SURVIVAL OF SUBSURFACE MICROORGANISMS EXPOSED TO UV-RADIATION AND HYDROGEN-PEROXIDE

Aerobic and microaerophilic subsurface bacteria were screened for resi stance to UV light. Contrary to the hypothesis that subsurface bacteri a should be sensitive to UV light, the organisms studied exhibited res istance levels as efficient as those of surface bacteria. A total of 3 1% of the aerobic subsurface isolates were UV resistant, compared with 26% of the surface soil bacteria that were tested. Several aerobic, g ram-positive, pigmented, subsurface isolates exhibited greater resista nce to UV light than all of the reference bacterial strains tested exc ept Deinococcus radiodurans. None of the microaerophilic, gram-negativ e, nonpigmented, subsurface isolates were UV resistant; however, these isolates exhibited levels of sensitivity similar to those of the gram -negative reference bacteria Escherichia coli B and Pseudomonas fluore scens. Photoreactivation activity was detected in three subsurface iso lates, and strain UV3 exhibited a more efficient mechanism than E. col i B. The peroxide resistance of four subsurface isolates was also exam ined. The aerobic subsurface bacteria resistant to UV light tolerated higher levels of H2O2 than the microaerophilic organisms. The conserva tion of DNA repair pathways in subsurface-microorganisms may be import ant in maintaining DNA integrity and in protecting the organisms again st chemical insults, such as oxygen radicals, during periods of slow g rowth.