Why sulphide is toxic to microorganisms?

Answer 1

It's not toxic to all of them. There's a bacterium that lives in volcanic temperatures whose metabolism depends on hydrogen sulfide. But just as cyanohemoglobin and thiohemoglobin interfere with oxygen transfer in the bloodstream of humans, the sulfide anion can be seen as interfering in the normal cell chemistry of microorganisms. by tying up as insoluble sulfides metal ions that might otherwise serve as essential coenzymes.

That's just a guess.

Answer 2

HS- and S= react with proteins and render them useless.