WICHITA, Kan.—The billionaire brothers Charles and David Koch get lots of attention for bankrolling conservative causes. They would like more notice for another passion: buying and developing companies.

Koch Industries Inc., their closely held industrial conglomerate with annual sales of $115 billion, made a splash last month by acknowledging an interest in buying newspapers. But Koch Industries also is looking at other possible investments, particularly in energy and agriculture-related businesses.

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