Potential of Cometabolic Transformation of Polysaccharides and Lignin in Lignocellulose by Soil Actinobacteria

Abstract

While it is known that several Actinobacteria produce enzymes that decompose polysaccharides or phenolic compounds in dead plant biomass, the occurrence of these traits in the environment remains largely unclear. The aim of this work was to screen isolated actinobacterial strains to explore their ability to produce extracellular enzymes that participate in the degradation of polysaccharides and their ability to cometabolically transform phenolic compounds of various complexities. Actinobacterial strains were isolated from meadow and forest soils and screened for their ability to grow on lignocellulose. The potential to transform 14C-labelled phenolic substrates (dehydrogenation polymer (DHP), lignin and catechol) and to produce a range of extracellular, hydrolytic enzymes was investigated in three strains of Streptomyces spp. that possessed high lignocellulose degrading activity. Isolated strains showed high variation in their ability to produce cellulose- and hemicellulose-degrading enzymes and were able to mineralise up to 1.1% and to solubilise up to 4% of poplar lignin and to mineralise up to 11.4% and to solubilise up to 64% of catechol, while only minimal mineralisation of DHP was observed. The results confirm the potential importance of Actinobacteria in lignocellulose degradation, although it is likely that the decomposition of biopolymers is limited to strains that represent only a minor portion of the entire community, while the range of simple, carbon-containing compounds that serve as sources for actinobacterial growth is relatively wide.

An in-depth analysis of actinobacterial communities shows their high diversity in grassland soils along a gradient of mixed heavy metal contamination

“…Probably other members of this genus use similar mechanisms to survive in Pbcontaminated soils, notably because lead is often the main contaminant in mining and smelting areas, as in the case of this study. There are also multiple reports on their ability to degrade lignocellulose (Crawford 1978;Chater et al 2010;Petrosyan et al 2002;Větrovský et al 2014), and together with members from genus Acidothermus, which also includes efficient degraders of cellulose, e.g. Acidothermus cellulolyticus (Blumer-Schuette et al 2014;Parales et al 2014) and Microlunatus, which are also involved in the decomposition of plant biomass (Fan et al 2014), these taxa could be potentially responsible for important organic matter degrading processes in heavy metal-contaminated soils.…”

“…We hypothesised that the increasing heavy metal toxicity only allows the existence of a limited number of resistant actinobacterial taxa, decreasing their overall diversity in soil. This can be potentially of critical importance for soil functioning: several actinobacterial taxa from the area of this study were previously demonstrated to decompose multiple polysaccharides and phenolics and to grow on complex lignocellulose compounds (Větrovský et al 2014). This indicates their involvement in the decomposition of plant-derived biomass in the studied soil which can be potentially harmed by heavy metal toxicity.…”

“…Among bacteria, the members of the phylum Actinobacteria show the highest abundance of genes involved in cellulose decomposition in their genomes (Berlemont and Martiny 2013), and many isolates have been shown to be able to efficiently degrade polysaccharides and polyphenols (Abdulla and El-Shatoury 2007;Anderson et al 2012;Chater et al 2010;Enkhbaatar et al 2012;Větrovský et al 2014;Yin et al 2010). Bulk lignocellulose materials are more accessible for decomposition by filamentous microorganisms such as fungi and Actinobacteria (de Boer et al 2005), and efficient growth on straw was indeed demonstrated for environmental isolates of Actinobacteria (Větrovský et al 2014). Filamentous mycelial growth, the ability to form spores and a powerful secondary metabolism also represent suitable traits for the survival of Actinobacteria under stress conditions such as heavy metal-contaminated soils, for which these bacteria have also developed several resistance mechanisms (Bajkic et al 2013;Ivshina et al 2013;Schmidt et al 2005).…”

Bacterial diversity and community structure in lettuce soil are shifted by cultivation time

“…Actinobacteria are known as decomposers of dead plant biomass (Warren RAJ, 1996;McCarthy AJ, 1987;Větrovský T et al, 2014), with the increase of lettuce growth time, dead plant biomass will increase, so members of the actinobacterial group will increase accordingly. This result was different from the notion of Susanne Schreiter et al (Schreiter S et al, 2014).…”

Bioconversion of agricultural lignocellulosic residues into branched-chain fatty acids usingStreptomyces lividans

“…A xylose-fermenting Rhodococcus strain was constructed using heterologous expression of the Streptomyces enzymes involved in the xylose metabolism pathway (Kurosawa et al, 2013;Xiong et al, 2012). Interestingly, the Streptomyces species has the natural capacity to grow on and catabolize the phenolic compounds and polysaccharides present in lignocellulose (Antai and Crawford 1981;Crawford 1978;Davis and Sello 2010;Vetrovsky et al, 2014). In addition, Streptomyces species, historically studied and exploited for antibiotic production, can also accumulate TAG under specific nutritional conditions (high C/N ratios) (Arabolaza et al, 2008;Comba et al, 2013;Le Marechal et al, 2013).…”