THE NEAR‐SPINELESS TRACHELOMONAS GRANDIS (EUGLENOPHYCEAE) SUPERFICIALLY APPEARS SPINY BY ATTRACTING BACTERIA TO ITS SURFACE1,2

Abstract

ABSTRACT Trachelomonas grandis Singh has a mucilaginous, highly porous mineralized lorica (envelope) generally without ornamentation except occasionally for a few short, tapered, anterior or posterior spines. However, as our first cultures of this species aged, rod‐shaped structures appeared on the loricas. That these surface projections were bacteria was determined by scanning and transmission electron microscopy. The bacteria, 2‐6 μm long with rounded apices, were oriented perpendicular to the exterior lorica surface and were attached on one end by apically produced tie‐down fibers. The bacteria also secreted fibers over their entire surface, forming a network between them that collapsed during specimen preparation for scanning electron microscopy. The density of the surface bacteria increased with time until the lorica took on a “spiny” appearance superficially similar to lorica extensions of algal origin. In mature algal specimens, an estimated 1200‐1800 bacteria per lorica occurred as a monolayer, the maximum number related to the surface area of the lorica available for bacterial colonization. The bacteria, always motionless while attached, showed putative evidence of budding. Fission formed short chains of up to three cells on the lorica. Our cultures maintained this association for 8 years (1972‐1979). However, cultures ordered for further study in the past year have failed to develop loricas with more than just a few bacterial cells, and most have none.