The Arctic plant growth promoting rhizobacteria Pseudomonas putida GR122 secretes an antifreeze protein (AFP) that promotes survival at subzero temperature.
Expression of afpA in E. coli yielded an intracellular 72 kDa protein modified with
both sugar and lipid that exhibited lower level of antifreeze and ice nucleation
activities. The AfpA sequence was most similar to cell wall associated proteins
and less similar to ice nucleation proteins (INPs). Hydropathy plots revealed that the
amino acid sequence of AfpA was more hydrophobic than those of the INPs in the
domain that forms the ice template, thus suggesting that AFPs and INPs interact
differently with ice (Muryoi et al. 2004). The Antarctic Moraxella sp. produce
52-kDa antifreeze protein (AFP) and confirmed by formation of hexagonal ice
crystal. The purified protein was found to have a TH value of 0.104
C. This was
lipoglycoprotein and showed no N-terminal amino acid sequence similarity with
Pseudomonas putida GR12-2, but it had high sequence similarity with outer membrane proteins of Moraxella catarrhalis (Yamashita et al. 2002). This was confirmed
that AFP induced in Moraxella sp. by low temperature had adaptive strategy to
survive at subzero temperature.
An Antarctic sea ice bacterium of the Gram-negative genus Colwellia strain
SLW05 produces an extracellular substance that changes the morphology of growing ice. The full gene sequence was determined and was found to encode a
253-amino acid protein with a calculated molecular mass of 26,350 Dalton. The
predicted amino acid sequence is similar to predicted sequences of ice-binding
proteins recently found in two species of sea ice diatoms and a species of snow
mold. The function of the protein is unknown, but it may act as an ice recrystallization inhibitor to protect membranes at frozen state (Raymond et al. 2007). Table 6.2
represents characteristics of AFP identified in psychrotolerant bacteria.
Two reports reveal a breach in this widely believed notion. In one investigation,
concentrated supernatant of the cell lysate of a bacterium Marinomonas
primoryensis, isolated from a saline and permanently cold Antarctic lake was
found to cause over 2
C freezing point depression, which is higher than the TH
value of most of the AFPs isolated from fishes. The activity was reduced in the
presence of EDTA but could be restored by saturation of EDTA with calcium
chloride. Thus, the antifreeze activity was Ca 2
+ dependent, a feature known so far
to be associated with fish AFPs but not with bacterial AFPs (Garnham et al. 2008).
Subsequently, a cell-free extract of an Antarctic strain Flavobacterium xanthum
IAM12026 has been found to have both freezing point depression and ice
recrystallization-inhibiting activities. The purified protein was found to have a TH
value of 1.19
C (Kawahara et al. 2007). These reports indicate that like fish and
insect AFPs, bacterial AFPs can also act by the mechanism of freeze avoidance.
6.14 Biotechnological Applications
Over the past two decades, understanding of the microbial cold tolerance has much
increased considerably, which could be attributed by several factors, such as the
awareness of accelerated environmental changes in polar regions, evaluation of the
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 207
Expression of afpA in E. coli yielded an intracellular 72 kDa protein modified with
both sugar and lipid that exhibited lower level of antifreeze and ice nucleation
activities. The AfpA sequence was most similar to cell wall associated proteins
and less similar to ice nucleation proteins (INPs). Hydropathy plots revealed that the
amino acid sequence of AfpA was more hydrophobic than those of the INPs in the
domain that forms the ice template, thus suggesting that AFPs and INPs interact
differently with ice (Muryoi et al. 2004). The Antarctic Moraxella sp. produce
52-kDa antifreeze protein (AFP) and confirmed by formation of hexagonal ice
crystal. The purified protein was found to have a TH value of 0.104
C. This was
lipoglycoprotein and showed no N-terminal amino acid sequence similarity with
Pseudomonas putida GR12-2, but it had high sequence similarity with outer membrane proteins of Moraxella catarrhalis (Yamashita et al. 2002). This was confirmed
that AFP induced in Moraxella sp. by low temperature had adaptive strategy to
survive at subzero temperature.
An Antarctic sea ice bacterium of the Gram-negative genus Colwellia strain
SLW05 produces an extracellular substance that changes the morphology of growing ice. The full gene sequence was determined and was found to encode a
253-amino acid protein with a calculated molecular mass of 26,350 Dalton. The
predicted amino acid sequence is similar to predicted sequences of ice-binding
proteins recently found in two species of sea ice diatoms and a species of snow
mold. The function of the protein is unknown, but it may act as an ice recrystallization inhibitor to protect membranes at frozen state (Raymond et al. 2007). Table 6.2
represents characteristics of AFP identified in psychrotolerant bacteria.
Two reports reveal a breach in this widely believed notion. In one investigation,
concentrated supernatant of the cell lysate of a bacterium Marinomonas
primoryensis, isolated from a saline and permanently cold Antarctic lake was
found to cause over 2
C freezing point depression, which is higher than the TH
value of most of the AFPs isolated from fishes. The activity was reduced in the
presence of EDTA but could be restored by saturation of EDTA with calcium
chloride. Thus, the antifreeze activity was Ca 2
+ dependent, a feature known so far
to be associated with fish AFPs but not with bacterial AFPs (Garnham et al. 2008).
Subsequently, a cell-free extract of an Antarctic strain Flavobacterium xanthum
IAM12026 has been found to have both freezing point depression and ice
recrystallization-inhibiting activities. The purified protein was found to have a TH
value of 1.19
C (Kawahara et al. 2007). These reports indicate that like fish and
insect AFPs, bacterial AFPs can also act by the mechanism of freeze avoidance.
6.14 Biotechnological Applications
Over the past two decades, understanding of the microbial cold tolerance has much
increased considerably, which could be attributed by several factors, such as the
awareness of accelerated environmental changes in polar regions, evaluation of the
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 207