Structure and function of microbial communities involved in biomineralization

by Aysha Kamran née Aysha Naseem
Doctoral thesis
Date of Examination:2022-01-20
Date of issue:2022-01-27
Advisor:PD Dr. Michael Hoppert
Referee:Prof. Dr. Rolf Daniel
Referee:Prof. Dr. Volker Thiel
Referee:Prof. Dr. Joachim Reitner
Referee:PD Dr. Wilfried Kramer
Referee:PD Dr. Heiko Liesegang
Persistent Address: http://dx.doi.org/10.53846/goediss-9065

 

 

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Abstract

English

Different aspects of carbonate precipitation are considered in this study. The first part examines carbonates in a model system that helps to explain the initial steps in the formation of so-called concretions, which are solidified sedimentary masses, cemented with carbonate minerals. Formation of carbonate concretions under participation of microorganisms is common in oceans and in freshwater systems and is also considered as an important fossilization process. The role of the involved microbial communities, however, is largely unknown. In this study, siderite (FeCO3) formation in microbial microcosms, mimicking processes in marine sediments, is observed. For inoculation, Wadden Sea sediments were used and fatty acyl compounds (lipids, surfactants) served as substrates. In actively growing microcosms, sulfate reducing bacteria (the genus Desulfofrigus in particular) dominate the microbial community. Submicroscopic mineral precipitates forming on bacterial cell surfaces were identified as siderite (FeCO3). This biologically influenced mineralization process may, in the natural environment, initiate the formation of large concretions under suboxic conditions in coastal sediments. In the second part of this study, a natural carbonate precipitating system was considered. Calcification in terrestrial, highly alkaline springs, is an obvious process; the participation of microorganisms, however, is not well understood. Serpentinization-driven springs of the Voltri Massif (Italy) expel highly alkaline fluids (pH 10-12); precipitated calcite forms soft layers and solidified sinter terraces. Metagenomics studies, based on analysis of 16 amplicons, were used for identification of the microbial communities growing as biofilms intermixed with calcite structures. Few cyanobacterial genera dominated these communities. The general discussion considers the formation of organominerals and preservation of biological macromolecules in different carbonate precipitating systems.
Keywords: siderite, carbonate concretions, mineralization, calcification, metagenomics, precipitation, organominerals
 
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