• Harinder Singh

      Articles written in Journal of Biosciences

    • Unusual radioresistance of nitrogen-fixing cultures of Anabaena strains

      Harinder Singh Tonina Fernandes Shree Kumar Apte

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      Nitrogen-fixing cultures of two species of the filamentous, heterocystous cyanobacterium Anabaena, namely Anabaena sp. strain L-31 and Anabaena torulosa were found to be highly tolerant to 60Co gamma radiation. No adverse effect on diazotrophic growth and metabolism were observed up to a dose of 5 kGy. At higher doses, radiation tolerance showed a correspondence with the inherent osmotolerance, with Anabaena L-31 being the more radiation tolerant as well as osmotolerant strain. In Anabaena L-31, exposure to 6 kGy of gamma rays resulted in genome disintegration, but did not reduce viability. Irradiation delayed heterocyst differentiation and nitrogen fixation, and marginally affected diazotrophic growth. All the affected parameters recovered after a short lag, without any discernible post-irradiation phenotype. The radiation tolerance of these Gram-negative photoautodiazotrophs is comparable with that of the adiazotrophic photoautotrophic cyanobacterium Chroococcidiopsis or adiazotrophic heterotroph Deinococcus radiodurans. This is the first report of extreme radioresistance in nitrogen-fixing Anabaena cultures.

    • Low concentrations of ethanol during irradiation drastically reduce DNA damage caused by very high doses of ionizing radiation

      HARINDER SINGH SHREE KUMAR APTE

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      Presence of low concentrations (1–2%) of ethanol during irradiation exhibited significant protection against DNA damagecaused by very high doses (2–12 kGy) of 60Co-gamma-rays in vitro. Radiation-induced DNA damage was substantiallyreduced in different types of DNA molecules (chromosomal DNA from Anabaena 7120 or Deinococcus radiodurans orbacteriophage Lambda, and plasmid pBluescript DNA) when irradiated in the presence of ethanol, thus indicating thegeneric nature of ethanol protection. The radioprotection appeared to be a consequence of the well known ability of ethanolto scavenge hydroxyl radicals. Addition of ethanol during 6 kGy irradiation also reduced DNA damage in vivo andimproved post-irradiation growth recovery of Anabaena 7120 cultures. To our knowledge, this is the first instance of abilityof very low ethanol concentrations to protect DNA from damage triggered by extremely high doses of 60Co-gamma rays.

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