Stress-Tolerant Dormant Bacterial Forms: Biological and Ultrastructural Properties of Moraxella catarrhalis and Kocuria rhizophila

Dormant forms of causative agents of healthcare-acquired infections Moraxella catarrhalis and Kocuria rhizophila have been obtained. Dormant forms cells retained viability during long-term storage (≈107 CFU/ml after 2 months) under provocative conditions (lack of nutrient sources; temperature 20°C, oxygen access) were characterized by heat resistance, and acquired special ultrastructural organization typical of dormant forms (compacted nucleoid, thickened cell wall). They were also capable of forming alternative phenotypes (dominant and small colony variants) in a new cycle of germination in a fresh medium. These results demonstrate that the dormant forms can be responsible both for survival in the environment and persistence in the host organism.

From Rest to Growth: Life Collisions of Gordonia polyisoprenivorans 135

In the process of evolution, living organisms develop mechanisms for population preservation to survive in unfavorable conditions. Spores and cysts are the most obvious examples of dormant forms in microorganisms. Non-spore-forming bacteria are also capable of surviving in unfavorable conditions, but the patterns of their behavior and adaptive reactions have been studied in less detail compared to spore-forming organisms. The purpose of this work was to study the features of transition from dormancy to active vegetative growth in one of the non-spore-forming bacteria, Gordonia polisoprenivorans 135, which is known as a destructor of such aromatic compounds as benzoate, 3-chlorobenzoate, and phenol. It was shown that G. polyisoprenivorans 135 under unfavorable conditions forms cyst-like cells with increased thermal resistance. Storage for two years does not lead to complete cell death. When the cells were transferred to fresh nutrient medium, visible growth was observed after 3 h. Immobilized cells stored at 4 °C for at least 10 months regenerated their metabolic activity after only 30 min of aeration. A study of the ultrathin organization of resting cells by transmission electron microscopy combined with X-ray microanalysis revealed intracytoplasmic electron-dense spherical membrane ultrastructures with significant similarity to previously described acidocalcisomas. The ability of some resting G. polyisoprenivorans 135 cells in the population to secrete acidocalcisome-like ultrastructures into the extracellular space was also detected. These structures contain predominantly calcium (Ca) and, to a lesser extent, phosphorus (P), and are likely to serve as depots of vital macronutrients to maintain cell viability during resting and provide a quick transition to a metabolically active state under favorable conditions. The study revealed the features of transitions from active growth to dormant state and vice versa of non-spore-forming bacteria G. polyisoprenivorans 135 and the possibility to use them as the basis of biopreparations with a long shelf life.