Bistat and pH-auxostat fermentations have been used to study the effec
t of Cu++ on Methylococcus capsulatus (Bath) growing on natural gas. A
n optimum for growth rate and yield was found to be within the range o
f 3-6 mu mole Cu/g dry cells. The cells absorb quantitatively Cu++ fro
m surrounding broth until 6 mu mole Cu/g dry cells has been reached. A
lso the effect of copper on sMMO activity has been investigated. A com
plete suppressing of sMMO is obtained with 1.5 mu M Cu/g dry cells.