Holman says, "The main difference is in their membrane lipids. Bacterial membrane lipids consist of fatty acids with long alkylic chains" functional groups of singly bonded carbon and hydrogen atoms "which have only one to two terminal methyl groups," groups with one carbon and three hydrogen. "By contrast, archaeal membrane lipids generally consist of branched and saturated isoprenes" a more complex common hydrocarbon "and are relatively less alkylic but have more methyl groups."
By revealing the bright spectral signals of alkylic and methyl groups, together with sulfur functional groups, synchrotron FTIR unambiguously identified the sulfate-reducing metabolic activity of the bacteria within the SM1 samples. The archaeal cells themselves showed no such activity, leading the researchers to posit a thriving mutual metabolism of the archaea and bacteria.
In many cases, such syntrophy requires close physical association. Covering the surface of each SM1 cell the researchers found spines made of three protein strands, equipped with terminal hooks where the strands divided. Moissl-Eichinger named them hami, Latin for barbs or hooks. These "nano-grappling hooks" apparently hold the microbial partners together, working in synchronization. The major hami protein is unlike any known proteinaceous archaeal or bacterial filaments.
How SM1 Euryarchaea interact with their bacterial partners may be a model for understanding other syntrophic relations essential to the carbon and s
|Contact: Paul Preuss|
DOE/Lawrence Berkeley National Laboratory