Been following this topic for a little bit now, and one thing I don't see being discussed very often is the possibility that the phosphine gas is being created

Been following this topic for a little bit now, and one thing I don't see being discussed very often is the possibility that the phosphine gas is being created by bacteria or microbes of terrestrial origin. I.e. who's to say that the lander that made planetfall a while ago wasn't contaminated with a hardy strain of bacteria?