Identification of a possible cytadherence regulatory locus in Mycoplasma pneumoniae.

Transposon mutagenesis was used to analyze Mycoplasma pneumoniae cytadherence. Mycoplasmas were electroporated with Tn4001, and transformants were identified by antibiotic selection using gentamicin. The resulting colonies were screened for hemadsorption (HA) as an indicator for cytadherence. Six HA- colonies from independent transformations were isolated, filter cloned, and characterized in more detail. Southern hybridization analysis revealed that all six transposon insertions mapped to the same 252-kbp ApaI fragment and 19.5-kbp XhoI fragment. More detailed analysis localized the insertion to two adjacent EcoRI fragments. This site is distinct from the locus containing the genes for the high-molecular weight cytadherence-accessory proteins HMW1 and HMW3, and yet these proteins were absent from the protein profiles of all six transformants. To determine if transposon insertion was responsible for the HA- phenotype, reversion frequencies of the transformants were assessed after passage in the presence of antibiotic selection. In contrast to a spontaneously arising HMW-deficient variant, which reverted to an HA+ phenotype readily, no HA+ revertants were identified for any of the six transformants. These observations suggest that a potential regulatory locus that may be important in the expression of the HMW cytadherence-accessory proteins has been identified.