Pantothenate auxotrophy in a naturally occurring biocontrol yeast
The genus Hanseniaspora is characterized by some of the smallest genomes among budding yeasts. These fungi are primarily found on plant surfaces and in fermented products and represent promising biocontrol agents against notorious fungal plant pathogens. In this work, we identify a Hanseniaspora meyeri isolate that shows strong antagonism against the plant pathogen Fusarium oxysporum as a pantothenate auxotroph. Furthermore, strong biocontrol activity in vitro required both pantothenate and biotin in the growth medium. We show that the H. meyeri isolate APC 12.1 can obtain the vitamin from plants and other fungi. The underlying reason for the auxotrophy is the lack of key pantothenate biosynthesis genes, but at least six genes encoding putative pantothenate transporters are present in the genome. By constructing and using a Saccharomyces cerevisiae reporter strain, we identified one Hanseniaspora transporter, out of the six candidate proteins, that conferred pantothenate uptake activity to S. cerevisiae. Pantothenate auxotrophy is rare and has only been described in a few bacteria and in S. cerevisiae strains that were isolated from sake. Such auxotrophic strains may seem an unexpected and unlikely choice as potential biocontrol agents, but they may be particularly competitive in their ecological niche and their specific growth requirements are an inherent biocontainment strategy preventing uncontrolled growth in the environment. Auxotrophic strains such as the H. meyeri isolate APC 12.1 may thus represent a new strategy for developing biocontrol agents that will be easier to register than prototrophic strains, which are normally used for such applications. Significance StatementAs a precursor of the essential coenzyme CoA, pantothenate is present in all organisms. Plants, bacteria and fungi are known to synthesize this vitamin, while animals must obtain it through their diet. Pantothenate auxotrophy has not been described in naturally occurring, environmental fungi and is an unexpected property for an antagonistic yeast. Here, we report that yeasts from the genus Hanseniaspora lack key enzymes for pantothenate biosynthesis and identify a transporter responsible for the acquisition of pantothenate from the environment. Hanseniaspora isolates are strong antagonists of fungal plant pathogens. Their pantothenate auxotrophy is a natural biocontainment feature that could make such isolates interesting candidates for new biocontrol approaches and allow easier registration as plant protection agents compared to prototrophic strains.