1. ¹Microbial Ecology Laboratory, National University of Ireland, Galway, Ireland
2. ²Microbial Ecophysiology Research Group, Department of Microbiology and Environmental Change Institute, National University of Ireland, Galway, Ireland

Correspondence: V O'Flaherty, Microbial Ecology Laboratory, National University of Ireland, Galway (NUI, Galway), University Road, Galway, Ireland. E-mail: vincent.oflaherty@nuigalway.ie

³These authors contributed equally to this work.

⁴Current address: Centre for Resource Management and Efficiency, School of Applied Science, Cranfield University, College Road, Cranfield, Bedfordshire, MK43 0AL, UK

Received 4 February 2009; Revised 27 April 2009; Accepted 1 May 2009; Published online 25 June 2009.

Abstract

Granular biomass was temporally sampled from a cold (4–15 °C) anaerobic bioreactor, which was inoculated with mesophilic biomass and used to treat industrial wastewater in a long-term (3.4 year) study. Data from 16S rRNA gene clone libraries, quantitative PCR and terminal restriction fragment length polymorphism analyses indicated that microbial community structure was dynamic, with shifts in the archaeal and bacterial communities' structures observed following start-up and during temperature decreases from 15 to 9.5 °C (phase 1). Specifically, the relative abundance of architecturally important Methanosaeta-like (acetoclastic) methanogens decreased, which was concomitant with granule disintegration and the development of a putatively psychrophilic hydrogenotrophic methanogenic community. Genetic fingerprinting suggested the development of a psychroactive methanogenic community between 4 and 10 °C (phase 2), which was dominated by acetogenic bacteria and Methanocorpusculum-like (hydrogenotrophic) methanogens. High levels of Methanosaeta-like acetoclastic methanogens and granular biofilm integrity were maintained during phase 2. Overall, decreasing temperature resulted in distinctly altered microbial community structure during phase 1, and the development of a less dynamic psychroactive methanogenic consortium during phase 2. Moreover, psychrophilic H₂-oxidizing methanogens emerged as important members of the psychroactive consortia after >1200 days of low-temperature cultivation. The data suggest that prolonged psychrophilic cultivation of mesophilic biomass can establish a well-functioning psychroactive methanogenic consortium, thus highlighting the potential of low-temperature anaerobic digestion technology.