Cobetia amphilecti sp. nov., Cobetia litoralis sp. nov. and Cobetia pacifica sp. nov., transfer of Halomonas halodurans NBRC 15607T to Cobetia marina and emended descriptions of the genus Cobetia and Cobetia marina
A group of five Gram-negative aerobic halotolerant non-pigmented bacteria isolated from shallow sediment samples and invertebrate specimen collected from the Gulf of Alaska and from the Sea of Japan was subjected to the taxonomic study. On the basis of 16S rRNA sequence analysis the novel isolates were affiliated to the genus Cobetia sharing the highest sequence similarities of 99.3-99.9% with the type strain of Cobetia marina DSM 4741T. The DNA-DNA hybridization experiments between novel strains themselves and towards Cobetia marina DSM 4741T and Cobetia crustatorum JCM 15644T revealed that five strains represent three separate genospecies, which could be differentiated in their morphological, physiological and biochemical characteristics. Strain Halomonas halodurans NBRC 15607T was included to the study as it has been recently reported to exhibit a high 16S rRNA gene sequence similarity to Cobetia marina DSM 4741T and it showed a high DNA relatedness value of 96% to C. marina DSM 4741T, indicating that they belong to the same species. On the basis of phylogenetic analysis, DNA-DNA hybridization and phenotypic characterization, three novel species, for which the names Cobetia amphilecti sp. nov. with the type strain KMM 1561T (=NRIC 0815T =CCUG 49560T), Cobetia litoralis sp. nov. with the type strain KMM 3880T (=NRIC 0814T =CCUG 49563T) and Cobetia pacifica sp. nov. with the type strain KMM 3879T (=NRIC 0813T =CCUG 49562T), are proposed.
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"Isolate NSA_12 is related to Psychromonas arctica (98.9 % identity) which has been isolated from the alga Undaria pinnatifida (Korean, Miyok) (Lee et al. 2006). The closest relative of isolate MA_12 is a newly described species Cobetia amphilecti (98.91 %) which has been isolated from a marine sponge in the Gulf of Alaska (Romanenko et al. 2013). 16S rRNA gene analysis of isolate NA_1 was unable to differentiate between Pseudomonas poae (99.86 %% identity) and Pseudomonas fluorescens (99.73 % identity). "
[Show abstract][Hide abstract]ABSTRACT: Marine macroalgae host diverse bacterial communities with which they share a complex array of chemical interactions based on the exchange of nutrients, minerals and secondary metabolites. The brown alga Splachnidium rugosum is a rich source of a valuable fucose-containing sulphated polysaccharide (fucoidan). It grows exclusively in the Southern Hemisphere along temperate shores. While growth and development are dependent on specific microbial interactions, the microbiome of S. rugosum has not been characterized. This study reports on the composition and uniqueness of epiphytic bacterial communities associated with S. rugosum. Sporophytes were collected during winter (July 2012) from the Western Cape (−34° 18′ 5.0004″, +18° 48′ 59.0004″), South Africa. Culture-based methods relied on a range of selective marine media including marine agar, nutrient sea water agar, nutrient agar and thiosulfate-citrate-bile-salts-sucrose agar. Epiphytic isolates were identified to species level by 16S rRNA gene sequence analysis and encompassed 39 Gram-negative and 2 Gram-positive bacteria. Isolates were classified as Gamma-Proteobacteria, Alpha-Proteobacteria, Firmicutes or Bacteriodetes. Gamma-Proteobacteria were the most abundant, dominated by Vibrio and Pseudoalteromonas species. Three isolates displayed low sequence identity (˂97 %) with their closest relatives and were grouped into the genera Shewanella, Sphingomonas and Sulfitobacter. All bacterial isolates (41) were screened for anti-microbial activity against indicator strains of Bacillus cereus, Staphylococcus epidermidis, Mycobacterium smegmatis, Micrococcus luteus and Pseudomonas putida. Fifteen isolates (36 %) displayed antimicrobial activity against one or more of the indicator strains. One isolate (Pseudomonas sp.) was active against all strains tested. Splachnidium rugosum is a valuable source for the discovery of bioactive compounds of bacterial origin active against human pathogens.
Full-text · Article · Oct 2015 · Journal of Applied Phycology
[Show abstract][Hide abstract]ABSTRACT: Biosurfactants are produced by hydrocarbon-degrading marine bacteria in response to the presence of water-insoluble hydrocarbons. This is believed to facilitate the uptake of hydrocarbons by bacteria. However, these diffusible amphiphilic surface-active molecules are involved in several other biological functions such as microbial competition and intra- or inter-species communication. We report the isolation and characterization of a marine bacterial strain identified as Cobetia sp. MM1IDA2H-1, which can grow using the sulfur-containing heterocyclic aromatic hydrocarbon dibenzothiophene (DBT). As with DBT, when the isolated strain is grown in the presence of a microbial competitor, it produces a biosurfactant. Because the obtained biosurfactant was formed by hydroxy fatty acids and extracellular lipidic structures were observed during bacterial growth, we investigated whether the biosurfactant at its critical micelle concentration can interfere with bacterial communication systems such as quorum sensing. We focused on Aeromonas salmonicida subsp. salmonicida, a fish pathogen whose virulence relies on quorum sensing signals. Using biosensors for quorum sensing based on Chromobacterium violaceum and Vibrio anguillarum, we showed that when the purified biosurfactant was mixed with N-acyl homoserine lactones produced by A. salmonicida, quorum sensing was inhibited, although bacterial growth was not affected. In addition, the transcriptional activities of A. salmonicida virulence genes that are controlled by quorum sensing were repressed by both the purified biosurfactant and the growth in the presence of Cobetia sp. MM1IDA2H-1. We propose that the biosurfactant, or the lipid structures interact with the N-acyl homoserine lactones, inhibiting their function. This could be used as a strategy to interfere with the quorum sensing systems of bacterial fish pathogens, which represents an attractive alternative to classical antimicrobial therapies in fish aquaculture.
Full-text · Article · Jan 2013 · Microbial Biotechnology