Department of Bacteriology and Biochemistry, Idaho Agricultural Experiment Station, University of Idaho, Moscow, Idaho 83843.
Appl Environ Microbiol. 1986 Aug;52(2):246-50. doi: 10.1128/aem.52.2.246-250.1986.
Lignocellulose degradation by Streptomyces viridosporus results in the oxidative depolymerization of lignin and the production of a water-soluble lignin polymer, acid-precipitable polymeric lignin (APPL). The effects of the culture pH on lignin and cellulose metabolism and APPL production by S. viridosporus are reported. Dry, ground, hot-water-extracted corn (Zea mays) lignocellulose was autoclaved in 1-liter reagent bottles (5 g per bottle) and inoculated with 50-ml volumes of S. viridosporus cells suspended in buffers of specific pH (pH 6.0 to 9.2 at 0.4 pH unit intervals). Four replicates of inoculated cultures and of uninoculated controls at each pH were incubated as solid-state fermentations at 37 degrees C. After 6 weeks of incubation the percent loss of lignocellulose, lignin, and carbohydrate and the amount of APPL produced were determined for each replicate. Optimal lignocellulose degradation, as shown by substrate weight loss, was observed in the pH range of 8.4 to 8.8. Only minor differences were seen in the Klason lignin, carbohydrate, protein, and ash contents of the APPLS produced by cultures at each pH. The effects of pH on the degradation of a spruce (Picea pungens) [C-lignin]lignocellulose and a Douglas fir (Pseudotsuga menziesii) [C-glucan]-lignocellulose were also determined at pH values between 6.5 and 9.5 (0.5 pH unit intervals). The incubations were carried out for 3 weeks at 37 degrees C with bubbler-tube cultures. The percentage of initial C recovered as CO(2), C-labeled water-soluble products, and [C]APPL was then determined. The mineralization of lignin and cellulose to CO(2) was optimal at pHs 6.5 and 7.0, respectively. However, the optimum for lignin and cellulose solubilization was pH 8.5, which correlated with the pH 8.5 optimum for APPL production. Overall, the data show that, whereas lignin mineralization is optimal at neutral to slightly acidic pHs, lignocellulose degradation with lignin solubilization and APPL production is promoted by alkaline pHs. These findings indicate that lignin-solubilizing actinomycetes may play an important role in the metabolism of lignin in neutral to alkaline soils in which ligninolytic fungi are not highly competitive.
里氏木霉对木质纤维素的降解导致木质素的氧化解聚和水溶性木质素聚合物——酸沉淀聚合木质素（APPL）的产生。本文报道了培养 pH 值对里氏木霉木质素和纤维素代谢以及 APPL 产生的影响。干燥、粉碎、热水提取的玉米（Zea mays）木质纤维素在 1 升试剂瓶中进行高压灭菌（每瓶 5 克），并用悬浮在特定 pH 值缓冲液中的里氏木霉细胞（pH6.0 至 9.2，每隔 0.4 pH 单位）50 毫升体积进行接种。每个 pH 值下的接种培养物和未接种对照物各有 4 个重复，在 37°C 下进行固态发酵。培养 6 周后，对每个重复的木质纤维素、木质素和碳水化合物的损失百分比以及 APPL 的产生量进行了测定。结果表明，在 pH8.4 至 8.8 的范围内，木质纤维素的降解效果最佳，表现在底物失重方面。在每个 pH 值下培养的 APPL 的 Klason 木质素、碳水化合物、蛋白质和灰分含量仅略有差异。还在 pH 值为 6.5 至 9.5（0.5 pH 单位间隔）之间测定了云杉（Picea pungens）[C-木质素]木质纤维素和花旗松（Pseudotsuga menziesii）[C-葡聚糖]木质纤维素对 pH 值的影响。在 37°C 下用冒泡管培养物进行孵育 3 周。然后确定初始 C 作为 CO2、C 标记水溶性产物和[C]APPL 的回收百分比。木质素和纤维素矿化为 CO2 的最佳 pH 值分别为 6.5 和 7.0。然而，木质素和纤维素的溶解最佳 pH 值为 8.5，这与 APPL 生产的最佳 pH 值 8.5 相关。总的来说，这些数据表明，尽管木质素矿化在中性至略酸性 pH 值下最佳，但碱性 pH 值有利于木质素的溶解和 APPL 的产生，从而促进木质纤维素的降解。这些发现表明，在木质素氧化酶真菌竞争不高的中性至碱性土壤中，木质素溶解放线菌可能在木质素代谢中发挥重要作用。
