An open reading frame encoding a polypeptide with significant homology (about 28% identity and 16% similarity) to human aspartoacylase (ASPA) was identified in the genome of Prochlorococcus marinus CCMP 1375, an oxyphototrophic bacterium. Sequence alignments show that, in particular, the regions previously suggested to form the catalytic core of human ASPA are evolutionarily conserved and nearly identical to that found in the Prochlorococcus putative ASPA. A glutamate at position 273 is located central to the strongly conserved INEAAY motif and corresponds to a glutamate-285 in human ASPA. A point mutation at this site, resulting in a Glu285Ala missense mutation, was identified previously as the molecular basis for Canavan disease, a form of leukodystrophy. The data provide new insights about conserved and hence functionally important domains of ASPA. The detection of this gene in an unicellular prokaryote demonstrates that this enzymatic activity is more widespread than expected previously. Furthermore, bacteria may be used as simple model organisms to study different forms of ASPA.