甲烷菌对厌氧真菌不同碳源代谢的影响

Effect of methanogens on carbon metabolism of anaerobic fungi

摘要:

[目的]探讨碳源和甲烷菌对厌氧真菌碳代谢的影响。[方法]利用体外批次厌氧发酵法，比较厌氧真菌纯培养（Orpinomyces sp.和Neocallimastix sp.）及其与甲烷菌共培养（F1：Orpinomyces sp.+Methanobrevibacter sp.和N3：Neocallimastix sp.+Methanobrevibacter sp.）发酵不同类型碳水化合物代谢产物的差异。[结果]对厌氧真菌和甲烷菌共培养F1和N3的研究显示，F1发酵木薯粉[（26.44±0.22）mmol/L]的乳酸产量是发酵玉米芯[（1.31±0.04）mmol/L]的20.18倍，是N3发酵木薯粉[（1.59±0.03）mmol/L]的16.63倍，玉米芯[（0.79±0.08）mmol/L]的33.47倍。当F1和N3中的厌氧真菌纯培养时，各组乳酸产量均 <1.90 mmol/L。对F1进一步研究，结果显示发酵体系中木薯粉添加量在0.8%-2.0%之间时，乳酸产量随木薯粉添加量增加而增加。当含量在1.0%-2.4%之间时，随木薯粉添加量增加，甲烷和乙酸产量逐渐降低。比较F1发酵大米粉、木薯粉、玉米粉、小麦粉和土豆粉的发酵结果，发现乳酸产量与底物中支链淀粉的含量成正相关（R₂=0.9554）。当F1发酵葡萄糖和麦芽糖时，乳酸产量 <5.00 mmol/L。当以麦芽糊精为底物时，乳酸产量高达（28.00±0.95）mmol/L。[结论]本文首次报道碳源和甲烷菌能够增强厌氧真菌的乳酸代谢途径并且这种增强存在种属特异性。

关键词:共培养;厌氧真菌;甲烷菌;碳源类型;代谢

Abstract:

[Objective] To explore the effect of methanogens on the carbon metabolism of anaerobic fungi.[Methods] End-metabolites of different carbon sources by two anaerobic fungi (Orpinomyces sp. and Neocallimastix sp.) with or without co-culture methanogens (Methanobrevibacter sp.) were compared after 96 h in vitro anaerobic batch fermentation.[Results] Co-culture F1 (Orpinomyces sp. +Methanobrevibacter sp.) greatly enhanced the production of methane, acetate and lactate after corn core and cassava fermentation compared to pure fungal culture F1^* (Orpinomyces sp.). In particular, lactate production by F1 reached (26.44±0.22) mmol/L when fermenting on cassava, 14 times more than those produced by F1^*. On the contrast, co-culture N3 (Neocallimastix sp. + Methanobrevibacter sp.) showed lower level of lactate production after corn core and cassava fermentation compared to the pure fungal culture N3^* (Neocallimastix sp.). In addition, lactate production varied greatly depending on the substrate amount and types of carbon. Lactate production by F1 showed an overall positive correlation with the amount of cassava, peaked (56.29±2.04) mmol/L when cassava amount was 2.0%. Besides, end-metabolites of five starch-rich materials fermented by F1 varied. In particular, there was a highly positive correlation (R₂=0.9554) between lactate yields and the proportions of amylopectin of substrates. Further fermentation on pure sugars by F1 was performed. Polysaccharide (maltodextrin) produced substantially greater amount of lactate than monosaccharide (glucose) and disaccharide (maltose).[Conclusion] Co-culture of anaerobic fungi with methanogens shifted the fungal carbon metabolism during fermentation, which depended on the carbon sources and fungal species.

Key words:co-culture;anaerobic fungi;methanogens;carbons;metabolism