by Elio
Fig. 1. Electron micrographs of Ca. A. hamiconexum cells within the biofilm. (A) Scanning electron micrograph of dividing cells in the biofilm, showing particles close to the hami and the cells. Bar: 1 μm. (B) Thin-section of one cell, showing dark-stained inclusions likely to contain phosphorus and sulfur (no, they're not phages!). Bar: 200 nm. The dark. Source
Among the microbial world's most unusual structure is a pilus-like filament that looks for all the world like strands of barbed wire with a three-pronged grappling hook at the end. Discovered in 2005 by Moissl and colleagues sticking out from an archaeon, this structure has been called the hamus (pl.: hami), which is Latin for claw, hook, barb, or fishing rod. You might as well add this term to your vocabulary: it’ll show up again. Each cell has about 100 hami distributed all over its surface. Each hamus consist of a long filament decorated by strands that give it the appearance of barbed wire, terminating in a structure that looks like a Ninja grappling hook.
A paper describing the structure in more detail has appeared recently. The hami-bearing organism studied here is an uncultivated archaeon that makes biofilms in a cold sulfidic spring in Germany, where it is found in nearly pure culture. It was given the name Candidatus Altiarchaeum hamiconexum. The proportion of this organism in the biofilms is high enough to permit detailed analysis even if pure cultures are unavailable.
Fig. 2 (a) Electron micrograph of hamus filaments (negatively contrasted. Bars: 100 nm. (b, c) Hamus anchoring structure as visualized after release of the hami by dissolving the membrane. In c, the positions of the two membranes are indicated (white line). (d) Assembly and formation model, based on microscopic and genetic data. The individual threads (colored differently but composed of the same subunits) are formed at the inner membrane, and the hamus structure is built in the periplasm, before being pushed through the outer membrane. The first prickle appears right outside of the cell. Source
Hami consist of many copies of a single protein that is homologous, of all things, to some archaeal surface S-proteins. The hamus protein (I haven’t seen it called "hamin") is rich in beta-sheets, suggesting that it may be able to self-assemble, and is highly glycosylated. These organisms have two cell membranes (rare for an archaeon) and the hami span both, like the flagella and pili of gram-negatives. As discussed here, the most obvious role for hami is for cell attachment and biofilm formation.
In the article that first described the hami, you read: "It appears that one of the most basic forms of the microbial world long ago developed a tool that mankind now uses in technology worldwide, a parallel of direct interest to the fields of bionics and biomimetrics." What's next?
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