Morphology engineering for enhanced production of medium-chain-length polyhydroxyalkanoates in Pseudomonas mendocina NK-01

Polyhydroxyalkanoates (PHAs) can be produced by microorganisms from renewable resources and are regarded as promising bioplastics to replace petroleum-based plastics. A medium-chain-length PHAs (mcl-PHA)-producing strain Pseudomonas mendocina NK-01 was isolated previously by our lab and its whole-genome sequence is currently available. Morphology engineering of manipulating cell morphology–related genes has been applied for enhanced accumulation of the intracellular biopolymer short-chain-length PHAs (scl-PHA). However, it has not yet been reported to improve the yield of mcl-PHA by morphology engineering so far. In this work, several well-characterized cell morphology–related genes, including the cell fission ring (Z-ring) location genes minCD , peptidoglycan degradation gene nlpD , actin-like cytoskeleton protein gene mreB , Z-ring formation gene ftsZ , and FtsZ inhibitor gene sulA , were intensively investigated for their impacts on the cell morphology and mcl-PHA accumulation by gene knockout and overexpression in P . mendocina NKU, a upp knockout mutant of P . mendocina NK-01. For a minCD knockout mutant P . mendocina NKU-∆ minCD , the average cell length was obviously increased and the mcl-PHA production was improved. However, the nlpD knockout mutant had a shorter cell length and lower mcl-PHA yield compared with P . mendocina NKU. Overexpression of mreB in P . mendocina NKU resulted in spherical cells. When ftsZ was overexpressed in P . mendocina NKU, the cell division was accelerated and the mcl-PHA titer was improved. Furthermore, mreB , ftsZ , or sulA was overexpressed in P . mendocina NKU-∆ minCD . Consequently, the mcl-PHA titers were all increased compared with P . mendocina NKU-∆ minCD carrying the empty vector. The multiple fission pattern was finally achieved in ftsZ -overexpressing NKU-∆ minCD . In this work, improved production of mcl-PHA in P. mendocina NK-01 has been achieved by morphology engineering. This work provides an alternative strategy to enhance mcl-PHA accumulation in mcl-PHA-producing strains.