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Some key carotenogenic genes (crts) in Dunaliella bardawil are regulated in response to salt stress partly due to salt-inducible cisacting elements in their promoters. Thus, we isolated and compared the z-carotene desaturase (Dbzds) promoter with other crts promoters including phytoene synthase (Dbpsy), phytoene desaturase (Dbpds), and lycopene b-cyclase1 (DblycB1) to identify salt-inducible element(s) in the Dbzds promoter. In silico analysis of the Dbzds promoter found several potential cis-acting elements, such as abscisic acid response element-like sequence, myelocytomatosis oncogene1 recognition motif, AGC box, anaerobic motif2, and activation sequence factor1 binding site. Remarkably, instead of salt-inducible elements, we found a unique regulatory sequence architecture in the Dbzds promoter: a hypoosmolarity-responsive element (HRE) candidate followed by a potential hypoosmolarity-inducible factor GBF5 binding site. Deletion experiments demonstrated that only HRE, but not the GBF5 binding site, is responsible for hypoosmotic expression of the fusion of Zeocin resistance gene (ble) to the enhanced green fluorescent protein (egfp) chimeric gene under salt stress. Dbzds transcripts were in accordance with those of ble-egfp driven by the wild-type Dbzds promoter. Consequently, Dbzds is hypoosmotically regulated by its promoter, and HRE is responsible for this hypoosmotic response. Finally, the hypoosmolarity mechanism of Dbzds was studied by comparing transcript profiles and regulatory elements of Dbzds with those of Dbpsy, Dbpds, DblycB1, and DblycB2, revealing that different induction characteristics of crts may correlate with regulatory sequence architecture.Carotenoids are a structurally diverse class of isoprenoids synthesized by all photosynthetic organisms and many nonphotosynthetic organisms, such as certain species of bacteria, fungi, and archaea (Goodwin, 1980). They possess many advantageous properties for the human body on account of their vitamin A activity as essential nutrients (Farré et al., 2010), prevention and treatment functions against several kinds of diseases as health care products (Michaud et al., 2000;Landrum and Bone, 2001;Shaish et al., 2006), as well as industrial agents as colorants, forages, and cosmetics (SchmidtDannert, 2000). Therefore, the investigation of biosynthetic mechanisms and commercial exploitation of carotenoids have gained increasing attraction in many laboratories and companies. Recently, at least 700 carotenoids have been characterized from natural carotenoid biosynthetic pathways (Feltl et al., 2005).Some carotenogenic microorganisms have been commercially employed to produce important carotenoids (Johnson et al., 1995;Raja et al., 2007). Among these microorganisms, the Dunaliella genus, especially Dunaliella salina and Dunaliella bardawil, has been researched extensively and exploited as a natural source of carotenoids due to its striking ability to accumulate carotenoids under certain circumstances (Amotz et al., 1982), including high light intensity, high sa...

jgjiang@scut.edu.cn.

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SummaryThe mitigation of biofouling has received significant research attention, with particular focus on non‐toxic and sustainable strategies. Here, we investigated quorum sensing inhibitor (QSI) bacteria as a means of controlling biofouling in a laboratory‐scale system. Approximately, 200 strains were isolated from coral (Pocillopora damicornis) and screened for their ability to inhibit quorum sensing (QS). Approximately, 15% of the isolates exhibited QSI activity, and a typical coral symbiotic bacterium, H12‐Vibrio alginolyticus, was selected in order for us to investigate quorum sensing inhibitory activity further. Confocal microscopy revealed that V. alginolyticus extract inhibited biofilm formation from Pseudomonas aeruginosa PAO1. In addition, the secondary metabolites of V. alginolyticus inhibited PAO1 virulence phenotypes by downregulating motility ability, elastase activity and rhamnolipid production. NMR and MS spectrometry suggested that the potential bioactive compound involved was rhodamine isothiocyanate. Quantitative real‐time PCR indicated that the bacterial extract induced a significant downregulation of QS regulatory genes (lasB, lasI, lasR, rhlI, rhlR) and virulence‐related genes (pqsA, pqsR). The possible mechanism underlying the action of rhodamine isothiocyanate analogue involves the disruption of the las and/or rhl system of PAO1. Our results highlight coral microbes as a bioresource pool for developing QS inhibitors and identifying novel antifouling agents.

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A central goal in marine microecology is to understand the ecological factors shaping spatiotemporal microbial patterns and the underlying processes. We hypothesized that abiotic and/or biotic interactions are probably more important for explaining the distribution patterns of marine bacterioplankton than environmental filtering. In this study, surface seawater samples were collected about 7000 miles from the Mediterranean Sea, transecting the North Atlantic Ocean, to the Brazilian marginal sea. In bacterial biosphere, SAR11, SAR86, Rhodobacteraceae, and Rhodospiriaceae were predominant in the Mediterranean Sea; Prochlorococcus was more frequent in Atlantic Ocean; whereas in the Brazilian coastal sea, the main bacterial members were Synechococcus and SAR11. With respect to archaea, Euryarchaeota were predominant in the Atlantic Ocean and Thaumarchaeota in the Mediterranean Sea. With respect to the eukaryotes, Syndiniales, Spumellaria, Cryomonadida, and Chlorodendrales were predominant in the open ocean, while diatoms and microzooplankton were dominant in the coastal sea. Distinct clusters of prokaryotes and eukaryotes displayed clear spatial heterogeneity. Among the environmental parameters measured, temperature and salinity were key factors controlling bacterial and archaeal community structure, respectively, whereas N/P/Si contributed to eukaryotic variation. The relative contribution of environmental parameters to the microbial distribution pattern was 45.2%. Interaction analysis showed that Gammaproteobacteria, Alphaproteobacteria, and Flavobacteriia were the keystone taxa within the positive-correlation network, while Thermoplasmata was the main contributor in the negative-correlation network. Our study demonstrated that microbial communities are co-governed by environmental filtering and biotic interactions, which are the main deterministic driving factors modulating the spatiotemporal patterns of marine plankton synergistically at the regional or global levels.