MATERIALS AND METHODS
Sample collection. A 500-g garden soil sample was collected from 15 cm below
the surface at Macquarie University, Sydney, New South Wales, Australia, and
was passed through a 2-mm-mesh sieve. The pH (24) and water content (ex-
pressed as a percentage of the dry weight) of the soil sample were determined on
the day of collection to be pH 6.42 and 21%, respectively.
Microcultivation in a soil slurry membrane system. For microcultivation, a
subsample of soil was diluted 1:200 in prefiltered (pore size, 0.2 ?m) distilled
H2O and vortexed for 30 s. This was the bacterial inoculum used for the study.
Sand particles were allowed to sediment for 1 min before 50 ?l of the inoculum
was placed into 10 ml distilled H2O and filtered onto a 0.2-?m, white, isopore PC
* Corresponding author. Mailing address: Department of Biological
Sciences, Division of Environmental and Life Sciences, Macquarie
University, Sydney 2109, NSW, Australia. Phone: 61 2 9850 9252. Fax:
61 2 9850 8253. E-mail: bferrari@rna.bio.mq.edu.au.
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membrane (Millipore, North Ryde, New South Wales, Australia) using a syringe
filter holder (Sartorius, East Oakleigh, Victoria, Australia). Inoculated PC mem-
branes were then placed on top of a sterile 0.02-?m anopore membrane, which
was fixed within 25-mm TCIs (Nunc A/S, Roskilde, Denmark). Before addition
of the PC membranes, the TCIs were inverted and filled with 3 g of the sieved
garden soil (Fig. 1) that was wetted with 750 ?l of prefiltered distilled H2O. The
soil was gently vortexed until the soil texture was broken down to a muddy soil
slurry. A TCI was then placed upside down in a sterile six-well multidish (Nunc).
The underside of the inoculated PC membrane was then placed on the TCI’s
fixed anopore membrane. The top side of the anopore membrane was also sterile
and served as a barrier between the nonsterile soil slurry and the underside of the
PC membrane, which was also sterile. The culture vessels were incubated at 22°C
in the dark for 7 to 10 days. To confirm sterility, negative control preparations
consisted of uninoculated PC membranes that were placed on top of the TCI
growth support system containing nonsterile soil slurries.