title: Bacterial microcompartment-directed polyphosphate kinase promotes stable polyphosphate accumulation in E. coli.
abstract: Processes for the biological removal of phosphate from wastewater rely on temporary manipulation of bacterial polyphosphate levels by phased environmental stimuli. In E. coli polyphosphate levels are controlled via the polyphosphate-synthesizing enzyme polyphosphate kinase (PPK1) and exopolyphosphatases (PPX and GPPA), and are temporarily enhanced by PPK1 overexpression and reduced by PPX overexpression. We hypothesised that partitioning PPK1 from cytoplasmic exopolyphosphatases would increase and stabilise E. coli polyphosphate levels. Partitioning was achieved by co-expression of E. coli PPK1 fused with a microcompartment-targeting sequence and an artificial operon of Citrobacter freundii bacterial microcompartment genes. Encapsulation of targeted PPK1 resulted in persistent phosphate uptake and stably increased cellular polyphosphate levels throughout cell growth and into the stationary phase, while PPK1 overexpression alone produced temporary polyphosphate increase and phosphate uptake. Targeted PPK1 increased polyphosphate in microcompartments 8-fold compared with non-targeted PPK1. Co-expression of PPX polyphosphatase with targeted PPK1 had little effect on elevated cellular polyphosphate levels because microcompartments retained polyphosphate. Co-expression of PPX with non-targeted PPK1 reduced cellular polyphosphate levels. Thus, subcellular compartmentalisation of a polymerising enzyme sequesters metabolic products from competing catabolism by preventing catabolic enzyme access. Specific application of this process to polyphosphate is of potential application for biological phosphate removal.
authors.affiliation: Department of Microbiology, University College Cork, Cork, Ireland.|School of Biosciences, University of Kent, Canterbury, Kent, UK.
authors.forename: Mingzhi
authors.initials: M
authors.lastname: Liang
authors.affiliation: Department of Biochemical Engineering, University College London, London, UK.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Frank
authors.affiliation: Central Facility for Microscopy, Helmholtz Center of Infection Research, Braunschweig, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Lünsdorf
authors.affiliation: School of Biosciences, University of Kent, Canterbury, Kent, UK.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Warren
authors.affiliation: Department of Microbiology, University College Cork, Cork, Ireland.|Department of Pathology, University College Cork, Cork, Ireland.|APC Microbiome Institute, University College Cork, Cork, Ireland.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Prentice
mesh_terms: D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011122:Polyphosphates / Q000302:isolation & purification*; D062065:Wastewater / Q000737:chemistry; D018508:Water Purification / Q000379:methods*
chemical_list: D029968:Escherichia coli Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); D011122:Polyphosphates; D062065:Wastewater; C475691:polyphosphate kinase, E coli
keywords: Bacteria; Biopolymers; Metabolic engineering; Microreactors; Synthetic biology