Structural and functional rearrangements in the cells of actinobacteria Microbacterium foliorum BN52 during transition from vegetative growth to a dormant state and during germination of dormant forms

Cellular organization of the cystlike cells (CLC) of non-spore-forming heterotrophic actinobacteria isolated from soils contaminated with chemical plant waste (Bereznyaki, Russia) and identified as Microbacterium foliorum BN52 was studied. CLC were obtained in laboratory conditions in limited or starving cultures. Two morphotypes of CLC capable of reversion to the vegetative growth were revealed and characterized in detail. The morphological, ultrastructural, and physiological peculiarities of germination and transition to the vegetative growth were studied at first for the dormant forms of M. foliorum BN52. Germination of morphotype II CLC was associated with gradual recovery of the cell shape and subcellular structures. In contrast to the germination of morphotype II CLC, during the first hours of germination of morphotype I CLC cell volume increased significantly with the subsequent formation of very large cell with sizes several times larger than the typical vegetative cells of the strain. The obtained cells were characterized by polynucleoidity, being polyploids undergoing fission at the next stage of germination, resulting in formation of numerous small and ultrasmall viable cell forms. Formation of cyst-like dormant cells, germinating in the form of polyploid cells is assumed to be the basis of survival and adaptation strategies of heterotrophic bacteria, which are incapable of toxicant degradation in natural habitats, under the conditions of the toxic pressure.