Experimental analysis of organ decay and pH gradients within a carcass and the implications for phosphatization of soft tissues

Replacement of soft tissues by calcium phosphate can yield spectacular fossils. However, in the fossil record, the phosphatization of internal organs is highly selective; some internal organs, such as muscles, stomachs, and intestines, appear to preferentially phosphatize while other organs seldom phosphatize. The reasons for this are unclear but one hypothesis is that, during decay, organs create distinct chemical microenvironments and only some fall below the critical pH threshold for mineralization to occur (i.e. below the carbonic acid dissociation constant: pH 6.38). Here, we present a novel investigation using microelectrodes that record dynamic spatial and temporal pH gradients inside organs within a fish carcass in real time. Our experiments demonstrate that within a decaying fish carcass, organ-specific microenvironments are not generated. Rather, a pervasive pH environment forms within the body cavity which persists until integumentary failure. With no evidence to support the development of organ-specific microenvironments during decay our data suggest other factors must control differential organ phosphatization. We propose, that when conditions are amenable, it is tissue biochemistry that plays an important role in selective phosphatization. Tissues with high phosphate content (and those rich in collagen) are most likely to phosphatize. Internal organs that typically have lower tissue-bound phosphate, including the integuments of the stomach and intestine, may require other sources of phosphate such as ingested phosphate-rich organic matter. If tissue biochemistry is the driver behind selective phosphatization, this may provide insights into other highly selective modes of soft-tissue preservation (e.g. pyritization)

Human-specific phages infecting Enterococcus host strain MW47: Are they reliable microbial source tracking markers?

Aim: The aim of this study was to determine the morphological diversity and environmentalsurvival of human-specific phages infecting Enterococcus faecium host strain MW47, tosupport their use as microbial source tracking (MST) markers. Methods and Results: Twenty phages capable of infecting strain MW47 were propagatedand their morphologies determined using transmission electron microscopy (TEM), whichrevealed that a heterogeneous group of phages was able to infect strain MW47. Three distinctmorphologies from two different families (Myoviridae and Siphoviridae) were observed. Insitu inactivation experiments were subsequently conducted to determine their environmentalpersistence. Conclusion: The findings revealed a statistically significant link between morphology andthe rate of inactivation, with phages belonging to the Myoviridae family demonstrating morerapid inactivation in comparison to those belonging to the Siphoviridae family. Significance and Impact of Study: The results suggest that whilst Enterococcus MW47phages appear to be a potentially valuable MST tools, significant variations in the persistenceof the different phages mean that the approach should be used with caution, as this mayadversely affect the reliability of the approach, especially when comparing MW47 phagelevels or presence across different matrices (e.g. levels in sediments or shellfish). Thishighlights the importance of elucidating the ecological characteristics of newly proposedMST markers before they are used in full-scale MST investigations