High gas pressure survival/reactivation of soil microorganisms

Abstract : Deep sea sediments constitute a considerable reserve of microorganisms belonging to different microbial communities. Our researches aimed to better understand cellular mechanisms related to cellular plasticity involved in resistance of such microbial communities to extreme conditions and more particularly to high level of pressure (> 50 MPa). Obviously, the first step is to isolate microorganisms present in deep sea sediments and then cultivate. The comparison of the cultivation of such microorganisms under atmospheric conditions and under pressure conditions will afford a possible reactivation of specific piezotolerants and/or piezophiles organisms from dormancy. The aim of the present study is to validate the use of original processes of culture under high gaseous pressures (50 MPa). (1) « Blind » chambers, of about 100 cm3, are designed to maintain microorganisms spread on solid medium contained in 3 small Petri Dishes (4 cm diameter) at 25-200 MPa. Observation in real time of colonies is not possible. (2) « Optical » or microscopic chambers are designed to resist up to 400 MPa and to visualize the microbial growth during hyperbaric treatment in real time. They can be used to cultivate and visualize microorganisms under gaseous isostatic pressure on solid medium or under hydrostatic pressure in liquid medium. The yeast Saccharomyces cerevisiae was used as a model of microorganism. Results show that its growth rate, measured between 1 and 50 MPa, decreased when the pressure level increased. The “optical” chamber is more adapted to the follow-up of the microbial growth because the growth rate can be calculated without decompression of the chamber and cells can be followed-up individually. The “blind” chamber is more adapted to cultivate samples in order to isolate piezotolerants and/or piezophiles microorganisms. Thus, they will be used to cultivate and isolate microorganisms present in deep sea sediments (-5000 m under Indian Ocean surface).