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Naegleria species (& their close relative Acanthamoeba) are pathogenic free-living amoebae, i.e. opportunistic rather than obligate pathogens, e.g. Naegleria fowleri. These organisms are ubiquitous in the environment, in soil, water and air. Infections in humans are rare but may be acquired through water entering the nasal passages (usually during swimming) and by inhalation.
Naegleria gruberi is an amoeba-flagellate, so called because the organism can exist as an amoeba and also as swimming flagellates. The amoeboid (trophozoite) stage is 10 to 15 µm in diameter and feeds by phagocytosis of bacteria and divides by binary fission. The flagellated stage does not feed or divide. You can watch Naegleria feeding in the following realtime video clip:
The differentiation of Naegleria provides a valuable system for examining a number of interesting problems in eukaryote cell and developmental biology. Some of the advantages of the system arise from the ease and speed with which cells can be grown and induced to differentiate. Another important advantage is that the differentiation of amoebae into flagellates is relatively synchronous. This means that following the population of amoebae as they differentiate into flagellates is similar to following the changes in a single cell: