Note­wor­thy — This pa­per de­scribes the highly evolved in­ter­ac­tions be­tween anaer­o­bic pro­tists and their syn­trophic sul­fate-re­duc­ing sym­bionts. Re­mark­ably, the sym­bionts re­side in an elab­o­rate sym­bio­so­mal mem­brane net­work...