Your guess is as good as anyone's at this point of our knowledge, but, if they are growing entirely suspended in atmosphere, I can imagine that, even though for

Your guess is as good as anyone's at this point of our knowledge, but, if they are growing entirely suspended in atmosphere, I can imagine that, even though for most common elements (oxygen, nitrogen...) passive diffusion (like respiration) would suffice, for rarer nutrients these organisms would need some kind of "scooping" to gather and filter bigger swathes of air. Although these organisms may not exist at all, for all we know...