Molybdenum as a Micronutrient for Nitrobacter

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Abstract
The requirement of Nitrobacter for molybdenum was investigated by use of a medium purified by chemical means, as well as by depletion by the prior growth of this autotrophic bacterium. During 5 days of growth, added molybdenum induced an approximately 11-fold increase in both nitrite utilization and cell-mass development. In short-term studies, maximal response was obtained with concentrations as low as 10-9 M. No other metal tested substituted for molybdenum. It is estimated that a minimum of 2,000 atoms of molybdenum is required for the synthesis of one Nitrobacter cell. Molybdenum did not directly influence the thermodynamic efficiency of Nitrobacter. The efficiency of molybdenum-deficient cultures and of cultures supplied with the micro-nutrient declined equally during the early stage of development, despite large differences in the amount of nitrite consumed. After the utilization of about 100 [mu]moles of nitrite per ml, cultures supplied with molybdenum became relatively less efficient. A procedure is described whereby large masses of Nitrobacter cells can be obtained with relative ease.