Growth of a lower eukaryote in non-aromatic hydrocarbon media ⩾C12 and its exobiological significance

The fungus termed Fusarium alkanophyllum Palacios-Prü & V. Marcano is able to grow in and degrade several saturated hydrocarbons in the presence of UV radiation at 253.7 nm or 354.5 nm, H2O2, and CO2, with little or no oxygen and with minimum water requirements showing several phenotypes and optimal growth. Further, this species is also able to produce important amounts of metabolic water from the substrate. Therefore, different simulation experiments were done to evaluate the biological, physiological and biochemistry responses taking into account conditions similar to solar and extrasolar environments having various CO2 contents and occupying the habitable zone around the main sequence stars with spectral types in the F to mid-K range with L(L/)∼1. Solar and extrasolar environments similar to those of the jovian satellites and Titan were also considered. Accordingly, the growth of F. alkanophyllum was inhibited in <n-C10 or aromatic hydrocarbons. The organism is proteolytic, since it grows in culture media of hydrocarbons containing albumin, glycoprotein and gammaglobulin as a source of carbon and nitrogen; however, in media containing other proteins that lack sulphur linkages, no growth was observed. Analysis by electron microscopy (EM) of F. alkanophyllum grown from germinated spores in heavy and light hydrocarbon media in the presence or absence of UV radiation and oxidizing or reducing gases revealed the absence of plasmalemma, nuclear membranes and other cytomembranes as an adaptative response. Aqueous extracts of secreted material from several hydrocarbon cultures analysed by FTIR spectroscopy revealed the presence of fatty acids and UV-protective indole pigments. An additional protection against UV radiation is offered by the hydrocarbon media which have substantial absorbances between 200 and 354 nm. The absence of lipidic membranes in F. alkanophyllum constitute an important finding in the cell biology of the terrestrial species that deserve careful evaluation. The results of this work allows to encourage exobiology experiments utilizing extremophile eukaryotes such as fungi in the International Space Station or on Mars. Moreover, the study of the physiological mechanisms involved in anhydrous conditions must be of interest in the exobiology of solar and extrasolar bodies having hydrocarbon potential niches because it offers an alternative vision related with the search for life in the universe.