Molecular signature of chitin-protein complex in Paleozoic arthropods

Abstract

The conventional geochemical view holds that the chitin and structural protein are not preserved in ancient fossils because they are readily degradable through microbial chitinolysis and proteolysis. Here we show a molecular signature of a relict chitin-protein complex preserved in a Pennsylvanian (310 Ma) scorpion cuticle and a Silurian (417 Ma) eurypterid cuticle via analysis with carbon, nitrogen, and oxygen X-ray absorption near edge structure (XANES) spectromicroscopy. High-resolution X-ray microscopy reveals the complex laminar variation in major biomolecule concentration across modern cuticle; XANES spectra highlight the presence of the characteristic functional groups of the chitin-protein complex. Modifi cation of this complex is evident via changes in organic functional groups. Both fossil cuticles contain considerable aliphatic carbon relative to modern cuticle. However, the concentration of vestigial chitin-protein complex is high, 59% and 53% in the fossil scorpion and eurypterid, respectively. Preservation of a high-nitrogen-content chitin-protein residue in organic arthropod cuticle likely depends on condensation of cuticle-derived fatty acids onto a structurally modifi ed chitin-protein molecular scaffold, thus preserving the remnant chitin-protein complex and cuticle from degradation by microorganisms.

Estimation of nitrogen-to-carbon ratios of organics and carbon materials at the submicrometer scale

“…Carefully preparing the samples for NanoSIMS experiments has led to a confidence level for N/C estimations of ±0.009 (95%), which is twice as better as previously reported in the literature by Hatton et al [1] or Thomen et al [19]. Similar precision can be reached using STXM-based XAS as shown by the experiments reported in the present contribution which validates the methodology recently adopted by Cody et al [20,21].…”

“…Yet, due to large topographical effects, their calibration lacks the precision required to obtain meaningful data in the small range of N/C values typical of terrestrial environments. On the other hand, Cody et al [20,21] and Van Dommele et al [22] have used synchrotronbased X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS), respectively, to quantify the N/ C ratios of submicrometric organic particles or carbon materials. Unfortunately, although it would have accredited their methodology, these authors did not report any measurement on reference compounds.…”

Nano-scale investigation of the association of microbial nitrogen residues with iron (hydr)oxides in a forest soil O-horizon

“…3B). The spectral peak at 401.7 eV (b) dominating spectra of fungal cell wall material is less pronounced and shifted to lower energies (401.5 eV) in spectra corresponding to mineralassociated N. This peak is commonly attributed to amide N (Mitra-Kirtley et al, 1993;Gillespie et al, 2009;Cody et al, 2011), but may contain contributions of pyrrolic and nitro N (Leinweber et al, 2007). The same peak also dominates the average N NEXAFS spectrum of the Feassociated OM.…”

Exaggerated expectations in ancient starch research and the need for new taphonomic and authenticity criteria

“…Normally, ancient and modern molecular counterparts display significant architectural and elemental differences . During burial, the shielding of labile molecules from complete destruction can take place through aliphatic structural enrichment in the preserved organic matter, a product of diagenesis and kerogen formation (Cody et al 2011), which results in hydrophobicity (Gupta and Pancost 2004) and chemically resistant, neoformed geo-macromolecules (Gupta et al 2009). …”