Whole shotgun pyrosequencing of Mycoplasma haemofelis: throwing new light on an old pathogen

First described in 1942, Mycoplasma haemofelis is a pathogenic hemotropic mycoplasma of cats. Due to it being uncultivable, little is known about its metabolic pathways or mechanism of pathogenicity and whole genome sequencing of feline hemoplasmas has not yet been reported. The aim of this study was to completely sequence the genome of M. haemofelis to further characterise this important pathogen. Mycoplasma haemofelis genomic DNA was purified and subjected to whole shotgun Roche 454 sequencing. Gaps were closed using targeted PCR and amplicon sequencing. Ribosomal genes and potential open reading frames (ORFs) were predicted in silico. Putative ORFs were annotated and orthologous groups identified. Analysis showed a circular genome of 1.15 Mbp with a GC content of 38.9%. Thirty-one transfer RNAs (tRNAs) were identified, accounting for all amino acids, including a tryptophan tRNA for the opal codon (UGA). Of the 1,545 putative proteins identified, 328 (21.2%) matched to proteins from other bacterial species. In common with the pneumoniae group of mycoplasmas, the closest phylogenetic relatives of the hemoplasmas, genes involved in carbohydrate metabolism were limited to enzymes of the glycolytic pathway, with glucose appearing to be the sole energy source for M. haemofelis. The majority of the pentose phosphate pathway genes present in other cultivatable mycoplasmas appear to be incomplete or absent in M. haemofelis, suggesting an alternative mechanism for sourcing purine and pyramidine bases such as scavenging from the host. A gene encoding a glyceraldehyde-3-phosphate dehydrogenase homolog of the immunogenic MSG1 protein of Mycoplasma suis was present. Of the uncharacterized hypothetical proteins, 1,115 were arranged in series of orthologous repeats, or comprised fragments there-of, encoding putative proteins of approximately 200 amino acids. The predicted motifs of the majority of these putative proteins were consistent with these proteins being presented on the cell surface; an N’ terminal signal peptide or transmembrane region followed by a non-cytoplasmic tail. These data have provided valuable information as to why this pathogen remains highly fastidious; it lacks some of the metabolic pathways found in cultivatable mycoplasmas. We have also identified a homolog of a known M. suis immunogenic protein, and identified a potential mechanism for host immune system evasion by way of highly repetitive, putatively surface-expressed hypothetical proteins with variable sequences.

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