复合菌系XCP-8对稻杆干发酵定向产乙酸机理与技术研究

In the process of anaerobic biodigestion of rice straw for biogas production, acetic acid is the most important substrate of methanogens for methane production. However, methane produced by degradation of rice straw is still not successfully commercialized due to its low biodegradation rates and the low content of acetic acid. To investigate the roles of various microbes in the system has significance for improving production of acetic acid. XCP-8, is a mesophilic microbial consortium from soil of continuous cropping cotton field of Xinjiang. Our previous studies indicated that XCP-8 could effectively digest preteated rice straw for production of acetic acid. This project seeks to uncover the mechanism of XCP-8 producing acetic acid. To understand the microbes' roles of XCP-8, various substrates will be inoculated respectively with the various microbes.The products and enzyme activities will be examined. The products and microbes will be detected in the process of rice straw digested with XCP-8 using DGGE and GC-MS. These data will provide important clues to interpret how the acclimated XCP-8 produces acetic acid by digesting rice straw. Furthermore, we will also to explore the effect of adding various microbes from XCP-8 on acetic acid production, aiming to find a new way to improve the conversion of rice straw to acetic acid.

厌氧发酵工艺中，乙酸是直接被产甲烷菌利用转化为甲烷的重要底物，提高稻杆生物降解率，促进稻杆向乙酸的定向转化是实现稻杆资源化利用及沼气工业化生产的前提。申请人在前期研究中，采用限制性培养和定向驯化技术，从新疆多年连作的棉田土壤中获得一组稳定的中温复合菌系XCP-8，该菌系具有高效降解稻杆定向产乙酸的特点。本项目拟研究复合菌系XCP-8降解稻杆过程中，菌群变化与产乙酸的关系；对菌群中可培养微生物进行分离鉴定，研究微生物对单一底物（纤维素、半纤维素、木质素、稻杆等）的降解作用，分析微生物对底物的代谢途径，解析复合菌系XCP-8降解稻杆定向产乙酸的机理；在此基础上，进一步利用全混合反应器进行稻杆降解的干发酵试验，在发酵不同阶段，添加源于复合菌系XCP-8的纯培养微生物，研究强化或保持优势菌群对稻杆降解效率和乙酸积累的影响，优化复合菌系XCP-8降解稻杆的干发酵工艺参数。

提高稻秆生物降解率，促进稻秆向目标产物的定向生物转化是实现稻秆资源化利用的前提。本项目利用中温复合菌系XCP-8对碱处理稻秆进行生物降解，结果显示，复合菌系对碱处理稻秆有良好的降解效果，在第8天，稻秆的失重率达到了65.7%，乙酸产量达到2.3g/L。通过构建复合菌系16S rDNA基因文库分析了复合菌系XCP-8的微生物菌群结构，包含10个不同类群。通过纯培养和产物鉴定，获得了5个能产乙酸的菌株。利用得到的单一菌株对单一底物（稻秆、脱脂棉、木质素、葡萄糖）进行降解，发现各菌株对单一底物的降解表现出明显的差异性，但葡萄糖是所有菌株的偏好性碳源。在5个单一菌株中，XCD1降解脱脂棉产乙酸的量最高，达0.79g/L。将5个单一菌株分别在第1d、2d和3d加入复合菌系，考察单一菌株对复合菌系降解稻秆产乙酸的强化作用，结果显示，单一菌株在第2天加入时，强化后的复合菌系对稻秆的降解效果最好，加入单一菌株XCD-4后，稻秆降解率较原始复合菌系提高了9.6%，在第1天加入单一菌株XCD-5，乙酸产量较原始复合菌系增加了0.82g/L。这表明加入同源复合菌系中的单一菌株，对复合菌系的功能是有强化作用的。这一结果在研究的另一个产甲酸为主的复合菌系NJF中也得到体现，这一发现对其它复合菌系功能与发酵效率的强化也具有重要的指导与借鉴意义。