Summary Agmatine is the decarboxylation product of arginine and a number of bacteria have devoted enzymatic pathways for its metabolism. Pseudomonas aeruginosa harbours the aguBA operon that metabolizes agmatine to putrescine, which can be subsequently converted into other polyamines or shunted into the TCA cycle for energy production. We discovered an alternate agmatine operon in the P. aeruginosa strain PA14 named agu2ABCA′ that contains two genes for agmatine deiminases (agu2A and agu2A′). This operon was found to be present in 25% of clinical P. aeruginosa isolates. Agu2A′ contains a twin-arginine translocation signal at its N-terminus and site-directed mutagenesis and cell fractionation experiments confirmed this protein is secreted to the periplasm. Analysis of the agu2ABCA′ promoter demonstrates that agmatine induces expression of the operon during the stationary phase of growth and during biofilm growth and agu2ABCA′ provides only weak complementation of aguBA, which is induced during log phase. Biofilm assays of mutants of all three agmatine deiminase genes in PA14 revealed that deletion of agu2ABCA′, specifically its secreted product Agu2A′, reduces biofilm production of PA14 following addition of exogenous agmatine. Together, these findings reveal a novel role for the agu2ABCA′ operon in the biofilm development of P. aeruginosa.
Deep ocean blue holes possess steep physicochemical gradients, especially low dissolved oxygen concentration, which shape the extraordinary microbial communities. However, the environmental responses of microorganisms with different lifestyles and knowledge of culturable microorganisms in the blue holes are still unknown. Here, we investigated the bacterial community structure with different lifestyles of the world’s deepest blue hole - the Yongle Blue Hole (YBH) in the South China Sea using both culture-dependent and -independent methods. YBH can be divided by oxygen content into an oxic zone, a suboxic zone and two anoxic zones. The abundance of bacteria, archaea, genes dsrB and soxB were all higher in the free-living (FL) lifestyle than in the particle-associated (PA) lifestyle, yet the diversity and richness of PA bacteria were higher than that of FL bacteria. More Gammaproteobacteria and less Alphaproteobacteria, Chloroflexi and Nitrospinae were observed within the FL fraction than within the PA fraction. The relative abundance of sulfur-oxidizing bacteria (SOB) was dominant between 100-140 m (anoxic zone I) in YBH, with a maximum of 90.0% (140 m FL fraction). The SOB in YBH were mainly colorless sulfur bacteria and purple non-sulfur bacteria, of which Thiomicrorhabdus and Sulfurimonas were the main representatives. In addition, a total of 294 bacterial strains were isolated on a variety of media and culture conditions, and 22.2% (18/81) of anaerobic strains were identified as potential novel species. Our study reveals a distinction between FL and PA bacteria in YBH. It contributes to further understanding of the bacterial community in deep ocean blue holes, and provides bacterial resources for subsequent studies on their adaptation to extreme marine environments.
To elucidate the roles of oral keratinocytes in the adaptive immune response of oral mucosa, global gene expression analysis was performed by microarray technique and integrating computational methods, including hierarchical clustering, biological process Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes pathway analysis, self-organizing maps (SOMs) and biological association network analysis (BAN). Raw data from microarray experiments were uploaded to the Gene Expression Omnibus Database, http://www.ncbi.nlm.nih.gov/geo/ (GEO accession GSE28035). We identified 666 differentially expressed genes in the early stage (48 h) and 993 in the late stage (96 h) of the oral mucosal adaptive immune response. The analysis revealed that oral keratinocytes exerted diverse biological functions in different stages of immune response. Specifically, in 48 h the differentially expressed genes encompassed an array of biological ontology associated with immune response, such as antigen processing and presentation, and positive regulation of T-cell-mediated cytotoxicity. Several pathways which have been reported to be critical in inflammation, including mitogen-activated protein kinase pathway, were activated. Furthermore, after BAN construction, some putative hub genes and networks such as interleukin-1α and its subnetwork were recognized. Taken together, these results give substantial evidence to support the active roles of keratinocytes in the oral mucosal adaptive immune response.
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