title: Preservation of microbial communities enriched on lignocellulose under thermophilic and high-solid conditions.
abstract: BACKGROUND
  Microbial communities enriched from diverse environments have shown considerable promise for the targeted discovery of microorganisms and enzymes for bioconversion of lignocellulose to liquid fuels. While preservation of microbial communities is important for commercialization and research, few studies have examined storage conditions ideal for preservation. The goal of this study was to evaluate the impact of preservation method on composition of microbial communities enriched on switchgrass before and after storage. The enrichments were completed in a high-solid and aerobic environment at 55 °C. Community composition was examined for each enrichment to determine when a stable community was achieved. Preservation methods included cryopreservation with the cryoprotective agents DMSO and glycerol, and cryopreservation without cryoprotective agents. Revived communities were examined for their ability to decompose switchgrass under high-solid and thermophilic conditions.
  
  
  RESULTS
  High-throughput 16S rRNA gene sequencing of DNA extracted from enrichment samples showed that the majority of the shift in composition of the switchgrass-degrading community occurred during the initial three 2-week enrichments. Shifts in community structure upon storage occurred in all cryopreserved samples. Storage in liquid nitrogen in the absence of cryoprotectant resulted in variable preservation of dominant microorganisms in enriched samples. Cryopreservation with either DMSO or glycerol provided consistent and equivalent preservation of dominant organisms.
  
  
  CONCLUSIONS
  A stable switchgrass-degrading microbial community was achieved after three 2-week enrichments. Dominant microorganisms were preserved equally well with DMSO and glycerol. DMSO-preserved communities required more incubation time upon revival to achieve pre-storage activity levels during high-solid thermophilic cultivation on switchgrass. Despite shifts in the community with storage, the samples were active upon revival under thermophilic and high-solid conditions. The results suggest that the presence of microorganisms may be more important than their relative abundance in retaining an active microbial community.
authors.affiliation: Department of Biological and Agricultural Engineering, University of California, One Shields Ave, Davis, CA 95616 USA.
authors.forename: Chaowei
authors.initials: C
authors.lastname: Yu
authors.affiliation: Department of Biological and Agricultural Engineering, University of California, One Shields Ave, Davis, CA 95616 USA ; Joint BioEnergy Institute, Emeryville, CA 94608 USA.
authors.forename: Amitha P
authors.initials: AP
authors.lastname: Reddy
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA 94608 USA ; Department of Food Science and Technology, University of California, Davis, CA 95616 USA.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Simmons
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA 94608 USA ; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA 94551 USA.
authors.forename: Blake A
authors.initials: BA
authors.lastname: Simmons
authors.affiliation: Joint BioEnergy Institute, Emeryville, CA 94608 USA ; Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Singer
authors.affiliation: Department of Biological and Agricultural Engineering, University of California, One Shields Ave, Davis, CA 95616 USA ; Joint BioEnergy Institute, Emeryville, CA 94608 USA.
authors.forename: Jean S
authors.identifier: 0000-0002-1455-8254
authors.initials: JS
authors.lastname: VanderGheynst
keywords: Biological lignocellulose deconstruction; Cryopreservation; Microbial community enrichment