Structure, mechanism, and evolution of the last step in vitamin C biosynthesis.

Photosynthetic organisms, fungi, and animals comprise distinct pathways for vitamin C biosynthesis. Besides this diversity, the final biosynthetic step consistently involves an oxidation reaction carried out by the aldonolactone oxidoreductases. Here, we study the origin and evolution of the diversified activities and substrate preferences featured by these flavoenzymes using molecular phylogeny, kinetics, mutagenesis, and crystallographic experiments. We find clear evidence that they share a common ancestor. A flavin-interacting amino acid modulates the reactivity with the electron acceptors, including oxygen, and determines whether an enzyme functions as an oxidase or a dehydrogenase. We show that a few side chains in the catalytic cavity impart the reaction stereoselectivity. Ancestral sequence reconstruction outlines how these critical positions were affixed to specific amino acids along the evolution of the major eukaryotic clades. During Eukarya evolution, the aldonolactone oxidoreductases adapted to the varying metabolic demands while retaining their overarching vitamin C-generating function.

Characterization and survival of broad-spectrum biocontrol agents against phytopathogenic fungi.

The current study intended to isolate, characterize and identify biocontrol bacteria possessing broad-spectrum antifungal activity from the phyllosphere of different crops including maize, wheat and potato and to assess their growth-promoting activity. In this study 14/113 biocontrol bacteria showed antifungal activity. Bacterial isolates M11 and M33 from maize out of 113 were re-selected on the basis of their strong (more than 50%) broad spectrum antifungal activity after their assessment against four economically important phytopathogenic fungi including Alternaria alternata, Rhizoctonia solani, Fusarium oxysporum and Fusarium verticillioides. The isolates were further assessed for plant growth promoting traits, i.e., indole-3-acetic acid production, phosphate solubilization, production of cellulase, microbial volatile compounds, hydrogen cyanide and siderophores. All fourteen isolates showed positive results for the production of indole-3-acetic acid hormone and cellulase enzyme, 10 isolates were positive for hydrogen cyanide production; siderophores production was observed in 7 isolates while 5 isolates showed ability to solubilize inorganic phosphate. Microbial volatile compounds were only synthesized by M11 and M33, which were identified as Bacillus amyloliquefaciens and Bacillus subtilis respectively by 16S rRNA gene sequencing. The survival study revealed that biocontrol bacteria B. amyloliquefaciens and B. subtilis have the ability to survive in cost effective molasses containing carrier material up to a three-month period.