Structural and Biosynthetic Analysis of the Fabrubactins, Unusual Siderophores from Agrobacterium fabrum Strain C58

Fatty acyl-AMP ligases in bacterial natural product biosynthesis

Covering: covering up to 2024Fatty Acyl-AMP Ligases (FAALs) belong to the family of adenylate-forming enzymes and activate fatty acyl substrates through adenylation. FAALs were discovered as key players in various natural product biosynthetic pathways, particularly in the assembly of polyketides and non-ribosomal peptides. These enzymes exhibit a conserved structural architecture that distinguishes them from their close relatives, the Fatty Acyl-CoA Ligases. FAALs display the starter unit in the biosynthesis of diverse natural products where they shuttle fatty acyl substrates into secondary metabolism for further chain elongation and/or modification. In this review, we cover the discovery, distribution and structure of FAALs as well as their role in natural product biosynthesis. In addition, we provide an overview about their genomic and biosynthetic contexts and summarize approaches used to analyze FAAL activity, predict their substrate specificity and to discover new compounds whose biosyntheses involve these enzymes.

Pseudomonas rossensis sp. nov., a novel psychrotolerant species produces antimicrobial agents targeting resistant clinical isolates of Pseudomonas aeruginosa

The extreme conditions of the Antarctic environment have driven the evolution of highly specialized microbial communities with unique adaptations. In this study, we characterized five Pseudomonas isolates from James Ross Island, which displayed notable taxonomic and metabolite features. Phylogenomic analysis revealed that strain P2663T occupies a distinct phylogenetic position within the Pseudomonas genus, related to species Pseudomonas svalbardensis, Pseudomonas silesiensis, Pseudomonas mucoides, Pseudomonas prosekii, and Pseudomonas gregormendelii. The novelty of five Antarctic isolates was further confirmed through analyses of housekeeping genes, ribotyping, and REP-PCR profiling. MALDI-TOF MS analysis identified 11 unique mass spectrometry signals shared by the Antarctic isolates, which were not detected in other related species. Additionally, chemotaxonomic characterization, including fatty acid composition, demonstrated similarities with related Pseudomonas species. Phenotypic assessments revealed distinctive biochemical and physiological traits. In-depth genomic analysis of strain P2663T uncovered numerous genes which could be involved in survival in extreme Antarctic conditions, including those encoding cold-shock and heat-shock proteins, oxidative and osmotic stress response proteins, and carotenoid-like pigments. Genome mining further revealed several biosynthetic gene clusters, some of which are associated with antimicrobial activity. Functional assays supported the antimicrobial capabilities of this novel species, showing antagonistic effects against clinical isolates of Pseudomonas aeruginosa, possibly mediated by tailocins (phage tail-like particles). This comprehensive polyphasic study characterized a new cold-adapted species, for which we propose the name Pseudomonas rossensis sp. nov.

Investigating the interaction of uranium(VI) with diatoms and their bacterial community: A microscopic and spectroscopic study

Diatoms and bacteria play a vital role in investigating the ecological effects of heavy metals in the environment. Despite separate studies on metal interactions with diatoms and bacteria, there is a significant gap in research regarding heavy metal interactions within a diatom-bacterium system, which closely mirrors natural conditions. In this study, we aim to address this gap by examining the interaction of uranium(VI) (U(VI)) with Achnanthidium saprophilum freshwater diatoms and their natural bacterial community, primarily consisting of four successfully isolated bacterial strains (Acidovorax facilis, Agrobacterium fabrum, Brevundimonas mediterranea, and Pseudomonas peli) from the diatom culture. Uranium (U) bio-association experiments were performed both on the xenic A. saprophilum culture and on the four bacterial isolates. Scanning electron microscopy and transmission electron microscopy coupled with spectrum imaging analysis based on energy-dispersive X-ray spectroscopy revealed a clear co-localization of U and phosphorus both on the surface and inside A. saprophilum diatoms and the associated bacterial cells. Time-resolved laser-induced fluorescence spectroscopy with parallel factor analysis identified similar U(VI) binding motifs both on A. saprophilum diatoms and the four bacterial isolates. This is the first work providing valuable microscopic and spectroscopic data on U localization and speciation within a diatom-bacterium system, demonstrating the contribution of the co-occurring bacteria to the overall interaction with U, a factor non-negligible for future modeling and assessment of radiological effects on living microorganisms.

Genome mining strategies for metallophore discovery

Many bacteria use small-molecule chelators called metallophores to acquire trace metals from their environment. These molecules play a central role in interactions between bacteria, plants, and animals. Hence, knowing their full diversity is key to combatting infectious diseases as well as harnessing beneficial microbial communities. Metallophore discovery has been streamlined by advances in genome mining, where genomes are scanned for genes involved in metallophore biosynthesis. This review highlights recent trends and advances in predicting the presence and structure of metallophores based solely on genomic information. Recent work suggests new families of metallophores remain hidden from current homology-based approaches. Their discovery will require new genome mining approaches that move beyond biosynthesis to consider metallophore transporters, regulation, and evolution.

Genetically engineered rpsL merodiploidy impacts secondary metabolism and antibiotic resistance in Streptomyces

Certain point mutations within gene for ribosomal protein S12, rpsL, are known to dramatically change physiological traits of bacteria, most prominently antibiotic resistance and production of various metabolites. The rpsL mutants are usually searched among spontaneous mutants resistant to aminoglycoside antibiotics, such as streptomycin or paromomycin. The shortcomings of traditional selection are as follows: random rpsL mutants may carry undesired genome alterations; many rpsL mutations cannot be isolated because they are either not associated with increased antibiotic resistance or non-viable in the absence of intact rpsL^WT gene. Introduction of mutant rpsL alleles in the rpsL^WT background can be used to circumvent these obstacles. Here we take the latter approach and report the generation and properties of a set of stable rpsL merodiploids for Streptomyces albus J1074. We identified several rpsL alleles that enhance endogenous and heterologous antibiotic production by this strain and show that rpsL^WTrpsL^K88E merodiploid displays increased streptomycin resistance. We further tested several promising rpsL alleles in two more strains, Streptomyces cyanogenus S136 and Streptomyces ghanaensis ATCC14672. In S136, plasmid-borne rpsL^K88E+P91S and rpsL^K88R led to elevated landomycin production; no changes were detected for ATCC14672 merodiploids. Our data outline the prospects for and limitations to rpsL merodiploids as a tool for rapid enhancement of secondary metabolism in Streptomyces.