Mechanistically Diverse Pathways for Sulfoquinovose Degradation in Bacteria

Sulfoquinovose (6-deoxy-6-sulfo-d-glucose, SQ) is the polar headgroup of sulfolipids present in plants and other photosynthetic organisms and is one of the most abundant organosulfur compounds in nature. Bacterial degradation of SQ, termed sulfoglycolysis, is thus an important part of the global sulfur cycle. Three sulfoglycolysis pathways have been reported to date, the first analogous to the Embden–Meyerhof–Parnas (sulfo-EMP) glycolytic pathway (reported in Gram-negative γ-proteobacteria), the second analogous to the Entner–Doudoroff (sulfo-ED) glycolytic pathway, and the third involving a transaldolase (sulfo-TAL) related to that in the pentose phosphate pathway. Here, we report the discovery of three additional sulfoglycolysis pathways, the first involving a transketolase (sulfo-TK) related to that in the pentose phosphate pathway, the second involving oxygenolytic C–S cleavage of SQ by a flavin-dependent alkanesulfonate monooxygenase (sulfo-ASMO), and the third being a variant of the sulfo-EMP pathway in Gram-positive bacteria (sulfo-EMP2). Our findings underscore the diversity of mechanisms through which bacteria degrade and utilize this ubiquitous organosulfur compound as a nutrient source.