Importance of Defluviitalea raffinosedens for Hydrolytic Biomass Degradation in Co-Culture with Hungateiclostridium thermocellum.

Regina Rettenmaier,Michael Lebuhn,Vladimir Zverlov,Sebastian Jünemann,Irena Maus,Wolfgang Liebl,Alexander Sczyrba,Martina Schneider,Bernhard Munk

doi:10.3390/microorganisms8060915

Abstract

Bacterial hydrolysis of polysaccharides is an important step for the production of sustainable energy, for example during the conversion of plant biomass to methane-rich biogas. Previously, Hungateiclostridium thermocellum was identified as cellulolytic key player in thermophilic biogas microbiomes with a great frequency as an accompanying organism. The aim of this study was to physiologically characterize a recently isolated co-culture of H. thermocellum and the saccharolytic bacterium Defluviitalea raffinosedens from a laboratory-scale biogas fermenter. The characterization focused on cellulose breakdown by applying the measurement of cellulose hydrolysis, production of metabolites, and the activity of secreted enzymes. Substrate degradation and the production of volatile metabolites was considerably enhanced when both organisms acted synergistically. The metabolic properties of H. thermocellum have been studied well in the past. To predict the role of D. raffinosedens in this bacterial duet, the genome of D. raffinosedens was sequenced for the first time. Concomitantly, to deduce the prevalence of D. raffinosedens in anaerobic digestion, taxonomic composition and transcriptional activity of different biogas microbiomes were analyzed in detail. Defluviitalea was abundant and metabolically active in reactor operating at highly efficient process conditions, supporting the importance of this organism for the hydrolysis of the raw substrate.

Highlights

The microbial conversion of lignocellulosic biomass to methane-rich biogas has become an important sustainable generating industry [1,2,3]
These attempts resulted again in co-cultures dominated by D. raffinosedens and, in minor amounts, H. thermocellum, as verified by 16S rRNA gene sequencing and species-specific PCR, respectively
The frequency of isolating D. raffinosedens growing in co-culture with H. thermocellum on crystalline cellulose pointed to a putative synergism of these two organisms

Summary

Introduction

The microbial conversion of lignocellulosic biomass to methane-rich biogas has become an important sustainable generating industry [1,2,3]. Integrated omics approaches describing biogas microbiology previously indicated the presence a huge fraction of unassignable sequences, suggesting that most of the microorganisms in biogas communities are still unknown [6,7,8,9,10]. This is due to insufficient availability of reference strains and their corresponding genome sequences in public databases. Addressing this issue, Maus et al [11] isolated and genetically characterized novel cellulolytic, hydrolytic, and acidogenic/acetogenic Bacteria as well as methanogenic Archaea originating from different anaerobic digestion communities. Such cross-feeding has already been reported, e.g., for cellulolytic Bacteria of the genus Hungateiclostridium [16], formerly known as Clostridium [17,18,19]

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Conclusion