Catch the Subterranean Slug-FestNow, Live on Video
By Jan Suszkiw
December 1, 2009
To learn of
Mazzola's research, you'd think the amoebas he studiesand the
bacteria they "stalk" in the soilwere lion and wildebeest
battling it out on the plains of the Serengeti in East Africa.
The Agricultural Research Service
(ARS) plant pathologist is studying such microbial strife as part of a broader
effort to devise new, integrated approaches to managing "apple
replant" disease. In western states including Washington, this
growth-sapping disease of young trees can cause diminished gross returns of up
to $40,000 over 10 years, an orchard's average productive life.
A complex of pathogens causes the disease, notably Rhizoctonia fungi,
Pythium oomcetes and the parasitic nematode Pratylenchus
penetrans. Chemically fumigating the soil helps suppress them, but the
practice is costly and environmentally worrisome.
As an alternative, Mazzola is examining ways to bolster resident populations
of Pseudomonas bacteria, whose habitation of soils around tree roots
helps keep the pathogens at bay. While conducting research at the ARS
Fruit Research Laboratory in Wenatchee, Wash., Mazzola observed something
interesting. When pursued in soils by single-celled predatory amoebas, the
rod-shaped Pseudomonads "band together" and secrete a
biochemical defense of surfactant-like proteins, called cyclic lipopeptides
Normally, the amoebas hunt down and engulf their prey with the help of
"false feet." But the Pseudomonads' CLPs stop them
coldor, more precisely, blow them apart, reports Mazzola, who's
videotaped the action.
His observations are based on petri dish, soil-tube and plant-root
experiments pitting two CLP-producing strains (P. fluorescens SBW25 and
SS101) and two nonproducing mutant strains (17A8 and 10.24) against the amoeba
Naegleria americana. In the experiments, the amoeba avoided areas
inhabited by SBW25 and SS101, but "overran" and feasted upon the
CLP-free mutant strains.
Besides survival, the CLPs also enable the Pseudomonads to form
biofilms, further contributing to their usefulness as apple replant controls,
according to Mazzola.
He and Wageningen
Raaijmakers report their findings, including the identification of two
CLPsviscosin and massetolide Ain the
November issue of
Applied and Environmental Microbiology
ARS is the principal intramural scientific research agency of the
U.S. Department of