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.

The effect of biogenic and chemically manufactured silver nanoparticles on the benthic bacterial communities in river sediments.

This study was conducted to determine and compare the effect of chemically-synthesised and biogenic silver nanoparticles on the benthic bacterial community structure in mesocosms containing sediment from three rivers in geographical sites with different population densities (low, medium, high), and therefore likely to be associated with respective low, moderate and high degrees of anthropogenic input. The nanoparticles were applied at the upper limit expected to accumulate in impacted environments (4 µg kgsed-1). The biomass, concentrations of elements, including selection metals (P, K, Na, K, Ca, Mg, Zn, Cu, Al, Ag) were all significantly higher at the high density than at the low density sites. Bacterial community profiling (terminal restriction fragment length polymorphism and amplicon sequencing) showed that the bacterial community structure in the sediments from the high population density site were resilient to environmental perturbations [adjustment from in-situ to ex-situ (laboratory) conditions], as well as to exposure to silver nanoparticles, with the converse being true for the low population density site. Results obtained from amplicon sequencing were interrogated to the lowest taxonomic level with a relative abundance >5%. Proteobacteria was the most abundant phylum in all the sediments. Notable resistance (increased relative abundance) to one or both forms of silver nanoparticles was seen in the class Thermoleophilia, and the orders Myxococcales, Bacteriodales, Pirellules CCU21 and iii 1-15 (class Acidobacteria 6). Conversely, sensitivity was demonstrated in the family Koribacteraceae and the orders Rhizobiales, Ellin 329 and Gemmatales. It is recommended that pro-active environmental monitoring is performed in aquatic systems receiving point source pollution from wastewater treatment plants in order to assess the accumulation of silver nanoparticles. If necessary, measures should be implemented to mitigate the entry of silver nanoparticles, especially into more vulnerable environments.

Actinobacterial peroxidases: an unexplored resource for biocatalysis.

Peroxidases are redox enzymes that can be found in all forms of life where they play diverse roles. It is therefore not surprising that they can also be applied in a wide range of industrial applications. Peroxidases have been extensively studied with particular emphasis on those isolated from fungi and plants. In general, peroxidases can be grouped into haem-containing and non-haem-containing peroxidases, each containing protein families that share sequence similarity. The order Actinomycetales comprises a large group of bacteria that are often exploited for their diverse metabolic capabilities, and with recent increases in the number of sequenced genomes, it has become clear that this metabolically diverse group of organisms also represents a large resource for redox enzymes. It is therefore surprising that, to date, no review article has been written on the wide range of peroxidases found within the actinobacteria. In this review article, we focus on the different types of peroxidases found in actinobacteria, their natural role in these organisms and how they compare with the more well-described peroxidases. Finally, we also focus on work remaining to be done in this research field in order for peroxidases from actinobacteria to be applied in industrial processes.