The development of new methodologies and genetic "tools" for proteomicand "metabolic engineering" applications within the ethanol-producingbacterium Zymomonas mobilis

Abstract

Zymomonas mobilis is a non-pathogenic, facultatively-anaerobic Gram-negative bacterium, which has historically been used for the fermentation of alcoholic beverages in many tropical/sub-tropical countries. Due to its excellent ethanol-producing capabilities, significant effort has been undertaken over recent years to utilize it for industrial ‘bioethanol’ production. Its physiological and metabolic properties indicate that it may also be an excellent organism for the bio-production of many different types of organic molecules. Consequently, the aim of my thesis was to develop new molecular methodologies that would enable Z. mobilis to be ‘engineered’ for use in future ‘bioproduction’ endeavours.

In the first part of my study, I analyzed the native (cryptic) plasmids present within a variety of Z. mobilis strains, including two poorly-studied Z. mobilis strains: NCIMB 11163 and NCIMB 8227. Several plasmid libraries containing restriction-digested fragments of Z. mobilis cryptic plasmid DNA were prepared, and their inserts were sequenced. This enabled the complete DNA sequences of three small (non-integrating, double-stranded DNA) cryptic plasmids to be determined: pZMO1A and pZMO7 from NCIMB 11163, and pZMO1B from NCIMB 8227. Their DNA sequences were analyzed using bioinformatic approaches, to identify open reading frames, and regions of DNA that were putatively involved in transcription or DNA replication.

In the second part of this thesis, the minimally-replicating region from plasmid pZMO7 was used to construct a series of Escherichia coli-Z. mobilis shuttle vectors. These vectors were found to be stable within several Z. mobilis strains for over 60 generations without antibiotic selective pressure. A reliable and reproducible method based on quantitative real time PCR (Q-RT-PCR) was developed to accurately determine the copy number of cryptic plasmids and shuttle-vectors present in Z. mobilis cultures. The pZMO7-based shuttle vectors exhibited good compatibility with cryptic plasmids as well as the widely-used pZM2-based shuttle vectors. Genes encoding glutathione S-transferase (GST) as well as green and red fluorescent protein (GFP and RFP) reporters were cloned into various shuttle vector constructs; placing them under the control of endogenous (Ppdc) or exogenous (Plac and Ptac) promoters. Promoter strength was evaluated by quantifying the reporter gene expression. The plasmid-based expression of GFP and RFP was visualized within planktonic and biofilm cultures using confocal laser scanning microscopy (CLSM). Shuttle vector-based GST pull-down experiments were used to study intracellular protein-protein binding interactions.

In the third part of my thesis, I explored the potential use of Z. mobilis for the bioproduction of isoprenoid (terpenoid) compounds. Five predicted sesquiterpene synthases (terpene cyclases) of unknown function from the dimorphic fungus Penicillium marneffei, and several terpene cyclases from several other bacteria, fungi and plants were initially functionally-analyzed in E. coli. Several cyclase genes were cloned into E. coli-Z. mobilis shuttle vectors for expression trials within Z. mobilis cells.

In summary, this thesis describes the development of a variety of novel methodologies and genetic ‘tools’ that may be used to express heterologous genes within Z. mobilis cells. These will be invaluable for future studies concerned with exploring the biology and industrial applications of this ‘microbial cell factory’.