A self-stimulating system based on a polyhydroxyalkanoates coupled induction mechanism and its applications for Halomonas

Abstract

Inducible gene expression systems are vital tools for synthetic biology. This study focused on a microbial polyhydroxyalkanoate (PHA) related inducible expression system, namely, the regulation mechanism of PHA synthesis associated protein PhaR and PhaP1 in Halomonas bluephagenesis which has employed to enhance PHA synthesis under open unsterile conditions. H. bluephagenesis strains ZS19 and ZS49 with one and two copies of the PHA synthesis system (PphaP1*-phaAB) were constructed based on the PHA self-stimulating synthesis mechanism. When grown in a 7-L bioreactor, H. bluephagenesis ZS19 and ZS49 were grown to 97.4 g/L and 89.6 g/L containing 76.3% and 77.1% PHA in the cell dry weights (CDW), with productivity of 2.06 g/L/h and 2.16 g/L/h, respectively. Compared with its control, their CDW, PHB percent and productivity increased by 20.4% and 10.8%, 13.5% and 14.7 %, and 36.4 % and 43.0 %, respectively. Furthermore, H. bluephagenesis ZS97, engineered with an elongated morphology induced by the PHA-mediated PhaR-phaP1 regulatory system, exhibited a 10 % increase in cell dry weight and a morphology approximately 10 times longer than the wild-type strain, allowing easy separation from the culture broth via centrifugation.