Halomonas as a chassis

Abstract

With the rapid development of systems and synthetic biology, the non-model bacteria, Halomonas spp., have been developed recently to become a cost-competitive platform for producing a variety of products including polyesters, chemicals and proteins owing to their contamination resistance and ability of high cell density growth at alkaline pH and high salt concentration. These salt-loving microbes can partially solve the challenges of current industrial biotechnology (CIB) which requires high energy-consuming sterilization to prevent contamination as CIB is based on traditional chassis, typically, Escherichia coli, Bacillus subtilis, Pseudomonas putida and Corynebacterium glutamicum. The advantages and current status of Halomonas spp. including their molecular biology and metabolic engineering approaches as well as their applications are reviewed here. Moreover, a systematic strain engineering streamline, including product-based host development, genetic parts mining, static and dynamic optimization of modularized pathways and bioprocess-inspired cell engineering are summarized. All of these developments result in the term called next-generation industrial biotechnology (NGIB). Increasing efforts are made to develop their versatile cell factories powered by synthetic biology to demonstrate a new biomanufacturing strategy under open and continuous processes with significant cost-reduction on process complexity, energy, substrates and fresh water consumption.

Keywords: Halomonas; Metabolic engineering; Microbial chassis; Next generation industrial biotechnology; PHA; Synthetic biology.

Figure 1. Overview of Halomonas engineering for biotechnological industry

Many systems and synthetic biology tools and approaches, for example CRISPR/Cas9-based gene editing, omics profiling, parts mining, static and dynamic optimization methods, have been developed for Halomonas spp. It is thus advanced, the genetic reprogramming of Halomonas spp. allowing construction of high-performance Halomonas cell factories for production of a variety of chemicals, polyesters and proteins. A cost-effective NGIB has been developed based on extremophilic bacteria especially Halomonas spp. for bioproduction in various scales. Abbreviation: CRISPR, clustered regularly interspaced short palindromic repeats.

Figure 2. Metabolic pathways for diverse bioproductions by engineered Halomonas

Halomonas spp. have been engineered to produce different chemicals and polyesters from glucose, fatty acids, gluconate or other structure-related carbon sources (light gray). Three major metabolic modules involved in glucose metabolism, PHA biosynthesis (light blue), and productions of amino acids and their derivates (light orange) are summarized according to the published studies. Crosses in red represent bypasses (letters in light gray) required to be knockout.

Figure 3. Streamlined engineering of Halomonas as a chassis

(A) Genetic tools development includes promoter engineering, novel type T7-like inducible system, expression correlation cross vectors and/or different genomic locus. (B) Stimulus response-based pathway tuning approach enables fast and exquisite gene expression optimization on chromosome-based system in corporation of GFP-mediated transcription mapping approach. (C) Innovative strain engineering strategies boosts the industrial performance of engineered cells by enhancing oxygen availability, increasing the cell volume, achieving self-flocculation at the end of the growth and production processes. (D) Strain engineering pipeline of Halomonas for industrial purposes. ABbreviation: GFP, green fluorescent protein.