When looking for a bacterial agent to control turfgrass diseases, it is not surprising that one could be found not far from the shadows of Martin Hall where streptomycin was discovered. Indeed, that was the case when Dr. Donald Kobayashi initiated a project supported by the Rutgers Turfgrass Center, the New Jersey Agricultural Experiment Station, and the United States Golf Association to identify and develop biological control agents for turfgrass diseases. Among hundreds of bacteria that were isolated from soil collected from surrounding areas of the Cook Campus, one stood out for its ability to inhibit fungal growth in culture and effectively control summer patch disease of Kentucky bluegrass (Fig. 1). The bacterium was identified as Lysobacter enzymogenes, a common inhabitant of soil and water known as a predator of other microorganisms. As its name implies, L. enzymogenes produces an abundance of enzymes that can lyse, or break open, other living cells.
Deeper investigation of L. enzymogenes indicated that the bacterium establishes unexpected complex, intimate interactions with fungal hosts. Light and electron microscopy showed bacteria entering and proliferating within fungal cells prior to rupturing them and releasing more bacteria into the local environment (Fig. 2). The unprecedented nature of the Lysobacter/fungus interaction led to Dr. Kobayashi to collaborate with the labs of Drs. Bradley Hillman and Michael Lawton to examine the pathogenic host range of Lysobacter.
Surprisingly, the bacterium can attack and internalize in a broad range of lower eukaryotic hosts, including the moss Physcomitrella patens, which is emerging as a model system for lower plants (Fig. 3); the nematode Caenorhabditis elegans, which has long served as a simple model for animals; and the fungus Magnaporthe oryzae, which causes rice blast disease and gray leaf spot disease of turfgrasses, and is considered a model for plant pathogenic fungi. Each of these host organisms has been completely sequenced, allowing for the most technologically advanced tools to be used in studies of their interactions with Lysobacter.
Molecular studies to date have already shown that L. enzymogenes uses a diverse set of mechanisms to infect its various hosts. With grant support from the USDA Microbial Genome Sequencing Program to Dr. Kobayashi and colleagues, sequencing of the L. enzymogenes genome has been initiated. These studies will provide practical knowledge about biological control of plant diseases, and fundamental information about the ongoing microbial battles underground.
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