Massiliamide, a cyclic tetrapeptide with potent tyrosinase inhibitory properties from the Gram-negative bacterium Massilia albidiflava DSM 17472T.

A cyclic tetrapeptide, designated massiliamide, was isolated from the liquid culture of the Gram-negative bacterium Massilia albidiflava DSM 17472T. The structure was elucidated through extensive spectroscopic analysis, including HR-MS and 1D and 2D NMR experiments. The absolute configuration was determined using the Marfey´s method. Massiliamide showed potent inhibitory activity towards tyrosinase with an IC50 value of 1.15 µM and no cytotoxicity.

Antitumor astins originate from the fungal endophyte Cyanodermella asteris living within the medicinal plant Aster tataricus.

Medicinal plants are a prolific source of natural products with remarkable chemical and biological properties, many of which have considerable remedial benefits. Numerous medicinal plants are suffering from wildcrafting, and thus biotechnological production processes of their natural products are urgently needed. The plant Aster tataricus is widely used in traditional Chinese medicine and contains unique active ingredients named astins. These are macrocyclic peptides showing promising antitumor activities and usually containing the highly unusual moiety 3,4-dichloroproline. The biosynthetic origins of astins are unknown despite being studied for decades. Here we show that astins are produced by the recently discovered fungal endophyte Cyanodermella asteris. We were able to produce astins in reasonable and reproducible amounts using axenic cultures of the endophyte. We identified the biosynthetic gene cluster responsible for astin biosynthesis in the genome of C. asteris and propose a production pathway that is based on a nonribosomal peptide synthetase. Striking differences in the production profiles of endophyte and host plant imply a symbiotic cross-species biosynthesis pathway for astin C derivatives, in which plant enzymes or plant signals are required to trigger the synthesis of plant-exclusive variants such as astin A. Our findings lay the foundation for the sustainable biotechnological production of astins independent from aster plants.

The contribution of genome mining strategies to the understanding of active principles of PGPR strains.

Pathogenic microorganisms and insects affecting plant health are a major and chronic threat to food production and the ecosystem worldwide. As agricultural production has intensified over the years, the use of agrochemicals has in turn increased. However, this extensive usage has had several detrimental effects, with a pervasive environmental impact and the emergence of pathogen resistance. In addition, there is an increasing tendency among consumers to give preference to pesticide-free food products. Biological control, through the employment of plant growth-promoting rhizobacteria (PGPR), is therefore considered a possible route to the reduction, even the elimination, of the use of agrochemicals. PGPR exert their beneficial influence by a multitude of mechanisms, often involving antibiotics and proteins, to defend the host plant against pathogens. To date, these key metabolites have been uncovered only by systematic investigation or by serendipity; their discovery has nevertheless been propelled by the genomic revolution of recent years, as increasing numbers of genomic studies have been integrated into this field, facilitating a holistic view of this topic and the rapid identification of ecologically important metabolites. This review surveys the highlights and advances of genome-driven compound and protein discovery in the field of bacterial PGPR strains, and aims to advocate for the benefits of this strategy.

The Novel Lipopeptide Poaeamide of the Endophyte Pseudomonas poae RE*1-1-14 Is Involved in Pathogen Suppression and Root Colonization.

Endophytic Pseudomonas poae strain RE*1-1-14 was originally isolated from internal root tissue of sugar beet plants and shown to suppress growth of the fungal pathogen Rhizoctonia solani both in vitro and in the field. To identify genes involved in its biocontrol activity, RE*1-1-14 random mutagenesis and sequencing led to the identification of a nonribosomal peptide synthetase (NRPS) gene cluster predicted to encode a lipopeptide (LP) with a 10-amino-acid peptide moiety. The two unlinked gene clusters consisted of three NRPS genes, designated poaA (cluster 1) and poaB and poaC (cluster 2), spanning approximately 33.7 kb. In silico analysis followed by chemical analyses revealed that the encoded LP, designated poaeamide, is a structurally new member of the orfamide family. Poaeamide inhibited mycelial growth of R. solani and different oomycetes, including Phytophthora capsici, P. infestans, and Pythium ultimum. The novel LP was shown to be essential for swarming motility of strain RE*1-1-14 and had an impact on root colonization of sugar beet seedlings The poaeamide-deficient mutant colonized the rhizosphere and upper plant cortex at higher densities and with more scattered colonization patterns than the wild type. Collectively, these results indicate that Pseudomonas poae RE*1-1-14 produces a structurally new LP that is relevant for its antagonistic activity against soilborne plant pathogens and for colonization of sugar beet roots.

Three new spongian diterpenes from the Fijian marine sponge Spongia sp.

Chemical investigation of the marine sponge Spongia sp., collected from the Fiji Islands resulted in the isolation of three new furanoditerpenoids 1-3, along with the known compounds epispongiatriol (4) and 17,19-dihydroxyspongia-13(16),14-dien-2,3-dione (5) While 1 is a new spongian diterpene with a modified oxidation pattern, compounds 2 and 3 represent two new ring A-contracted spongians, displaying a novel and unprecedented nor-spongian carbon skeleton. Despite their labile nature the structures could be established through a combined strategy including complete analysis of spectroscopic data (NMR, MS), molecular modeling and quantum-mechanical calculations.