, 2008, Turmel et al., 2002a and Wolff et al., 1994) are also characterised by low gene density. The apparent “junk” DNA associated with the recombinases may have been
caught between the recombinase binding sites upon excision from an ancestral donor. Due to the lack of selection pressure, the non-coding parts of the transferred DNA have diverged quickly. We report the complete plastid genome and the sequence of a plasmid (pSr1) of the benthic diatom S. robusta. Our study shows that diatom plastid genomes are subject to major changes due to HGT events. The enlarged size of the S. robusta chloroplast genome is due to various HGT events that have occurred through different mechanisms (homing introns, recombinases) and from different sources (the pSr1 plasmid, other heterokonts, green algae). High sequence similarity indicates that two of the HGT events (resulting MG 132 in the introduction of ORF161 I BET 762 and the atpB intron) may be recent. Diatom plasmids may act as vectors for transfer of genetic material between chloroplasts of different diatom species, and even other heterokonts. The bacterial origin of at least two of the plasmid-localised genes suggests that they are derived from bacteria belonging to the Clostridia. Sequencing of other diatom and heterokont chloroplast genomes will likely lead to a better
understanding of HGT between chloroplast genomes and the possible role of diatom plasmids in this process Alectinib in vitro in heterokonts. S. robusta strains were obtained from the BCCM/DCG culture collection (http://bccm.belspo.be), accession numbers DCG
0115 and DCG 0230. These were mated, and one of the progeny strains (D6) was used further. The strains were cultivated in f/2 medium based on 0.2 μm filtered and autoclaved seawater supplemented with vitamins and inorganic nutrients ( Guillard, 1975). Cells were grown at 22 °C in a 16 hour light:8 hour dark photoperiod at an illumination of approximately 100 μmol m− 2 s− 1. Isolation of genomic DNA was based on a modified protocol from Bowler et al. (Bowler et al., 2008). Six litres of S. robusta culture in late exponential phase was centrifuged at 2000 g for 10 min at 4 °C. The cell pellet was frozen in liquid nitrogen and resuspended in lysis buffer (50 mM Tris–HCl pH 8.0, 50 mM EDTA pH 8.0, 1% SDS, 10 mM DTT, 10 mg/mL of proteinase K; 10 ml buffer/l of culture) and incubated at 50 °C for 45 min. Three phenol/chloroform extractions were performed to remove proteins. The lysate was treated with RNase (10 mg/ml, 2 μl per ml lysate) at 37 °C for 60 min after the first phenol/chloroform extraction. A subsequent extraction with chloroform isoamyl alcohol (24:1) was made to eliminate completely the phenol residues. Genomic DNA was precipitated (2 volumes ethanol, 0.1 M NaCl), and the visible DNA was wound up on a glass rod and transferred to a 15 ml tube. 10 ml 70% EtOH was added and the pellet was incubated at 4 °C over night.