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
Acidithiobacillus ferrooxidans mediate the bioleaching of metal sulfides at such
temperatures (Rossi 1999).
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 (Gratia et al. 2009). 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 degrade
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 (Margesin et al. 2005b).
These studies indicated cold-adapted bacteria inocula as a promising source for
accelerated wastewater treatment and also for the construction of biosensors for
the rapid monitoring or in situ analysis of pollution (Margesin et al. 2007).
6.14.2 Biological Cryoprotectants
Microbial cryoprotectants like trehalose have immense biotechnological potential
and can be used as biological cryoprotectants in a wide range of applications
(Lillford and Holt 2002). Similarly, the cold-active enzymes and Anti-Freeze
Proteins (Afps) from bacteria can be used in a wide variety of ways. Commercially,
there appear to be an infinite number of applications for antifreeze proteins. AFPs
appear to be useful in cryosurgery and also in the cryopreservation of whole
organisms, isolated organs, cell lines, and tissues (Tange et al. 2003).
The cryoprotective exopolysaccharides producing Pseudoalteromonas arctica
were isolated from sediment in King George Island, Antarctica. The presence of
0.1% (w/v) purified exopolysaccharide of bacterium showed the survival ratio of
E. coli cells, which was as high as 82.6% over three repeated freeze–thaw cycles. In
addition, at much lower concentrations (0.1–1.0%), purified exopolysaccharide
(P-21653) resulted in survival ratios was 83.1–98.4% similar to those of two
commercially available cryoprotectants (VEG plus X-1000, 92.9% and VM3,
95.3%), which were utilized at the recommended concentrations (90%). Thus,
biochemical characteristics of EPS reflect that this compound may be used as
bio-cryoprotectant in medical applications and in the food industry (Kim and Yim
2007).
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 213
the use of bacteria. Several mines worldwide operate at average temperatures of
8–10
C with satisfactory bioleaching performance. Cold-adapted strains of
Acidithiobacillus ferrooxidans mediate the bioleaching of metal sulfides at such
temperatures (Rossi 1999).
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 (Gratia et al. 2009). 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 degrade
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 (Margesin et al. 2005b).
These studies indicated cold-adapted bacteria inocula as a promising source for
accelerated wastewater treatment and also for the construction of biosensors for
the rapid monitoring or in situ analysis of pollution (Margesin et al. 2007).
6.14.2 Biological Cryoprotectants
Microbial cryoprotectants like trehalose have immense biotechnological potential
and can be used as biological cryoprotectants in a wide range of applications
(Lillford and Holt 2002). Similarly, the cold-active enzymes and Anti-Freeze
Proteins (Afps) from bacteria can be used in a wide variety of ways. Commercially,
there appear to be an infinite number of applications for antifreeze proteins. AFPs
appear to be useful in cryosurgery and also in the cryopreservation of whole
organisms, isolated organs, cell lines, and tissues (Tange et al. 2003).
The cryoprotective exopolysaccharides producing Pseudoalteromonas arctica
were isolated from sediment in King George Island, Antarctica. The presence of
0.1% (w/v) purified exopolysaccharide of bacterium showed the survival ratio of
E. coli cells, which was as high as 82.6% over three repeated freeze–thaw cycles. In
addition, at much lower concentrations (0.1–1.0%), purified exopolysaccharide
(P-21653) resulted in survival ratios was 83.1–98.4% similar to those of two
commercially available cryoprotectants (VEG plus X-1000, 92.9% and VM3,
95.3%), which were utilized at the recommended concentrations (90%). Thus,
biochemical characteristics of EPS reflect that this compound may be used as
bio-cryoprotectant in medical applications and in the food industry (Kim and Yim
2007).
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 213