Properties relevant to atmospheric dispersal of the ice-nucleation active Pseudomonas syringae strain R10.79 isolated from rain water

Transport of microbes in the atmosphere allows them to spread and to colonize new habitats. To survive the harsh environmental conditions encountered in the atmosphere, these microorganisms have to possess properties that allow them to resist atmospheric stress. We combined physiological experiments and genome analysis of Pseudomonas syringae strain R10.79, previously isolated from rain, to decipher the strain’s ability to withstand these challenges and identify the mechanisms behind the resistance. We used laboratory experiments to simulate different atmospheric stress factors and evaluated cell survival using fluorescent staining and flow cytometry. We found that while P. syringae R10.79 was resistant to oxidative, osmotic, UVB radiation-induced and freezing stress, it was sensitive to desiccation on surfaces. Strain R10.79 possesses a range of genes that would allow the strain to mitigate atmospheric stresses, such as cold shock and osmotic shock genes as well as genes encoding for properties that relate to UV irradiation resistance. Studying the substrate spectrum of strain R10.79, we uncovered that it can utilize carbon compounds abundant in the atmosphere including acetate, succinate and formate. In addition, strain R10.79 possesses metabolic pathways to utilize formaldehyde and methanol as sole carbon sources. These compounds could support the metabolic activity of strain R10.79 while suspended in the atmosphere during periods with sufficiently high relative humidity. Finally, we found that when growing on acetate, strain R10.79 produces several volatile organic compounds such as isoprene and methanol, for which we propose biochemical pathways and which are relevant for atmospheric chemistry and climate. The results reported in this study will support our general aim at establishing this strain as a model organism to study microbial responses to atmospheric conditions.

     

The Mycoplasma hominis vaa gene displays a mosaic gene structure

Mycoplasma hominis contains a variable adherence-associated ( vaa ) gene. To classify variants of the vaa genes, we examined 42 M. hominis isolates by PCR, DNA sequencing and immunoblotting. This uncovered the existence of five gene categories. Comparison of the gene types revealed a modular composition of the Vaa proteins. The proteins constituted a conserved N-terminal part followed by a varying number of interchangeable cassettes encoding approximately 110 amino acids with conserved sequence boxes flanking the cassettes. The interchangeable cassettes showed a high mutual homology and a conserved leucine zipper motif. The smallest product contained only one cassette and the largest five. Additionally, two types of stop mutations caused by substitutions resulting in the expression of truncated Vaa proteins were observed. Our results expand the known potential of the Vaa system in generating antigen variation.