The sensitivity of a forest soil microbial community to acute gamma-irradiation

The community response of soil microbes exposed to acute gamma (γ)-irradiation at 0, 1, 5 and 10 kGy doses were examined for 56 days after irradiation. Physiological activity was determined by community substrate utilisation potentials (BIOLOG™) and a glucose substrate assay. Culture dependant analysis was used to track the changes in fungal and bacteria numbers while culture independent analyses were carried out to assess changes in bacterial community composition. As a consequence of irradiation, bacterial populations initially decreased and then exceeded control populations at the higher radiation doses, while fungal populations did not recover substantially after irradiation. These data suggest that either changes in niche competition between bacteria and fungi or a change in nutrient availability has led to the re-establishment of bacterial populations. The recovery in bacterial populations was mirrored by substrate utilisation potentials increasing in both the rate of utilisation as well as the number of substrates being used. Molecular profiling (DGGE) at later time points showed discrete dominant bands in profiles from the 5 and 10 kGy treatments suggesting outgrowth of certain taxa above background levels. The identities of these taxa were typical of soil environments. In conclusion microbial functioning and physiology can recover from acute doses of γ-irradiation, yet higher doses may lead to changes in the underlying community structure, presumably due to competition for recently opened niches.