In order to accelerate the isolation and characterisation of structurally new or novel secondary metabolites, it is crucial to develop efficient strategies that prioritise samples with greatest promise early in the workflow so that resources can be utilised in a more efficient and costeffective manner. We have developed a metrics-based prioritisation approach using exact LC-HRMS which uses data for 24,618 marine natural products held in the PharmaSea database. Each sample was evaluated and allocated a metric score by a software algorithm based on the ratio of new masses over the total (sample novelty), ratio of known masses over the total (chemical novelty), number of peaks above a defined peak area threshold (sample complexity), and peak area (sample diversity). Samples were then ranked and prioritized based on these metric scores. To validate the approach, 8 marine sponges and 6 tunicate samples collected from the Fiji Islands were analysed, metric scores calculated and samples targeted for isolation and characterisation of new compounds. Structures of new compounds were elucidated by spectroscopic techniques, including 1D and 2D NMR, MS and MS/MS. Structures were confirmed by Computer Assisted Structure Elucidation methods (CASE) using the ACD/Structure Elucidator Suite.

A biological evaluation of a library of extracts from entomopathogen strains showed that Pantoea sp. extract has significant antimicrobial and insecticidal activities. Three hydroxyacyl-phenylalanine derivatives were isolated from this strain. Their structures were elucidated by a comprehensive analysis of their NMR and MS spectroscopic data. The antimicrobial and insecticidal potencies of these compounds were evaluated, and compound 3 showed 67% mortality against Aedes aegypti larvae at a concentration of 100 ppm, and a minimum inhibitory concentration (MIC) of 16 µg/mL against methicillin-resistant Staphylococcus aureus. Subsequently, hydroxyacyl-phenylalanine analogues were synthesized to better understand the structure-activity relationships within this class of compounds. Bioassays highlighted the antimicrobial potential of analogues containing saturated medium-chain fatty acids (12 or 14 carbons), whereas an unsaturated long-chain fatty acid (16 carbons) imparted larvicidal activity. Finally, using a molecular networking-based approach, several close analogues of the isolated and newly synthesized lipoamino acids were discovered in the Pantoea sp. extract.

A library of 197 endophytic fungi and bacteria isolated from the Amazonian palm tree Astrocaryum sciophilum was extracted and screened for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). Four out of five antibacterial ethyl acetate extracts were also cytotoxic for the MRC-5 cells line. Liquid chromatography coupled to tandem mass spectrometry (UPHLC-HRMS/MS) analyses combined with molecular networking data processing were carried out to allow the identification of depsipeptides and cyclopeptides responsible for the cytotoxicity in the dataset. Specific ion clusters from the active Luteibacter sp. extract were also highlighted using an MRSA activity filter. A chemical study of Luteibacter sp. was conducted leading to the structural characterization of eight fatty acid exhibiting antimicrobial activity against MRSA in the tens of µg/mL range.

1. Community assembly theory assumes that ecological communities are spatially delimited into patches. Within these patches, coexistence results from environmental filtering, competition and immigration. Truly delineated communities exist in laboratory studies of microbial cultures in Petri dishes, yet empirical tests conducted in continuous environments often use patches defined by convention as opposed to realized boundaries. 2. Here we perform a test of ecological community assembly rules using foliar endophyte communities from a tropical rainforest, where leaves are considered as patches for both fungal and bacterial communities. We determined the diversity of fungal and bacterial endophytes using environmental DNA sequencing of 365 topcanopy leaves, collected from 38 host trees belonging to 22 different species across a 4-ha research plot. Three leaves were collected from three or more branches within each tree crown. We tested the effect of host tree species and their level of phylogenetic relatedness on community composition as well as the contribution of geographic distance between leaves to endophyte community diversity. 3. Endophyte diversity significantly differed across host tree species, as did community composition. Within certain endophytic orders (Xylariales, Rhizobiales) species assemblages significantly differed across host tree species, but this trend was weaker or non-existent in other orders known to contain pathogens and saprotrophs (Polyporales, Solirubrobacterales). Phylogenetically related host tree species displayed more similar endophyte communities than expected by chance, but geographically close trees did not. Consistent with the finding of host-specificity, nearby leaves tended to host more similar communities than distantly positioned ones. 4. These findings demonstrate that foliar endophytes are structured by dispersal across small spatial scales, but at the scale of the canopy they display patterns of neutral filtering, with only a small part of variation described by host tree differences. Endophyte communities thus act as a model system in evoking the rules predicted by theoretical community ecology.