Isolation of chromosomal mutations of Lactococcus lactis subsp. lactis biovar. diacetylactis 18-16 after introduction of Tn919

Abstract: The conjugative transposon Tn 919 was introduced at high frequency to L. lactis subsp. lactis biovar. diacetylactis 18-16 and transconjugants were screened for mutations in two chromosomally located genotypes; citrate metabolism and maltose utilization. A citrate negative mutant, lacking citritase activity, was isolated at a frequency of 1.18 × 10⁻⁴. The mutant, 18-16C5, contained a single copy of Tn 919 in a chromosomal location. A junction fragment of Tn 919 ::18-16C5 chromosomal DNA was cloned in Escherichia coli . Mutations in maltose metabolism were detected at a frequency of 4.0 × 10⁻⁴. No mutants were detected when Tn 919 was not introduced. Reversion to a Mal⁺ phenotype occurred at high frequency, but was not due to Tn 919 transposition.