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Bacillus cereus , a common food-borne pathogen, forms biofilms and generates virulence factors through a quorum sensing (QS) mechanism. In this study, six compounds (dankasterone A, demethylincisterol A 3 , zinnimidine, cyclo-(L-Val-L-Pro), cyclo-(L-Ile-L-Pro), and cyclo-(L-Leu-L-Pro)) were isolated from the endophytic fungus Pithomyces sacchari of the Laurencia sp. in the South China Sea. Among them, demethylincisterol A 3 , a sterol derivative, exhibited strong QS inhibitory activity against B. cereus . The QS inhibitory activity of demethylincisterol A 3 was evaluated through experiments. The minimum inhibitory concentration (MIC) of demethylincisterol A 3 against B. cereus was 6.25 μg/mL. At sub-MIC concentrations, it significantly decreased biofilm formation, hindered mobility, and diminished the production of protease and hemolysin activity. Moreover, RT-qPCR results demonstrated that demethylincisterol A 3 markedly inhibited the expression of QS-related genes ( plcR and papR ) in B. cereus . The exposure to demethylincisterol A3 resulted in the downregulation of genes ( comER , tasA , rpoN , sinR , codY , nheA , hblD , and cytK ) associated with biofilm formation, mobility, and virulence factors. Hence, demethylincisterol A 3 is a potentially effective compound in the pipeline of innovative antimicrobial therapies.

An unusual sesquiterpene glycoside trichoacorside A ( 1 ) and two novel sorbicillinoid glycosides sorbicillisides A ( 2 ) and B ( 3 ), together with a known compound sorbicillin ( 4 ), were isolated and identified from the culture extract of an endophytic fungus Trichoderma longibrachiatum EN-586, obtained from the marine red alga Laurencia obtusa . Trichoacorside A ( 1 ) is the first representative of a glucosamine-coupled acorane-type sesquiterpenoid. Their structures were elucidated based on detailed interpretation of NMR and mass spectroscopic data. The absolute configurations were determined by X-ray crystallographic analysis, chemical derivatization, and DP4+ probability analysis. The antimicrobial activities of compounds 1 - 4 against several human, aquatic, and plant pathogens were evaluated.

Four new ( 1 - 4 ) and six previously reported ( 5 - 10 ) α-pyrone polyketides, along with benzoic acid, hydrocinnamic acid, and ( E )-cinnamic acid, were isolated from the organic extract resulting from the cultivation of the algicolous strain Streptomyces ambofaciens BI0048, which in turn was isolated from the inner tissues of the red alga Laurencia glandulifera . The structure elucidation of the isolated natural products was based on extensive analysis of their spectroscopic data (NMR, MS, UV, IR). Compounds 1 - 10 were evaluated for their antibacterial and cytotoxic activities against two multidrug-resistant strains of Staphylococcus aureus and one strain of Escherichia coli , as well as two human cancer cell lines., Competing Interests: The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Marine macroalgae are known to harbor large populations of microbial symbionts, and yet, microbe symbiosis in invasive macroalgae remains largely unknown. In this study, we applied molecular methods to study microbial communities associated with two invasive algae Acanthophora spicifera and Gracilaria salicornia and the two native algae Gracilaria coronopifolia and Laurencia nidifica at spatial and temporal scales in Hawaiian coral reef ecosystems. Bacterial communities of both the invasive and native macroalgae displayed little spatial and temporal variations, suggesting consistent and stable bacterial associations with these macroalgae. Results of this study identified three types of bacterial populations: nonspecific (present in both algal and water samples); algae-specific (found in all algal species); and species-specific (only found in individual species). The bacterial diversity of invasive algae was lower than that of their native counterparts at phylum and species levels. Notably, the vast majority (71 %) of bacterial communities associated with the invasive algae G. salicornia were representatives of Cyanobacteria, suggesting a potential ecological significance of symbiotic Cyanobacteria.

Background: Seaweeds of the Laurencia genus have a broad geographic distribution and are largely recognized as important sources of secondary metabolites, mainly halogenated compounds exhibiting diverse potential pharmacological activities and relevant ecological role as anti-epibiosis. Host-microbe interaction is a driving force for co-evolution in the marine environment, but molecular studies of seaweed-associated microbial communities are still rare. Despite the large amount of research describing the chemical compositions of Laurencia species, the genetic knowledge regarding this genus is currently restricted to taxonomic markers and general genome features. In this work we analyze the transcriptomic profile of L. dendroidea J. Agardh, unveil the genes involved on the biosynthesis of terpenoid compounds in this seaweed and explore the interactions between this host and its associated microbiome., Results: A total of 6 transcriptomes were obtained from specimens of L. dendroidea sampled in three different coastal locations of the Rio de Janeiro state. Functional annotations revealed predominantly basic cellular metabolic pathways. Bacteria was the dominant active group in the microbiome of L. dendroidea, standing out nitrogen fixing Cyanobacteria and aerobic heterotrophic Proteobacteria. The analysis of the relative contribution of each domain highlighted bacterial features related to glycolysis, lipid and polysaccharide breakdown, and also recognition of seaweed surface and establishment of biofilm. Eukaryotic transcripts, on the other hand, were associated with photosynthesis, synthesis of carbohydrate reserves, and defense mechanisms, including the biosynthesis of terpenoids through the mevalonate-independent pathway., Conclusions: This work describes the first transcriptomic profile of the red seaweed L. dendroidea, increasing the knowledge about ESTs from the Florideophyceae algal class. Our data suggest an important role for L. dendroidea in the primary production of the holobiont and the role of Bacteria as consumers of organic matter and possibly also as nitrogen source. Furthermore, this seaweed expressed sequences related to terpene biosynthesis, including the complete mevalonate-independent pathway, which offers new possibilities for biotechnological applications using secondary metabolites from L. dendroidea.

Extracts of the Egyptian marine actinomycete, Nocardia sp. ALAA 2000, were found to be highly bioactive. It was isolated from the marine red alga Laurenica spectabilis collected off the Ras-Gharib coast of the Red Sea, Egypt. According to detailed identification studies, the strain was classified as a member of the genus Nocardia. The cultivation and chemical analysis of this species yielded four structurally related compounds namely, chrysophanol 8-methyl ether (1), asphodelin; 4,7'-bichrysophanol (2) and justicidin B (3), in addition to a novel bioactive compound ayamycin; 1,1-dichloro-4-ethyl-5-(4-nitro-phenyl)-hexan-2-one (4) which is unique in contain both chlorination and a rarely observed nitro group. The compounds were isolated by a series of chromatographic steps and their structures of 1approximately 3 secured by detailed spectroscopic analysis of the MS and NMR data whereas that of 4 was elucidated by single crystal X-ray diffraction studies. These compounds displayed different potent antimicrobial activity against both Gram-positive and Gram-negative bacteria as well as fungi with MIC ranging from 0.1 to 10 microg/ml.