Oxygen tolerance and occurrence of superoxide dismutase as an antioxidant enzyme in Metopus es.
The free-living anaerobic ciliate Metopus es was found to possess moderate tolerance to oxygen. Direct oxygen exposure led to the death of >80% of the population within 24h, but the remaining cells exhibited some oxygen tolerance and survived up to 4 days without any growth. Survival of the ciliate was observed only in an oxygen tension up to 7.0microM, and higher O(2) concentrations (>7.0microM) were found to be detrimental with a K(m) value of 3.5microM. The percentage of survival (50%) was higher when the culture was exposed to a low oxygen level (1.3microM) and it decreased with increasing oxygen tension. No catalase activity was detected in the extract of surviving ciliates. Maximum superoxide dismutase (SOD) activity of 1.52+/-0.4U/mg protein was observed at 1.3microM oxygen. SOD activity was not affected by cyanide or hydrogen peroxide, indicating that it belongs to the Mn type of SOD. Methanogenic endosymbionts in M. es lost their autofluorescence on oxygen exposure of >5.0microM, but their viability was not permanently affected, as indicated by the maintenance of a similar number of methanogens/cell upon restoring the anaerobic condition.
Process Engineering and Environmental Technology Division, National Institute for Interdisciplinary Science and Technology, CSIR, Thiruvananthapuram, 695019 Kerala, India. niminarayan@gmail.com <niminarayan@gmail.com>
Nimi
N
Narayanan
Bhaskaran
B
Krishnakumar
Vattakkatt Balakrishnan
VB
Manilal
D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D016798:Ciliophora / Q000187:drug effects* / Q000201:enzymology*; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism / Q000633:toxicity*; D013482:Superoxide Dismutase / Q000378:metabolism*; D016019:Survival Analysis
D000975:Antioxidants; D013482:Superoxide Dismutase; D010100:Oxygen