The Fish Pathogen Vibrio ordalii Under Iron Deprivation Produces the Siderophore Piscibactin

Vibrio ordalii is the causative agent of vibriosis, mainly in salmonid fishes, and its virulence mechanisms are still not completely understood. In previous works we demonstrated that V. ordalii possess several iron uptake mechanisms based on heme utilization and siderophore production. The aim of the present work was to confirm the production and utilization of piscibactin as a siderophore by V. ordalii. Using genetic analysis, identification by peptide mass fingerprinting (PMF) of iron-regulated membrane proteins and chemical identification by LC-HRMS, we were able to clearly demonstrate that V. ordalii produces piscibactin under iron limitation. The synthesis and transport of this siderophore is encoded by a chromosomal gene cluster homologous to another one described in V. anguillarum, which also encodes the synthesis of piscibactin. Using β-galactosidase assays we were able to show that two potential promoters regulated by iron control the transcription of this gene cluster in V. ordalii. Moreover, biosynthetic and transport proteins corresponding to piscibactin synthesis and uptake could be identified in membrane fractions of V. ordalii cells grown under iron limitation. The synthesis of piscibactin was previously reported in other fish pathogens like Photobacterium damselae subsp. piscicida and V. anguillarum, which highlights the importance of this siderophore as a key virulence factor in Vibrionaceae bacteria infecting poikilothermic animals.

Bacteria push the limits of chemotactic precision to navigate dynamic chemical gradients

Ephemeral aggregations of bacteria are ubiquitous in the environment, where they serve as hotbeds of metabolic activity, nutrient cycling, and horizontal gene transfer. In many cases, these regions of high bacterial concentration are thought to form when motile cells use chemotaxis to navigate to chemical hotspots. However, what governs the dynamics of bacterial aggregations is unclear. Here, we use an experimental platform to create realistic submillimeter-scale nutrient pulses with controlled nutrient concentrations. By combining experiments, mathematical theory, and agent-based simulations, we show that individual Vibrio ordalii bacteria begin chemotaxis toward hotspots of dissolved organic matter (DOM) when the magnitude of the chemical gradient rises sufficiently far above the sensory noise that is generated by stochastic encounters with chemoattractant molecules. Each DOM hotspot is surrounded by a dynamic ring of chemotaxing cells, which congregate in regions of high DOM concentration before dispersing as DOM diffuses and gradients become too noisy for cells to respond to. We demonstrate that V. ordalii operates close to the theoretical limits on chemotactic precision. Numerical simulations of chemotactic bacteria, in which molecule counting noise is explicitly taken into account, point at a tradeoff between nutrient acquisition and the cost of chemotactic precision. More generally, our results illustrate how limits on sensory precision can be used to understand the location, spatial extent, and lifespan of bacterial behavioral responses in ecologically relevant environments.

Analisis Variasi Komponen Fotoprotein dan Aldehid Pada Reaksi Bioluminesen Bakteri Luminesen Vibrio ordalii Asal Perairan Laut Papua

Riset pemancaran cahaya yang dilakukan pada bakteri luminesen semakin banyak dipelajari. Hal ini disebabkan bakteri ini sangat mudah untuk dikerjakan di laboratorium, dan mudah diperoleh. Salah satu bakteri yang telah diisolasi dari laut lokal Papua adalah spesies Vibrio ordalii, dan karakteristik biologi dan fisikanya telah dilakukan. Pemancaran cahaya yang dilakukan oleh bakteri ini terjadi melalui reaksi kimia, yang dikenal sebagai reaksi bioluminesen, yang melibatkan tiga komponen fotoprotein, yaitu lusiferase, lusiferin, dan oksigen. Pada riset ini dilakukan variasi terhadap dua komponen, lusiferase dan lusiferin, dan aldehid sebagai komponen pendukung dalam reaksi bioluminesen. Tujuan yang dicapai adalah untuk mengetahui pengaruh variasi kedua komponen terhadap pemancaran cahaya bakteri. Metode yang digunakan adalah metode assay ditionit dan spektrometri dengan menggunakan spektrofotometer uv-vis. Hasil penelitian menunjukkan bahwa aldehid dengan konsentrasi di atas 0,01% tidak meningkatkan luminesen.Key words: bioluminescent, Vibrio ordalii, fotoprotein, aldehid, lusiferin, lusiferase.

Multilocus Sequence Analysis of Close Relatives Vibrio anguillarum and Vibrio ordalii

ABSTRACTThe genetic heterogeneity of the close relativesVibrio anguillarumandVibrio ordalii, both serious pathogens of fish causing extensive losses in aquaculture, was studied. Eight housekeeping genes, i.e.,atpA,ftsZ,gapA,gyrB,mreB,rpoA,topA, andpyrH, were partially sequenced in 116 isolates from diverse fish species and geographical areas. The eight genes appear to be under purifying selection, and the genetic diversity in the total data set was estimated to be 0.767 ± 0.026. Our multilocus sequence analysis (MLSA) scheme identified several widespread clonal complexes and resolved the isolates, for the most part, according to serotype. Serotype O2b isolates from diseased cod in Norway, Ireland, and Scotland were found to be extremely homogeneous. Horizontal gene transfer appears to be fairly common within and between clonal complexes. Taken together, MLSA andin silicoDNA-DNA hybridization (DDH) calculations suggest that some isolates previously characterized asV.ordalii, i.e., 12B09, FF93, FS144, and FS238, are in factV. anguillarumisolates. The precise taxonomic situation for two isolates from Atlantic cod that display several traits consistent withV. ordalii, i.e., NVI 5286 and NVI 5918, and a single environmental strain that was previously considered to representV. ordalii, i.e., FF167, is less clear.IMPORTANCEIt is still being debated whetherV. anguillarumandV.ordaliirepresent separate bacterial species. Our study addresses this issue and elucidates the degree of genetic variability within this group of closely related bacteria, based on a substantial number of isolates. Our results clearly illustrate the existence of different populations among putativeV.ordaliiisolates. On the basis of additional full-length genomic analysis, we conclude that most environmental isolates previously identified asV.ordaliilie firmly within the speciesV. anguillarum. Whilebona fidefish-pathogenicV.ordaliiisolates display a very close genetic relationship withV. anguillarum, they combine a clearly divergent evolutionary pattern with clear phenotypic differences. The study also highlights the need for further characterization of fish-pathogenic isolates from the northern Atlantic region that share phenotypic characteristics withV. ordaliibut are genetically closer toV. anguillarum. The retention of taxonomic distinctions between the phenotypically different groups of bacteria is of practical advantage to microbial ecologists and veterinarians.