Sustainability potentials of novel laccase tinctures from Stenotrophomonas maltophilia BIJ16 and Bordetella bronchiseptica HSO16: From dye decolourization to denim bioscouring

Abstract

The aim of this present study was to investigate the environmental proficiency of two laccase producing bacterial strains, Hb16c and Berl1¹b₂. Here, laccases, which were secreted in media containing environmental wastes, were characterized for biochemical and kinetic novelty and applied in the decolourization of some synthetic dyes and subsequently, denim bleaching. The laccases exhibited enhanced pH-, thermo-, psychro-, metal-, halo-, and surfacto-tolerance, eliciting residual activities of at least ca. 71%. Thereafter, the enzymes were able to decolourize novel high concentrations of synthetic dyes (0.2% w v^-1) at 56 h of incubation, and also elicit a mediator-assisted perpetual wash up and decolourization of indigo pigment from fabric under 6 h. The outcomes observed in this study therefore warrant the adoption of these isolates for applications toward a sustainable and total environment through production of fine biochemicals, and the minimization of environmental wastes.

Keywords: Denim bleaching; Dye decolourization; Environmental sustainability; Laccase.

Fig. 1

Effect on pH on the stability of laccases from (a) Hb16c (Bordetella bronchiseptica HSO16) and (b) Berl1¹b₂ (Stenotrophomonas maltophilia BIJ16) with ABTS as substrate.

Fig. 2

Effect on temperature on the stability of laccases from (a) Hb16c (Bordetella bronchiseptica HSO16) and (b) Berl1¹b₂ (Stenotrophomonas maltophilia BIJ16) with ABTS as substrate.

Fig. 3

Pattern of substrate specificity in (a) Bordetella bronchseptica HSO16 and (b) Stenotrophomonas maltophilia BIJ16.

Fig. 4

Molecular snapshot of amplified fragments of laccase genes from (a) Bordetella bronchiseptica HSO16 and (b) Stenotrophomonas maltophilia BIJ16. Lane 1: ladder mix, lane 2: CueOP gene, lane 3: MCOStm gene, lane 4: CueOCit gene.

Fig. 5

Decolourization of different classes of synthetic dyes (0.2 %) by Hb16c (Bordetella bronchiseptica HSO16) laccase, and Berl1¹b₂ (Stenotrophomonas maltophila BIJ16) laccase. A.B; azure B, M.G; malachite green, R.B; reactive blue, M.O; methyl orange, C.R; congo red, B.B; brilliant blue, Imm; immobilized laccase. Phosphate buffer (pH 6) was used and no mediator was added. Error bars are deviations from means of replicate readings; asterisks indicate significant difference (P < 0.05) among treatments (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

Fig. 6

Empirical denim bleaching using; (a) Hb16c (Bordetella bronchiseptica HSO16) laccase, and (b) Berl1¹b₂ (Stenotrophomonas maltophilia BIJ16) laccase. Enzyme + Mediator (E + M) is on the left; Enzyme only treatment (E) is on the right, while the middle (M + TCA) is the control containing the mediator and TCA.

Fig. 7

× 30 magnification of the dissection microscope: Denim bioscouring by (a) Hb16c (Bordetella bronchiseptica HSO16) and (b) Ie1c (Stenotrophomonas maltophilia BIJ16). Comparisons were made between untreated fabric (control) and the treated variants; laccase only (middle), and laccase + mediator; ABTS (right).

Fig. 8

Spectrum plots of denim treated with laccase, and ABTS + laccase from, (a) Bordetella bronchiseptica HSO16, (b) Stenotrophomonas maltophilia BIJ16. Absorbance (A) of samples was read from 200 to 900 nm and the log inverse (10^−A) was plotted as reflectance.