Thede novosynthesized polar lipids ofMycoplasmaspecies are rather simple, comprising primarily of the acidic glycerophospholipids PG and CL. In addition, when grown in a medium containing serum, significant amounts of PC and SPM are incorporated into the mycoplasma cell membrane although these lipids are very uncommon in wall-covered bacteria. The exogenous lipids are either incorporated unchanged or the PC incorporated is modified by a deacylation-acylation enzymatic cycle to form disaturated PC. Although their small genome, in someMycoplasmaspecies, other genes involved in lipid biosynthesis were detected, resulting in the synthesis of a variety of glycolipis, phosphoglycolipids and ether lipids. We suggest that analyses and comparisons of mycoplasma polar lipids may serve as a novel and useful tool for classification. Nonetheless, to evaluate the importance of polar lipids in mycoplasma, further systematic and extensive studies on moreMycoplasmaspecies are needed. While studies are needed to elucidate the role of lipids in the mechanisms governing the interaction of mycoplasmas with host eukaryotic cells, the finding that a terminal phosphocholine containing glycolipids ofM. fermentansserves both as a major immune determinants and as a trigger of the inflammatory responses, and the findings that the fusogenicity ofM. fermentanswith host cells is markedly stimulated by lyso-ether lipids, are important steps toward understanding the molecular mechanisms ofM. fermentanspathogenicity.

Mycoplasma hyorhinis(strain MCLD) was recently isolated from a melanoma cell culture. Growth of MCLD was considerably improved by 24 serial passages in a modified Hayflick's mycoplasma medium. Transmission electron microscopy showed that MCLD exhibits a polymorphic appearance, with ovoid or elongated cells frequently harboring an electron-dense core at one of the poles. Adherence ofM. hyorhinisto melanoma cells followed saturation kinetics. Furthermore, althoughM. hyorhinishas been considered to remain attached to the surface of the host cells, we show for the first time, qualitatively by confocal laser scanning microscopy and quantitatively by a gentamicin resistance assay, that MCLD is able to invade melanoma cells. The ingested mycoplasmas were randomly distributed in the cytoplasm, tending to concentrate near the plasma membrane. Both adherence to and invasion of melanoma cells byM. hyorhinisstrain MCLD were dramatically enhanced by mild proteolytic digestion with proteinase K (2.5 μg/mg cell protein for 2.5 min at 37°C) that affected the surface-exposed proteins of this organism, mainly the major 47-kDa lipoprotein. We suggest that the intracellular location ofM. hyorhinisstrain MCLD is a privileged niche, which may explain the survival ofM. hyorhinisin tissue cultures. The enhanced binding to and invasion of melanoma cells by protease treatment may be due to either the activation or the enhanced exposure of an adhesin(s) on the mycoplasmal cell surface.

Brucellosis has a wide range of clinical severity in humans that remains poorly understood. Whole genome sequencing (WGS) analysis may be able to detect variation in virulence genes. We used Brucella melitensis sequences in the NCBI Sequence Read Archive (SRA) database to assemble 248 whole genomes, and additionally, assembled 27 B. melitensis genomes from samples of human patients in Southern Israel. We searched the 275 assembled genomes for the 43 B. melitensis virulence genes in the Virulence Factors of Pathogenic Bacteria Database (VFDB) and 10 other published putative virulence genes. We explored pan-genome variation across the genomes and in a pilot analysis, explored single nucleotide polymorphism (SNP) variation among the ten putative virulence genes. More than 99% of the genomes had sequences for all Brucella melitensis virulence genes included in the VFDB. The 10 other virulence genes of interest were present across all the genomes, but three of these genes had SNP variation associated with particular Brucella melitensis genotypes. SNP variation was also seen within the Israeli genomes obtained from a small geographic region. While the Brucella genome is highly conserved, this novel and large whole genome study of Brucella demonstrates the ability of whole genome and pan-genome analysis to screen multiple genomes and identify SNP variation in both known and novel virulence genes that could be associated with differential disease virulence. Further development of whole genome techniques and linkage with clinical metadata on disease outcomes could shed light on whether such variation in the Brucella genome plays a role in pathogenesis.

The complete genome of Mycoplasma hyorhinis strain MCLD has been sequenced and annotated. This genome differs by the inversion of a 14.4-kb and a 3.7-kb fragment and the deletion of a 9.9-kb fragment from M. hyorhinis strain HUB-1, isolated from swine respiratory tract. The genome revealed 778 coding sequences (CDSs), with a limited number of vlp genes encoding variable surface lipoproteins.

The live attenuated Brucella melitensis Rev.1 (Elberg-originated) vaccine strain is widely used to control the zoonotic infection brucellosis in small ruminants, but the molecular mechanisms underlying the attenuation of this strain have not been fully characterized. Following their uptake by the host cell, Brucella replicate inside a membrane-bound compartment—the Brucella-containing vacuole—whose acidification is essential for the survival of the pathogen. Therefore, identifying the genes that contribute to the survival of Brucella in acidic environments will greatly assist our understanding of its molecular pathogenic mechanisms and of the attenuated virulence of the Rev.1 strain. Here, we conducted a comprehensive comparative transcriptome analysis of the Rev.1 vaccine strain against the virulent reference strain 16M in cultures grown under either normal or acidic conditions. We found 403 genes that respond differently to acidic conditions in the two strains (FDR < 0.05, fold change ≥ 2). These genes are involved in crucial cellular processes, including metabolic, biosynthetic, and transport processes. Among the highly enriched genes that were downregulated in Rev.1 under acidic conditions were acetyl-CoA synthetase, aldehyde dehydrogenase, cell division proteins, a cold-shock protein, GroEL, and VirB3. The downregulation of these genes may explain the attenuated virulence of Rev.1 and provide new insights into the virulence mechanisms of Brucella.