Genome-Scale Analysis of Mycoplasma agalactiae Loci Involved in Interaction with Host Cells

Mycoplasma agalactiae is an important pathogen of small ruminants, in which it causes contagious agalactia. It belongs to a large group of “minimal bacteria” with a small genome and reduced metabolic capacities that are dependent on their host for nutrients. Mycoplasma survival thus relies on intimate contact with host cells, but little is known about the factors involved in these interactions or in the more general infectious process. To address this issue, an assay based on goat epithelial and fibroblastic cells was used to screen a M. agalactiae knockout mutant library. Mutants with reduced growth capacities in cell culture were selected and 62 genomic loci were identified as contributing to this phenotype. As expected for minimal bacteria, “transport and metabolism” was the functional category most commonly implicated in this phenotype, but 50% of the selected mutants were disrupted in coding sequences (CDSs) with unknown functions, with surface lipoproteins being most commonly represented in this category. Since mycoplasmas lack a cell wall, lipoproteins are likely to be important in interactions with the host. A few intergenic regions were also identified that may act as regulatory sequences under co-culture conditions. Interestingly, some mutants mapped to gene clusters that are highly conserved across mycoplasma species but located in different positions. One of these clusters was found in a transcriptionally active region of the M. agalactiae chromosome, downstream of a cryptic promoter. A possible scenario for the evolution of these loci is discussed. Finally, several CDSs identified here are conserved in other important pathogenic mycoplasmas, and some were involved in horizontal gene transfer with phylogenetically distant species. These results provide a basis for further deciphering functions mediating mycoplasma-host interactions

Measurement of Solid-Liquid Interfacial Energy for Solid Zn in Equilibrium with the ZnMg Eutectic Liquid

The equilibrated grain boundary groove shapes for solid Zn in equilibrium with the ZnMg eutectic liquid were observed on rapidly quenched samples. The Gibbs-Thomson coefficient for the solid Zn has been determined to be (10.64 +/- 0.43) x 10(-8) K m from the observed grain boundary groove shapes with the present numerical model, and the solid-liquid interfacial energy for the solid Zn in equilibrium with the ZnMg eutectic liquid has been obtained to be (89.16 +/- 8.02) x 10(-3) J m(-2) from the Gibbs-Thomson equation. The grain boundary energy for the solid Zn has also been calculated to be (172.97 +/- 20.76) x 10(-3) J m(-2) from the observed grain boundary groove shapes