comproportionation:
A reaction in which an element in a higher oxidation state reacts with the same element in a lower oxidation state to give the element in an intermediate oxidation state. For example Ag2+(aq)+Ag(s) → 2Ag+(aq) It is the reverse of disproportionation.
Ag2+(aq)+Ag(s) → 2Ag+(aq)
[Oxford Reference]
Noted in “Why the hunt for alien life is under way far beneath Earth’s surface,” Donna Lu, NewScientist (16 November 2019, paywall):
Just as photosynthesis in effect reverses the chemistry of aerobic respiration, does anything make a living by turning hydrogen sulphide and sulphate back into pure sulphur? No such organisms, known as sulphur comproportionators, have ever been found. But in theory, at least, the answer is yes. “It’s likely that in 3 billion plus years of evolution and the right pressures, some species have developed the ability to do this,” says [Pennsylvania State University astrobiologist Jennifer] Macalady.
