Are there (unicellular) Earth lifeforms that most of their life fly high in the atmosphere without contact with surface? For instance, in clouds, etc? If so, at what max altitude have they been detected?
It sounds like you are talking about aeroplankton, a general term for a wide range of tiny life-forms borne on the wind.
While some of these are essentially passive while airborne (e.g., pollen, spores), others like arthropods and microbes are quite capable of being active in the air as well. In essence, anything that can be easily swept up by the wind can be swept up as high as the wind will take it, often all the way to the jet-stream, and kept aloft for a potentially long time before being deposited elsewhere in the world.
For many of these species, this is a key part of their life cycle and dispersal strategy, and as such they are well adapted to survival at altitude.
The density of available resources at altitude, however, is extremely low, and thus, to the best of my knowledge, there has not yet been any species discovered that primarily lives high in the air, as opposed to merely transiting at altitude before landing elsewhere.
Apparently yes. Caveat: the experimenters are are potentially biased because they believe in panspermia (the idea that life came to Earth from outer space), which is clearly fringe. However, I don't think that invalidates the detection of the three new species, only the interpretation.
(PhysOrg.com) -- Three new species of bacteria, which are not found on Earth and which are highly resistant to ultra-violet radiation, have been discovered in the upper stratosphere by Indian scientists ... In all, 12 bacterial and six fungal colonies were detected, nine of which, based on 16S RNA gene sequence, showed greater than 98% similarity with reported known species on earth. Three bacterial colonies, namely, PVAS-1, B3 W22 and B8 W22 were, however, totally new species. All the three newly identified species had significantly higher UV resistance compared to their nearest phylogenetic neighbours.
The samples were collected at 20km to 41km altitude.
The article doesn't say if the bacteria land. Most probably, we don't know.