Multiplication of certain soil micro-organisms under simulated Martian conditions. 
According to earlier observations, severe UV irradiation kills all micro-organisms in a chamber with simulated Martian conditions.  However, even a thin soil layer protects buried micro-organisms from UV irradiation.  The chief limiting factor for microbial multiplication under simulated Martian conditions seems to be soil humidity.  Several micro-organisms were isolated from harsh environments (e.g., from Arctic, Antarctic desert and high-mountain soil samples).  A strain of an oligonitrophilic mycococcus, isolated from Dixon Island, proved to be most resistant to low humidity.  It multiplied in a mixture of limonite (maximal hygroscopical humidity 3.8%) + 2% (w/w) garden soil kept in a chamber simulating Martian conditions.  Total cell count increased 7.6-fold and, in some experiments, 26-fold in 14 days.  The oligonitrophilic mycococcus was able to grow even at a humidity level of 2.5%, that is less than maximal hygroscopical (3.8%).  Under these conditions cell count increased 10-fold in 36 days.  Thus, it was shown that even in Earth soils there are xerophytic micro-organisms which are able to multiply in limonite of low humidity.  These data might correct our current concepts concerning microbial water requirements.  One might speculate that Martian micro-organisms belong to xerophytic species.