Survey of soil bacteria capable of inducing trap
formation in A. oligospora
A sandy agricultural soil studied previously for the presence
of nematophagous fungi (Zhang et al., 2005) was used.
Areas of 15 m2 of soil were selected at random and two
independent rhizosphere samples were taken from each
area. Each of the rhizosphere samples comprised total roots
from five randomly selected wheat plants. The roots were
shaken vigorously to eliminate the soil not tightly associated
with roots. About 100 rhizosphere samples were taken and
mixed thoroughly in a plastic bag to yield a composite
sample.
One gram of the composite sample was suspended in
5.0 mL of sterile-distilled water, vortexed (1 min) and sonicated
(1 min) in an ultrasonic cleaner. Soil dilution plates
(105
) were prepared on nutrient agar and incubated for 7
days at 251C. Eighty colonies of bacteria were selected at
random for the ability to induce trap formation. After
culturing all isolates at 251C for 3 days in a 25-mL vial
containing 10 mL nutrient broth (0.1 mg mL1
, final concentration),
the cultures were evaluated for trap formation.
The negative controls were nutrient broth (0.1 mg mL1
,
final concentration) without bacteria. The first screening
step for trap formation among 80 bacterial isolates was
performed on only one Petri plate for each bacterium. Only
the bioassay experiments for active strains were prepared in
triplicate and repeated three times. This procedure was
repeated three times.