Production and characterisation of a novel actinobacterial DyP-type peroxidase and its application in coupling of phenolic monomers.

The extracellular peroxidase from Streptomyces albidoflavus BSII#1 was purified to near homogeneity using sequential steps of acid and acetone precipitation, followed by ultrafiltration. The purified peroxidase was characterised and tested for the ability to catalyse coupling reactions between selected phenolic monomer pairs. A 46-fold purification of the peroxidase was achieved, and it was shown to be a 46 kDa haem peroxidase. Unlike other actinobacteria-derived peroxidases, it was only inhibited (27 % inhibition) by relatively high concentrations of sodium azide (5 mM) and was capable of oxidising eleven (2,4-dichlorophenol, 2,6-dimethoxyphenol, 4-tert-butylcatechol, ABTS, caffeic acid, catechol, guaiacol, l-DOPA, o-aminophenol, phenol, pyrogallol) of the seventeen substrates tested. The peroxidase remained stable at temperatures of up to 80 °C for 60 min and retained >50 % activity after 24 h between pH 5.0-9.0, but was most sensitive to incubation with hydrogen peroxide (H2O2; 0.01 mM), l-cysteine (0.02 mM) and ascorbate (0.05 mM) for one hour. It was significantly inhibited by all organic solvents tested (p ≤ 0.05). The Km and Vmax values of the partially purified peroxidase with the substrate 2,4-DCP were 0.95 mM and 0.12 mmol min-1, respectively. The dyes reactive blue 4, reactive black 5, and Azure B, were all decolourised to a certain extent: approximately 30 % decolourisation was observed after 24 h (1 µM dye). The peroxidase successfully catalysed coupling reactions between several phenolic monomer pairs including catechin-caffeic acid, catechin-catechol, catechin-guaiacol and guaiacol-syringaldazine under the non-optimised conditions used in this study. Genome sequencing confirmed the identity of strain BSII#1 as a S. albidoflavus strain. In addition, the genome sequence revealed the presence of one peroxidase gene that includes the twin arginine translocation signal sequence of extracellular proteins. Functional studies confirmed that the peroxidase produced by S. albidoflavus BSII#1 is part of the dye-decolourising peroxidase (DyP-type) family.

Bioflocculant production from Streptomyces platensis and its potential for river and waste water treatment

ABSTRACT A bacterium isolated from Sterkfontein dam was confirmed to produce bioflocculant with excellent flocculation activity. The 16S rDNA nucleotide sequence analyses revealed the bacteria to have 99% similarity to Streptomyces platensis strain HBUM174787 and the sequence was deposited in the Genbank as Streptomyces platensis with accession number FJ 486385.1. Culture conditions for optimal production of the bioflocculant included glucose as a sole carbon source, resulting in flocculating activity of 90%. Other optimal conditions included: peptone as nitrogen source; presence of Mg2+ as cations and inoculum size of 1.0% (v/v) at neutral pH of 7. Optimum dose of the purified bioflocculant for the clarification of 4 g/L kaolin clay suspension at neutral pH was 0.2 mg/mL. Energy Dispersive X-ray analysis confirmed elemental composition of the purified bioflocculant in mass proportion (%w/w): carbon (21.41), oxygen (35.59), sulphur (26.16), nitrogen (0.62) and potassium (7.48). Fourier Transform Infrared Spectroscopy (FTIR) indicated the presence of hydroxyl, carboxyl, methoxyl and amino group in the bioflocculant. The bioflocculant produced by S. platensis removed chemical oxygen demand (COD) in river water and meat processing wastewater at efficiencies of 63.1 and 46.6% respectively and reduced their turbidity by 84.3 and 75.6% respectively. The high flocculating rate and removal efficiencies displayed by S. platensis suggests its industrial application in wastewater treatment.