Indexing the Pseudomonas specialized metabolome enabled the discovery of poaeamide B and the bananamides

Pseudomonads are cosmopolitan microorganisms able to produce a wide array of specialized metabolites. These molecules allow Pseudomonas to scavenge nutrients, sense population density and enhance or inhibit growth of competing microorganisms. However, these valuable metabolites are typically characterized one-molecule–one-microbe at a time, instead of being inventoried in large numbers. To index and map the diversity of molecules detected from these organisms, 260 strains of ecologically diverse origins were subjected to mass-spectrometry-based molecular networking. Molecular networking not only enables dereplication of molecules, but also sheds light on their structural relationships. Moreover, it accelerates the discovery of new molecules. Here, by indexing the Pseudomonas specialized metabolome, we report the molecular-networking-based discovery of four molecules and their evolutionary relationships: a poaeamide analogue and a molecular subfamily of cyclic lipopeptides, bananamides 1, 2 and 3. Analysis of their biosynthetic gene cluster shows that it constitutes a distinct evolutionary branch of the Pseudomonas cyclic lipopeptides. Through analysis of an additional 370 extracts of wheat-associated Pseudomonas, we demonstrate how the detailed knowledge from our reference index can be efficiently propagated to annotate complex metabolomic data from other studies, akin to the way in which newly generated genomic information can be compared to data from public databases

Use of combined inoculum of Azospirillum and Rhizobium in winged bean Psophocarpus tetragonolobus (L) D.C

The potential of using the free living N -fixing Azospirillum in increasing the nodulation and N2-fixation by Rhizobium in winged bean was analysed. Various strains of winged bean Rhizobium and several strains of Azospirillum were tested in combined inoculations. Substantial increases in nodulation, N2-fixation, shoot dry matter production and N gain due to the mixed inoculation were obtained in one Rhizobium strain namely KUL-BH and most of the Azospirillum strains used. The influence of Rhizobium genotype in expressing the association effect was more decisive than that of Azospirillum. The cell-free extract of Azospirillum produced the same enhancement effect as that of the organism itself, while the culture supernatant also showed the same in some instances. Since the response to combined inoculation in winged bean was obtained only with one strain of Rhizobium, the factors that could influence the nodulation enhancement were investigated in detail. An attempt was made in finding out the possible mechanism involved in the enhancement effect by Azospirillum

Microbial Biomass Changes during Decomposition of Plant Residues in a Lixisol

A lixisol was amended with four different alley cropping species: Senna siamea, Leucaena leucocephala, Dactyladenia barteri and Flemingia macrophylla. Soil samples were incubated for 140 days at 25 °C and the soil microbial biomass was determined by the ninhydrin extraction method along the incubation period. The soil microbial biomass values ranged between 80 and 600 mg.kg-1 and followed, in all cases, the decreasing order: Leucaena> Senna> Flemingia> Dactyladenia