Enhanced degradation of ammonium-pretreated wheat straw by lignocellulolytic Streptomyces spp.

Abstract

Eleven actinomycetes, isolated from the gut of worker termites (Macrotermes, Armitermes, Microcerotermes, Odontotermes), were identified as Streptomyces chromofuscus, S. chromogenus, S. diastaticus, and S. rochei. Their ability to grow on natural lignocellulosic substrates was tested in solid state fermentation experiments using wheat straw (C/N = 49.8) as a sole carbon source. Weight loss was 4.7–20.9% of the initial substrate, after 5 weeks at 30 °C; lignin and cellulose content decreased 2.0–16.1 and 3.5–32.9%, respectively. When the 11 Streptomyces were grown on wheat straw pretreated with (NH4)HCO3 (C/N = 28.2), weight loss was 9.3–29.9% of the initial substrate, indicating an overall enhancement of lignocellulose degradation. Weight, lignin, and cellulose losses were enhanced when S. chromofuscus (strain A2 and A11) and S. rochei A4 were grown on pretreated wheat straw instead of the untreated substrate. With S. rochei A10 the weight loss and lignin degradation were enhanced, while cellulolysis was slightly depressed. Weight loss and cellulose degradation were both enhanced when the remaining strains were grown on pretreated wheat straw. In this case, lignin degradation was depressed (S. chromofuscus A6 and A8, S. diastaticus A12, S. rochei A14) or remained essentially the same (S. diastaticus A3 and S. chromogenus A7). Key words: Streptomyces, wheat straw, degradation, lignin, cellulose.