Frankia Vesicles |
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| Frankia CcI3 with vesicles (Phase contrast) (Benson, Bourret, Harriott-Sims, 2003) | Vesicles isolated from sucrose gradient (Noridge & Benson, 1986) |
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HFPCpI1 vesicle with envelope, and cross walls. (D. Benson, O. Harriot) |
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Vesicle stem region with lipid layers on the surface. (D. Benson, O. Harriot) |
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Vesicles of strain HFPCcI3- dark field (W. Silvester & R. Parsons) |
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Vesicles of strain HFPCcI3 germinating in medium with NH4+ (Harriott & Benson) |
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Bacteriohopane tetrol and bacteriohopane tetrol phenylacetate ester |
All Frankia strains tested make "vesicles" in N-deficient culture, and often in symbiosis. Vesicles are lipid-encapsulated, roughly spherical cellular structures that measure between 2 to 6 mm in diameter. They are attached to hyphae by a short vesicle stalk that is also encapsulated. Vesicles contain nitrogenase and ancillary enzymes.
Vesicle Envelopes
Vesicles have a laminated lipid envelope (Lamont et al., 1988; Torrey and Callaham, 1982). The number of laminae is correlated with the pO2 of the surrounding medium (Parsons et al, 1987). The layers are extracted during fixation for TEM, leaving a "void area" (Lalonde et al, 1976) but they can be visualized by permanganate fixation (Harriott et al., 1991). Each layer is about 4 nm thick. Isolated vesicle envelopes are comprised primarily of hopanoid lipids (Harriott et al, 1991; Berry et al., 1993).
Bacteriohopanes play a role in membrane stability and fluidity (Demel et al, 1976; Kannenberg et al., 1980). In Frankia vesicles, they may limit oxygen diffusion into the O2 labile nitrogenase.
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