Background-Improvement in lung function following macrolide antibiotic therapy has been attributed to reduction in bronchial infection due to specific bacteria. However, the airway may be populated by a more diverse microbiota, and clinical features of asthma may be associated with characteristics of the airway microbiota present.

We examined bacterial dynamics in batch cultures of two axenic marine diatoms (Thalassiosira rotula and Skeletonema costatum). The axenic diatoms were inoculated with natural bacterial assemblages and monitored by 4,6-diamidino-2-phenolindole (DAPI) counts, denaturing gradient gel electrophoresis (DGGE) with subsequent analysis of excised, sequenced 16S rRNA gene fragments, and fluorescence in situ hybridization (FISH) with group-specific 16S rRNA oligonucleotide probes. Our results show that algal growth exhibited pronounced differences in axenic treatments and when bacteria were present. Bacterial abundance and community structure greatly depended on species, growth and physiological status of even closely related algae. Free-living and phytoplankton-associated bacteria were very different from each other and were dominated by distinct phylogenetic groups. The diatom-associated bacteria mainly belonged to the Flavobacteria-Sphingobacteria group of the Bacteroidetes phylum whereas free-living bacteria, which were rather similar in both cultures, comprised mainly of members of the Roseobacter group of alpha-Proteobacteria. Presence and disappearance of specific bacteria during algal growth indicated pronounced differences in environmental conditions over time and selection of bacteria highly adapted to the changing conditions. Tight interactions between marine bacteria and diatoms appear to be important for the decomposition of organic matter and nutrient cycling in the sea.

Bacterial communities in the airways of cystic fibrosis (CF) patients are, as in other ecological niches, influenced by autogenic and allogenic factors. However, our understanding of microbial colonization in younger versus older CF airways and the association with pulmonary function is rudimentary at best. Using a phylogenetic microarray, we examine the airway microbiota in age stratified CF patients ranging from neonates (9 months) to adults (72 years). From a cohort of clinically stable patients, we demonstrate that older CF patients who exhibit poorer pulmonary function possess more uneven, phylogenetically-clustered airway communities, compared to younger patients. Using longitudinal samples collected form a subset of these patients a pattern of initial bacterial community diversification was observed in younger patients compared with a progressive loss of diversity over time in older patients. We describe in detail the distinct bacterial community profiles associated with young and old CF patients with a particular focus on the differences between respective “early” and “late” colonizing organisms. Finally we assess the influence of Cystic Fibrosis Transmembrane Regulator (CFTR) mutation on bacterial abundance and identify genotype-specific communities involving members of the Pseudomonadaceae, Xanthomonadaceae, Moraxellaceae and Enterobacteriaceae amongst others. Data presented here provides insights into the CF airway microbiota, including initial diversification events in younger patients and establishment of specialized communities of pathogens associated with poor pulmonary function in older patient populations.

To date no study exists that directly addresses changes in dynamics of heterotrophic bacteria in surface waters in relation to partial pressure of CO 2 (pCO 2 ). Therefore, we studied the effect of changes in pCO 2 on bacterial abundance and activities by using mesocosms with different pCO 2 levels (ϳ190, ϳ370, and ϳ700 ppmV, representing past, present-day, and future atmospheric pCO 2 , respectively). Abundance of total bacteria did not differ with increasing pCO 2 throughout the whole study period, whereas bacterial protein production (BPP) was highest at highest pCO 2 . This effect was even more pronounced for cell-specific production rates, especially those of attached bacteria, which were up to 25 times higher than those of free bacteria. During the breakdown of the bloom, however, the abundance of both free and attached bacteria was significantly increased with pCO 2 . Differences in bacterial growth rate () were smaller than those of BPP, but both and BPP of attached bacteria were elevated under high pCO 2 . Averages of total protease as well as ␣-and ␤-glucosidase activities were highest at elevated pCO 2 levels, but a statistically significant dependence on pCO 2 was only evident for protease activity. There is a measurable but indirect effect of changes in pCO 2 on bacterial activities that are mainly linked to phytoplankton and presumably particle dynamics.The world's oceans are currently absorbing one third of the anthropogenic carbon emissions each year and will presumably absorb even higher percentages in the near future. According to the Intergovernmental Panel on Climate 1 Corresponding author (hgrossart@igb-berlin.de). AcknowledgmentsWe thank the staff of the Large Scale Facility (LFS) in Bergen, in particular Jorun Egge and Celia Booman for their great help in conducting our study. Kirsten Pohlmann is thanked for statistical analyses and comments on an earlier version of the manuscript, and Scarlett Trimborn for Chl a measurements and field assistance. We are grateful to all other participants of the PeECE (Pelagic Ecosystem CO 2 Enrichment) study for their valuable technical assistance,

More than 100 bacterial isolates from various marine habitats were screened for AHL production by using gfp reporter constructs based on the lasR system of Pseudomonas aeruginosa and the luxR system of Vibrio fischeri. Of the 67 Alphaproteobacteria tested, most of which belonged into the so-called Roseobacter clade, 39 induced fluorescence in either one or both sensor strains up to 103-fold compared to controls. Acylated homoserine lactones were identified by GC-MS analysis and shown to have chain lengths of C8, C10, C13-C16, and C18. One or two double bonds were often present, while a keto or hydroxyl group occurred only rarely in the side chain. Most strains produced several different AHLs. C18-en-HSL and C18-dien-HSL were produced by Dinoroseobacter shibae, an aerobic anoxygenic phototrophic bacterium isolated from dinoflagellates, and are among the longest AHLs found to date. Z7-C14-en-HSL, which has previously been detected in Rhodobacter sphaeroides, was produced by Roseovarius tolerans and Jannaschia helgolandensis. This signal molecule was synthesised and shown to induce a similar response to the culture supernatant in the respective sensor strain. The widespread occurrence of quorum-sensing compounds in marine Alphaproteobacteria, both free-living strains and those associated to eukaryotic algae, points to a great importance of this signalling mechanism for the adaptation of the organisms to their widely different ecological niches.