For understanding the directing influence of primary biopolymers on composite material formation, we synthesized with Bacillus subtilis, Mycobacterium phley, Mycobacterium smagmatis, Pseudomonas putida EPS composite aggregates and investigated the influence of EPS matrices on calcite organization and composite aggregate formation. Aggregates were characterized with FTIR, FE-SEM and EBSD; the occluded EPS/hydrogel polymers were visualized with selective etching techniques and kernel-misorientation-analysis gained from EBSD data.
Relative to reference aggregates that are devoid of bacterial EPS, composites that contain EPS are reduced in size and show, for the EPS of a specific bacterium, distinctive morphologies. Bacterial EPS/agarose hydrogel distribution within aggregates is inhomogeneous. In P. putida and M. phley composites the occluded polymer is mainly present as membranes, while for M. smagmatis and B. subtilis the occluded biopolymer is developed as membranes and as networks of fibrils. Relative to reference aggregates, subunit formation in EPS/hydrogel-calcite-composites is extensive. These vary significantly in shape, size and mode of organization. For M. smagmatis and B. subtilis subunit organization is radial to spherulitic, for P. putida it is almost random, for M. phley subunit organization is highly co-aligned.
Bacterial EPS changes the microstructure and texture of the composite in a substantial and specific manner. This is a specific characteristic for a given bacterium and can be developed as a tool for the recognition/identification of bacterially mediated calcification in present and past environments (1).
(1) Xiaofei Yin, Florian Weitzel, Concepción Jiménez-López, Erika Griesshaber, Lurdes Fernández-Díaz, Alejandro Rodríguez-Navarro, Andreas Ziegler, Wolfgang. W. Schmahl (2019). The directing effect of bacterial EPS on calcite organization and EPS-carbonate composite aggregate formation, accepted manuscript in Crystal Growth and Design 2019.