Jayashree Pohnerkar ^* Vaidehi Chatupale

• Maharaja Sayajirao University of Baroda, Vadodara, India

Bacterial lifespan ranges from a few hours to geological timescales. The prolonged survival trait under extreme energy starvation is immensely important for perpetuation of their existence. The theme for long-term survival (LTSP) in non-growing state may be dependent on the diversity in the environmental niche and the lifestyle of the bacteria, exemplified by longevity studies, albeit few, with model organisms. In the present study, we characterized LTSP of mycelial cells of S. minutiscleroticus which remain metabolically active, demonstrate ongoing protein synthesis, killed by protein synthesis inhibitors, and remarkably by the cell-wall synthesis inhibitors, vancomycin and ampicillin, suggesting 'growth'. Their rapid turnover is also evident in ~10-fold loss of CFU over a year suggesting that for death of one 'old' cell, slightly less than one 'new' cell is born. This longevity is consequent to (i) induction of the gene expression program effected by non-metabolizable, non-ionic osmolyte, sucrose, thus conditional and (ii) possibly rendering this carbon utilizable by production of a slow hydrolytic activity generating glucose, reinforcing the relevance of low-level energy resource for long term survival in the starvation phase. Viability parameters of LTSP cells measured through up to 90 days suggest stationary phase transitioning into LTSP following nutrients exhaustion is nearly quantitative. Expectedly, viability in LTSP is (p)ppGpp/RelA dependent. Whereas mutation in chaperone clpX, negatively affect survival in stationary phase, overexpression of signal sensor-transducer histidine kinase, SasA8, enhances cell survivability. Relevance of longevity functions identified here requires further deduction of the genetic program.