Bacillus subtilis biofilms resemble cross-linked hydrogels in their morphology and swelling properties. All the water in these biofilms is bound water. Water binding is mostly related with accumulated solutes.
Biomineralization
is a mineral precipitation process occurring
in the presence of organic molecules and used by various organisms
to serve a structural and/or a functional role. Many biomineralization
processes occur in the presence of extracellular matrices that are
composed of proteins and polysaccharides. Recently, there is growing
evidence that bacterial biofilms induce CaCO3 mineralization
and that this process may be related with their extracellular matrix
(ECM). In this study we explore, in vitro, the effect
of two bacterial ECM proteins, TasA and TapA, and an exopolysaccharide,
EPS, on calcium carbonate crystallization. We have found that all
the three biopolymers induce the formation of complex CaCO3 structures. The crystals formed in the presence of the EPS are very
diverse in morphology and they are either calcite or vaterite in structure.
However, more uniformly sized calcite crystals are formed in the presence
of the proteins; these crystals are composed of single crystalline
domains that assemble together into spherulites (in the presence of
TapA) or dumbbell-like shapes (in the presence of TasA). Our results
suggest the EPS affects the nucleation of calcium carbonate when it
induces the formation of vaterite crystals and that unlike EPS, the
proteins stabilize preformed calcite nuclei and induce their aggregation
into complex calcite structures. Biomineralization processes induced
by bacterial ECM macromolecules make biofilms more robust and difficult
to remove when they form, for example, on pipes and filters in water
desalination systems or on ship hulls. Understanding the formation
conditions and mechanism of formation of calcium carbonate in the
presence of bacterial biopolymers may lead to the design of suitable
mineralization inhibitors.
Biofilms are multicellular microbial communities that encase themselves in an extracellular matrix (ECM) of secreted biopolymers and attach to surfaces and interfaces. Bacterial biofilms are detrimental in hospital and industrial settings, but they can be beneficial, for example, in agricultural as well as in food technology contexts. An essential property of biofilms that grants them with increased survival relative to planktonic cells is phenotypic heterogeneity, the division of the biofilm population into functionally distinct subgroups of cells. Phenotypic heterogeneity in biofilms can be traced to the cellular level; however, the molecular structures and elemental distribution across whole biofilms, as well as possible linkages between them, remain unexplored. Mapping X-ray diffraction across intact biofilms in time and space, we revealed the dominant structural features in Bacillus subtilis biofilms, stemming from matrix components, spores, and water. By simultaneously following the X-ray fluorescence signal of biofilms and isolated matrix components, we discovered that the ECM preferentially binds calcium ions over other metal ions, specifically, zinc, manganese, and iron. These ions, remaining free to flow below macroscopic wrinkles that act as water channels, eventually accumulate and may possibly lead to sporulation. The possible link between ECM properties, regulation of metal ion distribution, and sporulation across whole, intact biofilms unravels the importance of molecular-level heterogeneity in shaping biofilm physiology and development.
Functional amyloid proteins are self-secreted by microbial cells that aggregate into extracellular networks and provide microbial colonies with mechanical stability and resistance to antibiotic treatment. In order to understand the...
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