Abstract The aims were to explore an appropriate isolating medium for
obtaining purple nonsulfur bacteria (PNSB) for use as biofertilizers in
saline paddy fields and to obtain pure cultures. We therefore chose a
defined isolating medium containing 0.25% NaCl, (Glutamate-Acetate
broth, GA) and a rice straw broth to compare them for numbers of PNSB
obtained, time to obtain pure cultures, diversity and costs. A total of
30 water and 30 sediment samples were collected from saline paddy
fields in southern Thailand and used to isolate PNSB in both the
isolating media. Based on 60 samples and a period of 13 days incubation
under anaerobic light conditions, a greater number of samples produced
PNSB growth in GA broth after only day 3; however, after that the rice
straw broth provided about a 2 fold increase in the number of samples
that produced PNSB growth. Colonies isolated from GA broth required a
significantly higher number of repeated streaking to obtain a pure
culture (average 3.5) than those from rice straw broth (average 2.7)
and the latter medium also produced significantly (P < 0.05) more
isolates per sample. Sixty samples of water and sediment, from rice
paddies with salinity (average, 3.43 \ub1 0.67 mS/cm) and slight
acidity (average, pH 5.84 \ub1 0.42) provided 62 PNSB isolates by GA
broth and 210 isolates by rice straw broth, and rice straw broth also
produced a greater prevalence of PNSB. Estimates of the costs based on
current prices of media, Gas Pak and electricity to obtain PNSB with
the use of GA broth was roughly 6 times higher than for the rice straw
broth