Variation in susceptibility to microbial lignin oxidation in a set of wheat straw cultivars: influence of genetic, seasonal and environmental factors

An alkali lignin preparation from wheat straw was found to be compatible with a previously developed nitrated lignin assay for microbial lignin oxidation, allowing comparison of the susceptibility of different wheat lignins to microbial oxidation. Alkali lignin was prepared from a panel of 18 wheat varieties, and was analysed by FT-IR spectroscopy, revealing minor variations in the lignin structure. Samples of nitrated alkali lignin were assayed against five lignin-degrading bacteria: Streptomyces viridosporus, Rhodococcus jostii RHA1, Pseudomonas putida mt-2, Microbacterium phyllosphaerae, and Sphingobacteriumsp. T2. Up to 5-fold variation in rates of lignin oxidation were observed between different wheat varieties, and between different bacterial strain, with Sphingobacteriumsp. T2 showing consistently highest absorbance changes. Testing of wheat varieties from two consecutive harvests, and from different locations, revealed that the observed variation was due to a combination of genetic, seasonal and environmental factors, but that some wheat varieties showed consistently higher rates of oxidation. Samples of wheat straw treated with Sphingobacterium sp. T2 were analysed by FT-IR spectroscopy after 7 and 14 days’ treatment, showing changes in lignin structure versus time, consistent with lignin breakdown