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Total (TWW) and tapioca starch wash wastewater (TSWW) from a cassava processing plant in Thailand were analyzed for their composition with a view to evaluate their potential as substrates for solvent production by ABE fermentation with Clostridium spp. Starch was detected at a 1.63-fold higher level in the TWW than that in the TSWW (24.4% and 15.0% (w/w), respectively). The chemical oxygen demand (COD) was broadly similar (20,093 and 20,433 mg/L), but the biological oxygen demand (BOD) was 1.84-fold higher (18,000 and 9,750 mg/L) in the TWW than that in the TSWW. Thus, the TSWW was selected as a substrate to evaluate its potential for butanol and ethanol production by two Clostridium spp. The combined ethanol plus butanol production in the TSWW at pH 6.5 was higher than that at pH 4.5, being around 27.8- and 3.4-fold higher in C. butyricum TISTR 1032 and C. acetobutylicum ATCC 824, respectively. In both strains, the butanol (and combined butanol plus ethanol) production level was improved at pH 5.5. The addition of yeast extract increased the bacterial cell production, but did not significantly improve solvent productivity in C. acetobutylicum, and even decreased butanol production by C. butyricum.

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The genetic heterogeneity of the nitrite reductase gene (nirK and nirS) fragments from denitrifying prokaryotes in a non-agricultural forest soil in Thailand was investigated using soil samples from the Plant Germplasm-Royal Initiation Project area in Kanchanaburi Province, Thailand. Soil bacteria were screened for denitrification activity and 13 (from 211) positive isolates were obtained and further evaluated for their ability to reduce nitrate and to accumulate or reduce nitrite. Three species with potentially previously unreported denitrifying activities were recorded. Analysis of the partial nirK and nirS sequences of these 13 strains revealed a diverse sequence heterogeneity in these two genes within the same environment and even potentially within the same host species, the potential existence of lateral gene transfer and the first record of both nirK and nirS homologues in one bacterial species. Finally, isolates of two species of bacteria (Corynebacterium propinquum and Micrococcus lylae) are recorded as denitrifiers for the first time.

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