Abstract
Mycoplasma suis, a member of the hemotrophic mycoplasma (HM) group, parasitize erythrocytes of pigs. Increasing evidence suggests that M. suis is also a zoonotic agent. Highly pathogenic strains of M. suis (e.g., M. suis KI3806) have been demonstrated to invade erythrocytes. This complete sequenced and manually annotated genome of M. suis KI3806 is the first available from this species and from the HM group. The DNA was isolated from blood samples of experimentally infected pigs due to the lack of an in vitro cultivation system. The small circular chromosome of 709,270 bp, encoding an unexpectedly high number of hypothetical proteins and limited transport and metabolic capacities, could reflect the unique lifestyle of HM on the surface of erythrocytes.
TEXT
Hemotrophic mycoplasmas (HM) are epierythrocytic, wall-less bacteria that comprise a single phylogenetic cluster within the genus Mycoplasma (5). HM infections are found in a wide range of animals (e.g., Mycoplasma suis in pigs), causing infectious anemia (3, 4). The unique life cycle of M. suis and other HM on erythrocytes implies special features allowing HM to adhere to erythrocytes or to perform metabolic exchanges. Moreover, M. suis can invade erythrocytes, leading to high virulence and resistance to antibiotics (2). So far, HM cultivation in cell-free medium has failed, indicating that HM have a special metabolism and/or a high adaption to their hosts.
We determined the genome of M. suis strain KI3806, a highly pathogenic and invasive strain. DNA was isolated from experimentally infected piglets using pulsed-field gel electrophoresis and sequenced (EurofinsMedigenomix; Germany) (1, 2).
The circular chromosome of M. suis KI3806 is composed of 709,270 bp with a 31%-GC content. The genome includes 32 tRNAs and a single-copy 16S rRNA which is separated from the 23S and 5S rRNA by ∼165 kb and encoded on the opposite strand. The predicted 809 open reading frames (ORFs) comprise a density of 1.119 genes per kilobase. The average protein size is 259 amino acids, with a coding percentage of 87%. The low number of estimated paralogs (36 coding determining regions [CDS]; 70% identity) corresponds to only one putative transposase. The genome differs from other mycoplasma genomes in the high portion of predicted proteins without functional assignment (64.6%; 523/809), which may reflect the adaptation of M. suis to a special environment but could also be a result of large integration events due to the unit-like organization of these proteins (RG1_33888.0.50303 [region_position], RG2_77345.0.182976, RG3_214881.0.233523, RG4_416009.0.454949, RG5_456815.0.523918, and RG6_581193.0.614049). These six regions encode 19 proteins of unknown function per unit at least and sum up to ∼280 kb, which does not include housekeeping genes but does include sequences for 413 unassigned proteins. A similar scenario is known for the integrative conjugative elements (ICEs) from Mycoplasma agalactiae (6), but ICEs show different genetic content. In M. suis some phage-related proteins, i.e., an integrase, a tape measure protein, a tail protein, and a terminase, are encoded, indicating a phage-derived origin of these large regions. However, in M. suis genome extension is suggested to act against genome condensation due to the limited number of transporters and metabolic capacities. Transporters for spermidine/putrescine, hemin, ferrichrome, cobalt, magnesium, and probably amino acids and phosphate are encoded. M. suis generates ATP through glycolysis, but the tricarboxylic acid cycle, arginine hydrolysis, or urea hydrolysis is incomplete or missing. Glycolysis is fed by the uptake of glucose via the phosphoenolpyruvate-dependent sugar phosphotransferase system and conversion by glucose 6-phosphate isomerase. Nucleotide biosynthesis lacks reductases (nrdA, nrdB, and nrdD) and also the nucleoside diphospate kinases (ndk). The proton gradient is probably regulated by the F1F0 ATPase system.
Altogether, the genome sequence of M. suis KI3806 will provide the basis for a better understanding of the nature of HM, especially their nutritional requirements, which have prevented in vitro cultivation so far, and the pathogenicity-determining mechanisms.
Nucleotide sequence accession number.
The nucleotide sequence accession number of the complete M. suis KI3806 genome sequence is FQ790233.
Acknowledgments
This work was supported by Promedica Foundation, Chur, Switzerland, and the Jubiläumsstiftung, University Zurich, Switzerland.
Footnotes
Published ahead of print on 11 March 2011.
REFERENCES
- 1. Berent L. M., Messick J. B. 2003. Physical map and genome sequencing survey of Mycoplasma haemofelis (Haemobartonella felis). Infect. Immun. 71:3657–3662 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2. Groebel K., Hoelzle K., Wittenbrink M. M., Ziegler U., Hoelzle L. E. 2009. Mycoplasma suis invades porcine erythrocytes. Infect. Immun. 77:576–584 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3. Hoelzle L. E. 2008. Haemotrophic mycoplasmas: recent advances in Mycoplasma suis. Vet. Microbiol. 130:215–226 [DOI] [PubMed] [Google Scholar]
- 4. Messick J. B. 2004. Hemotrophic mycoplasmas (hemoplasmas): a review and new insights into pathogenic potential. Vet. Clin. Pathol. 33:2–13 [DOI] [PubMed] [Google Scholar]
- 5. Neimark H., Johansson K. E., Rikihisa Y., Tully J. G. 2001. Proposal to transfer some members of the genera Haemobartonella and Eperythrozoon to the genus Mycoplasma with descriptions of ‘Candidatus Mycoplasma haemofelis,’ ‘Candidatus Mycoplasma haemomuris,’ ‘Candidatus Mycoplasma haemosuis’ and ‘Candidatus Mycoplasma wenyonii.’ Int. J. Syst. Evol. Microbiol. 51:891–899 [DOI] [PubMed] [Google Scholar]
- 6. Nouvel L. X., et al. 2010. Comparative genomic and proteomic analyses of two Mycoplasma agalactiae strains: clues to the macro- and micro-events that are shaping mycoplasma diversity. BMC Genomics 11:86. [DOI] [PMC free article] [PubMed] [Google Scholar]