Controlling cell volume for efficient PHB production by Halomonas.

Bacterial morphology is decided by cytoskeleton protein MreB and cell division protein FtsZ encoded by essential genes mreB and ftsZ, respectively. Inactivating mreB and ftsZ lead to increasing cell sizes and cell lengths, respectively, yet seriously reduce cell growth ability. Here we develop a temperature-responsible plasmid expression system for compensated expression of relevant gene(s) in mreB or ftsZ disrupted recombinants H. campaniensis LS21, allowing mreB or ftsZ disrupted recombinants to grow normally at 30°C in a bioreactor for 12h so that a certain cell density can be reached, followed by 36h cell size expansions or cell shape elongations at elevated 37°C at which the mreB and ftsZ encoded plasmid pTKmf failed to replicate in the recombinants and thus lost themselves. Finally, 80% PHB yield increase was achieved via controllable morphology manipulated H. campaniensis LS21. It is concluded that controllable expanding cell volumes (widths or lengths) provides more spaces for accumulating more inclusion body polyhydroxybutyrate (PHB) and the resulting cell gravity precipitation benefits the final separation of cells and product during downstream.