P. ubique’ HTCC1062 (tonBDR: 0 genes; abc: 24 genes) ( Pinhassi et al.,

1997). Overall, the Kinase Inhibitor Library metatranscriptome data support our previous metaproteomic analyses of membrane transporter expression profiles (Teeling et al., 2012). However, even though both methods agreed on class level, slight differences were detected on deeper taxonomic levels. Based on the metaproteome analysis (Teeling et al., 2012), members of the Roseobacter clade showed a higher expression of transporters than the more abundant members of the SAR11 clade, whereas our Illumina metatranscriptomic detected the opposite trend ( Fig. 3c). Therefore we suggest that the lower amounts of detected transcripts for Rhodeobacteraceae might be a result of fast mRNA turnover coupled to high rRNA expression. This supports not only the cellular strategy to an environmental stimulus as described

by Yu and Zhang (2012), but also provides another indicator that members of Rhodobacteraceae adapt readily to changing nutrient conditions induced by an algae bloom ( Giebel et al., 2011). Rhodobacteraceae expressed a high amount of transcripts encoding SnoaL-like polyketide cyclases. SnoaL belongs to a family of small polyketide cyclases involved in nogalamycin biosynthesis ( Sultana et al., 2004). Nogalamycin is a member Osimertinib in vivo of an anthracycline group ( Arora, 1983) Erlotinib ic50 that intercalates into DNA and interacts with topoisomerase II ( Sinha, 1995, Binaschi et al., 2001 and Tran et al., 2011), thereby preventing transcription and subsequent protein synthesis. In research, nogalamycin has also been successfully used as antibiotic against algae ( Guha-Mukherjeea and Keller, 1973). Considering that algae and bacteria most likely compete over the same limiting nutrients, SnoaL expression might confer a competitive advantage. Frequency analysis of expressed rRNA sequences allowed us to interrogate the major findings of the Teeling et al. study down to genus level despite methodological

differences. The results substantiated the view that the successive bacterioplankton bloom was largely governed by substrate availability. Expression of glycoside hydrolases most likely allowed Formosa and Polaribacter members to decompose complex algae polysaccharides resulting in an increasing availability of sugar oligomers and monomers. Algae-derived substrates provided a series of ecological niches for specific populations to bloom, and at the same time generated a selective advantage for bacteria with an opportunistic lifestyle like members of the Roseobacter clade. Furthermore, Rhodobacteraceae seemed to pursue a competitive strategy due to as yet unknown mechanisms, possibly by biosynthesis of algicidal polyketides.