CHARACTERIZATION OF THE GENE ENCODING THE AUTOTROPHIC ATP SULFURYLASEFROM THE BACTERIAL ENDOSYMBIONT OF THE HYDROTHERMAL VENT TUBEWORM RIFTIA-PACHYPTILA

ATP sulfurylase is a key enzyme in the energy-generating sulfur oxidat ion path,ways of many chemoautotrophic bacteria. The utilization of re duced sulfur compounds to fuel CO2 fixation by the still-uncultured ba cterial endosymbionts provides the basis of nutrition in invertebrates , such as the tubeworm Riftia pachyptila, found at deep-sea hydrotherm al vents. The symbiont-containing trophosome tissue contains high leve ls of ATP sulfurylase activity, facilitating the recent purification o f the enzyme. The gene encoding the ATP sulfurylase from the Riftia sy mbiont (sopT has now been cloned and sequenced by using the partial am ino acid sequence of the purified protein. Characterization of the sop T gene has unequivocally shown its bacterial origin. This is the first ATP sulfurylase gene to be cloned and sequenced from a sulfur-oxidizi ng bacterium. The deduced amino acid sequence was compared to those of ATP sulfurylases reported from organisms which assimilate sulfate, re sulting in the discovery that there is substantial homology with the S accharomyces cerevisiae MET3 gene product but none with the products o f the cysDN genes from Escherichia coil nor with the nodP and node gen es from Rhizobium meliloti. This and emerging evidence from other sour ces suggests that E. coli may be atypical, even among prokaryotic sulf ate assimilators, in the enzyme it employs for adenosine 5'-phosphosul fate fate formation. The sopT gene probe also was shown to specificall y identify chemoautotrophic bacteria which utilize ATP sulfurylase to oxidize sulfur compounds.