FIG. 1.

Schematic representation of the luxS locus of S. gordonii DL1 wild type (A), luxS mutant strain 1.1L (B), and complemented strain 1.1LC (C). The luxS gene was amplified from S. gordonii DL1 genomic DNA with the primers LuxF and LuxR; ermAM was ligated to a unique NdeI site (N) within the luxS gene, and the construct was transformed back onto the streptococcal chromosome (see Materials and Methods). Complemented strain 1.1LC was created by Campbell-like integration of plasmid pVALuxS carrying an intact copy of the luxS gene. The solid line indicates chromosomal DNA, and the broken line represents pVA981 DNA. (D) Expression of luxS by S. gordonii DL1 (lane 1) or mutant strains 1.1L (lane 2) or 1.1LC (lane 3). Total RNA was isolated from cells harvested at the late exponential phase of growth in TSBY medium and used in RT-PCR with luxS-specific primers LuxF3 and LuxR3.