The structure and diversity of bacterial communities associated with the oxygen minimum zone (OMZ) of the eastern tropical South Pacific was studied through phylogenetic analysis. Clone libraries of 16S rRNA gene fragments were constructed using environmental DNA collected from the OMZ (60 m and 200 m), the sea surface (10 m), and the deep oxycline (450 m). At the class level, the majority of sequences affiliated to the gamma- (53.7%) and alpha-Proteobacteria (19.7%), and to the Bacteroidetes (11.2%). A vertical partitioning of the bacterial communities was observed, with main differences between the suboxic OMZ and the more oxygenated surface and deep oxycline waters. At the surface, the microbial community was predominantly characterized by SAR86, Loktanella and unclassified Flavobacteriaceae, whereas the deeper layer was dominated by Sulfitobacter and unclassified Alteromonadaceae. In the OMZ, major constituents affiliated to the marine SAR11 clade and to thiotrophic gamma-symbionts (25% of all sequences), a group not commonly found in pelagic waters. Sequences affiliating to the phylum Chloroflexi, to the AGG47 and SAR202 clades, to the delta-Proteobacteria, to the Acidobacteria, and to the 'anammox group' of the Planctomycetes were found exclusively in the OMZ. The bacterial richness in the OMZ was higher than in the oxic surface and deeper oxycline, as revealed by rarefaction analysis and the Chao1 richness estimator (surface: 45 +/- 8, deeper oxycline: 76 +/- 26; OMZ (60 m): 97 +/- 33, OMZ (200 m): 109 +/- 31). OMZ bacterial diversity indices (Fisher's: approximately 30 +/- 5, Shannon's: approximately 3.31, inverse Simpson's: approximately 20) were similar to those found in other pelagic marine environments. Thus, our results indicate a distinct and diverse bacterial community within the OMZ, with presumably novel and yet uncultivated bacterial lineages.

The Wadden Sea is a tidal flat ecosystem at the land-sea interface of the southern North Sea with a high load of suspended matter and nutrients. Despite the general importance of microbial processes, the composition of bacterial communities in this ecosystem has been little studied. Therefore, we investigated the composition of the bacterial communities freely suspended (FL) in the bulk water, associated with suspended aggregates (AG) and with the oxic sediment surface (SE) over an annual cycle (April 1999 to June 2000 in the East Frisian Wadden Sea, by applying denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments. Wind strength, suspended particulate matter (SPM), particulate organic carbon (POC), chlorophyll, phaeopigments, and the composition of the phytoplankton community were also studied. The dynamics of these parameters covaried to various extents, but not systematically, with that of bacterial numbers and community composition. A cluster analysis revealed that the DGGE banding patterns of the 3 communities grouped separately even though band overlaps among the communities occurred. Some identical or highly similar phylotypes were found in the FL-and AG-associated communities, and in the AG-and SE-associated communities, as shown by sequence analysis of excised bands. Prominent members of each community occurred over most of or during the entire study period. Dominant phylotypes in the FL-, AG-and SE-associated communities affiliated with α-Proteobacteria (mainly Roseobacter clade) and γ-Proteobacteria. Phylotypes affiliating with δ-Proteobacteria and Flavobacteria/Sphingobacteria of the Bacteroidetes phylum were detected occasionally in the AG-and SE-associated communities. During certain periods, 1 phylotype affiliating with Actinobacteria and 1 with β-Proteobacteria was detected in the FL-community. The prevalence of the rather stable composition of the communities over time, despite strong hydrodynamic forcing and pronounced seasonal changes in the phytoplankton community, SPM and POC, indicated that the bacterial communities were adapted to the environmental conditions in this highly dynamic system. The band overlaps between the various communities, however, also reflected that exchange processes between the dissolved and particulate phase and the sediment occurred. KEY WORDS: Bacteria · Phytoplankton · Aggregates · POC · Sediment · DGGE · Wadden SeaResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 38: 15-30, 2005 Niesel & Günther 1999, Tillmann et al. 2000, Wolfstein et al. 2000. Bacterial production and turnover of organic matter have also been assessed, and studies have shown that the Wadden Sea is net-heterotrophic, emphasizing the significance of heterotrophic over autotrophic processes (Admiraal et al. 1985, Van Duyl & Kop 1988, Poremba et al. 1999a. Because of the shallow, turbid and highly dynamic nature of the Wadden Sea, free-living as well as aggregate-associated bacteria and those associated wit...

Bacteria of the phyla Proteobacteria and Bacteroidetes are known to be the most prominent heterotrophic organisms in marine surface waters. In order to investigate the occurrence of these phyla in a coastal environment, the tidal flat ecosystem German Wadden Sea, we analyzed a clone library of PCR-amplified and sequenced 16S rRNA gene fragments and isolated 46 new strains affiliated with these phyla from the water column with various polymers and complex media as substrates. The phylogenetic affiliation of these strains was analyzed on the basis of sequenced 16S rRNA gene fragments. Subsequently, a comprehensive phylogenetic analysis of Proteobacteria and Bacteroidetes including available sequences from oxic habitats of earlier studies of this ecosystem was performed. Sequences of the earlier studies were derived from isolation approaches and from denaturing gradient gel electrophoresis (DGGE) analyses of environmental samples and high dilution steps of MPN (most probable number) cultures. The majority of the 265 sequences included in this analysis affiliated with alpha-Proteobacteria (45.3%), gamma-Proteobacteria (31.7%), and Bacteroidetes (16.2%). Almost 7% belong to the delta-Proteobacteria and several of these clones affiliated with the Myxococcales, a group comprising obligate aerobic organisms. Within the alpha- and gamma-Proteobacteria specific clusters were identified including isolates from high dilution steps of dilution cultures and/or clones from the clone library or DGGE gels, implying a high abundance of some of these organisms. Within the gamma-Proteobacteria a new cluster is proposed, which consists of marine surface-attached organisms. This SAMMIC (Surface Attached Marine MICrobes) cluster comprises only uncultured phylotypes and exhibits a global distribution. Overall, the analysis indicates that Proteobacteria and Bacteroidetes of the Wadden Sea have a surprisingly high diversity, presumably a result of the signature of this ecosystem as a melting pot at the land-sea interface and comprising a great habitat variety.

Gram positive bacteria recently have been identified as important components of freshwater ecosystems and are also present in marine environments. However, their quantitative significance and possible role in the latter systems is still little studied, in particular in coastal regions. Therefore, we investigated the abundance and composition of Gram positive bacteria in the Wadden Sea, a tidal flat ecosystem in the German Bight of the North Sea. Applying fluorescence in situ hybridization we found that Actinobacteria constitute 4-7% of total bacteria in the Wadden Sea and slightly higher proportions in a freshwater drainage channel connected to the sea by a sluice. The application of denaturing gradient gel electrophoresis of 16S rRNA gene fragments after amplification by an Actinobacteria-specific primer set and subsequent sequencing showed that the composition of the actinobacterial community in the Wadden Sea was distinctly different from that in the freshwater system. A bacterial clone library of 111 clones yielded eight Gram positive phylotypes which are related closely to other marine phylotypes including the Marine Actinobacteria Clade but also to freshwater phylotypes. We applied dilution cultures, enriched with various biopolymers, Marine Broth and Fucus vesiculosus extracts, for isolating bacteria from the bulk water, suspended aggregates, the oxic surface and oxic/anoxic transition zone of the sediment. Fifty-three isolates affiliated to seven families of the order Actinomycetales and nine isolates to the family Bacillaceae. The salinity range (1-45 per thousand NaCl) and growth optimum of 14 strains from various families showed that all except one strain exhibited a rather broad range of sustained growth from 1 per thousand to >or= 20 per thousand NaCl and several strains exhibited an optimum of > 10 per thousand NaCl. The results indicate that the Gram positive bacterial community in the Wadden Sea is surprisingly diverse and consists mainly of indigenous species which appear to be well adapted to the environmental conditions of this coastal ecosystem.

The new marine Halomonas sp. strain GWS-BW-H8hM (DSM 17996) was found to produce 3-(4'-hydroxyphenyl)-4-phenylpyrrole-2,5-dicarboxylic acid (HPPD-1) and 3,4-bis(4'-hydroxy- phenyl)pyrrole-2,5-dicarboxylic acid (HPPD-2). In initial cultivations using marine broth, only low contents of these compounds have been isolated. Improving the conditions and growing the strain on artificial seawater supplemented with tryptone 10 g l(-1), yeast extract 5 g l(-1), L-tyrosine 0.6 g l(-1), glycine 1 g l(-1), and glucose 6 g l(-1), the growth-associated HPPD-1 and HPPD-2 production of a 40-l batch cultivation reached the amounts of 47 mg l(-1) and 116 mg l(-1), respectively, after 65 h. Both compounds showed potent anti-tumor-promoting activities.