ABSTRACT
The icy continent of the Southern hemisphere on this planet consists most part frozen water and ∼0.32% ice-free Dry Valleys (Ugolini and Bockheim 2008). The explorative nature of humans had encouraged early explorers to sail to this continent simply by steam-powered ships and wind. Since then there has been a steady increase in the human presence on this continent, as the means of transportation by sea and air improved and the capability of carrying larger quantity of supplies increased. Historically Australia, France, Argentina, Chile, New Zealand, United Kingdom, and Norway have territorial claims; however, currently over 30 countries have signed the Antarctic treaty and maintain research stations supporting over 4000 research and logistics personnel during polar summer months and 1000 support personnel during polar winter period. Although the United States has the largest operation, they never claimed any territory on the Antarctic continent. Besides the scienti c activities, the International Association of Antarctic Tour Operators (https:// www.iaato.org) reported that in 2007-2008 season over 33,000 tourists landed on
this continent either by sea or by air. According to their estimate, the tourism in Antarctica has increased almost three times since 2000-2001. To maintain the scienti c stations supporting the effective science missions and a steady increase in the tourism, it is necessary to transport and store adequate volume of fossil fuels (jet fuels, diesel fuel, kerosene, and other petroleum hydrocarbon-based fuels) to this continent. Moreover transportation within the continent requires the use of either land vehicles or xed-or rotary-winged airplane. Storage and the use of the fuel for transportation and maintaining the permanent and temporary research stations and tourism would inevitably lead to small or large quantities of fuel spills. One may argue that the Antarctic continent is stretched about 14.4 million km2 (5.4 million sq mi) and relatively a very small fraction of this vast ice-covered continent has been explored and traversed by humans. Moreover, the Antarctic treaty of environmental protection mandates that all visitors to the continent avoid oil spill or at least minimize such events. Although these arguments have some merit, the steady increase in the establishment of additional research stations, their extended activities at remote locations, and more importantly an unprecedented surge of tourism during the last decade have led to more events of oil spills and contamination of the pristine environment affecting the ecosystems and food web starting from the microorganisms to mammals, who may not have previously experienced the toxic effects of the petroleum hydrocarbon and other fossil fuels. For example, in 1989, an Argentina supply ship with tourists on board spilled over 158,000 gallons of fuel near the U.S. Palmer station after running into an underwater reef. Although this event did not cause major impact to the natural ecosystems in Antarctic continent, a serious concern has been raised that such accidents could affect the regional food web including the birds, mammals, crustacean and other invertebrates, macroalgae, lichens, and numerous other microscopic organisms. A containment and cleanup policy for small or large oil spills due to the research activities, maintenance of the scienti c stations, and tourism is an obvious issue that has been discussed (Aislabie et al. 2004). Several biodegradative microbial species indigenous to Antarctica have been isolated, identi ed, and shown to possess biodegradative function (Aislabie et al. 2006, Leys et al. 2005). Therefore, the use of the natural bioremediation process inherent to these biodegradative microorganisms to the cleanup of the spilt oil has been proposed as a method for cleaning up such oil spills. Unlike a mesophilic environment, petroleum hydrocarbons behave differently in a cold temperature environment and when trapped on ice. Unfortunately, Antarctica’s relatively low microbial biomass and the extreme conditions of polar winter months without sunlight and freezing conditions would predict relatively slow or ineffective biodegradative processes. Another obvious issue is the microbial adaptation to evolve rapidly and maintain optimum biodegradative activity in Antarctic cold and dry environmental conditions when confronted with novel hydrocarbon contaminants. Although nonbiodegradative microbial adaptation in cold temperature environment in Antarctic continent has been described, such adaptive mechanisms are yet to be clearly elucidated in biodegradative species isolated from this continent. So far only a few biodegradative microorganisms have been subjected to the study of the cold adaptation (Ayub et al. 2009, Baraniecki et al. 2002, Kawamoto et al. 2009, Panicker et al. 2002). The biodegradative Antarctic bacteria possess enzymes, which are active at low
temperature. They help these organisms biodegrade fuels or petroleum hydrocarbons and obtain nutrient from surroundings; continue the vital processes of cellular function or life, i.e., the replication of DNA, the synthesis of RNA from DNA, and the synthesis of proteins; and maintain an optimum cell membrane uidity. All of these capabilities are required for these microbial communities to remain viable and metabolically active at low temperatures. To sustain life in persistent cold environment, these microorganisms produce speci c sets of proteins, which are regulated both at transcriptional and translational levels that may impart metabolic differences from their mesophilic relatives. However many of the microbial species isolated from the oil-contaminated soils in Antarctica are also found in mesophilic environments, and some of them have helped to advance the study of the mechanisms of the cold adaptation. At present it is useful to assume that the cold adaptive pro le of Antarctic biodegradative microorganisms could be similar to the mesophilic microorganisms. The possible roles of cryoprotectants that are spilt near scienti c bases in protecting the bacterial cells have been elaborated by Aislabie and Foght (Chapter 9). This chapter will discuss the physiological and genetic mechanisms of cold adaptations in Antarctic microorganisms and their mesophilic relatives that may well apply to the Antarctic biodegradative microorganisms. Four classes of proteins for coping with the cold temperatures have been described: (1) Csps or cold-shock proteins that are expressed immediately after downshift in temperature; (2) Caps or cold acclimation proteins that are expressed during prolonged growth at cold temperatures (acclimation); (3) AFP or antifreeze proteins that are expressed to avoid freezing at subzero temperatures; and (4) IBP or ice-binding proteins whose exact function is still unknown but may act as recrystallization inhibitors to protect membranes in the frozen state. Moreover, the maintenance of membrane uidity in cold adaptive bacteria; role of pigments; and extracellular polymeric substance (EPS) secreted by Antarctic bacteria in cold adaptation will also be discussed.
