Time-dependent microbial shifts during crayfish decomposition in freshwater and sediment under different environmental conditions

Abstract

Fossilization processes and especially the role of bacterial activity during the preservation of organic material has not yet been well understood. Here, we report the results of controlled taphonomic experiments with crayfish in freshwater and sediment. 16S rRNA amplicon analyzes showed that the development of the bacterial community composition over time was correlated with different stages of decay and preservation. Three dominating genera, Aeromonas, Clostridium and Acetobacteroides were identified as the main drivers in the decomposition of crayfish in freshwater. Using micro-computed tomography (µ-CT), scanning electron microscopy (SEM) and confocal Raman spectroscopy (CRS), calcite clusters were detected after 3-4 days inside crayfish carcasses during their decomposition in freshwater at 24 °C. The precipitation of calcite clusters during the decomposition process was increased in the presence of the bacterial genus Proteocatella. Consequently, Proteocatella might be one of the bacterial genera responsible for fossilization.

Figure 1

Experimental setup design conducted at a constant temperature of 24 °C. Exp. 1 was conducted under aerobic conditions with untreated water and sediment. Exp. 2 was conducted under aerobic conditions with sterile water and sediment. Exp. 3 was conducted under anaerobic conditions with untreated water and sediment. Exp. 4 was conducted under anaerobic conditions with sterile water and sediment.

Figure 2

Time-dependent abundance of dominant genera and optical decay of body areas and inner organs of decaying crayfish for a duration of 21 days at 24 °C.

Figure 3

Calcite precipitation inside decomposing crayfish. (a) Median value of the increase in the total volume of calcite of Exp. 1–4 for a duration of 21 days at a constant temperature of 24 °C, including a translucent 3D-model of an individual showing reconstructed 3D-models of calcite clusters at the inner side of the cuticle (Yellow structures). (b) Representative Raman spectra of observed crystal clusters compared to Raman reference spectra of crystalline apatite, aragonite and calcite, taken from the RRUFF Raman data base (#R060070, 0R060070, *R040170). Raman spectra of the crystal clusters exhibit main Raman bands typically for crystallized calcite and the β-carotene, astaxanthin. (c) Optical image of a semi-circular calcite cluster with three mineralized setae (pink arrows). (d) SEM image of the calcite cluster shown in (c).