ИСТИНА

An ascomycete fungus with a limited lifespan Podospora anserina is a very useful model organism for senescence investigation, because of easiness of its cultivation, well-studied lifecycle, sequenced genome and stable phenomenon of aging and death. Present work focuses on determination of external factors allowing the fungus to overcome its death programme. It was found that dying, not growing any more mycelia in the late stage of aging being removed from agarized to liquid medium loses the features of senescence and become immortal. Such mycelia needed 6-9 days in liquid to become performing new hyphae, whereas young mycelia started to grow in liquid medium almost immediately. Electronic microscopy observations revealed from 60 to 86% of mitoptotic mitochondria with fractured cristae in just reanimated mycelia. But after some passages such cultures became to grow faster and finally formed normally growing mycelia with common features of liquid cultures. The percentage of successful reanimations in rotated cultures was 75%, in non-rotated – 100%. P. anserina did not stop its growth being serially passaged in liquid culture with a period of 3 days, independently was it obtained from young control culture or reanimated. The longest experiment of mycelium passaging was stopped when the strain was 200 days old (from ascospore germination) and had not got any features of senescence whereas control strain growing on agarized medium died after 20.5±1.7 days. During the liquid cultivation small pieces of mycelia were transferred to agarized medium and cultivated before death. They were named V-strains. V-strains obtained during several passages after reanimation of old mycelia had the shortest lifespan observed (not more than 3 days), but then their average longevity became longer and longer from one passage to another and finally some long-lived and even immortal V-strains were obtained (in case of rotation). We have clarified that without essential airing (cultivation without rotation) nether long-lived not immortal V-strains could be obtained in spite of long-term growing of P. anserina mycelia in such conditions without death. In this model reversed order of cellular changes from dying to “healthy” mycelium may be studied. It seems P. anserina adapted to new conditions and being subjected to some modifications obtained a capability for life prolongation and even immortality both in liquid and agarized medium.