KAIST scientists visualise PHA production inside living bacterial cells

A research team at KAIST has for the first time successfully visualised living bacteria actually making PHA inside the cell.

PHA is a polyester material that is synthesised by numerous different strains of bacteria as an energy and carbon storage material. The microbes start producing the substance under stress conditions and in the presence of excess carbon sources, accumulating it in the form of intracellular granules.

PHA materials are viewed as offering a good potential alternative to fossil fuel-based conventional resins. 100% bio-based, they are biodegradable and in some cases even marine degradable, with properties that are suitable for a range of different applications.

Previous studies investigating PHA granules inside microbial cells have been performed by using fluorescence microscopy, transmission electron microscopy (TEM), and electron cryotomography. Neither technique permitted living cells to be visualised in action. This made it difficult to fully understand the formation of PHA granules in cells. Until now, therefore, only various mechanism models based on observations had been proposed, without the process actually having been observed.

The Korean scientists - a team of metabolic engineering researchers led by Distinguished Professor Sang Yup Lee and Physics Professor YongKeun Park - used 3D holographic microscopy and optical diffraction tomography to study the formation and growth of PHA granules in the cells of live bacteria.

From the reconstructed 3D refractive index distribution of the cells, the team succeeded in the 3D visualization and quantitative analysis of cells and intracellular PHA granules at a single-cell level. The research team also presented 3D time-lapse movies showing the actual processes of PHA granule formation combined with cell growth and division. Movies showing the living cells synthesizing and accumulating PHA granules in their native state had never been reported before. 

According to Professor Lee, the study provides insights among others, into the unique mechanisms of PHA granule formation, as the PHA undergoes the phase transition from soluble monomers into the insoluble polymer, followed by granule formation.

“Through this study, a deeper understanding of PHA granule formation within the bacterial cells is now possible, which has great significance in that a convergence study of biology and physics was achieved,” he said. “This study will help develop various bioplastics production processes in the future.”