PT - JOURNAL ARTICLE AU - Anna Christine Trego AU - Cristina Morabito AU - Simon Mills AU - Stephanie Connelly AU - Isabelle Bourven AU - Giles Guibaud AU - Christopher Quince AU - Umer Zeeshan Ijaz AU - Gavin Collins TI - Diversity Converges During Community Assembly in Methanogenic Granules, Suggesting a Biofilm Life-Cycle AID - 10.1101/484642 DP - 2018 Jan 01 TA - bioRxiv PG - 484642 4099 - http://biorxiv.org/content/early/2018/12/04/484642.short 4100 - http://biorxiv.org/content/early/2018/12/04/484642.full AB - Anaerobic biological decomposition of organic matter is ubiquitous in Nature wherever anaerobic environments prevail, and is catalysed by hydrolytic, fermentative, acetogenic, methanogenic, and various other groups, including syntrophic bacteria. It is also harnessed in innovative ways in engineered systems that may rely on small (0.1-4.0 mm), spherical, anaerobic granules, which we have found to be highly-replicated, whole-ecosystems harbouring the entire community necessary to mineralise complex organics. We hypothesised distinct granule sizes correspond to stages in a biofilm life-cycle, in which small granules are ‘young’ and larger ones are ‘old’. Here, granules were separated into 10 size fractions used for physico-chemical and ecological characterisation. Gradients of volatile solids, density, settleability, biofilm morphology, methanogenic activity, and EPS profiles were observed across size fractions. Sequencing of 16S rRNA genes indicated linear convergence of diversity during community assembly as granules increased in size. A total of 155 discriminant OTUs were identified, and correlated strongly with physico-chemical parameters. Community assembly across sizes was influenced by a niche effect, whereby Euryarchaeota dominated a core microbiome presumably as granules became more anaerobic. The findings indicate opportunities for precision management of environmental biotechnologies, and the potential of aggregates as playgrounds to study assembly and succession in whole microbiomes.