Aims:  Several Gram‐negative bacterial species use N‐acyl homoserine lactone (AHL) molecules as quorum‐sensing (QS) signals to regulate various biological functions. Similarly, various bacteria can stimulate, inhibit or inactivate QS signals in other bacteria by producing molecules called as quorum‐sensing inhibitors (QSI). Our aim was to screen and identify the epibiotic bacteria associated with brown algae for their ability of producing QS‐inhibiting activity. Methods and Results:  QSI screenings were conducted on several epibiotic bacteria isolated from a marine brown alga Colpomenia sinuosa, using Serratia rubidaea JCM 14263 as an indicator organism. Strain JCM 14263 controls the production of red pigment, prodigiosin by AHL QS. Out of 96 bacteria, which were isolated from the surface of the brown alga, 12% of strains showed the ability to produce QSI, which was observed from the pigmentation inhibition on Ser. rubidaea JCM 14263 without affecting its growth. Phylogenetic analysis using 16S rRNA gene sequencing method demonstrated bacterial isolates showing QS inhibition‐producing bacteria belonging to the Bacillaceae (Firmicutes), Pseudomonadaceae (Proteobacteria), Pseudoalteromonadaceae (Proteobacteria) and Vibrionaceae (Proteobacteria). Conclusion:  An appreciable percentage of bacteria isolated from the brown alga produced QSI‐like compounds. Significance and Impact of the Study:  The screening method using Ser. rubidaea described in this report will facilitate the rapid identification of QSI‐producing bacteria from marine environment. This study reveals new avenue for future environmental applications. This study also suggests that these algal epibiotic bacteria may play a role in the defensive mechanism for their host by producing QSI or QSI‐like compounds to suppress the settlement of other competitive bacteria.

Aims:  Isolation of novel alginate degrading bacteria for the disposal of seaweed waste in composting process. Methods and Results:  Decomposition of alginate polymers was checked by the 3,5‐dinitrosalicylic acid (DNS) method for reducing sugar, and absorbance at 235 nm for unsaturated sugar. A bacterium A7 was isolated from wakame compost and confirmed to belong to the genus Gracilibacillus by partial 16S rDNA analysis. The optimum condition for the growth of A7 in a medium containing 5 g l−1 of sodium alginate is as follows: pH, 8·5–9·5; NaCl, 0·5 mol l−1; temperature, 30°C and polypeptone as nutrient content, 2–5 g l−1. In a laboratory‐scale composting experiment, the alginate content in wakame compost decreased to 14·3% after 72 h of composting from an initial value of 36%, indicating the effectiveness of alginate decomposition of A7 in wakame composting. Conclusions:  The bacterium A7 was found to be alginate lyase‐producing in genus Gracilibacillus and effective in degrading alginate to oligosaccharides in wakame during composting process. Significance and Impact of the Study:  Development of new methods for the disposal of marine wastes and production of functional products.

We investigated the diversity of epibiotic bacteria possessing antimicrobial activity isolated from nine species of red algae, and identified their phylogenetic position. For the isolation of epibiotic bacteria, nine species of red algae, Pachymeniopsis lauceolata, Plocamium telfairiae, Gelidium amansii, Chondrus oncellatus, Grateloupia filicina, Ceramium kondoi, Lomentaria catenata, Schizymenia dubyi and Porphyra yezoensis, were collected from the intertidal zone of Awaji Island, Japan. In total 92 bacteria were collected from the above red algal species. Primary screening results using disc diffusion assay revealed that 33% of bacteria possess antibacterial activity. Ten bacteria that showed high antibacterial activity were further studied for their ability to inhibit a set of fouling bacteria, some luminescent Vibrio and Photobacterium species and a panel of pathogenic bacteria. In general, the inhibitory activities were high against fouling and luminescent bacteria, while low against various pathogenic bacteria tested. These results suggest that some epibiotic bacteria have adapted to defend their position in their surface environment through the production of antibacterial metabolites giving defense against a broad spectrum of bacterial competitors. The phylogenetic analysis using 16 S rRNA sequences identified 7 of the 10 strains as belonging to the genus Bacillus, and other strains each 1 belonging to genus Microbacterium, Psychrobacter, and Vibrio species.

One hundred and sixteen epibiotic bacteria were isolated from the surface of nine species of brown algae Sargassum serratifolium, S. fusiforme, S. filicinum, Padina arborescens, Undaria pinnatifida, Petalonia fascia, Colpomenia sinuosa, Scytosiphon lomentaria and Ecklonia cava which were collected at Awaji Island, Japan. Primary screening results using disc-diffusion assay revealed that, among the bacteria isolated 20% of epibiotic bacteria exhibited antibacterial activity. Among them, 10 bacteria which showed high antibacterial activity were further studied for their ability against (i) a set of fouling bacteria isolated from marine natural biofilm, (ii) some luminescent Vibrio and Photobacterium species and (iii) a panel of pathogenic bacteria. In general, inhibitory activities were high or moderate against fouling bacteria, Vibrio and Photobacterium species, while they were found to be low against pathogenic bacteria tested. The phylogenetic analysis using 16S rRNA sequencing revealed that all of the bacteria with high antibacterial activity showed a close affiliation with genus Bacillus. This result suggested that the genus Bacillus are efficient producers of antibacterial compounds and these epibiotic bacteria isolated are highly successful colonizers on macroalgal surfaces.

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Aims:  To isolate and characterize copper‐resistant halophilic bacteria from the polluted Maruit Lake, Egypt and identify the role of plasmids in toxic metal resistance. Methods and Results:  We isolated strain MA2, showing high copper resistance up to the 1·5 mmol l−1 concentration; it was also resistant to other metals such as nickel, cobalt and zinc and a group of antibiotics. Partial 16S rRNA analysis revealed that strain MA2 belonged to the genus Halomonas. Copper uptake, measured by atomic absorption spectrophotometery, was higher in the absence of NaCl than in the presence of 0·5–1·0 mol l−1 NaCl during 5–15 min of incubation. Cell fractionation and electron microscopic observation clarified that most of the copper accumulated in the outer membrane and periplasmic fractions of the cells. Plasmid screening yielded two plasmids: pMA21 (11 kb) and pMA22 (5 kb). Plasmid curing resulted in a strain that lost both the plasmids and was sensitive to cobalt and chromate but not copper, nickel and zinc. This cured strain also showed weak growth in the presence of 0·5–1·0 mol l−1 NaCl. Partial sequencing of both plasmids led to the identification of different toxic metals transporters but copper transporters were not identified. Conclusions:  The highest cell viability was found in the presence of 1·0 mol l−1 NaCl at different copper concentrations, and copper uptake was optimal in the absence of NaCl. Plasmid pMA21 encoded chromate, cobalt, zinc and cadmium transporters, whereas pMA22 encoded specific zinc and RND (resistance, nodulation, cell division) efflux transporters as well as different kinds of metabolic enzymes. Copper resistance was mainly incorporated in the chromosome. Significance and Impact of the Study:  Strain MA2 is a fast and efficient tool for copper bioremediation and the isolated plasmids show significant characteristics of both toxic metal and antibiotic resistance.

Halophilic bacteria strain Halomonas salina DSM 5928 was found to excrete ectoine, suggesting its potential in the development of a new method of ectoine production. We performed HPLC and LC-MS analyses that showed that Halomonas salina DSM 5928 excreted ectoine under constant extracellular osmolarity. Medium adopting monosodium glutamate as a sole source of carbon and nitrogen was beneficial for ectoine synthesis. The total concentration of ectoine was not affected by NaCl concentration in the range 0.5-2 mol l(-1). The total concentration of ectoine and productivity in a 10-l fermentor with 0.5 mol l(-1) NaCl were 6.9 g l(-1) and 7.9 g l(-1) d(-1), respectively. These findings show that Halomonas salina DSM 5928 efficiently produces ectoine at relatively low NaCl concentration. This research also indicates the potential application of free or immobilized cells for continuous culture to produce ectoine.

Using ectoine-excreting strain Halomonas salina DSM 5928(T), we developed a new process for high-efficiency production of ectoine, which involved a combined process of batch fermentation by growing cells and production by resting cells. In the first stage, batch fermentation was carried out using growing cells under optimal fermentation conditions. The second stage was the production phase, in which ectoine was synthesized and excreted by phosphate-limited resting cells. Optimal conditions for synthesis and excretion of ectoine during batch fermentation in a 10 l fermentor were 0.5 mol l(-1) NaCl and an initial monosodium glutamate concentration of 80 g l(-1) respectively. The pH was adjusted to 7.0 and the temperature was maintained at 33°C. In phosphate-limited resting cells medium, monosodium glutamate and NaCl concentration was 200 g l(-1) and 0.5 mol l(-1), respectively, as well as pH was 7.0. The total concentration of ectoine produced was 14.86 g l(-1), the productivity and yield of ectoine was 7.75 g l(-1) day(-1) and 0.14 g g(-1), respectively, and the percentage of ectoine excreted was 79%. These levels of ectoine production and excretion are the highest reported to date.