3 / 2025-02-10 22:54:40

Bacteriophage-mineral interactions: past, present, and future

bacteriophage, organomineralisation, calcium carbonate, experiments

Theme 2: Geobiology of Modern Habitable Earth > Session 2b: The Geological Roles and Records of Viruses

Viruses, and specifically bacteriophages (viruses that infect bacteria), are widespread in natural ecosystems, especially in those with rich microbial activity. Compared to other microorganisms, viruses are present in superabundance; while a millilitre of seawater may contain millions of bacteria, there are likely to be millions to a billion viruses as well. An equally vast number live within microbial mats and biofilms. where they may also influence biofilm formation and extracellular polymeric substances (EPS), leading to, for example, stromatolite formation. Viruses play a major role in the carbon cycle by lysing bacterial host cells, with the resulting dissolved organic matter associated with the lysed bacterial biomass supplying organic matter and nutrients.

In this context, the role of viruses near-surface geological processes is particularly intriguing, as the activities of viruses and virus-like particles (VLPs) can be associated with mineral nucleation, potentially transforming our understanding of organomineral precipitation. In recent years, experiments with phages and various mineral solutions have shown that viruses and VLPs are capable of controlling the mineralisation process, mineral stability, and the formation of new minerals. Bacteriophages have been shown to be associated with the precipitation of silica, sulphide minerals, and, mostly notably, calcium carbonate. The latter, chiefly composed of vaterite nanospheres - a thermodynamically metastable phase that rapidly transforms into calcite or aragonite - has also been reported from modern microbial mats, fossil microbialites, and even phosphorites or cherts. Although laboratory experiments have demonstrated that vaterite nanospheres can be formed and stabilised by phages, other possible origins for these crystal forms include bacterial processes at the nanometre scale. Nevertheless, in our recent experiments, spherical vaterite was formed either by the aggregation of vaterite nanocrystals, which can subsequently form larger spherical structures, or through the influence of phages on this process via organomineralisation and phage aggregation. Alterantively, crystal growth and the formation of spherical structures can occur on a crystalline precursor, where the viral capsid may act as a nucleus for primary vaterite precipitation. In this case, the organic molecules of viruses could function as catalysts for carbonate precipitation, similar to the role of EPS in bacteria.

Beyond its significance in microbially rich, calcium carbonate-supersaturated systems, this newly proposed mechanism may also have significant potential applications in biomedical technologies. Vaterite possesses important biocompatibility characteristics, enabling it to selectively bind to phages, which could facilitate the development of technologies related to phage therapie and drug delivery. The observed influence of phages on calcium carbonate crystallisation could be particularly advantageous in drug delivery, as the presence of vaterite may enhance adsorption processes.

Finally, biofilms developing on the growing surfaces of modern carbonate tufa and travertine revealed distinct variations in viral composition between these two different carbonate-precipitating systems. Differences between viral groups have allowed the formulation of a viral proxy based on the Caudoviricetes/Megaviricetes ratio, established using the most abundant virus groups. This ratio may potentially be applied to the analysis of ancient DNA preserved in carbonate formations, providing an additional source of information on the microbiological community during sedimentation.