title: Cellular adhesiveness and cellulolytic capacity in Anaerolineae revealed by omics-based genome interpretation.
abstract: BACKGROUND
  The Anaerolineae lineage of Chloroflexi had been identified as one of the core microbial populations in anaerobic digesters; however, the ecological role of the Anaerolineae remains uncertain due to the scarcity of isolates and annotated genome sequences. Our previous metatranscriptional analysis revealed this prevalent population that showed minimum involvement in the main pathways of cellulose hydrolysis and subsequent methanogenesis in the thermophilic cellulose fermentative consortium (TCF).
  
  
  RESULTS
  In further pursuit, five high-quality curated draft genomes (>98 % completeness) of this population, including two affiliated with the inaccessible lineage of SBR1031, were retrieved by sequence-based multi-dimensional coverage binning. Comparative genomic analyses revealed versatile genetic capabilities for carbohydrate-based fermentative lifestyle including key genes catalyzing cellulose hydrolysis in Anaerolinea phylotypes. However, the low transcriptional activities of carbohydrate-active genes (CAGs) excluded cellulolytic capability as the selective advantage for their prevalence in the community. Instead, a substantially active type VI pili (Tfp) assembly was observed. Expression of the tight adherence protein on the Tfp indicated its function for cellular attachment which was further testified to be more likely related to cell aggregation other than cellulose surface adhesion. Meanwhile, this Tfp structure was found not contributing to syntrophic methanogenesis. Members of the SBR1031 encoded key genes for acetogenic dehydrogenation that may allow ethanol to be used as a carbon source.
  
  
  CONCLUSIONS
  The common prevalence of Anaerolineae in anaerobic digesters should be originated from advantageous cellular adhesiveness enabled by Tfp assembly other than its potential as cellulose degrader or anaerobic syntrophs.
authors.affiliation: Department of Civil Engineering, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Xia
authors.affiliation: Department of Civil Engineering, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Yubo
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Computer Science, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Computer Science, The University of Hong Kong, Hong Kong SAR, China ; Department of Computing, Hang Seng Management College, Hong Kong SAR, China.
authors.forename: Francis Y L
authors.initials: FY
authors.lastname: Chin
authors.affiliation: Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen, China ; Department of Civil Engineering, The University of Hong Kong, Hong Kong SAR, China ; Environmental Biotechnology Lab, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
authors.forename: Tong
authors.initials: T
authors.lastname: Zhang
keywords: Aggregation; Anaerolinales; Anaerolineae; Cellular adhesion; Cellulolytic capacity; Chloroflexi