In five experiments, Leishmania (Leishmania) major (MRHO/SU/59/P-strain)
grew poorly when seeded in FYTS medium supplemented with 15% fetal calf
serum, but presented several peculiar pairs of promastigotes diametrically
opposed and attached at their posterior ends (5.8-13.5%). As seen in
Giemsa-stained smears, a ring-like line and/or an enlargement, generally
occurred at the parasite junction. A close proximity of nuclei, which
sometimes were difficult to distinguish from each other, was also observed
at this junction. Several of these pairs appeared to be composed of fused
cells in which the nuclei could be apparently fused, as shown by
fluorescence microscopy to detect beta-tubulin and DNA, and by scanning
electron microscopy. Under other culture conditions these pairs were absent
or occurred at very low rates (0.2-2.2%). Such pairs differ markedly from
longitudinally dividing cells and resemble those described in two other
Leishmania species, as well as in Herpetomonas megaseliae and Phytomonas
davidi, suggesting steps of a putative sexual process.
