Bacterial microcompartment‐directed polyphosphate kinase promotes stable polyphosphate accumulation in E. coli. Issue 3 (10th February 2017)

• Record Type: Journal Article
• Authors: Liang, Mingzhi; Frank, Stefanie; Lünsdorf, Heinrich; Warren, Martin J.; Prentice, Michael B.
• Is Part Of: Biotechnology journal. Volume 12:Issue 3(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-02-10
• Subjects: Bacteria -- Biopolymers -- Metabolic engineering -- Microreactors -- Synthetic biology; Biotechnology -- Periodicals; 660.605
• DOI: 10.1002/biot.201600415
• Languages: English
• ISSNs: 1860-6768

Abstract

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. Abstract : Polyphosphate is a polymer which provides phosphate and energy reserves to microorganisms. Levels of polyphosphate in bacteria change in response to the environment and growth phase with accompanying excretion or uptake of phosphate. Environmental manipulation of wastewater bacteria to make them increase phosphate stores causes them to take up phosphate, which is useful as part of water treatment, but they later release the phosphate back into the wastewater. In this study the authors show that targeting the polymerising enzyme polyphosphate kinase (PPK1) to bacterial microcompartments in E. coli causes stable polyphosphate storage by sequestering it away from other depolymerising enzymes inside the bacteria. These bacteria now take up phosphate without subsequent excretion.