The role of clay minerals in the preservation of Precambrian organic-walled microfossils.

Precambrian organic-walled microfossils (OWMs) are primarily preserved in mudstones and shales that are low in total organic carbon (TOC). Recent work suggests that high TOC may hinder OWM preservation, perhaps because it interferes with chemical interactions involving certain clay minerals that inhibit the decay of microorganisms. To test if clay mineralogy controls OWM preservation, and if TOC moderates the effect of clay minerals, we compared OWM preservational quality (measured by pitting on fossil surfaces and the deterioration of wall margins) to TOC, total clay, and specific clay mineral concentrations in 78 shale samples from 11 lithologic units ranging in age from ca.

Fossilisation processes and our reading of animal antiquity.

Estimates for animal antiquity exhibit a significant disconnect between those from molecular clocks, which indicate crown animals evolved ∼800 million years ago (Ma), and those from the fossil record, which extends only ∼574 Ma. Taphonomy is often held culpable: early animals were too small/soft/fragile to fossilise, or the circumstances that preserve them were uncommon in the early Neoproterozoic. We assess this idea by comparing Neoproterozoic fossilisation processes with those of the Cambrian and its abundant animal fossils.

A site-directed Staphylococcus aureus hemB mutant is a small-colony variant which persists intracellularly.

Although small-colony variants (SCVs) of Staphylococcus aureus have been recognized for many years, this phenotype has only recently been related to persistent and recurrent infections. Clinical S. aureus SCVs are frequently auxotrophic for menadione or hemin, two compounds involved in the biosynthesis of the electron transport chain elements menaquinone and cytochromes, respectively.