Members of the Bacteroidetes, formerly known as the Cytophaga-Flavobacteria-Bacteroides (CFB) phylum, are among the major taxa of marine heterotrophic bacterioplankton frequently found on macroscopic organic matter particles (marine snow). In addition, they have been shown to also represent a significant part of free-living microbial assemblages in nutrient-rich microenvironments. Their abundance and distribution pattern in combination with enzymatic activity studies has led to the notion that organisms of this group are specialists for degradation of high molecular weight compounds in both the dissolved and particulate fraction of the marine organic matter pool, implying a major role of Bacteroidetes in the marine carbon cycle. Despite their ecological importance, comprehensive molecular data on organisms of this group have been scarce so far. Here we report on the first whole genome analysis of a marine Bacteroidetes representative, 'Gramella forsetii' KT0803. Functional analysis of the predicted proteome disclosed several traits which in joint consideration suggest a clear adaptation of this marine Bacteroidetes representative to the degradation of high molecular weight organic matter, such as a substantial suite of genes encoding hydrolytic enzymes, a predicted preference for polymeric carbon sources and a distinct capability for surface adhesion.

Genes involved in magnetite biomineralization are clustered within the genomic magnetosome island of Magnetospirillum gryphiswaldense. Their transcriptional organization and regulation were studied by several approaches. Cotranscription of genes within the mamAB, mamDC, and mms clusters was demonstrated by reverse transcription-PCR (RT-PCR) of intergenic regions, indicating the presence of long polycistronic transcripts extending over more than 16 kb. The transcription start points of the mamAB, mamDC, and mms operons were mapped at 22 bp, 52 bp, and 58 bp upstream of the first genes of the operons, respectively. Identified ؊10 and ؊35 boxes of the P mamAB , P mamDC , and P mms promoters showed high similarity to the canonical 70 recognition sequence. The transcription of magnetosome genes was further studied in response to iron and oxygen. Transcripts of magnetosome genes were detected by RT-PCR both in magnetic cells grown microaerobically under iron-sufficient conditions and in nonmagnetic cells grown either aerobically or with iron limitation. The presence of transcripts was found to be independent of the growth phase. Further results from partial RNA microarrays targeting the putative magnetosome transcriptome of M. gryphiswaldense and real-time RT-PCR experiments indicated differences in expression levels depending on growth conditions. The expression of the mam and mms genes was down-regulated in nonmagnetic cells under iron limitation and, to a lesser extent, during aerobic growth compared to that in magnetite-forming cells grown microaerobically under iron-sufficient conditions.Magnetic orientation in magnetotactic bacteria is based on the synthesis of magnetosomes, which consist of crystals of magnetite (Fe 3 O 4 ) enclosed within intracytoplasmic vesicles of the magnetosome membrane (MM) (1, 29). The MM consists of a lipid bilayer, which provides spatial and physicochemical control over magnetite biomineralization and has a distinct biochemical composition. In the microaerophilic alphaproteobacterium Magnetospirillum gryphiswaldense, the MM is associated with a characteristic subset of magnetosome membrane proteins (MMPs), which are present in different quantities, with relative abundances between Ͻ1% and Ͼ15% (11). Classes of MMPs include those with presumed functions in the activation of magnetosomes, magnetosome-directed transport of iron, nucleation and control of crystal growth, and the assembly of magnetosome chains (16,26,28,29). The targeting of MMPs to the MM is controlled by an unknown mechanism, but it can be assumed that stoichiometric synthesis of individual constituents is regulated for proper assembly of magnetosomes (29).In M. gryphiswaldense, the MMPs are encoded within a hypervariable 130-kb genomic magnetosome island (MAI) (28,35). In addition to all known magnetosome genes, the MAI contains further genes putatively involved in magnetosome biomineralization and is particularly rich in insertion elements. The mam (magnetosome membrane) and mms (magnetic particle membrane-specific) ge...

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