Thesis

Uncovering bioactive metabolites from the agriculturally important strain QST 2808, Bacillus pumilus, through bioassay-guided fractionation

Modern agriculture faces many challenges in the twenty-first century. Sustainability and productivity must move together in stride if humans expect to minimize the impact to the environment with pesticides and fertilizers while still producing the volume and quality of food needed to feed a growing world population. Biological control is an important tool to reduce both synthetic pesticide and fertilizer application amounts, by offering disease control and plant growth promotion, while lowering synthetic chemical load on the environment. Bacteria of the genus Bacillus are great biological control options considering their natural origins, vast production of bioactive metabolites, ability to promote the growth of plants, ease of producing end-products at a manufacturing scale, and potential for stability as a product due to the resilient spores they form. In this work, fermentation whole broth (WB) of a specific strain of Bacillus pumilus, QST 2808, was investigated for bioactive metabolites of agricultural relevance. An amino sugar, active against two crop disease targets, downy mildew and bacterial spot, was isolated and characterized from a B. pumilus QST 2808 fermentation product. Two additional fractions were identified, distinct from the amino sugar, one with activity against bacterial spot and one with activity against cucumber anthracnose. With the identification of these three bioactive fractions, this work adds to the knowledge of Bacillus biological control possibilities for developing safe and effective crop protection products.

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