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

自然界对环境条件的变化，如化学品污染，具有恢复能力。细菌可以发挥重要作用，因为它们在化学分解方面的多样性和生成时间短，使它们能够对新的环境做出快速反应。因此，我们尝试在兼性厌氧条件下，通过还原硝酸盐生成铵的方法，检测出具有中和能力的土壤耐酸细菌，并成功地分离到这类细菌。因此，从土壤和沉积物样品中分离到的49个菌株可以在以硝酸盐为唯一氮源的琼脂培养基上，在pH为4的氮气气氛中生长。其中，有25株菌株还原硝酸盐和产铵。我们对3株生长较好的菌株进行了鉴定，它们具有较高的还原硝酸盐和产铵能力。其中两株为气单胞菌，另一株为梭状芽胞杆菌。在以硝酸盐为唯一氮源的液体介质中，所有菌株均能在pH为4~7的范围内生长，但在pH为3、8和10的条件下不能生长。在氨离子存在下，所有菌株都表现出硝酸盐还原的能力，土壤中有两株气单胞菌的这一能力不受土壤含量的影响。

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.