ABSTRACT
Two plasmids, 76 and 148 kb in size, isolated from Ruegeria strain PR1b were entirely sequenced. These are the first plasmids to be characterized from this genus of marine bacteria. Sequence analysis revealed a biased distribution of function among the putative proteins encoded on the two plasmids. The smaller plasmid, designated pSD20, encodes a large number of putative proteins involved in polysaccharide biosynthesis and export. The larger plasmid, designated pSD25, primarily encodes putative proteins involved in the transport of small molecules and in DNA mobilization. Sequence analysis revealed uncommon potential replication systems on both plasmids. pSD25, the first repABC-type replicon isolated from the marine environment, actually contains two repABC-type replicons. pSD20 contains a complex replication region, including a replication origin and initiation protein similar to iteron-containing plasmids (such as pSW500 from the plant pathogen Erwinia stewartii) linked to putative RepA and RepB stabilization proteins of a repABC-type replicon and is highly homologous to a plasmid from the phototrophic bacterium Rhodobacter sphaeroides. Given the nature of the putative proteins encoded by both plasmids it is possible that these plasmids enhance the metabolic and physiological flexibility of the host bacterium, and thus its adaptation to the marine sediment environment.
Subject(s)
Plasmids/metabolism , Rhodobacteraceae/genetics , ATP-Binding Cassette Transporters/metabolism , DNA/metabolism , DNA Replication , DNA, Bacterial , Erwinia/metabolism , Polysaccharides/metabolism , Recombination, Genetic , Replication Origin , Replicon , Rhodobacter sphaeroides/metabolismABSTRACT
A 50,709-bp cryptic plasmid isolated from a marine Micrococcus has been sequenced and found to contain a number of putative mobile genetic elements. The coding regions for 11 putative transposases comprise approximately 17% of the total plasmid sequence. The majority of these transposases are located within a 13-kb cluster which includes a 1553-bp direct repeat consisting of a duplicated pair of transposase genes. The remaining putative ORFs showed similarity to a variety of proteins, the most notable being spider silk.