Abstract
Conjugation is a driving force in the evolution and shaping of bacterial genomes. In antibiotic producing streptomycetes even small plasmids replicating via the rolling-circle mechanism are conjugative. Although they encode only genes involved in replication and transfer, the molecular function of most plasmid encoded proteins is unknown. In this work we show that the conjugative plasmid pIJ101 encodes an overlooked protein, SpdA2. We show that SpdA2 is a DNA binding protein which specifically recognizes a palindromic DNA sequence (sps). sps is localized within the spdA2 coding region and highly conserved in many Streptomyces plasmids. Elimination of the palindrome or deletion of spdA2 in plasmid pIJ303 did not interfere with conjugative plasmid transfer or pock formation, but affected segregational stability.
Highlights
Streptomycetes, mycelial growing gram-positive soil bacteria with a complex life cycle are the most important producers of antibiotics and other secondary metabolites (Aigle et al, 2014)
In this work we show that the conjugative plasmid pIJ101 encodes an overlooked protein, SpdA2
Since the antibiotic biosynthetic gene clusters encode the biosynthetic enzymes for the synthesis and resistance mechanisms to protect the producer from its own antibiotic, streptomycetes are regarded as the original source of antibiotic resistance genes (Thaker et al, 2013)
Summary
Streptomycetes, mycelial growing gram-positive soil bacteria with a complex life cycle are the most important producers of antibiotics and other secondary metabolites (Aigle et al, 2014). Many mobile genetic elements have been described in the genus Streptomyces (Vogelmann et al, 2011a). These include small plasmids replicating via the rolling-circle mechanism (Kieser et al, 1982; Kataoka et al, 1994; Muth et al, 1995; ServínGonzález et al, 1995; Reuther et al, 2006), larger low copy number plasmids (Schrempf and Goebel, 1977; Wohlleben and Pühler, 1987; Haug et al, 2003), plasmid-phages that can propagate and conjugate as episomal DNA but can produce infective phage particles (Chen et al, 2012), and linear plasmids of several hundred kbp in size (Kinashi et al, 1987). Streptomyces chromosomes often contain several copies of integrated chromosomal elements that can be excised and conjugally transferred to other bacteria where they integrate again, usually within a specific tRNA gene (Boccard et al, 1988; te Poele et al, 2008)
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