Separation of cells in density gradients with temporary solidification of the gradient: Application to Escherichia coli forms obtained by microwave treatment of pure cultures

Gelatin added in certain concentration into the density gradient mixtures allows to solidify and melt the gradient reversibly. Such a method was applied to separation of partially disintegrated Escherichia coli VKM B-125 cells in discontinuous sucrose gradient which was optimized to obtain small round “nano-cells” free from other cell components. Gelatin added to the sucrose solutions had the advantages: i) accurate gradient layers were formed, ii) gelatin did not interfere with the cells and sub-particles during centrifugation, iii) solidified gelatin allowed to cut out the separated cell components, and iv) gelatin allowed to prepare ready-made solidified gradient centrifugation tubes into storage. [Display omitted] •The differential cedntrifugation method was improved by adding gelatin which can be solidified and melted.•The high performance of the method is shown with separation of microwave-modified Escherichia coli cells.