Citrobacter freundii A1 isolated from a sewage treatment facility was demonstrated to be able to effectively decolorize azo dyes as pure and mixed culture. This study reports on the investigation on the enzymatic systems involved. An assay performed suggested the possible involvement of flavin reductase (Fre) as an azo reductase. A heterologouslyexpressed recombinant Fre from C. freundii A1 was used to investigate its involvement in the azo reduction process. Three model dyes were used, namely Acid Red 27 (AR27), Direct Blue 15 (DB15) and Reactive Black 5 (RB5). AR27 was found to be reduced the fastest by Fre, followed by RB5, and lastly DB15. Redox mediators nicotinamide adenine dinucleotide (NADH) and riboflavin enhance the reduction, suggesting the redox activity of the enzyme. The rate and extent of reduction of the model dyes correlate well with the reduction potentials ( E p ). The data presented here strongly suggest that Fre is one of the enzymes responsible for azo reduction in C. freundii A1, acting via an oxidation-reduction reaction.

/pdf/reduction-of-azo-dyes-by-flavin-reductase-from-citrobacter-4bs1uftroe.pdf

Reduction of azo dyes by flavin reductase from Citrobacter freundii A1

One important factor in microbial fuel cells (MFCs) study is the anode. In MFCs, the anode acts as the key component in the generation of bioelectricity and power. Despite the fact that there have been some improvements in the electrochemical performance of MFCs in recent years, their low power generation is still deemed a major drawback. The effects of surface modifications of the anode as biofilm carrier on the performance of MFCs were investigated. This research focused on the role of the novel fabricated anode as support material for the adhesion of bacterial consortium (NAR-2) consisted of Citrobacter sp. A1, Enterobacter sp. L17 and Enterococcus sp. C1 were used in MFCs reactor for the decolourisation of Acid Red 27 (AR27) and the simultaneous generation of electricity. The performance of a modified anode fabricated using surfactant-treated clinoptilolite (S-TC) with common type of carbonbased material, namely treated clinoptilolite-modified graphite felt (TC-MGF) anode was evaluated with different MFCs constructions. Prior to the MFCs experiments, the modification of anode was successfully verified using different spectroscopic and microscopic techniques such as EDX, FESEM, ATR-FTIR and BET analysis. In addition, screening of parameters for the adhesion of bacterial consortium NAR-2 onto TC-MGF anode (NAR-2-bioanode) was accomplished. The newly-developed TCMGF bioanode was implemented in the dual-chamber (H-type) of the MFC. The performance of TC-MGF bioanode was compared to the results obtained using nonmodified graphite felt (BGF) bioanode. Maximum power densities for BGF and TCMGF bioanodes were 458.8 ± 5.0 and 940.3 ± 4.2 mWm-2, respectively. In the following experimental, a small MFC reactor was fabricated with TC-MGF bioanode to compare the performance of the MFC with commonly used fuel cell membranes, Nafion (N-117 and N-115), which were examined along with the N-212 membrane in a single-chamber cubic di-air cathode (S-CCD-AC) design. The power density and columbic efficiency of N-115 membrane (1022.5 mWm-2 - 35.4%) were significantly higher than the values obtained for the N-117 (592 mWm-2 - 15.6%) and N-212 (493 mWm-2 - 12.3%) membranes. A novel MFC reactor with TC-MGF bioanode novel design (Conch shell) using the N-115 membrane having an air-cathode upflow (A-CU) MFC, as a combination of upflow and MFC technologies was used to compare the presence and absence of a membrane design. The A-CUMFC with membrane-less at flow rate 0.6 mL min-1, anode distance of 0.5 cm and a concentration of AR27 at 900 mg L-1, high decolourisation rate (98%) achieved in a 60-day operation, was 40% higher than that of the membrane-MFC. The average maximum power density obtained (1250 mWm-2) using the membrane-less MFC was higher than that of the membrane-MFC (1108 mWm-2) during the 80-day operation with TC-MGF bioanode.

Treated clinoptilolite-modified graphite felt bioanode microbial fuel cells for power generation and dye decolourisation

Abstract. Irawati W, Pinontoan R, Mouretta B, Yuwono T. 2021. The potential of copper-resistant bacteria Acinetobacter sp. strain CN5 in decolorizing dyes. Biodiversitas 23: 680-686. Bacteria with multi-resistance to copper and dyes may be employed in bioremediation of copper and dye waste more effectively than physical or chemical remediation. This study aims at determining the effect of the addition of various textile dyes and copper on the growth of Acinetobacter sp. CN5 and its ability to decolorize dyes. The dye resistance test was carried out by inoculating bacterial isolates into Luria Bertani media containing 50, 100, 150, 200, 250, 300, 350, 400, 450, and 500 ppm dyes. The twelve dyes used in the test were methylene blue, malachite green, congo red, mordant orange, reactive black, direct yellow, basic fuchsine, reactive orange, dispersion orange, remazol red, wantex yellow, and wantex red. The decolorization activity was analyzed by spectrophotometry at a 300-900 nm wavelength. The study results demonstrated that bacteria thrived in media containing 50 ppm of all dyes, except malachite green dye. Acinetobacter sp. CN5 was found to be resistant to up to 500 ppm methylene blue, basic fuchsine, and wantex red and resistant to congo red at 450 ppm. Acinetobacter sp. CN5 was also able to decolorize methylene blue, congo red, basic fuchsine, and red wantex by 57.64%, 53.17%, 91.37%, and 67.50%, respectively. The addition of 5 mM CuSO4 to the medium increased the ability of Acinetobacter sp. CN5 to decolorize the congo red from 57.64% to 82.58%.

/pdf/the-potential-of-copper-resistant-bacteria-acinetobacter-sp-3jxi7msr.pdf

The potential of copper-resistant bacteria Acinetobacter sp. strain CN5 in decolorizing dyes

Citrobacter freundii A1 isolated from a sewage treatment facility was demonstrated to be able to effectively decolorize azo dyes as pure and mixed culture. This study reports on the investigation on the enzymatic systems involved. An assay performed suggested the possible involvement of flavin reductase (Fre) as an azo reductase. A heterologously- expressed recombinant Fre from C. freundii A1 was used to investigate its involvement in the azo reduction process. Three model dyes were used, namely Acid Red 27 (AR27), Direct Blue 15 (DB15) and Reactive Black 5 (RB5). AR27 was found to be reduced the fastest by Fre, followed by RB5, and lastly DB15. Redox mediators nicotinamide adenine dinucleotide (NADH) and riboflavin enhance the reduc- tion, suggesting the redox activity of the enzyme. The rate and extent of reduction of the model dyes correlate well with the reduc- tion potentials (Ep). The data presented here strongly suggest that Fre is one of the enzymes responsible for azo reduction in C. freundii A1, acting via an oxidation-reduction reaction.

Citrobacter freundii A1

This paper focuses on the degradation of azo compound C.I. Acid Red 27 (AR27, amaranth) by the recombinant enzyme flavin reductase (FRE) from Citrobacter freundii strain A1. The enzyme was obtained via re-transformation of recombinant plasmid pET-43.1c(+)freBP containing the flavin reductase gene (fre) into E. coli NovaBlue. The plasmid was subsequently transformed into E. coli BL21(DE3)pLysS for overexpression of FRE fusion protein. Prior to that, the stability of fre gene was first verified using PCR amplification and also sequencing of the nucleotides and consequently compared with the original fre gene sequence from C. freundii A1. The protein was expressed as inclusion bodies and was isolated and refolded in order to obtain a properlyfolded and active flavin reductase. The activity and the protein yield were monitored using a modified flavin reductase assay and Bradford assay respectively. The active enzyme was further subjected to the degradation of AR27 and the degradation profile was constructed.

Abdull Rahim Hj

Papers

Degradation of Acid Red 27 by the Recombinant Flavin Reductase