MICROBIAL ECOLOGY AND BIOFILMS IN THE TAPHONOMY OF SOFT TISSUES

Authigenic mineralization of embryos (and potentially other soft-bodied organisms) requires first stabilization of cells against rapid self-autolytic destruction, and secondly a role for bacterial biofilms that preserve rather than destructively consume tissue. We predict that the ecology of the second stage in preservation will depend on environmental effects on the bacterial species present, coupled with mutual interactions between the bacteria themselves. We have created a simple experimental model made up of two antagonistic marine bacterial species, tested on a taphonomic target of autolysis-inhibited killed marine embryos. Pseudoalteromonas tunicata forms a three-dimensional preserving biofilm with killed embryos, whereas P. luteoviolacea destroys embryo tissue. Our model system allows controlled laboratory tests of microbial interactions under taphonomic conditions selected to test inferred paleoenvironments present in Lagerstätten. We varied environmental conditions one at a time, and observed the taphonomic outcome for killed embryos in the presence of each species alone, and with both species present in direct competition. Parameters tested include temperature, pH, oxygen level, salinity, and nutrient state. Pseudoalteromonas tunicata was robust in generating preserving biofilm pseudomorphs over a wide range of conditions. In competition, P. luteoviolacea destruction dominated in most conditions. However, we identified conditions of temperature, pH, and salinity where P. luteoviolacea grows poorly and preservation by P. tunicata dominates. Elevated external nutrients reduced the fidelity of P. tunicata pseudomorphs. In low oxygen, P. tunicata physiology was altered and it switched to become a destroyer, dramatically showing the extent to which environment can determine taphonomic outcomes.