Abstract
Mycoplasma suis, the causative agent of porcine infectious anemia, has never been cultured in vitro and mechanisms by which it causes disease are poorly understood. Thus, the objective herein was to use whole genome sequencing and analysis of M. suis to define pathogenicity mechanisms and biochemical pathways. M. suis was harvested from the blood of an experimentally infected pig. Following DNA extraction and construction of a paired end library, whole-genome sequencing was performed using GS-FLX (454) and Titanium chemistry. Reads on paired-end constructs were assembled using GS De Novo Assembler and gaps closed by primer walking; assembly was validated by PFGE. Glimmer and Manatee Annotation Engine were used to predict and annotate protein-coding sequences (CDS). The M. suis genome consists of a single, 742,431 bp chromosome with low G+C content of 31.1%. A total of 844 CDS, 3 single copies, unlinked rRNA genes and 32 tRNAs were identified. Gene homologies and GC skew graph show that M. suis has a typical Mollicutes oriC. The predicted metabolic pathway is concise, showing evidence of adaptation to blood environment. M. suis is a glycolytic species, obtaining energy through sugars fermentation and ATP-synthase. The pentose-phosphate pathway, metabolism of cofactors and vitamins, pyruvate dehydrogenase and NAD+ kinase are missing. Thus, ribose, NADH, NADPH and coenzyme A are possibly essential for its growth. M. suis can generate purines from hypoxanthine, which is secreted by RBCs, and cytidine nucleotides from uracil. Toxins orthologs were not identified. We suggest that M. suis may cause disease by scavenging and competing for host' nutrients, leading to decreased life-span of RBCs. In summary, genome analysis shows that M. suis is dependent on host cell metabolism and this characteristic is likely to be linked to its pathogenicity. The prediction of essential nutrients will aid the development of in vitro cultivation systems.
Highlights
Eperythrozoon and Haemobartonella organisms were first described in Germany in the 1920’s [1,2]
The risobomal RNA (rRNA) genes were found in single copies and unlinked; the 23S and the 5S are organized as an operon and the 16S rRNA is located 166 kb downstream of these genes
The presence of a single 16S rRNA gene unlinked to the other rRNAs is a unique feature of M. suis
Summary
Eperythrozoon and Haemobartonella organisms were first described in Germany in the 1920’s [1,2]. In 1997 the 16S risobomal RNA (rRNA) gene sequences of some of these organisms (Eperythrozoon suis, Eperythrozoon wenyonii, Haemobartonella muris and Haemobartonella felis) were sequenced and phylogenetically analyzed [4,5]. These bacteria showed close homology to members of the Mycoplasma genus, in the Mycoplasmataceae family, Mollicute class. An official proposal for reclassification of these four organisms was published in 2001 [6] and subsequent analyses of other Haemobartonella and Eperythrozoon organisms revealed that these organisms were members of the Mycoplasma genus [7].
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