2.1.2.2. Ability to reduce CH4 emissions. The PNSB strains that
passed our primary screening were also tested for their ability to
reduce CH4 emissions by following the method of Harada et al.
(2003). The PNSB strains were grown as described above for the
inoculum to obtain culture broths. Each culture broth was
centrifuged at 4307 g for 15 min, and its cell pellet was
washed twice with 0.25% NaCl solution. Finally the cell pellet
was suspended in 3 mL of sterile distilled water. The cell
suspension was adjusted to an optical density (OD) of 0.5 at
660 nm, by dilution with 0.25% NaCl solution, for use as the
inoculum. This provided approximately 108 CFUmL1 bacteria.
An in vitro model of flooded rice fields was created by adding
1 mL of each inoculum into a 120 mL serum bottle containing 0.3 g
of dry rice straw pieces, mixed with 10 g paddy soil, and filled with
90 mL saline solution (NaCl 0.25%), which left a small head space
on the top of the medium for microaerobic conditions. This
provided the selected PNSB roughly 106 cells mL1
in each inoculated
set and each serum bottle was closed with an aluminum cap
with a butyl rubber septum. The paddy soil used in this experiment
was collected from the area surrounding Talay Noi Lake Basin,
Phatthalung province and expected to serve as a source of
methanogens. Characteristic of soil used was saline soil (pH
4.81, EC 3.80 mS cm1
, 0.12% total N, 3.20% organic matter, 2.86%
organic carbon, 7.80 mg kg1 available phosphate and 1.30 acidity;
meq 100 g1 soil). All culture serum bottles were incubated with a
tungsten light intensity of 3500 200 lux for 10 days. An 0.70 mm
internal diameter hollow needle, connected to a 10 mL syringe, was
inserted through the septum to maintain the inside at atmospheric