Antifungal characteristics of a bacterium isolated from the eastern subterranean termite Reticulitermes flavipes

Observations of Reticulitermes flavipes (Kollar) suggest there is suppression of microorganisms within healthy, subterranean termite laboratory and field colonies. Termites’ requirement for moisture keeps humidity levels high in the soil and wood they inhabit, which is also ideal for growth of a number of organisms including bacteria, mold, entomopathogenic and decay fungi. The presence of termites however, appears to control and/or inhibit development of these types of microorganisms, although the mechanism for inhibition is not well defined or understood. This study presents observations regarding potential factors involved in microbial control including termite behavior during exposure to actively growing mycelium of various decay fungi. In addition, a red pigmented, gram-negative bacterium, presumed to be Serratia marcescens, was found on the head and legs of dead termites. This bacterium, thought to be an opportunistic pathogen, may occur naturally in termites or termite colonies acting as a selective antifungal agent. The bacterium was isolated on Levine eosine methylene blue agar from a live termite killed by freezing. Streaks of the bacteria were then made on one side of a triple sugar iron agar plate with inoculum of a white- or brown-rot decay fungus on the opposite side of the agar plate. Preliminary results showed no inhibition by the bacterium against the two brown-rot fungi, but did appear to inhibit growth of the white-rot fungus, Irpex lacteus (MAD-517). This antifungal activity may be important in protecting the colony from white-rot fungi which could potentially overwhelm the nest by growing on lignin left behind in termite tunnels.