Cultivable epiphytic bacteria of the Chlorophyta Ulva sp.: diversity, antibacterial, and biofilm-modulating activities

AIMS

Macroalgae harbor a rich epiphytic microbiota that plays a crucial role in algal morphogenesis and defense mechanisms. This study aims to isolate epiphytic cultivable microbiota from Ulva sp. surfaces. Various culture media were employed to evaluate a wide range of cultivable microbiota. Our objective was to assess the antibacterial and biofilm-modulating activities of supernatants from isolated bacteria.

METHODS AND RESULTS

Sixty-nine bacterial isolates from Ulva sp. were identified based on 16S rRNA gene sequencing. Their antibacterial activity and biofilm modulation potential were screened against three target marine bacteria: 45%, mostly affiliated with Gammaproteobacteria and mainly grown on diluted R2A medium (R2Ad), showed strong antibacterial activity, while 18% had a significant impact on biofilm modulation. Molecular network analysis was carried out on four bioactive bacterial supernatants, revealing new molecules potentially responsible for their activities.

CONCLUSION

R2Ad offered the greatest diversity and proportion of active isolates. The molecular network approach holds promise for both identifying bacterial isolates based on their molecular production and characterizing antibacterial and biofilm-modulating activities.

Epiphytic common core bacteria in the microbiomes of co-located green (Ulva), brown (Saccharina) and red (Grateloupia, Gelidium) macroalgae

BACKGROUND

Macroalgal epiphytic microbial communities constitute a rich resource for novel enzymes and compounds, but studies so far largely focused on tag-based microbial diversity analyses or limited metagenome sequencing of single macroalgal species.

RESULTS

We sampled epiphytic bacteria from specimens of Ulva sp. (green algae), Saccharina sp. (brown algae), Grateloupia sp. and Gelidium sp. (both red algae) together with seawater and sediment controls from a coastal reef in Weihai, China, during all seasons. Using 16S rRNA amplicon sequencing, we identified 14 core genera (consistently present on all macroalgae), and 14 dominant genera (consistently present on three of the macroalgae). Core genera represented ~ 0.7% of all genera, yet accounted for on average 51.1% of the bacterial abundances. Plate cultivation from all samples yielded 5,527 strains (macroalgae: 4,426) representing 1,235 species (685 potentially novel). Sequencing of selected strains yielded 820 non-redundant draft genomes (506 potentially novel), and sequencing of 23 sampled metagenomes yielded 1,619 metagenome-assembled genomes (MAGs), representing further 1,183 non-redundant genomes. 230 isolates and 153 genomes were obtained from the 28 core/dominant genera. We analyzed the genomic potential of phycosphere bacteria to degrade algal polysaccharides and to produce bioactive secondary metabolites. We predicted 4,451 polysaccharide utilization loci (PULs) and 8,810 biosynthetic gene clusters (BGCs). These were particularly prevalent in core/dominant genera.

CONCLUSIONS

Our metabolic annotations and analyses of MAGs and genomes provide new insights into novel species of phycosphere bacteria and their ecological niches for an improved understanding of the macroalgal phycosphere microbiome. Video Abstract.

Molecular Identification, Characterization and Antioxidant Activities of Some Bacteria Associated with Algae in the Red Sea of Jeddah

BACKGROUND AND OBJECTIVE

Algae-associated bacteria produce secondary metabolites that have a great biological impact. The aim of this study was isolation, identification and evaluation the antioxidant activities of the associated bacteria of seven algae, Padina pavonica, Dictyota dichotoma, Cystoseira myrica, Halimeda opuntia, Ulva lactuca, Digenea simplex and Jania sp. The bacteria were isolated, characterized and identified. Identification was carried out using 16S rRNA gene sequencing.

MATERIALS AND METHODS

The identified bacteria were belonging to 6 families, Alteromonadaceae, Bacillaceae, Lactobacillaceae, Pseudomonadaceae, Rhodobacteraceae and Vibrionaceae and 9 genera. The identified bacteria were belonging to genera, Alteromonas, Bacillus, Lysinibacillus Vibrio, Lactobacillus, Paracoccus, Leisingera, Pseudomonas and Pseudovibrio. The antioxidant activities of the bacterial ethyl acetate extracts was examined by scavenging DPPH (2,2-diphenyl-1-picrylhydrazyl) and FRAP (Ferric Reducing Antioxidant Power) methods.

RESULTS

Out of the 17 isolated bacteria, Lactobacillus plantarum showed 95.7% free radical scavenging with EC50 = 17.7 μg mL-1, which is nearly similar to the positive control (Butylated Hydroxytoluene, BHT). The FRAP value of Lactobacillus extract was 2.00 mM ferric equivalent/mg of the extract. Phytochemical analysis of the bacterial extract revealed the presence of some secondary metabolites such as steroids, saponins, tannins, flavonoids, anthocyanin and betacyanin in all tested extracts.

CONCLUSION

The Red Sea algal associated bacteria have a great antioxidant potential that can be used in pharmaceutical industries.

Antifouling Properties of Dendritic Polyglycerols against Marine Macrofouling Organisms

Dendritic polyglycerols (PGs) were synthesized and postmodified by grafting of poly(ethylene glycol) (PEG) and polypropylene glycol (PPG) diglycidyl ether groups, and their antifouling and fouling-release properties were tested. Coating characterization by spectroscopic ellipsometry, contact angle goniometry, attenuated total internal reflection-Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy showed brushlike morphologies with a high degree of microscale roughness and the ability to absorb large amounts of water within seconds. PGs with three different thicknesses were tested in laboratory assays against settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of zoospores of the alga Ulva linza. Very low coating thicknesses, e.g., 11 nm, reduced the settlement of barnacles, under static conditions, to 2% compared with 55% for an octadecyltrichlorosilane reference surface. In contrast, zoospores of U. linza settled readily but the vast majority were removed by exposure to a shear force of 52 Pa. Both PEG and PPG modification increased the antifouling properties of the PG films, providing a direct comparison of the ultralow fouling properties of all three polymers. Both, the modified and the nonmodified PGs are promising components for incorporation into amphiphilic fouling-resistant coatings.

Algihabitans albus gen. nov., sp. nov., isolated from a culture of the green alga Ulva prolifera

A bacterial strain, designated HHTR 118^T, was isolated from a culture of the green alga Ulvaprolifera obtained from offshore seawater of Qingdao, Shandong Province, China. Cells of strain HHTR 118^T were rod-shaped and motile with a single flagellum, and approximately 0.3-0.4 µm wide and 0.8-1.4 µm long. The strain was Gram-stain-negative, strictly aerobic, catalase-negative and oxidase-positive. Optimal growth was observed at 30 °C, at pH 8.0 and with 1 % (w/v) NaCl. Nitrate was not reduced. Sucrose, sodium citrate and l-leucine stimulated growth, but not lactose, fructose, xylose, d-mannose, glucose, raffinose, rhamnose, ornithine or lysine. The DNA G+C content of strain HHTR 118^T calculated on the basis of the genome sequence was 64.9 mol% and the genome size is 4.6 Mbp. The major quinone was ubiquinone 10 and the predominant cellular fatty acids (>10 % of total fatty acids) were summed feature 8 (C18 : 1ω6c and/or C18 : 1ω7c). The predominant polar lipids were phosphatidylglycerol, one unidentified phospholipid, two unidentified aminolipids and three unidentified polar lipids. Phylogenetic analysis, based on 16S rRNA gene sequences, demonstrated that strain HHTR 118^T was affiliated with the family Rhodospirillaceae. On the basis of the 16S rRNA gene sequence data as well as physiological and biochemical characteristics, we concluded that strain HHTR 118^T represents a novel species of a novel genus. We propose the name of Algihabitans albus gen. nov., sp. nov. for this novel species. The type strain of the novel species is strain HHTR 118^T (=KCTC 62395^T=MCCC 1K03486^T).

Study on immobilization of marine oil-degrading bacteria by carrier of algae materials

This study investigated the immobilizations with of bacteria two kinds of algal materials, Enteromorpha residue and kelp residue. The lipophilicity of them were compared by diesel absorption rates. The immobilization efficiency of Bacillus sp. E3 was measured to evaluate whether these carriers would satisfy the requirement for biodegradation of oil spills. The bacteria were immobilized through adsorption with the sterilized and non-sterilized carriers to compare the differences between the two treatments. Oil degradation rates were determined using gravimetric and GC-MS methods. Results showed the absorption rates of Enteromorpha residue and kelp residue for diesel were 411 and 273% respectively and remained approximately 105 and 120% after 2 h of erosion in simulated seawater system. After immobilized of Bacillus sp. E3, the oil degradation rates of them were higher than 65% after 21 days biodegradations. GC-MS analysis showed that two immobilizations degraded higher than 70% of the total alkane and the total PAHs, whereas the free bacteria degraded 63% of the total alkane and 66% the total PAHs. And the bacteria immobilized with the carriers degraded more HMW-alkanes and HMW-PAHs than the free bacteria. The bacteria immobilized by non-sterilized kelp residue showed a considerably higher degradation rate than that using sterilized kelp residue. A considerably higher cells absorption rate of immobilization was obtained when using kelp residue, and the preparation of immobilization was low cost and highly efficient. The experiments show the two algae materials, especially the kelp residue, present potential application in bioremediation of marine oil spills.

Bioactive Bafilomycins and a New N-Arylpyrazinone Derivative from Marine-derived Streptomyces sp. HZP-2216E

A MeOH extract prepared from culture of an actinomycete Streptomyces sp. HZP-2216E isolated from marine green algae Ulva pertusa was found to significantly inhibit proliferation of human glioma cells. Two different media were applied to culture this marine actinomycete, which produced two new compounds of 23-O-butyrylbafilomycin D and streptoarylpyrazinone A, together with known bafilomycin D, 9-hydroxybafilomycin D, and bafilomycin A₁. Structures of new compounds were determined by extensive NMR spectroscopic analyses and HRESIMS data. Bioactive assay indicated that all isolated bafilomycins significantly inhibited the proliferation of different glioma cell lines and the growth of methicillin-resistant Staphylococcus aureus with 23-O-butyrylbafilomycin D as the most active compound. Streptoarylpyrazinone A is a new N-arylpyrazinone derivative existing as a zwitterion, and this type of compounds was rarely found from natural resources.

Algicidal and growth-inhibiting bacteria associated with seagrass and macroalgae beds in Puget Sound, WA, USA

The algicidal and growth-inhibiting bacteria associated with seagrasses and macroalgae were characterized during the summer of 2012 and 2013 throughout Puget Sound, WA, USA. In 2012, Heterosigma akashiwo-killing bacteria were observed in concentrations of 2.8×10⁶CFUg^-1 wet in the outer organic layer (biofilm) on the common eelgrass (Zostera marina) in north Padilla Bay. Bacteria that inhibited the growth of Alexandrium tamarense were detected within the biofilm formed on the eelgrass canopy at Dumas Bay and North Bay at densities of ∼10⁸CFUg^-1 wet weight. Additionally, up to 4100CFUmL^-1 of algicidal and growth-inhibiting bacteria affecting both A. tamarense and H. akashiwo were detected in seawater adjacent to seven different eelgrass beds. In 2013, H. akashiwo-killing bacteria were found on Z. marina and Ulva lactuca with the highest densities of ∼10⁸CFUg^-1 wet weight at Shallow Bay, Sucia Island. Bacteria that inhibited the growth of H. akashiwo and A. tamarense were also detected on Z. marina and Z. japonica at central Padilla Bay. Heterosigma akashiwo cysts were detected at a concentration of 3400cystsg^-1 wet weight in the sediment from Westcott Bay (northern San Juan Island), a location where eelgrass disappeared in 2002. These findings provide new insights on the ecology of algicidal and growth-inhibiting bacteria, and suggest that seagrass and macroalgae provide an environment that may influence the abundance of harmful algae in this region. This work highlights the importance of protection and restoration of native seagrasses and macroalgae in nearshore environments, in particular those regions where shellfish restoration initiatives are in place to satisfy a growing demand for seafood.

Time Course Exo-Metabolomic Profiling in the Green Marine Macroalga Ulva (Chlorophyta) for Identification of Growth Phase-Dependent Biomarkers

The marine green macroalga Ulva (Chlorophyta) lives in a mutualistic symbiosis with bacteria that influence growth, development, and morphogenesis. We surveyed changes in Ulva’s chemosphere, which was defined as a space where organisms interact with each other via compounds, such as infochemicals, nutrients, morphogens, and defense compounds. Thereby, Ulva mutabilis cooperates with bacteria, in particular, Roseovarius sp. strain MS2 and Maribacter sp. strain MS6 (formerly identified as Roseobacter sp. strain MS2 and Cytophaga sp. strain MS6). Without this accompanying microbial flora, U. mutabilis forms only callus-like colonies. However, upon addition of the two bacteria species, in effect forming a tripartite community, morphogenesis can be completely restored. Under this strictly standardized condition, bioactive and eco-physiologically-relevant marine natural products can be discovered. Solid phase extracted waterborne metabolites were analyzed using a metabolomics platform, facilitating gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) analysis, combined with the necessary acquisition of biological metadata. Multivariate statistics of the GC-MS and LC-MS data revealed strong differences between Ulva’s growth phases, as well as between the axenic Ulva cultures and the tripartite community. Waterborne biomarkers, including glycerol, were identified as potential indicators for algal carbon source and bacterial-algal interactions. Furthermore, it was demonstrated that U. mutabilis releases glycerol that can be utilized for growth by Roseovarius sp. MS2.

Ornithinimicrobium algicola sp. nov., a marine actinobacterium isolated from the green alga of the genus Ulva

A Gram-staining-positive, non-spore-forming actinobacterium, strain JC311T, isolated from marine green alga of the genus Ulva was studied to examine its taxonomic position. On the basis of the 16S rRNA gene sequence similarity studies, strain JC311T was shown represent a member of the genus Ornithinimicrobium and to be closely related to Ornithinimicrobium pekingense LW6T (98.6 %), Ornithinimicrobium kibberense K22-20T (98.3 %) and Ornithinimicrobium humiphilum HKI 0124T (98.1 %). However, strain JC311T showed less than 22 % DNA reassociation value (based on DNA-DNA hybridization) with O. pekingense JCM14001T, O. kibberense JCM12763T and O. humiphilum KCTC19901T. The predominant menaquinone of strain JC311T was MK-8(H4). The peptidoglycan contained l-ornithine as the diagnostic diamino acid. The polar lipid profile consisted of the lipids diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, glycophospholipid, aminophospholipid, phospholipid and two unidentified lipids. The major fatty acids iso-C16 : 0, iso-C15 : 0, iso-C17 : 1ω9c and iso-C17 : 0 were consistent with the fatty acid patterns reported for members of the genus Ornithinimicrobium. The distinct genomic, morphological, physiological and chemotaxonomic differences from the previously described taxa support the classification of JC311T as a representative of a novel species of the genus Ornithinimicrobium, for which we propose the name Ornithinimicrobium algicola sp. nov., with the type strain JC311T ( = KCTC 39559 T =  LMG 28808T).

Bacterial community assembly based on functional genes rather than species

The principles underlying the assembly and structure of complex microbial communities are an issue of long-standing concern to the field of microbial ecology. We previously analyzed the community membership of bacterial communities associated with the green macroalga Ulva australis, and proposed a competitive lottery model for colonization of the algal surface in an attempt to explain the surprising lack of similarity in species composition across different algal samples. Here we extend the previous study by investigating the link between community structure and function in these communities, using metagenomic sequence analysis. Despite the high phylogenetic variability in microbial species composition on different U. australis (only 15% similarity between samples), similarity in functional composition was high (70%), and a core of functional genes present across all algal-associated communities was identified that were consistent with the ecology of surface- and host-associated bacteria. These functions were distributed widely across a variety of taxa or phylogenetic groups. This observation of similarity in habitat (niche) use with respect to functional genes, but not species, together with the relative ease with which bacteria share genetic material, suggests that the key level at which to address the assembly and structure of bacterial communities may not be "species" (by means of rRNA taxonomy), but rather the more functional level of genes.

Composition, uniqueness and variability of the epiphytic bacterial community of the green alga Ulva australis

Green Ulvacean marine macroalgae are distributed worldwide in coastal tidal and subtidal ecosystems. As for many living surfaces in the marine environment, little is known concerning the epiphytic bacterial biofilm communities that inhabit algal surfaces. This study reports on the largest published libraries of near full-length 16S rRNA genes from a marine algal surface (5293 sequences from six samples) allowing for an in-depth assessment of the diversity and phylogenetic profile of the bacterial community on a green Ulvacean alga. Large 16S rRNA gene libraries of surrounding seawater were also used to determine the uniqueness of this bacterial community. The surface of Ulva australis is dominated by sequences of Alphaproteobacteria and the Bacteroidetes, especially within the Rhodobacteriaceae, Sphingomonadaceae, Flavobacteriaceae and Sapropiraceae families. Seawater libraries were also dominated by Alphaproteobacteria and Bacteroidetes sequences, but were shown to be clearly distinct from U. australis libraries through the clustering of sequences into operational taxonomic units and Bray-Curtis similarity analysis. Almost no similarity was observed between these two environments at the species level, and only minor similarity was observed at levels of sequence clustering representing clades of bacteria within family and genus taxonomic groups. Variability between libraries of U. australis was relatively high, and a consistent sub-population of bacterial species was not detected. The competitive lottery model, originally derived to explain diversity in coral reef fishes, may explain the pattern of colonization of this algal surface.

Molecular investigation of the distribution, abundance and diversity of the genus Pseudoalteromonas in marine samples

The genus Pseudoalteromonas has attracted interest because it has frequently been found in association with eukaryotic hosts, and because many Pseudoalteromonas species produce biologically active compounds. One distinct group of Pseudoalteromonas species is the antifouling subgroup containing Pseudoalteromonas tunicata and Ps. ulvae, which both produce extracellular compounds that inhibit growth and colonization by different marine organisms. PCR primers targeting the 16S rRNA gene of the genus Pseudoalteromonas and the antifouling subgroup were developed and applied in this study. Real-time quantitative PCR (qPCR) was applied to determine the relative bacterial abundance of the genus and the antifouling subgroup, and denaturing gradient gel electrophoresis (DGGE) was applied to study the diversity of the genus in 11 different types of marine samples from Danish coastal waters. The detection of Ps. tunicata that contain the antifouling subgroup was achieved through specific PCR amplification of the antibacterial protein gene (alpP). The Pseudoalteromonas species accounted for 1.6% of the total bacterial abundance across all samples. The Pseudoalteromonas diversity on the three unfouled marine organisms Ciona intestinalis, Ulva lactuca and Ulvaria fusca was found to be low, and Ps. tunicata was only detected on these three hosts, which all contain accessible cellulose polymers in their cell walls.

Inhibition of fungal colonization by Pseudoalteromonas tunicata provides a competitive advantage during surface colonization

The marine epiphytic bacterium Pseudoalteromonas tunicata produces a range of extracellular secondary metabolites that inhibit an array of common fouling organisms, including fungi. In this study, we test the hypothesis that the ability to inhibit fungi provides P. tunicata with an advantage during colonization of a surface. Studies on a transposon-generated antifungal-deficient mutant of P. tunicata, FM3, indicated that a long-chain fatty acid-coenzyme A ligase is involved in the production of a broad-range antifungal compound by P. tunicata. Flow cell experiments demonstrated that production of an antifungal compound provided P. tunicata with a competitive advantage against a marine yeast isolate during surface colonization. This compound enabled P. tunicata to disrupt an already established fungal biofilm by decreasing the number of yeast cells attached to the surface by 66% +/- 9%. For in vivo experiments, the wild-type and FM3 strains of P. tunicata were used to inoculate the surface of the green alga Ulva australis. Double-gradient denaturing gradient gel electrophoresis analysis revealed that after 48 h, the wild-type P. tunicata had outcompeted the surface-associated fungal community, whereas the antifungal-deficient mutant had no effect on the fungal community. Our data suggest that P. tunicata is an effective competitor against fungal surface communities in the marine environment.

Microbial colonization and competition on the marine alga Ulva australis

Pseudalteromonas tunicata and Roseobacter gallaeciensis are biofilm-forming marine bacteria that are often found in association with the surface of the green alga Ulva australis. They are thought to benefit the plant host by producing inhibitory compounds that are active against common fouling organisms. We investigated factors that influence the ability of P. tunicata and R. gallaeciensis to attach to and colonize the plant surface and also the competitive interactions that occur between these organisms and other isolates from U. australis during biofilm formation on the plant surface. A surprisingly high number of P. tunicata cells, at least 10(8) cells ml(-1), were required for colonization and establishment of a population of cells that persists on axenic surfaces of U. australis. Factors that enhanced colonization of P. tunicata included inoculation in the dark and pregrowth of inocula in medium containing cellobiose as the sole carbon source (cellulose is a major surface polymer of U. australis). It was also found that P. tunicata requires the presence of a mixed microbial community to colonize effectively. In contrast, R. gallaeciensis effectively colonized the plant surface under all conditions tested. Studies of competitive interactions on the plant surface revealed that P. tunicata was numerically dominant compared with all other bacterial isolates tested (except R. gallaeciensis), and this dominance was linked to production of the antibacterial protein AlpP. Generally, P. tunicata was able to coexist with competing strains, and each strain existed as microcolonies in spatially segregated regions of the plant. R. gallaeciensis was numerically dominant compared with all strains tested and was able to invade and disperse preestablished biofilms. This study highlighted the fact that microbial colonization of U. australis surfaces is a dynamic process and demonstrated the differences in colonization strategies exhibited by the epiphytic bacteria P. tunicata and R. gallaeciensis.

A mannose-sensitive haemagglutinin (MSHA)-like pilus promotes attachment of Pseudoalteromonas tunicata cells to the surface of the green alga Ulva australis

This study demonstrates that attachment of the marine bacterium Pseudoalteromonas tunicata to the cellulose-containing surface of the green alga Ulva australis is mediated by a mannose-sensitive haemagglutinin (MSHA-like) pilus. We have identified an MSHA pilus biogenesis gene locus in P. tunicata, termed mshI1I2JKLMNEGFBACDOPQ, which shows significant homology, with respect to its genetic characteristics and organization, to the MSHA pilus biogenesis gene locus of Vibrio cholerae. Electron microscopy studies revealed that P. tunicata wild-type cells express flexible pili peritrichously arranged on the cell surface. A P. tunicata mutant (SM5) with a transposon insertion in the mshJ region displayed a non-piliated phenotype. Using SM5, it has been demonstrated that the MSHA pilus promotes attachment of P. tunicata wild-type cells in polystyrene microtitre plates, as well as to microcrystalline cellulose and to the living surface of U. australis. P. tunicata also demonstrated increased pilus production in response to cellulose and its monomer constituent cellobiose. The MSHA pilus thus functions as a determinant of attachment in P. tunicata, and it is proposed that an understanding of surface sensing mechanisms displayed by P. tunicata will provide insight into specific ecological interactions that occur between this bacterium and higher marine organisms.

Effect of marine bacterial isolates on the growth and morphology of axenic plantlets of the green alga Ulva linza

The green marine macroalga, Ulva linza, adopts an "atypical" form when grown in the absence of bacteria. Twenty unique strains of periphytic bacteria, isolated from three species of Ulva, were identified by 16S rDNA sequencing. These isolates were assessed for their effect on the growth and morphological development of axenic plantlets of U. linza. Results showed that the effect of bacterial strains was strain- but not taxon-specific. Thirteen isolates returned the aberrant morphology to normal and of these, five also significantly increased growth rate. One isolate increased growth, but had no effect on morphology. Biofilms of some of these isolates stimulated the settlement of Ulva zoospores but there was no correlation between bacterial isolates that stimulated zoospore settlement and those that initiated changes in morphology and/or growth of the cultured alga.

Arenibacter palladensis sp. nov., a novel marine bacterium isolated from the green alga Ulva fenestrata, and emended description of the genus Arenibacter

The taxonomic position of three novel, marine, heterotrophic, aerobic, pigmented, gliding bacteria, isolated from the green alga Ulva fenestrata in the Sea of Japan, was determined. 16S rRNA gene sequence analysis revealed that the strains belong to the genus Arenibacter. The results of DNA-DNA hybridization experiments supported by phenotypic and chemotaxonomic data showed that the isolates represent a novel species of the genus Arenibacter, for which the name Arenibacter palladensis sp. nov. is proposed. The type strain is KMM 3961T (= LMG 21972T = CIP 108849T).

Isolation of a lactic acid bacterium and yeast consortium from a fermented material of Ulva spp. (Chlorophyta)

AIMS

Microbiota in a fermented culture of Ulva spp. was examined with the objective to characterize the type of fermentation and to obtain starter microbes for performing seaweed fermentation.

METHOD AND RESULTS

Fermented Ulva spp. cultures which were obtained and transferred in a laboratory were examined for their microbiota. With phenotypic characterization and phylogenetic analysis based on rRNA gene nucleotide sequences, the predominant micro-organisms were identified as Lactobacillus brevis, Debaryomyces hanseni var. hansenii, and a Candida zeylanoides-related specimen, suggesting that the observed fermentation can be categorized to lactic acid and ethanol fermentation. Inoculating the individually cultured cell suspensions of the three kinds of micro-organisms with cellulase induced the fermentation in various kinds of seaweed.

CONCLUSIONS

A microbial consortium composed of a lactic acid bacterium, L. brevis, and yeasts, D. hansenii and a C. zeylanoides-related specimen, were predominant in a fermented culture of Ulva spp. Lactic acid and ethanol fermentation could be induced in various kinds of seaweed by adding this microbial consortium along with cellulase.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of lactic acid and ethanol fermentation in seaweed, which is expected to provide a new material for food and dietary applications.

Competitive interactions in mixed-species biofilms containing the marine bacterium Pseudoalteromonas tunicata

Pseudoalteromonas tunicata is a biofilm-forming marine bacterium that is often found in association with the surface of eukaryotic organisms. It produces a range of extracellular inhibitory compounds, including an antibacterial protein (AlpP) thought to be beneficial for P. tunicata during competition for space and nutrients on surfaces. As part of our studies on the interactions between P. tunicata and the epiphytic bacterial community on the marine plant Ulva lactuca, we investigated the hypothesis that P. tunicata is a superior competitor compared with other bacteria isolated from the plant. A number of U. lactuca bacterial isolates were (i) identified by 16S rRNA gene sequencing, (ii) characterized for the production of or sensitivity to extracellular antibacterial proteins, and (iii) labeled with a fluorescent color tag (either the red fluorescent protein DsRed or green fluorescent protein). We then grew single- and mixed-species bacterial biofilms containing P. tunicata in glass flow cell reactors. In pure culture, all the marine isolates formed biofilms containing microcolony structures within 72 h. However, in mixed-species biofilms, P. tunicata removed the competing strain unless its competitor was relatively insensitive to AlpP (Pseudoalteromonas gracilis) or produced strong inhibitory activity against P. tunicata (Roseobacter gallaeciensis). Moreover, biofilm studies conducted with an AlpP- mutant of P. tunicata indicated that the mutant was less competitive when it was introduced into preestablished biofilms, suggesting that AlpP has a role during competitive biofilm formation. When single-species biofilms were allowed to form microcolonies before the introduction of a competitor, these microcolonies coexisted with P. tunicata for extended periods of time before they were removed. Two marine bacteria (R. gallaeciensis and P. tunicata) were superior competitors in this study. Our data suggest that this dominance can be attributed to the ability of these organisms to rapidly form microcolonies and their ability to produce extracellular antibacterial compounds.

Maribacter gen. nov., a new member of the family Flavobacteriaceae, isolated from marine habitats, containing the species Maribacter sedimenticola sp. nov., Maribacter aquivivus sp. nov., Maribacter orientalis sp. nov. and Maribacter ulvicola sp. nov

Six novel gliding, heterotrophic, Gram-negative, yellow-pigmented, aerobic, oxidase- and catalase-positive bacteria were isolated from the green alga Ulva fenestrata, sea water and a bottom sediment sample collected in the Gulf of Peter the Great, Sea of Japan. 16S rRNA gene sequence analysis revealed that the strains studied were members of the family Flavobacteriaceae. On the basis of their phenotypic, chemotaxonomic, genotypic and phylogenetic characteristics, the novel bacteria have been assigned to the new genus Maribacter gen. nov., as Maribacter sedimenticola sp. nov., Maribacter orientalis sp. nov., Maribacter aquivivus sp. nov. and Maribacter ulvicola sp. nov., with the type strains KMM 3903T (=KCTC 12966T=CCUG 47098T), KMM 3947T (=KCTC 12967T=CCUG 48008T), KMM 3949T (=KCTC 12968T=CCUG 48009T) and KMM 3951T (=KCTC 12969T=DSM 15366T), respectively.

Algibacter lectus gen. nov., sp. nov., a novel member of the family Flavobacteriaceae isolated from green algae

Three strains of the marine, gliding, pigmented, facultatively anaerobic, heterotrophic, Gram-negative bacteria were isolated from the green algae Acrosiphonia sonderi (Kütz) Kornm and Ulva fenestrata Ruprecht inhabiting the Sea of Japan. 16S rDNA sequence analysis indicated that the strains were members of the family Flavobacteriaceae, in which they occupied separate lineages. The predominant cellular fatty acids were i15 : 0, a15 : 0, i15 : 1, 15 : 0, 15 : 1omega6c, i15 : 0 3-OH and i17 : 0 3-OH. The DNA base compositions were 31-33 mol% G+C. Based on the phenotypic, genotypic, chemotaxonomic and phylogenetic analyses, the novel bacteria should be placed in a novel taxon as Algibacter lectus gen. nov., sp. nov. with type strain KMM 3902G (=KCTC 12103T=DSM 15365T).

Real-time quantitative PCR for assessment of abundance of Pseudoalteromonas species in marine samples

A real-time quantitative PCR (RTQ-PCR) method for measuring the abundance of Pseudoalteromonas species in marine samples is presented. PCR primers targeting a Pseudoalteromonas-specific region of the 16S rRNA gene were tested at three different levels using database searches (in silico), a selection of pure cultures (in vitro), and a combined denaturing gradient gel electrophoresis and cloning approach on environmental DNA (in situ). The RTQ-PCR method allowed for the detection of SYBR Green fluorescence from double-stranded DNA over a linear range spanning six orders of magnitude. The detection limit was determined as 1.4 fg of target DNA (1,000 gene copies) measured in the presence of 20 ng of nontarget DNA from salmon testes. In this study, we discuss the importance of robust post-PCR analyses to overcome pitfalls in RTQ-PCR when samples from different complex marine habitats are analyzed and compared on a nonroutine basis. Representatives of the genus Pseudoalteromonas were detected in samples from all investigated habitats, suggesting a widespread distribution of this genus across many marine habitats (e.g., seawater, rocks, macroalgae, and marine animals). Three sample types were analyzed by RTQ-PCR to determine the relative abundance of Pseudoalteromonas ribosomal DNA (rDNA) compared to the total abundance of eubacterial rDNA. The rDNA fractions of Pseudoalteromonas compared to all Eubacteria were 1.55% on the green alga Ulva lactuca, 0.10% on the tunicate Ciona intestinalis, and 0.06% on the green alga Ulvaria fusca.

Arenibacter certesii sp. nov., a novel marine bacterium isolated from the green alga Ulva fenestrata

The taxonomic position of a novel, marine, heterotrophic, aerobic, pigmented, non-motile bacterium that was isolated from a green alga, Ulva fenestrata, inhabiting the Sea of Japan, was determined. 16S rRNA gene sequence analysis revealed that the strain, KMM 3941T, is a member of the genus Arenibacter. The results of DNA–DNA hybridization experiments, supported by phenotypic and chemotaxonomic data, showed that the isolate represents a novel species of the genus Arenibacter, for which the name Arenibacter certesii sp. nov. is proposed. The type strain is KMM 3941T (=KCTC 12113T=CCUG 48006T).

Competitive induction and enhancement of indole and a diketopiperazine in marine bacteria

Thirteen bacterial strains isolated from a sample of Ulva californica were cultured, extracted, and assayed for antibiotic activity. The target strains were 2 gram-positive isolates from the same algal sample. When cultured in monoculture, 2 of the 13 isolates produced extracts with antimicrobial activity. More significantly, one Bacillus isolate (UA-094) produced indole and cyclo(Phe-Pro) at active levels upon challenge with a different Bacillus target strain. These mildly antibiotic compounds were barely detectable in extracts without challenge. This technique of competitive induction and enhancement could be a valuable tool in the search for new antibiotics.

Gamma-pyrone derivatives, kojic acid methyl ethers from a marine-derived fungus Alternaria [correction of Altenaria] sp

Kojic acid dimethyl ether (1), and the known kojic acid monomethyl ether (2), kojic acid (3) and phomaligol A (4) have been isolated from the organic extract of the broth of the marine-derived fungus Alternaria sp. collected from the surface of the marine green alga Ulva pertusa. The structures were assigned on the basis of comprehensive spectroscopic analyses. Each isolate was tested for its tyrosinase inhibitory activity. Kojic acid (3) was found to have significant tyrosinase inhibitory activity, but compounds 1, 2, and 4 were found to be inactive.