Lignocarbohydrate Solubilization from Straw by Actinomycetes

Abstract

Actinomycetes grown on wheat straw solubilized a lignocarbohydrate fraction which could be recovered by acid precipitation. Further characterization of this product (APPL) during growth of Streptomyces sp. strain EC1 revealed an increase in carboxylic acid and phenolic hydroxyl content, suggesting progressive modification. This was also observed in dioxane-extracted lignin fractions of degraded straw, and some similarity was further suggested by comparative infrared spectroscopy. However, the molecular weight profile of APPL was relatively constant during growth of Streptomyces sp. strain EC1 on straw, while analysis of the dioxaneextracted lignin fractions appeared to show fragmentation followed by repolymerization. Lignocarbohydrate solubilization could be monitored in all cultures by routine assay of APPL-associated protein, which accounted for up to 20% of the extracellular culture protein in some cases. Interestingly, this protein fraction was found to include active hydrolytic and oxidative enzymes involved in the degradation of lignocellulose, and specific enzyme activities were often increased in the acid-insoluble fractions of culture supernatants. This was particularly important for peroxidase and veratryl oxidase activities, which could be readily detected in the acid-precipitable lignocarbohydrate complex but were virtually undetectable in untreated culture supernatants.

Screening actinomycetes for extracellular peroxidase activity

“…That is, Streptomyces strains EC1 and EC22, Thermomonospora mesophila BD123, and Amycolata autotrophica DSM 43099 can decolorize the polymeric dye Poly R, oxidize veratryl alcohol to veratraldehyde, and utilize highmolecular-mass (Ͼ100,000 Da) fractionated Kraft lignin as a growth substrate (2). Evidence for activity against lignin and related substrates by all of these strains has also been reported elsewhere (3,11,13,21). Therefore, it is concluded from the data presented here, that while extracellular peroxidase activity is common among actinomycetes, the best producers tend to be those strains for which there is evidence of activity against the lignin component of lignocellulose.…”

“…The L-3,4-dihydroxyphenylalanine (L-DOPA), guaiacol, and pyrogallol peroxidase assays gave low activity values with Streptomyces strain EC22 and could not be applied to S. thermoviolaceus because of the generation of gas bubbles, probably due to extracellular catalase activity, that interfered with the reproducible determination of absorbance. The L-DOPA assay has been commonly used in previous studies of actinomycete peroxidases (3,20,23,24,34), but we found the reproducibility to be relatively poor (Table 3), probably due to the extreme light sensitivity of the substrate. The data of Winter and coworkers (34), in which many actinomycete strains tested positive with L-DOPA compared with 2,4-dichlorophenol (2,4-DCP), also suggest interference due to nonspecific oxidation of the substrate.…”

Soil depth and grassland origin cooperatively shape microbial community co‐occurrence and function

“…Actinobacteria play important roles in humus formation (Ball et al. ), and their increased presence at lower depths could signify their role in the formation of long‐term C storage within prairie soils and should be considered in further studies. Additionally, Actinobacteria have mycelia growth patterns in soil, which could allow for greater surface area for nutrient acquisition at lower soil depths, as well as being potential active members in soil aggregation and water and nutrient retention.…”

Mass spectrometry in the biosynthetic and structural investigation of lignins

“…They make an important contribution to plant biomass degradation and nutrient recycling in soil and composts. Although their capacity to directly oxidize lignin is equivocal (Godden et al, 1992), actinomycetes solubilize lignin from different lignocellulosic materials according to a lignin‐depolymerizion process (Ball et al, 1990) [typically they degrade less than 20% of the total lignin content (Basaglia et al, 1992)]. The main intermediate of lignin degradation produced by actinomycetes also has been identified as acid‐precipitable polymeric lignin (APPL): that polymeric material is composed mainly of lignin, but also contains carbohydrates, proteins, and ashes.…”