NITROGEN-FIXATION (ACETYLENE-REDUCTION) IN STONY CORALS - EVIDENCE FOR CORAL-BACTERIA INTERACTIONS

Nitrogen fixation, as measured by acetylene reduction, has been detect ed to be associated with various hermatypic corals. Experiments were c arried out on the massive coral Favia favus both in situ and in the la boratory. Nitrogen fixation activity was found to be light dependent a nd fully inhibited by 5 x 10(-6) M DCMU [3-(3,4-dichlorophenyl)-1,1-di methylurea]. Addition of glucose restored nitrogen fixation activity b oth in the dark and in the presence of DCMU. Removal of the coral tiss ue prevented acetylene reduction, while addition of glucose to the cor al skeleton restored this activity. Bacteria isolated from the coral s keleton were found by dot blotting to contain the nifH gene. These res ults suggest that nitrogen-fixing bacteria found in the skeleton of co rals benefit from organic carbon excreted by the coral tissue. The int eraction between the nitrogen-fixing organisms and the coral may be of major importance for the nitrogen budget of the corals.