Diversity and activity of enriched ruminal cultures of anaerobic fungi and methanogens grown together on lignocellulose in consecutive batch culture

Abstract

Consecutive batch cultures (CBC), involving nine serial transfers at 3, 5 and 7 d intervals (21, 45 and 63 d, respectively) were established to enrich for plant fibre degrading co-cultures of anaerobic fungi and methanogens from rumen digesta. Microbial diversity and fermentation end-products were measured at appropriate intervals over each CBC time-course. While methanogenic populations remained diverse, anaerobic fungal diversity was related to transfer interval and appeared to decrease with increasing transfer number. Acetate was the principal aqueous fermentation end-product with minimal quantities of lactate and formate detected. Methane and carbon dioxide were detected in the gaseous head-space of all co-cultures and the total amounts of gas generated per transfer was greater with transfer intervals of 5 and 7 d compared with a 3 d interval, although the 3 d interval tended to be more efficient per unit time. In conclusion, rapidly growing, methane producing co-cultures of anaerobic fungi and methanogens from rumen digesta were easy to establish on lignocellulose (barley straw) and maintain over considerable time periods. These results suggest such co-cultures have potential in industrial scale anaerobic digestion (AD) of highly fibrous substrates, which are resistant to degradation in conventional AD plants.