Silicibacter

Abstract: Summary Silicibacter sp. TM1040, originally isolated from a culture of the dinoflagellate Pfiesteria piscicida, senses and responds to the dinoflagellate secondary metabolite dimethylsulfoniopropionate (DMSP) by flagella-mediated chemotaxis behaviour. In this report we show that swimming motility is important for initiating the interaction between the bacterium and dinoflagellate. Following transposon mutagenesis, three mutants defective in wild-type swimming motility (Mot–) were identified. The defects in motility were found to be in homologues of cckA and ctrA, encoding a two-component regulatory circuit, and in a novel gene, flaA, likely to function in flagellar export or biogenesis. Mutation of flaA or cckA results in the loss of flagella and non-motile cells (Fla–), while CtrA– cells possess flagella, but have reduced motility due to increased cell length. All three Mot– mutants were defective in attaching to the dinoflagellate, particularly to regions that colocalized with intracellular organelles. The growth rate of the dinoflagellates was reduced in the presence of the Fla– mutants compared with Fla+ cells. These results indicate that bacterial motility is important for the Silicibacter sp. TM1040–P. piscicida interaction.

Abstract: dehydration of erythro--methylmalyl-CoA to mesaconyl-CoA with rates of 1,300 mol min 1 mg protein 1 . Genes coding for similar enzymes with two (R)-enoyl-CoA hydratase domains are present in the genomes of Roseiflexus, Methylobacterium, Hyphomonas, Rhodospirillum, Xanthobacter, Caulobacter, Magnetospirillum, Jannaschia, Sagittula, Parvibaculum, Stappia, Oceanicola, Loktanella, Silicibacter, Roseobacter, Roseovarius, Dinoroseobacter, Sulfitobacter, Paracoccus, and Ralstonia species. A similar yet distinct class of enzymes containing only one hydratase domain was found in various other bacteria, such as Streptomyces species. The role of this widely distributed new enzyme is discussed.

Abstract: A Gram-negative, non-motile, rod-shaped bacterial strain, SW-255(T), was isolated from seawater from Hwajinpo, on the coast of the East Sea, Korea, and subjected to a polyphasic taxonomic study Strain SW-255(T) grew optimally at pH 70-80 and 37 degrees C in the presence of 2 % (w/v) NaCl It contained Q-10 as the predominant ubiquinone and C(18 : 1)omega7c as the major fatty acid The DNA G+C content was 670 mol% A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences showed that strain SW-255(T) is phylogenetically closely related to the genera Ruegeria and Silicibacter of the Alphaproteobacteria The levels of 16S rRNA gene sequence similarity between strain SW-255(T) and the type strains of Ruegeria atlantica and two Silicibacter species were in the range 958-962 % A phylogenetic tree based on gyrB sequences showed that strain SW-255(T) forms a distinct evolutionary lineage within the Alphaproteobacteria Differential phenotypic properties, polar lipid profiles and DNA G+C contents, together with the phylogenetic distinctiveness, suggest that strain SW-255(T) should be distinguished from the members of the genera Ruegeria and Silicibacter On the basis of the phenotypic, chemotaxonomic and phylogenetic data, strain SW-255(T) represents a novel genus and species, for which the name Pseudoruegeria aquimaris gen nov, sp nov is proposed The type strain of Pseudoruegeria aquimaris is SW-255(T) (=KCTC 12737(T)=JCM 13603(T))

Abstract: Nitric oxide (NO) plays an important signaling role in all domains of life. Many bacteria contain a h eme- n itric oxide/ ox ygen binding (H-NOX) protein that selectively binds NO. These H-NOX proteins often act as sensors that regulate histidine kinase (HK) activity, forming part of a bacterial two-component signaling system that also involves one or more response regulators. In several organisms, NO binding to the H-NOX protein governs bacterial biofilm formation; however, the source of NO exposure for these bacteria is unknown. In mammals, NO is generated by the enzyme nitric oxide synthase (NOS) and signals through binding the H-NOX domain of soluble guanylate cyclase. Recently, several bacterial NOS proteins have also been reported, but the corresponding bacteria do not also encode an H-NOX protein. Here, we report the first characterization of a bacterium that encodes both a NOS and H-NOX, thus resembling the mammalian system capable of both synthesizing and sensing NO. We characterized the NO signaling pathway of the marine alphaproteobacterium Silicibacter sp. strain TrichCH4B, determining that the NOS is activated by an algal symbiont, Trichodesmium erythraeum . NO signaling through a histidine kinase-response regulator two-component signaling pathway results in increased concentrations of cyclic diguanosine monophosphate, a key bacterial second messenger molecule that controls cellular adhesion and biofilm formation. Silicibacter sp. TrichCH4B biofilm formation, activated by T. erythraeum , may be an important mechanism for symbiosis between the two organisms, revealing that NO plays a previously unknown key role in bacterial communication and symbiosis. IMPORTANCE Bacterial nitric oxide (NO) signaling via h eme- n itric oxide/ ox ygen binding (H-NOX) proteins regulates biofilm formation, playing an important role in protecting bacteria from oxidative stress and other environmental stresses. Biofilms are also an important part of symbiosis, allowing the organism to remain in a nutrient-rich environment. In this study, we show that in Silicibacter sp. strain TrichCH4B, NO mediates symbiosis with the alga Trichodesmium erythraeum , a major marine diazotroph. In addition, Silicibacter sp. TrichCH4B is the first characterized bacteria to harbor both the NOS and H-NOX proteins, making it uniquely capable of both synthesizing and sensing NO, analogous to mammalian NO signaling. Our study expands current understanding of the role of NO in bacterial signaling, providing a novel role for NO in bacterial communication and symbiosis.