Spiroplasma species share common DNA sequences among their viruses, plasmids and genomes

Molecular characterization of Spiroplasma citri BR3 lines that differ in transmissibility by the leafhopper Circulifer tenellus

Four lines of Spiroplasma citri strain BR3, derived from different maintenance conditions over several years and differing in their ability to be transmitted by the beet leafhopper Circulifer tenellus were characterized. The lines included BR3-T (transmissible), maintained in turnip by leafhopper transmission; BR3-G (now nontransmissible), maintained in plants by periodic graft transmission; BR3-P (now rarely transmissible), subcultured in artificial medium over 130 times; and BR3-M (transmissible), subcultured 43 times. Although all four lines had similar overall protein profiles, the two transmissible lines each contained two proteins missing in the non- or rarely transmitted lines. In addition, one protein was unique to BR3-M and another was unique to BR3-P. Spiralin, a major S. citri membrane protein, had dual mobility in line BR3-G only. Patterns of extrachromosomal DNA and restricted total DNA also were similar, although differences occurred among the four lines. The genome of line BR3-G was larger than those of the other lines and unique restriction bands occurred in this line. Protein and DNA profiles of six to eight individual clones of each line also were compared. Protein patterns within each clone were indistinguishable except for a difference in the migration rate of spiralin in clones of BR3-G. Restricted total DNA showed differential patterns among clones of each line, possibly reflecting differences in extrachromosomal DNA. Molecular differences among the spiroplasma lines may reflect the selection pressures of the different environments in which they were maintained and suggest genes and proteins that may be involved in the biological phenotypes of these lines.Key words: spiroplasma, Mollicutes, insect transmission.

A Mycoplasma genetic element resembling prokaryotic insertion sequences

Nucleotide sequence analysis of two Mycoplasma hyopneumoniae-derived copies of a repetitive genetic element revealed structural similarities to typical prokaryotic insertion sequences. This is the first such sequence identified in the class Mollicutes. The element spans approximately 1550bp, with 28bp inverted terminal repeats. Two open reading frames occur within the sequence, one potentially encoding a protein with a size-variant alpha-helical domain containing heptameric leucine periodicity. Hybridization data with several strains from each of two mycoplasma species showed that the repetitive sequence is variably distributed within the M. hyopneumoniae and Mycoplasma hyorhinis chromosomes and indicated that in some cases the repeated sequence is contained within a larger genetic element which may be the result of phage or plasmid insertion.

Reiterated DNA sequences defining genomic diversity within the species Mycoplasma hyorhinis

Genomic restriction fragments isolated from Mycoplasma hyorhinis and Mycoplasma hyopneumoniae were shown by DNA hybridization and nucleotide sequence analyses to contain sequences common to these two species, as well as another porcine-derived mycoplasma, Mycoplasma flocculare. Intraspecies hybridization experiments using these fragments as probes indicated that the sequence is highly redundant in several strains of M. hyorhinis, but that there is diversity in the sizes of restriction fragments detected among these strains. In contrast, repetition of the sequence was limited in M. hyopneumoniae and M. flocculare, and no homologies to this repeated element were apparent in mycoplasma species isolated from animal hosts other than the swine. The reiterated sequence may reflect intraspecies genomic diversification in M. hyorhinis and its selective presence in otherwise unrelated species raises the possibility that it has been horizontally transmitted between these organisms.