Bioremediation by cold tolerant microbes
Bioremediation is a process to accelerate the natural biodegradation rates through the optimization of limiting environmental conditions and is an ecologically and economically effective method. Low-temperature biodegradation of organic contaminants in cold ecosystems is a result of the degradation capacity of the indigenous psychrophilic microbial population. They transform or mineralize organic pollutants into less harmful, non-hazardous substances, which are then integrated into natural biogeochemical cycles.
Several remediation schemes have been implemented successfully at petroleum-contaminated sites in the Arctic and Antarctic regions. Successful on-site treatments include biopiles and land farming, which is now well-developed for cold-regions and offers low cost treatment of petroleum-contaminated soils. The most widely used bioremediation procedure in cold soils is biostimulation of the indigenous microorganisms by supplementation of appropriate nutrients (and optimization of other limiting factors, such as oxygen content, pH and temperature control); however, care has to be taken to avoid inhibition of biodegradation due to over fertilization. Bioaugmentation by inoculating allochthonous hydrocarbon degraders has been used as a bioremediation option to treat petroleum contaminated sites in Alaska, Canada, Greenland, and Norway. Bioaugmentation with non-indigenous or genetically modified/engineered microorganisms is banned in Antarctica, Norway, Iceland, and. The construction of psychrophiles with specific degradative capabilities based on the transfer of the TOL plasmid from the mesophile Pseudomonas putida by conjugation to a psychrophile of the same species; the transconjugant degraded toluene at temperatures as low as 0°C. Recently, the gene coding for a monooxygenase involved in the degradation of aromatic hydrocarbons from the mesophile Pseudomonas stutzeri was recombinantly expressed in the Antarctic Pseudoalteromonas haloplanktis and performance of such strains has still to be proven.
Bioleaching is the extraction of specific valuable metals from their ores through the use of bacteria. Several mines worldwide operate at average temperatures of 8-10°C with satisfactory bioleaching performance. Cold-adapted strains of Acidothiobacillus ferrooxidans mediate the bioleaching of metal sulfides at such temperatures.
Cold-adapted microbial communities able to degrade high amounts of organic compounds within a short time at low temperatures represent a promising source as inocula for low energy wastewater treatment leads to a significant decrease in operational costs. For example, a cold-adapted Arthrobacter psychrolactophilus strain displayed all the features necessary for its use as microbial starter, both from the viewpoint of biosafety and production. At 10°C, the strain induced a complete clarification of a synthetic wastewater turbid medium, it hydrolyzed proteins, starch and lipids, and improved the biodegradability of organic compounds in the wastewater. Another example is low-temperature degradation of phenol, which is the most common representative of aromatic toxic pollutants in a wide variety of wastewaters. Psychrophilic Rhodococcus spp. able to fully degraded up to 12.5 mM phenol at 10°C under fed-batch cultivation; with some strains phenol degradation occurred even at temperatures as low as 1°C. These studies indicated cold adapted bacteria inocula as promising source for accelerated wastewater treatment and also for the construction of biosensors for the rapid monitoring or in situ analysis of pollution.
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