Engineering of bacteria towards programmed autolysis: why, how, and when?

Abstract

Programmed autolytic bacteria, also termed controlled self-disruptive or self-destructive bacteria, are bacterial systems that express certain lytic genes and undergo cell lysis at a predetermined time point to release the intracellular contents or to commit suicide. Such systems have wide applications in high-throughput screening of protein libraries, synthesis and recovery of bio-products, population control of heterogeneous cultures or synthetic co-cultures, drug delivery, and food fermentation. Recently, great achievements have been reported regarding on-demand control of cell autolysis for different purposes, highlighting the potential of autolytic strains in biomanufacturing and biomedicine. In this review article, we first introduce the various applications of such bacteria, followed by a summarization of the approaches used in the establishment of autolytic bacterial systems, including cell autolysis mediated by cell wall hydrolases with or without facilitating proteins and by membrane-disturbing proteins. Next, we describe in detail the methodologies adopted to control and initiate cell lysis, including induction by chemical inducers, stimulation by physical signals, auto-induction by metabolic status or nutrient limitation, and constitutive expression of the lytic genes. This article is ended with discussions on the remaining problems and possible future directions. This review provides comprehensive information on autolytic bacteria and insightful guidance to the development of highly efficient, robust, and smart autolytic bacterial platforms.

Keywords: Autolysis; Bio-product; Control; Endolysin; Release.

Fig. 1

Schematic representation of programmed autolytic bacterial systems and their applications. Programmed bacterial autolysis lies in the controlled expression of one or more lytic genes sometimes with facilitating proteins, aiming to disintegrate the cell wall and/or membrane structures. At a certain stage of bacterial growth, the lytic gene is induced in response to an external or internal stimulus or signal. This leads to lytic gene expression and cell disruption, thereby releasing intracellular contents for various purposes

Fig. 2

Schematic representation of bacterial autolysis via different mechanisms. (A) Lysis of bacterial cells by the holin-endolysin-spanin cassette. (B) Cell lysis by a cell wall hydrolase fused with a signal peptide for secretory expression. (C) Cell wall hydrolase fused with a cell-penetrating peptide for simultaneous membrane destruction and cell wall degradation. (D) Membrane deformation and fusion caused by protein E of phage X174. (E) Membrane digestion by lipases