A pathway for isethionate dissimilation in Bacillus krulwichiae

Abstract

Hydroxyethyl sulfonate (isethionate) is widely distributed in the environment as an industrial pollutant and as a product of microbial metabolism. It is used as a substrate for growth by metabolically diverse environmental bacteria. Aerobic pathways for isethionate dissimilation in Gram-negative bacteria involve the cytochrome c-dependent oxidation of isethionate to sulfoacetaldehyde by a membranebound flavoenzyme (IseJ), followed by C-S cleavage by the thiamine pyrophosphate (TPP)-dependent enzyme sulfoacetaldehyde acetyltransferase (Xsc). Here, we report a bioinformatics analysis of Xsc-containing gene clusters in Gram-positive bacteria, which revealed the presence of an alternative isethionate dissimilation pathway involving the NAD+-dependent oxidation of isethionate by a cytosolic metal-dependent alcohol dehydrogenase (IseD). We describe the biochemical characterization of recombinant IseD from the haloalkaliphilic environmental bacterium Bacillus krulwichiae AM31DT and demonstrate the growth of this bacterium using isethionate as its sole carbon source, with the excretion of sulfite as a waste product. The IseD-dependent pathway provides the only mechanism for isethionate dissimilation in Gram-positive species to date and suggests a role of the metabolically versatile Bacilli in the mineralization of this ubiquitous organosulfur compound.