MICROBIAL-GROWTH AND RESUSCITATION ALTER COMMUNITY STRUCTURE AFTER PERTURBATION

An increase in the number of culturable organisms and a decrease in the diversity of recoverable microbiota have been reported in deep subsurface materials after storage perturbation. The magnitude of the microbial community shift in stored samples was more pronounced at 4 degrees C compared to -20 degrees C. Phospholipid fatty acid analyses and acridine orange direct counts indicated that biomass did not increase significantly throughout storage. Changes in the types of fatty acid methyl eaters determined over the time course indicated that some of the microbial community shift was due to bacterial proliferation. However, the recovery of new bacterial types only after the storage process suggested that some of the increase in culturable cell count was due to the resuscitation of dormant microorganisms, possibly activated by some aspect of sampling, sample handling, and/or storage. Comparison of acridine orange direct counts with phospholipid and diglyceride fatty acid content suggested that much of the biomass may have been non-living at early time points; however, after 30 days of storage most of the bacterial biomass was viable.