Summary
The majority of eukaryotes found living in extreme environments are microbial and a central problem in the study of all microbial eukaryotes is the lack of reliable cultivation methods. Only a tiny fraction of the organisms that can be observed in environmental samples can be cultured in the laboratory, even from mesophilic environments. Extreme environments are generally more difficult to replicate in the laboratory and more difficult to keep stable. The ability to bring these fascinating creatures living into the laboratory is currently the biggest stumbling block to advancing knowledge.
Eukaryotic microbial life may be found actively growing in almost any extreme condition where there is a sufficient energy source to sustain it, with the exception of high temperature (>70ºC). For most eukaryotes, therefore, a central requirement for growth in a habitat is sufficient energy flowing through the biosphere to support a second trophic level, as illustrated by the soda lakes Simi and Nakuru (see below). If it were not for the high productivity of Lake Nakuru, the low diversity in Lake Simi could easily have been attributed to its extreme pH.
Colonisation of extreme habitats is not normally restricted to a single taxonomic group, with the exception of xerophilous habitats which are only tolerated by the fungi. Eukaryotic cells are exceedingly adaptable and not notably less adaptable than the prokaryotes, although most habitats have not been sufficiently well explored for sound generalisations.
http://www.nhm.ac.uk/research-curation/projects/euk-extreme/
Microorganisms in fiction
Microorganisms have frequently played an important part in science fiction, both as agents of disease, and as entities in their own right.
Some notable uses of microorganisms in fiction include:
The War of the Worlds, where microorganisms play important thematic and plot-related roles.
Fantastic Voyage, in which some scientists are miniaturised to microscopic size and observe micro-organisms from a new perspective
Blood Music, in which a colony of microorganisms is given intelligence
The Andromeda Strain, in which extraterrestrial microorganisms kill several people
Twelve Monkeys, James Cole (Bruce Willis) searches for a pure germ in the past, which creates a deadly plague in the future. Also, Brad Pitt (as Jeffery Goines) discusses his germaphobia.
http://en.wikipedia.org/wiki/Microorganism