TRACHELOMONAS HISPIDA VAR. CORONATA (EUGLENOPHYCEAE). III. ENVELOPE ELEMENTAL COMPOSITION AND MINERALIZATION1,2

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Abstract
This report is the first direct demonstration of Mn deposition in envelopes (loricas) of Trachelomonas in culture. The envelopes of Trachelomonas hispida var. coronata Lemm. were analyzed for elemental composition by X‐ray fluorescence spectrometry (XRF), atomic absorption spectrophotometry (AA), and electron microscopic, energy‐dispersive X‐ray spectroscopy (EM‐EDS). The envelopes contained extensive deposits of manganese (20–60 wt. %) and lesser amounts of Si, Ca and either Ba or Ti, the last three together totalling less than 5% by weight. The average amount of Mn per envelope was estimated at 1.5 × 10−10 g. Traces of Na, K, P, S and Cl were also detectable. Biomineralization of envelopes was studied by comparison of envelope substructure and composition in lightly colored, golden and dark brown envelopes that were isolated by micromanipulation, processed individually or in groups, and analyzed by SEM, TEM, EM‐EDS, and scanning transmission EM‐EDS (STEM‐EDS). Dark envelopes were thicker (1–4 μm), more ornate and less porous than light envelopes, but the ultrastructure of the two was similar. In both types of envelopes, distribution and thickness of Mn‐containing fibrillar to needle‐like microcrystallites were similar. However, dark envelopes contained a greater density of granular deposits around the needle‐like microcrystallites than did light envelopes. Dark envelopes contained 2–40 times more Mn than did light envelopes, but since envelope mass is proportionately greater, Mn concentrations were similar. Our results suggest that the extent of mineralization depends upon the amount of mucilage secreted. Biomineralization studies with Trachelomonas offer the rare advantage that mineral deposition occurs extracellularly, and not within membrane‐bound compartments as in many other unicellular model systems.