CONICET | Buscador de Institutos y Recursos Humanos

Environmental biotechnology requires an interdisciplinary approach. In the context of an agreement between the University of Patagonia and Oil M&S company, we started an interdisciplinary study for increasing the efficiency of bioremediation processes of contaminated soils in semiarid Patagonia, Argentina. Essential research will lead to selection of cleanup methodologies appropriate to local semiarid soils. The successful application of bioremediation depends on appropriate hydrocarbon-degrading microorganisms and environmental conditions in situ (Aislabie et al. 2006). Thus, in addition to the biodegradation capabilities of representative indigenous bacteria, we are investigating other aspects of their physiology that control their growth and activity in semiarid soil. Fundamental questions relevant to this area include: microbial adaptations to desiccation, nutrient limitation and metabolism and physiology of non-growing cells. Several conditions may limit hydrocarbon degradation by natural population of microorganisms in this area, including cold and fluctuating temperatures (between -20° C in winter to 37° C in summer), strong winds (up to 120 km/h), low moisture and low nutrient contents in soil and alkaline pH. These conditions represent a challenge to classic in situ bioremediation procedures, which were developed for more temperate climates. Using standard microbiological and chemical methods, we determined that members of Rhodococcus bacteria are able to degrade diverse hydrocarbons still under growth-restricting conditions, which are often found in natural environments. Under such conditions, cells stopped growth and transformed hydrocarbons into triacylglycerols with a chemical structure related to that of the hydrocarbon used as carbon source. In addition, Rhodococcus species were highly resistant to desiccation. Our studies revealed that R. opacus possesses specific mechanisms to withstand desiccation, which involve a wide range of physiological responses, including the ability of cells to tightly regulate its energy-producing system, among others. Results indicated that cells of R. opacus not only survive under dry conditions, but they are able to respond actively to the presence of hexadecane vapour increasing metabolic activity and showing limited growth on the hydrocarbon even under conditions of low water availability. Taking into account the ability of Rhodococcus spp. to withstand diverse environmental stresses, four soil microcosm experiments were run in parallel to evaluate the efficiency of two indigenous Rhodococcus strains (strains F7 and 006) for crude oil degradation under low humidity conditions (below 10 %, w/w). Total hydrocarbon content amounted up to 3.5-4 % (w/w) in microcosms. Inoculation by strains Rhodococcus sp. F7 and 006 in microcosms resulted in highest degradation rates (40.97 %) and (31.35 %) respectively, after 38 days of incubation, whereas native bacterial population promoted least degradation of crude oil (19.53 %) at the same time period. In other experiment, we performed a comparative evaluation of natural attenuation, biostimulation and bioaugmentation (using strains F7 and 006) for bioremediation of phenanthrene-contaminated soil in a real polluted site of semiarid Patagonia. Among the bioremediation treatments, the highest degradation rates of soil contaminated with phenanthrene was observed when indigenous strains F7 (99.1 %) and 006 (96.8 %) were added. Biostimulation and attenuation treatments promoted 92.2 % and 66.9 % of degradation, respectively, after 6 weeks of treatment. These results suggested that the isolated Rhodococcus strains are able to maintain degradative activities under environmental conditions of semiarid Patagonia. A better understanding of the physiology of Rhodococcus bacteria used in this study and their interactions with contaminants and environment will hopefully permit successful large-scale application of these inocula to bioremediate soils in semiarid Patagonia.

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