NifS-like cysteine desulfurases are widespread enzymes involved in the mobi-lization of sulfur from cysteine. The genome of the filamentous diazotrophic cyanobacterium AnabaenaPCC 7120 contains four open reading frames potentially encoding NifS-like proteins. One of them, alr2505, belongs to the pkn22operon, which enablesAnabaenato cope with oxidative stress.