Accumulation of a ferric mineral in the biofilm of Montacuta ferruginosa (Mollusca, Bivalvia). Biomineralization, bioaccumulation, and inference of paleoenvironments

Infrared absorption spectra of the amorphous and phosphorus-rich ferric min eral associated with the biofilm of Monracuta ferruginosa, a marine bivalve , were obtained by applying the KBr disc method. Phosphate absorption bands due to P-O stretching vibrations were observed at 1100 and 1020 cm(-1). Th is result, as well as the similarity of spectra with other well known (bio) minerals. suggests that the mineral is an amorphous iron oxyhydroxide gel w ith phosphate sorbed on its surface rather than a pure ferric phosphate. It is suggested that phosphate ions are of microbial origin because phosphate -producing enzymes were detected in vivo. Apart from iron, the mineral phas e is devoid of other heavy metals. Despite its similarity with other abioti cally precipitated phases, it is argued that the mineral is the result of i n situ microbial biomineralization processes in the biofilm and not the res ult of a simple bioaccumulation process. This is supported by microscopic o bservations. A geological implication is that the simple presence of such i ron minerals in ancient sedimentary environments, where microbes have not b een fossilized, might be considered as an indicator of microorganisms perfo rming biomineralization. By comparison with the present-day environment of M. ferruginosa, precise paleoenvironmental conditions may be inferred. (C) 2001 Elsevier Science B.V. All rights reserved.