Acid tolerant soil bacteria which reduce nitrate to produce ammonium under facultative anaerobic condition

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Nature has restoring capacity against change of environmental condition such as contamination of chemicals. The bacteria can play an important role because of their diversity in chemical decomposition and short generation time so that they can response rapidly to the new environment. Therefore we tried to detect the acid tolerant soil bacteria having neutralizing capacity by reducing nitrate to produce ammonium under facultative anaerobic condition, and succeeded to isolate such bacterial strains. Thus, 49 isolates from soil and sediment samples could grow at pH 4 on agar medium counting nitrate as a sole N source under nitrogen atmosphere. Among them, 25 strains reduced nitrate and produced ammonium. We characterized 3 better growing strains with higher capacities of reducing nitrate and producing ammonium. Two were classified to be Aeromonas and another to be Clostridium. In the liquid medium counting nitrate as a sole N source, all strains grew in the range of pH 4 to 7 with an increase of pH,although they failed to grow at pH 3,8 and 10. Any of them showed nitrate reduction in the presence of ammonium, and the contents of soil did not affect these capabilities of two Aeromonas strains.It is deduced from these findings that in soil there are many bacteria which can neutralize acidic pH by nitrate and they may be useful tools for bioremediation against acidification of soil.