This work centres on the genomic comparisons of two closely-related nitrogen-fixing symbiotic bacteria, Rhizobium leguminosarum biovar viciae 3841 and Rhizobium etli CFN42. These strains maintain a stable genomic core that is also common to other rhizobia species plus a very variable and significant accessory component. The chromosomes are highly syntenic, whereas plasmids are related by fewer syntenic blocks and have mosaic structures. The pairs of plasmids p42f-pRL12, p42e-pRL11 and p42b-pRL9 as well large parts of p42c with pRL10 are shown to be similar, whereas the symbiotic plasmids (p42d and pRL10) are structurally unrelated and seem to follow distinct evolutionary paths. Even though purifying selection is acting on the whole genome, the accessory component is evolving more rapidly. This component is constituted largely for proteins for transport of diverse metabolites and elements of external origin. The present analysis allows us to conclude that a heterogeneous and quickly diversifying group of plasmids co-exists in a common genomic framework.

Strains of the same bacterial species often show considerable genomic variation. To examine the extent of such variation in Rhizobium etli, the complete genome sequence of R. etli CIAT652 and the partial genomic sequences of six additional R. etli strains having different geographical origins were determined. The sequences were compared with each other and with the previously reported genome sequence of R. etli CFN42. DNA sequences common to all strains constituted the greater part of these genomes and were localized in both the chromosome and large plasmids. About 700 to 1,000 kb of DNA that did not match sequences of the complete genomes of strains CIAT652 and CFN42 was unique to each R. etli strain. These sequences were distributed throughout the chromosome as individual genes or chromosomal islands and in plasmids, and they encoded accessory functions, such as transport of sugars and amino acids, or secondary metabolism; they also included mobile elements and hypothetical genes. Sequences corresponding to symbiotic plasmids showed high levels of nucleotide identity (about 98 to 99%), whereas chromosomal sequences and the sequences with matches to other plasmids showed lower levels of identity (on average, about 90 to 95%). We concluded that R. etli has a pangenomic structure with a core genome composed of both chromosomal and plasmid sequences, including a highly conserved symbiotic plasmid, despite the overall genomic divergence.

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The authors present the cases of two young patients, a man and a woman, who presented with myocardial infarction, in the absence of ischemic heart disease or stenosis of the coronary arteries. The woman was known to have systemic lupus erythematosus (SLE) for the past 3 years (the immunoglobulin M [IgM] anticardiolipins antibodies were positive), without a history of coronary risk factors. Suddenly she presented with acute chest pain on rest that lasted 4 hours and culminated in anterior wall myocardial infarction. She was admitted to the coronary care unit, where no thrombolysis was given. She did not have echocardiographic evidence of Libman-Sacks endocarditis, but myocardial infarction was evident at the electrocardiogram (ECG). The young man had SLE (the IgM anticardiolipins were absent, but he was positive for lupus anticoagulant antibodies), he was hyperlipidemic, was a moderate smoker and moderately obese, and had no history of ischemic heart disease. He suddenly presented with an acute myocardial infarction documented by ECG, enzymes, and gammagraphy. In both patients, coronary angiography findings were normal and myocardial biopsy did not show evidence of arteritis. The relevance of these cases is the rare association of ischemic heart disease in SLE, with normal coronary arteries and without evidence of arteritis or verrucous endocarditis.