Citrobacter freundii as a test platform for recombinant cellulose degradation systems

S. S. Lakhundi, K. O. Duedu*, N. Cain, R. Nagy, J. Krakowiak, C. E. French

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    8 Citations (SciVal)


    Cellulosic biomass represents a huge reservoir of renewable carbon, but converting it into useful products is challenging. Attempts to transfer cellulose degradation capability to industrially useful micro-organisms have met with limited success, possibly due to poorly understood synergy between multiple cellulases. This is best studied by co-expression of many combinations of cellulases and associated proteins. Here, we describe the development of a test platform based on Citrobacter freundii, a cellobiose-assimilating organism closely related to Escherichia coli. Standard E. coli cloning vectors worked well in Cit. freundii. Expression of cellulases CenA and Cex of Cellulomonas fimi in Cit. freundii gave recombinant strains which were able to grow at the expense of cellulosic filter paper or microcrystalline cellulose (Avicel) in a mineral medium supplemented with a small amount of yeast extract. Periodic physical agitation of the cultures was highly beneficial for growth at the expense of filter paper. This provides a test platform for the expression of combinations of genes encoding biomass-degrading enzymes to develop effective genetic cassettes for degradation of different biomass streams. SIGNIFICANCE AND IMPACT OF THE STUDY: Biofuels have been shown to be the best sustainable and alternative source of fuel to replace fossil fuels. Of the different types of feedstocks used for producing biofuels, lignocellulosic biomass is the most abundant. Converting this biomass to useful products has met with little success. Different approaches are being used and microbial platforms are the most promising and sustainable method. This study shows that Citrobacter freundii is a better test platform than Escherichia coli for testing various combinations of cellulases for the development of microbial systems for biomass conversion.
    Original languageEnglish
    Pages (from-to)35-42
    Number of pages8
    JournalLetters in Applied Microbiology
    Issue number1
    Publication statusPublished (VoR) - 1 Jan 2017


    SSL acknowledges support from the Higher Education Commission (HEC), Pakistan. KOD acknowledges support from the Darwin Trust of Edinburgh. RN and JK's participation in iGEM 2012 was supported by the Scottish Universities Life Sciences Alliance (SULSA). We gratefully acknowledge the assistance of Dr Wendy Smith and Professor Anil Wipat of the Centre for Bacterial Cell Biology, University of Newcastle, with regard to sequencing of the genomes of Cit. freundii NCIMB11490 and SBS197. Parts of this project related to use of E. coli vector systems in Cit. freundii were presented at the International Genetically Engineered Machine competition (iGEM) 2012 by the University of Edinburgh student team, of which RN and JK were members.

    FundersFunder number
    Darwin Trust of Edinburgh
    Scottish Universities Life Sciences AllianceSBS197, NCIMB11490
    University of Edinburgh
    Higher Education Commission, Pakistan
    Darwin Trust of Edinburgh


      • biodegradation
      • biofuels
      • gene expression
      • plasmids
      • recombinant protein


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