Abiotic transformation of labile protein to refractory protein in sea water

Abstract

Abstract In order to determine if organic matter dissolved in sea water may undergo abiotic alterations that make it resistant to microbial degradation, the protein ribulose 1,5-bisphosphate carboxylase (RuBPcase) was abiotically aged in sterile sea water and then exposed to natural bacterial assemblages. Rates of protein assimilation decreased when protein was aged as little as 6 h; protein aged for 40 days was degraded 4-fold more slowly than non-aged protein. Abiotic modification rates, calculated from decreases in degradation rate with increasing aging time, were highest during the initial day of aging (0.8–4.8 d−1) and then decreased to 0.03 d−1. No aging effect was observed in organic-free sea water, indicating that organic-organic interactions produced the refractory protein. Amino acids from the protein were fully recovered after acid hydrolysis, indicating that the decreased lability was not caused by acid-stable molecular changes to the protein. Abiotic complexation of labile organic compounds with existing DOM may be a critical first step in the formation of refractory organic materials.