title: Physiological and molecular characterizations of the interactions in two cellulose-to-methane cocultures.
abstract: BACKGROUND
  The interspecies interactions in a biomethanation community play a vital role in substrate degradation and methane (CH4) formation. However, the physiological and molecular mechanisms of interaction among the microbial members of this community remain poorly understood due to the lack of an experimentally tractable model system. In this study, we successfully established two coculture models combining the cellulose-degrading bacteriumClostridium cellulovorans743B withMethanosarcina barkeriFusaro orMethanosarcina mazeiGö1 for the direct conversion of cellulose to CH4.
  
  
  RESULTS
  Physiological characterizations of these models revealed that the methanogens in both cocultures were able to efficiently utilize the products produced byC. cellulovoransduring cellulose degradation. In particular, the simultaneous utilization of hydrogen, formate, and acetate for methanogenesis was observed in theC. cellulovorans-M. barkericocultures, whereas monocultures ofM. barkeriwere unable to grow with formate alone. Enhanced cellulose degradation was observed in both cocultures, and the CH4yield of theC. cellulovorans-M. barkericocultures (0.87 ± 0.02 mol CH4/mol glucose equivalent) was among the highest compared to other coculture studies. A metabolic shift in the fermentation pattern ofC. cellulovoranswas observed in both cocultures. The expression levels of genes in key pathways that are important to the regulation and metabolism of the interactions in cocultures were examined by reverse transcription-quantitative PCR, and the expression profiles largely matched the physiological observations.
  
  
  CONCLUSIONS
  The physiological and molecular characteristics of the interactions of two CH4-producing cocultures are reported. CoculturingC. cellulovoranswithM. barkeriorM. mazeinot only enabled direct conversion of cellulose to CH4, but also stabilized pH forC. cellulovorans, resulting in a metabolic shift and enhanced cellulose degradation. This study deepens our understanding of interspecies interactions for CH4production from cellulose, providing useful insights for assembling consortia as inocula for industrial biomethanation processes.
authors.affiliation: B5423-AC1, School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
authors.forename: Hongyuan
authors.initials: H
authors.lastname: Lu
authors.affiliation: B5423-AC1, School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
authors.forename: Siu-Kin
authors.initials: SK
authors.lastname: Ng
authors.affiliation: B5423-AC1, School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
authors.forename: Yangyang
authors.initials: Y
authors.lastname: Jia
authors.affiliation: B5423-AC1, School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
authors.forename: Mingwei
authors.initials: M
authors.lastname: Cai
authors.affiliation: B5423-AC1, School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
authors.forename: Patrick K H
authors.initials: PKH
authors.lastname: Lee
keywords: Cellulose degradation; Coculture; Dark fermentation; Metabolism; Methanogenesis; Transcriptome