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The vast increase in the number of 16S ribosomal RNA gene sequences that are now available has led to an urgent need to implement taxonomic boundaries and classification principles that can apply to both cultured and uncultured microorganisms. In this Analysis article, the authors use 16S rRNA gene sequence identities to propose rational taxonomic boundaries for high taxa of bacteria and archaea and suggest a rationale for the circumscription of uncultured taxa that is compatible with the taxonomy of cultured bacteria and archaea.
Weitz and colleagues use a biophysical scaling model of intact virus particles to quantify differences in the elemental stoichiometry of marine viruses compared with their microbial hosts. They propose that, under certain circumstances, marine virus populations could make a previously unrecognised and important contribution to the reservoir and cycling of oceanic phosphorus.
Villanuevaet al. analyse the relationship between archaeal membrane lipids and the enzymes that are involved in their biosynthesis and conclude that our current understanding of the archaeal membrane lipid biosynthesis pathway needs some reconsideration. On the basis of amino acid sequence analysis, they present an alternative biosynthetic pathway that involves a 'multiple key, multiple lock' mechanism.