Abstract
Microbial biomineralization is a widespread phenomenon. The ability to induce calcium precipitation around bacterial cells has been reported in several Pseudomonas species but has not been thoroughly tested. We assayed 14 Pseudomonas strains representing five different species for the ability to precipitate calcium. Calcium phosphate precipitated adjacent to the colonies of all the Pseudomonas strains tested and also precipitated on the surface of colonies for several of the Pseudomonas strains assayed. The precipitate was commonly precipitated as amorphous calcium phosphate, however seven of the 14 Pseudomonas strains tested precipitated amorphous apatite in agar adjacent to the colonies. Out of the seven Pseudomonas strains that precipitated amorphous apatite, six are plant pathogenic. The formation of amorphous apatite was commonly observed in the area of the agar where amorphous calcium phosphate had previously formed. A transposon mutagenesis screen in Pseudomonas syringae pv. tomato DC3000 revealed genes involved in general metabolism, lipopolysaccharide and cell wall biogenesis, and in regulation of virulence play a role in calcium precipitation. These results shed light on the common ability of Pseudomonas species to perform calcium precipitation and the underlying genetic regulation involved in biomineralization.
Highlights
Biomineralization is the precipitation of inorganic minerals by biological organisms
Pseudomonas colonies were monitored for two days after spotting on nutrient broth (NB) supplemented with Ca2+ and 0.1% (w/v) bromothymol blue (BB)
Alizarin Red S (ARS) staining on the surface of colonies was prominent on P. syringae pv. morsprunorum 5795, P. fluorescens Pf0-1, P. fluorescens 55, P. syringae pv. tabaci ATCC11528, P. savastanoi pv. savastanoi 4352, and P. syringae pv. maculicola ES4326, suggesting that calcium is enriched on the surface of these Pseudomonas strains when grown on NB supplemented with Ca2+ (Fig. 2)
Summary
Biomineralization is the precipitation of inorganic minerals by biological organisms. In phosphate-sequestering Pseudomonas species, certain P. aeruginosa strains, and P. fluorescens strains, the precipitation of calcium results in apatite formation[6,16,17,18,19,20]. Phaseolicola 1448a infection and in the xylem of tobacco plants during Xyllela fastidiosa infection[23,24] It is currently unknown whether plant pathogenic Pseudomonas species can precipitate calcium when grown in high calcium environments. We demonstrate calcium precipitation by several plant-beneficial, rhizosphere-associated Pseudomonas species and by several plant-pathogenic, epiphytic Pseudomonas species. We show that this phenomenon occurs near neutral pH and that the spatial patterning and morphology of the calcium precipitate differs across species and strains. We identify several genes that are involved in apatite biomineralization in P. syringae pv. tomato DC3000
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