Carotenoid Pigmentation in Antarctic Heterotrophic Bacteria as a Strategy to Withstand Environmental Stresses

Bacterial strains isolated from Antarctic environments were used to assess the role of carotenoid pigments as cryo- and solar radiation protectants Isolates were subjected to one hundred 12-hr freeze-thaw cycles and exposed to ambient simulated solar radiation (300 Wm(-2)) with growth recovery evaluated after pre-set time intervals Differences in survival were observed between carotenoid pigmented and nonpigmented strains in response to the different stresses based upon the enumeration of colony forming units On average carotenoid pigmented strains were more resistant to freeze thaw cycles as compared to the non-pigmented strains Survival for nonpigmented strains decreased precipitously from 2 X 10(7) to 1 5 X 10(4) cells mL(-1) on average, within the first 20 cycles Similar results were found in the solar radiation experiments After 2 hrs of solar radiation exposure, 61% of the pigmented organisms survived versus 0 01% for the non-pigmented isolates We applied an additive mixed model to estimate differences between the carotenoid pigmented and non-pigmented bacterial groups Modeled results confirmed a positive effect of pigmentation on survivability and provide evidence that carotenoid pigmentation in heterotrophic bacteria isolated from Antarctic environments increases resistance to environmental stressors