The attine ants of South and Central America are ancient farmers, having evolved a symbiosis with a fungal food crop >50 million years ago. The most evolutionarily derived attines are the Atta and Acromyrmex leafcutter ants, which harvest fresh leaves to feed their fungus. Acromyrmex and many other attines vertically transmit a mutualistic strain of Pseudonocardia and use antifungal compounds made by these bacteria to protect their fungal partner against co-evolved fungal pathogens of the genus Escovopsis. Pseudonocardia mutualists associated with the attines Apterostigma dentigerum and Trachymyrmex cornetzi make novel cyclic depsipeptide compounds called gerumycins, while a mutualist strain isolated from derived Acromyrmex octospinosus makes an unusual polyene antifungal called nystatin P1. The novelty of these antimicrobials suggests there is merit in exploring secondary metabolites of Pseudonocardia on a genome-wide scale. Here, we report a genomic analysis of the Pseudonocardia phylotypes Ps1 and Ps2 that are consistently associated with Acromyrmex ants collected in Gamboa, Panama. These were previously distinguished solely on the basis of 16S rRNA gene sequencing but genome sequencing of five Ps1 and five Ps2 strains revealed that the phylotypes are distinct species and each encodes between 11 and 15 secondary metabolite biosynthetic gene clusters (BGCs). There are signature BGCs for Ps1 and Ps2 strains and some that are conserved in both. Ps1 strains all contain BGCs encoding nystatin P1-like antifungals, while the Ps2 strains encode novel nystatin-like molecules. Strains show variations in the arrangement of these BGCs that resemble those seen in gerumycin gene clusters. Genome analyses and invasion assays support our hypothesis that vertically transmitted Ps1 and Ps2 strains have antibacterial activity that could help shape the cuticular microbiome. Thus, our work defines the Pseudonocardia species associated with Acromyrmex ants and supports the hypothesis that Pseudonocardia species could provide a valuable source of new antimicrobials.

The psychotropic effectso fPsilocybe "magic" mushroomsa re caused by the l-tryptophan-derived alkaloid psilocybin.D espite their significance,t he secondary metabolome of these fungi is poorly understood in general. Our analysis of four Psilocybe speciesi dentified harmane, harmine, and ar ange of other l-tryptophan-derived b-carbolines as their natural products,w hichw as confirmed by 1D and 2D NMR spectroscopy.S table-isotope labeling with 13 C 11 -l-tryptophan verifiedt he b-carbolines as biosynthetic products of these fungi. In addition, MALDI-MS imaging showedt hat b-carbolines accumulate toward the hyphal apices.A sp otent inhibitors of monoamine oxidases, b-carbolines are neuroactive compounds and interfere with psilocybin degradation. Therefore, our findings represent an unprecedented scenario of natural product pathways that diverge from the same buildingb lock and produce dissimilar compounds, yet contribute directlyo ri ndirectly to the same pharmacological effects.

Burkholderia species such as B. mallei and B. pseudomallei are bacterial pathogens causing fatal infections in humans and animals (glanders and melioidosis), yet knowledge on their virulence factors is limited. While pathogenic effects have been linked to a highly conserved gene locus (bur/mal) in the B. mallei group, the metabolite associated to the encoded polyketide synthase, burkholderic acid (syn. malleilactone), could not explain the observed phenotypes. By metabolic profiling and molecular network analyses of the model organism B. thailandensis, the primary products of the cryptic pathway were identified as unusual cyclopropanol‐substituted polyketides. First, sulfomalleicyprols were identified as inactive precursors of burkholderic acid. Furthermore, a highly reactive upstream metabolite, malleicyprol, was discovered and obtained in two stabilized forms. Cell‐based assays and a nematode infection model showed that the rare natural product confers cytotoxicity and virulence.

In microbial interactions bacteria employ diverse molecules with specific functions, such as sensing the environment, communication with other microbes or hosts, and conferring virulence. Insights into the molecular basis of bacterial communication are thus of high relevance for ecology and medicine. Targeted gene activation and in vitro studies revealed that the cell‐to‐cell signaling molecule and disease mediator IQS (aeruginaldehyde) of the human pathogen Pseudomonas aeruginosa and related bacteria derives from the siderophore pyochelin. Addition of IQS to bacterial cultures (Burkholderia thailandensis) showed that the signaling molecule is captured by a congener of another siderophore family, malleobactin, to form a nitrone conjugate (malleonitrone) that is active against the IQS‐producer. This study uncovers complex communication processes with derailed siderophore functions, a novel nitrone bioconjugation, and a new type of antibiotic against Gram‐negative bacteria.

Nonribosomal peptide synthetases (NRPSs) are a vast source of valuable natural products, and re-engineering them is an attractive path toward structurally diversified active compounds. NRPS engineering often requires heterologous expression, which is hindered by the enormous size of NRPS proteins. Protein splitting and docking domain insertion have been proposed as a strategy to overcome this limitation. Here, we have applied the splitting strategy to the gramicidin S NRPS: Despite better production of the split proteins, gramicidin S production almost ceased. However, the addition of type II thioesterase GrsT boosted production. GrsT is an enzyme encoded in the gramicidin S biosynthetic gene cluster that we have produced and characterized for this purpose. We attribute the activity enhancement to the removal of a stalled intermediate from the split NRPS that is formed due to misinitiation. These results highlight type II thioesterases as useful tools for NRPS engineering.