additional treatment (Pumomo et al. 2011). They are also able to excrete organic acids that may react with copper to render it soluble (Vishwakamia 2019).

Fomitopsis pinicola

They are able to eliminate the pesticide DDT m contaminated soils (Pumomo et al. 2011).

Daedalea dickinsii

They are able to eliminate the pesticide DDT m contaminated soils (Pumomo et al. 2011).

Candida viswanathii (yeast)

They have the capability to biodegrade petroleum hydrocarbons and diesel oil (Junior et al. 2009).

Armillaria mellea

They present the skills to accumulate heavy metals like mercury, lead, cadmium, and copper. Furthermore, as the concentration of mercury increases in the soil, A. mellea is shown to store higher concentrations of Hg:' (Kumar 2017).

 
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