Sex Pheromones and Plasmid Transfer in Streptococcus faecalis

Abstract

INTRODUCTION
Within a highly evolved multicellular organism, communication between distally located cells occurs by means of a variety of different chemical signals. These hormonal substances play important roles in development, maintenance, and fertility and are also involved in coordinating immune and neurological responses to external stimuli. Chemical communication can also occur between individual organisms, and the molecules representing these signals are referred to as pheromones (Karlson and Luscher 1959). Well-known examples of pheromones in higher systems include those serving as sex attractants in insects and certain vertebrates.

Communication between unicellular organisms is, by definition, via pheromones, and the involvement of such substances in certain stages of development is well known or has been implicated in a number of microbial species (Ensign 1978; Hirosawa and Wolk 1979; Kaiser et al. 1979; Biro et al. 1980; Aaronson 1981; Stephens et al. 1982). Chemical substances that are excreted and facilitate mating between two organisms are called sex pheromones; these compounds and their behavior have been studied in fungi, algae (Kochert 1978), and ciliates (Nanney 1977). Much attention has been focused on the yeast α- and a-factors and the mating phenomena associated with their pheromonal activities (Manney et al. 1981; Kurjan and Herskowitz 1982; Sprague et al. 1983).

Although extracellular compounds that affect competence for transformation are well known in Streptococcus pneumoniae and S. sanguis (Lacks 1977), substantive evidence for bacterial sex pheromones that promote conjugative transfer of genetic material has been reported only in S. faecalis (discussed below). Sex-related chemotactic factors in Escherichia...