Symbiotic innovation in the oxymonad Streblomastix strix.
Streblomastix strix is an enigmatic oxymonad found exclusively in the hindgut of the damp-wood termite Zootermopsis. Streblomastix has a number of unusual morphological characters and forms a complex but poorly understood symbiosis with epibiotic bacteria. Here we described the ultrastructure of S. strix, with emphasis on the axial cytoskeleton and cell-cell associations, in its normal state and when treated with antibiotics. In untreated cells, epibiotic bacteria were orderly arranged end-to-end on six or seven longitudinal vanes, giving S. strix a stellate appearance in transverse section. The epibiotic bacteria were unusually long bacilli of at least three different morphotypes. Bacteria adhered to the oxymonad host by distinct cell-cell junctions that protruded between the poles of adjacent epibiotic bacteria. Treating termites with the antibiotic carbenicillin led to the loss of most (but not all) of the bacteria and the transformation of S. strix from a long slender cell to a teardrop-shaped cell, where the axostyle was compacted and became bifurcated near the posterior end.
Leander
Brian S
BS
Canadian Institute for Advanced Research, Program in Evolutionary Biology, Departments of Botany and Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. bleander@interchange.ubc.ca
Keeling
Patrick J
PJ
D000818:Animals; D001419:Bacteria / Q000302:isolation & purification* / Q000648:ultrastructure; D018407:Bacterial Physiological Phenomena; D056890:Eukaryota / Q000382:microbiology* / Q000502:physiology / Q000648:ultrastructure; D020049:Isoptera / Q000469:parasitology*; D013559:Symbiosis