MOLECULAR MECHANISMS ADOPTED BY CYANOBACTERIA TO SURVIVE EXPOSURE TO HIGH TEMPERATURE
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Date
2019
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DIVISION OF MICROBIOLOGY ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Molecular mechanisms adopted by cyanobacteria to survive exposure to high
temperature
Increase in global temperature is a serious constraint that limits the productivity of
cyanobacteria. Therefore in the present study, the fresh water nitrogen fixing cyanobacterium
Anabaenadoliolum was exposed to elevated temperature of 30, 35, 40 and 45 oC to investigate
the impact on growth and physiological variables. Elevated temperature resulted in severe
reduction in growth, cellular constituents and nitrogen fixation of the cyanobacterium. The
cyanobacterium was not able to survive temperature exposure beyond 40 oC. Further, random
mutagenesis was induced by exposing the cyanobacteria to ethyl methyl sulphonate (EMS) to
get further insights on the thermo tolerance. While the wild type cyanobacterium A. doliolum
was able to tolerate temperature of 40 oC, the mutant was able to tolerate temperature up to 48
oC. The mutant exhibited higher growth rate, heterocyst frequency and nitrogen fixation. As
compared to wild type, the mutant accumulated low levels of peroxides and lipid peroxidation
products and showed better levels of antioxidant enzymes such as superoxide dismutase,
ascorbate peroxidase, catalase and glutathione reductase. The mutant accumulated more proline
as compared to the wild type. Fatty acid methyl ester (FAME) analysis revealed significant
quantitative and qualitative changes in the fatty acid profile. Maximum number of saturated
fatty acids was found in the mutant strain followed by control where as the wild type exposed
to elevated temperature showed the least diversity of fatty acids. Further, the molecular
mechanisms underlying the temperature tolerance of the wild type and mutant was studied
employing 2D Gel electrophoresis. Fifty seven proteins showed significant changes in their
expression and out of which 17 proteins were significantly identified. Proteins involved in
chaperonin activity, DNA repair and antioxidative defense mechanism were the most
prominent proteins identified through 2DE analysis. The results indicate clear cut tolerance
/adaptation strategies operating in the cyanobacterium to combat the stress induced by exposure
to elevated temperature. The study also registered eight hypothetical proteins in the mutant
strain which were further characterized through in silico approaches. It is presumed that these
proteins are involved in temperature tolerance in the mutant cyanobacterium. Up regulation of
antioxidant enzymes coupled with efficient modulation of fatty acid profile and up regulation
of heat shock proteins confer enhanced thermo tolerance in the mutant. The results of the study
will help to devise strategies in enhancing the utility of A. doliolum as efficient biofertilizer for
rice keeping in view of the anticipated climate change scenario.
Description
T-10274
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