leptonema illini leptonema illini leptonema illini is a species of bacteria. it belongs to the spirochetes and it is the only species of the genus leptonema. it can be found in water and soil media. leptonema illini scientific classification domain: bacteria phylum: spirochaetota class: spirochaetia order: leptospirales family: leptospiraceae genus: leptonema species: l. illini binomial name leptonema illinihovind-hougen 1983 characteristics leptonema are gram-negative bacteria, very thin, helical bacteria of about 0.1-0.2 μm in diameter and 13 to 21 μm. length. they are usually unicellular, but can also be seen as short chains in growing cultures.