Complete Biochemical Characterization of Pantaphos Biosynthesis Highlights an Unusual Role for a SAM-Dependent Methyltransferase.

Pantaphos is small molecule virulence factor made by the plant pathogen Pantoea ananatis. An 11 gene operon, designated hvr for high virulence, is required for production of this phosphonic acid natural product, but the metabolic steps used in its production have yet to be established. Herein, we determine the complete biosynthetic pathway using a combination of bioinformatics, in vitro biochemistry and in vivo heterologous expression. Only 6 of the 11 hvr genes are needed to produce pantaphos, while a seventh is likely to be required for export. Surprisingly, the pathway involves a series of O-methylated intermediates, which are then hydrolyzed to produce the final product. The methylated intermediates are produced by an irreversible S-adenosylmethione (SAM)-dependent methyltransferase that is required to drive a thermodynamically unfavorable dehydration in the preceding step, a function not previously attributed to members of this enzyme class. Methylation of pantaphos by the same enzyme is also likely to limit its toxicity in the producing organism. The pathway also involves a novel flavin-dependent monooxygenase that differs from homologous proteins due to its endogenous flavin-reductase activity. Heterologous production of pantaphos by Escherichia coli strains expressing the minimal gene set strongly supports the in vitro biochemical data.

Investigating the culturable atmospheric fungal and bacterial microbiome in West Texas: implication of dust storms and origins of the air parcels.

Individuals often experience ailments such as allergies, asthma and respiratory tract infections throughout the year. Weather reports often include estimations of common allergens that can affect these individuals. To describe the local 'atmospheric microbiome' in Lubbock, Texas, USA, we examined the culturable fungal and bacterial microbiome present in the air on calm and dust storm days using internal transcribed spacer (ITS)-1 and 16S rRNA amplicon sequencing, respectively. While some types of airborne fungi were frequently present throughout the year, distinct differences were also observed between calm and dust storm days. We also observed the influence of the origin of air parcels and wind elevation of the air trajectory. The most abundant genera of fungi identified during the study period were Cryptococcus, Aureobasidium, Alternaria, Cladosporium and Filobasidium. This observation was not surprising considering the agricultural intensive environment of West Texas. Interestingly, Cladosporium, a common allergenic mold, was increased during days with dust storm events. The predominant bacterial genera observed were Bacillus, Pseudomonas, Psychrobacter, Massilia and Exiguobacterium. The relative abundance of the psychrophiles, Psychrobacter and Exiguobacterium, was surprising, given the semi-aridity of West Texas. Coupling our observations with back trajectories of the wind (Hybrid Single-Particle Lagrangian Integrated Trajectory models) demonstrated that dust storms, regional anthropogenic activity and origin of air parcels are important influences on the diversity and temporal presence of the atmospheric microbiome.