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Green & Sustainable Science & Technology
Dyes are frequently applied to many substrates in edibles, cosmetics, paper, rubber, and products of textile industries. Microbial-based bioremediation of dyes effluent from wastewater is the most economical and reliable globally. Azo dyes are a valuable family of dyes with the most significant colour diversity. Microorganisms degrade azo dyes in anaerobic conditions with the assistance of azoreductase, resulting in colourless aromatic amines as a by-product. Broadly, dye-degrading microbes could be classified as actinomycetes, bacteria, fungi, and algae. Moreover, based on the nature of microbes and the pathway followed for degradation it could be again aerobic and anaerobic degraders.
- bioremediation
- bacteria
- fungi
- microalgae
1. Bioremediation of Dyes by Actinomycetes
Actinomycetes are fungi-like, filamentous bacteria with high GC content generally present in the soil. Extracellular peroxidases produced by actinomycetes, especially Streptomyces species, are known to play a role in lignin biodegradation [31]. The initial oxidation of lignin is carried out by the peroxidase released by the Streptomyces, into different water-soluble polymeric compounds. It has also been observed that the actinomycetes catalyse hydroxylation, oxidation, and dealkylation reactions in the presence of xenobiotics [32]. Three groups initially looked into the potential of actinomycetes to decolorize and mineralize textile dyes. Ball et al., tested 20 actinomycetes strains from various genera for their potential to bleach polymeric dye Poly R in 1989. Streptomyces badius 252, Thermomonospora fusca MT800, and Streptomyces sp. strain EC22 were the only three strains that greatly decolorized dye [6].
Following that, it embarked on a more extensive screening procedure that looked at the decolorizing ability of 159 actinomycetes. Investigators who utilized real textile effluents in the screening process were excited about this research. Five different effluents were used, each having a single dye of known concentration. Structurally each dye was different from azo compound RR147 to phthalocyanine Reactive Blue 116. Positive findings were obtained for 83 isolates, demonstrating the extensive potential of actinomycetes to cause dye decolourization. Given compounds’ resistance to mineralization by other bacteria under similar conditions, a discovery that actinomycetes can aerobically decolourize and degrade azo dyes was important.
Finally, but perhaps most importantly, a team led by Don Crawford at the University of Idaho began investigating the potential of lignin lytic microbes, including white-rot fungi and Streptomyces, to mineralize and decolourize textile dyes. Initially, the ability of 14 Streptomyces to decolourize two polymeric dyes, Poly B-411 and Poly R-478, as well as azo dye Remazol Brilliant Blue R, was investigated (RBBR). With two dyes, RBBR and Poly B-411, nearly similar findings were reported, indicating a close link between the isolate’s ability to decolourize dyes and its ligninolytic ability. This investigation and the fact that extracellular H2O2 synthesis increased when actinomycetes sps, were allowed to grow in the presence of glucose indicated that peroxidases were involved in the decolourization process. Extracellular peroxidases were previously discovered in Streptomyces bacteria, and enzymes were exhibited to have substrate specificities identical to P. chrysosporium’s Mn (II)-peroxidase [33]. Surprisingly, there was no association between decolorizing activity and ligninolytic activity with the 3rd pigment, Poly R-478 [34]. Enzymatic processes that take place during the decolourization of this dye are unknown. [8]. Recently Blanquez et al., 2019 reported 6–70% removal of AO-63 by using Stp. Ipomoeae CECT 3341, from the textile dyes [35]. Actinomycetes-based removal of various dyes is shown in Table 1, where the removal percentage of dyes varies from 3–100%.
Table 1. Degradation of dyes by using actinomycetes.
| Actinomycetes | Dyes Used | Efficiency | References |
|---|---|---|---|
| Streptomyces sp. S27 | MR | 99% | [36] |
| Streptomyces bacillaris | Triphenylmethane dyes: MG, MV, CV, and CB |
MG (94.7%), MV (91.8%), CV (86.6%), CB (68.4%) |
[37] |
| Streptomyces ipomoeae CECT 3341 |
AO63 | 6–70% | [38] |
| Streptomyces sviceus (marine) | CR-21 | [39] | |
| Streptomyces sps | RR 147 (azo) RR 171 RB 114 RB 209 RB 116 |
3–100% | [40] |
| Streptomyces sps | MG, MV, CV CB |
(MG 95%, MV 92%, CV 87%, CB 68%). |
[41] |
2. Bioremediation of Dyes by Aerobic Bacteria
It is very difficult to isolate bacteria that could aerobically decolorize and mineralize dyes, except for actinomycetes. Various studies claim that different azo dyes can be converted aerobically, out of which one study reveals the development of the green color of instant chocolate puddings. including one notable study on the greening of instant chocolate puddings. It has been found that these preadapted aerobic bacteria obtain their energy by utilizing some carboxylated analogues of sulfonated azo compounds as their sole carbon and energy supply [9].
Orange-I azo-reductase [NAD(P)H:1-(4′-sulfophenylazo)-4-naphthol oxidoreductase] and Orange II azo-reductase [NAD(P)H:1-(4′-sulfophenylazo)-2-naphthol oxidoreductase] is distilled and characterized from Pseudomonas. Both of these enzymes are now categorized as the same enzyme, which is called azo-benzene reductase (EC 1.6.6.7). Aside from azo dyes, bacteria’s ability to aerobically metabolize other dye groups has piqued interest, but with little success. Aerobic mineralization of triphenylmethane pigment, MV, by a strain of Pseudomonas mendocina MCM B-402 was recently discovered. Isolate’s sole carbon and energy source was MV, which has several industrial uses in addition to its well-known utilization as a regular bacteriological and histological stain. According to preliminary research, Ps. mendocina degraded dye to phenol by a variety of unspecified metabolites, which then joined the ketoadipic acid pathway [10].
Karim et al., 2018 and Mustafa et al., 2022 reported the decolourization of reactive dyes of textiles by using monoculture and consortium.
John et al., 2020 reported the utilization of a halophilic bacterium (Salinivibrio kushneri HTSP) for the biological decolourization of synthetic dyes (CBB G-250 and Congo red and safranin). Originally this strain was isolated from the saltpan for decolourization and bioremediation of dyes. The investigators obtained about 80% decolorization within 48 h. The further investigator reported that the rate of decolorization by using a particular bacterial strain was in the order of CR > CBBG-25 > Safranin [42].
Aktar et al., 2020 isolated Bacillus sp. and Staphylococcus aureus from the textile dye effluent and applied them for the decolorization and degradation of BY HP-2R, BR-RS, and BR RS 01 (BB) dyes. The removal efficiency of BR and BB reached up to 71% and 83% with Bacillus sps. While with Staph. aureus efficiency of BY dye reached 79% after five days [43].
Shete et al., 2020 isolated Bacillus sps, Klebsiella, and Pseudomonas sps, from textile effluent and applied them for the decolorization of JR, JF, and JGY dyes. The removal or decolorization of dyes was achieved from 45–50% for the following dyes under optimized conditions [44]. Khaled et al., 2022, applied Bacillus cereus (B. Cereus) and Pseudomonas parafulva (Ps. parafulva) for the decolorization of textile azo dyes (T-blue, yellow GR, and orange 3R,) and obtained the removal efficiency of up to 91.69 and 89.21% for orange 3R [45]. Table 2 shows summarized studies of bacterial-based dye removal from the wastewater. From all the studies it was found that in some of the studies bacteria was used directly, while in some cases their dry powder was used while in a few cases a bacterial consortium was also used. In some of the studies, the dye removal was achieved up to 100% either with monoculture or with the consortium. Some of the bacterial consortiums reached up to 97–99% dye removal within a short period of time.
Table 2. Microbial remediation of dyes by using aerobic and aerobic bacteria.
| Bacteria | Dyes Used | Efficiency | References |
|---|---|---|---|
| Aeromonas hydrophila A. Hydrophila SK16 |
RR141 MG Acid fast yellow MR |
70–80% 96.8% 91.25% |
[18,46,47] |
| Comamonas sps UVS | DB GL, DB5B | [48] | |
| Bacillus sp. and Staph. aureus |
BY HP-2R, BS-RS, and B. blue RS 01 (BB) | 71–83% | [43] |
| Alcaligenes faecalis AZ26, Bacillus cereus AZ27 and Bacillus sp. |
NSB-G | 90% | [49] |
| Brevibacillus laterosporus | DB-MR, MO, Blue-2B, Golden yellow (GY) Brilliant blue |
100% | [50] |
| Shewanella oneidensis (MFC) | Acid orange (AO 7) | 80.4 | [51] |
| Alcaligenes faecalis and Rhodococcus erythropolis | Monoazo dye Acid orange | 80–95 | [52] |
| Consortium of Ps. aeruginosa, B. pumilis, B. thuringiensis, Enterococcus faecium in different combinations |
NR, N Black, N Blue dk, N Navy, N Yellow |
82–97% | [53] |
| Neisseria sp., Vibrio sp., Bacillus sp., Bacillus sp. and Aeromonas sps | N Orange FN-R, N Brilliant Blue FN-R, N Super Black G, BY S8-G, and BR S2-B | 60–90% | [54] |
| Acinetobacter (ST16.16/164 and Klebsiella (ST16.16/034) | Monoazo dye RO 16 and diazo dye RG-19 | More than 80% | [55] |
| Salinivibrio kushneri HTSP | CBB G-250 and CR and safranin | More than 80% | [42] |
| Pseudomonas sp. (S3, S11 and S12), Klebisiella sp. (S4). and Aeromonas sp. (S2) | JR, JB and JGY | 45–50% | [44] |
| Bacillus odyssey SUK3, Morganella morganii SUK5 and Proteus sps SUK 7 | Red HE3B, Reactive Blue 59 | 97–99% | [56] |
| B. circulans NPP1 | MR and other dyes | 98% | [57] |
| Ps. desmolyticum NCIM 2112 | DB 6, Red HEB7, and Green HE4B | 70, 90% | [58] |
| Acinetobacter calcoaceticus | MR, MO | 90–98% | [59] |
| Enterobacter sp. CV–S1 | CV | [60] | |
| B. subtilis (E1), Exiguobacterium acetylicum (D1), Klebsiella terrigena (R2), S. aureus (A22), Ps. pseudoalcaligenes (A17), and Ps. plecoglossicida (A14) |
Whale, mediblue, fawn and mixed dye, |
97.04%, 80.61%, 94.93% and 81.64% | [61] |
| Sulfate-reducing bacteria (SRB) | Orange II | 95% | [62] |
| Sterigmatomyces halophilus SSA1 575 | RB-5, RB-5 | 100% | [63] |
| Anoxybacillus ayderensis SK3-4 | DG 6 | 100% | [64] |
| A. hydrophila SK 16 | AFY MR | More than 70 | [46] |
| Serratia liquifaciens | Azure B | 90% | [65] |
| Bacillus cereus SKB12 | RB-5 | 88.7% | [66] |
| B. cereus and Ps. parafulva |
Azo dyes: T-blue, yellow GR, and orange 3R | 91.69 and 89.21% | [45] |
| B. circulans BWLI 061 | MO | 99.22% | [67] |
| Bacterial consortium-Bacillus flexus TS8 (BF), Proteus mirabilis PMS (PM), and Ps. aeruginosa NCH (PA) |
Indanthrene Blue RS | 99% | [68] |
| Bacillus pseudomycoides | MG | 96.8% | [19] |
| Citrobacter sp. | CR | 93% | [69] |
| Bacillus subtilis HAU-KK01 | CR | 92.8% | [70] |
| Thiosphaera pantotropha | RY | 100% | [71] |
| Staphylococcus sp. K2204 | RBB | 100% | [72] |
| Staphylococcus sp. | Reactive blue | 97% | [73] |
3. Mechanism of Bioremediation
The use of biological processes to reduce emissions from atmospheric, aquatic, or terrestrial systems is known as bioremediation. Microorganisms and plants are most often used as biological structures for this purpose. Microorganism-mediated biodegradation is one of the most common bioremediation methods. Microbes may simplify many complex substances to meet their development and energy requirements. Air may or may not be needed for these biodegradation processes. In certain circumstances, the same metabolic pathways that cells utilize for growth and supply of energy are often utilized to simplify the components of pollutants. Microorganisms do not benefit directly in these situations, known as metabolism, but investigators have taken the benefit of this effect and used it for bioremediation. Mineralization, or complete oxidation, results in the production of water and either CO2 or CH4. Incomplete biodegradation can result in the cleaving of the product which is less toxic than the initial pollutant. As a result, bioremediation overcomes the drawbacks of traditional methods by causing physical degradation of specific organic chemicals at a lower rate. As a result, bioremediation has evolved from a nearly unknown technique to one that has been used to clean up a wide variety of toxins over the past two decades [74].
This entry is adapted from the peer-reviewed paper 10.3390/w14193163
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