Deep subseafloor sediments may contain depressurization-sensitive, anaerobic, piezophilic prokaryotes. To test this we developed the DeepIsoBUG system, which when coupled with the HYACINTH pressure-retaining drilling and core storage system and the PRESS core cutting and processing system, enables deep sediments to be handled without depressurization (up to 25 MPa) and anaerobic prokaryotic enrichments and isolation to be conducted up to 100 MPa. Here, we describe the system and its first use with subsurface gas hydrate sediments from the Indian Continental Shelf, Cascadia Margin and Gulf of Mexico. Generally, highest cell concentrations in enrichments occurred close to in situ pressures (14 MPa) in a variety of media, although growth continued up to at least 80 MPa. Predominant sequences in enrichments were Carnobacterium, Clostridium, Marinilactibacillus and Pseudomonas, plus Acetobacterium and Bacteroidetes in Indian samples, largely independent of media and pressures. Related 16S rRNA gene sequences for all of these Bacteria have been detected in deep, subsurface environments, although isolated strains were piezotolerant, being able to grow at atmospheric pressure. Only the Clostridium and Acetobacterium were obligate anaerobes. No Archaea were enriched. It may be that these sediment samples were not deep enough (total depth 1126–1527 m) to obtain obligate piezophiles.

The use of Sporosarcina pasteurii to precipitate calcium carbonate in the anoxic subsurface via ureolysis has been proposed for reducing porosity and sealing fractures in rocks. Here we show that S. pasteurii is unable to grow anaerobically and that the ureolytic activity previously shown under anoxic conditions is a consequence of the urease enzyme already present in the cells of the aerobically grown inoculum. The implications are discussed, suggesting that de novo synthesis of urease under anoxic conditions is not possible and that ureolysis may decline over time without repeated injection of S. pasteurii as the urease enzyme degrades and/or becomes inhibited. Augmentation with a different ureolytic species that is able to grow anaerobically or stimulation of natural communities may be preferable for carbonate precipitation over the long term.

Clay minerals can be an important agent in the fossilization of soft tissues, notably in the Ordovician Soom Shale of South Africa and the Cambrian Burgess Shale of Canada. The replication of morphology has been attributed to adsorption of pre-existing clay minerals, or direct precipitation of authigenic clays onto tissues. Attachment of quartz and kaolinite to the surface of lobster eggs demonstrates experimentally for the first time that soft tissues could fossilize in pre-existing minerals. However, the eggs became coated only in the presence of metabolizing bacteria. This experimental approach could be used to explore why Burgess Shale-type preservation declined after the mid-Cambrian.

Both the timing and nature of early Metazoan evolution remain controversial, with complementary, and sometimes conflicting, evidence from molecular data and fossil occurrences. Exceptionally preserved embryos from the Neoproterozoic and early Phanerozoic remain an important source of direct evidence: fossil embryos of complex organisms at a relatively advanced stage of development provide a test of hypotheses based on comparative embryology and the evolutionary development of living forms. Understanding how these fossils are preserved, and what morphological changes are induced by decay, is essential to interpreting the evidence that they provide for early metazoan evolution. A range of decay experiments was performed on eggs of living arthropods to explore the controls on their mineralization and likely fossilization. Surface mineralization occurred within one month, mainly in calcium carbonate or in a combination of calcium carbonate and calcium phosphate. There was no enhancement of mineralization with increased phosphate or calcium concentrations, or with changing oxic/anoxic conditions, and mineralization occurred both in the absence and presence of an associated carcass. The eggs showed remarkable resistance to decay, indicating that an extended time-period (more than a year) would be available for mineralization and fossilization in some settings. Where sediment was available, it could become attached to the egg surface, replicating the morphology in a fashion analogous to mineralization. The interior of the eggs was not mineralized in the experiments. The degree of mineralization was very variable, reflecting conditions both in the natural environment and in the fossil record.

No abstract