Filamentous fungi with high paraquat-degrading activity isolated from contaminated agricultural soils in northern Thailand

The contamination of paraquat (1,1'-dimethyl-4,4'-bipyridylium dichloride) herbicide from the farming area has become a public concern in many countries. This herbicide harms to human health and negatively effects the soil fertility. Several methods have been introduced for the remediation of paraquat. In this study, 20 isolates of the paraquat-tolerant fungi were isolated from the contaminated soil samples in northern Thailand. We found that isolate PRPY-2 and PFCM-1 exhibited the highest degradation activity of paraquat on synthetic liquid medium. About 80 and 68% of paraquat were removed by PRPY-2 and PFCM-1 respectively after 15 days of cultivation. Based on the morphological characteristic and molecular analysis, the fungal isolate PRPY-2 and PFCM-1 were identified as Aspergillus tamarii and Cunninghamella sp. respectively. The biosorption of paraquat on these fungal mycelia was also investigated. It was found that only 8-10% of paraquat could be detected on their mycelia, while 24-46% of paraquat was degraded by fungal mycelia. This is the first report on paraquat degrading ability by A. tamarii and Cunninghamella sp. It is demonstrated that these filamentous fungi are promising microorganisms available for remediation of paraquat contaminated environment.

Optimization of soybean processing into kinema, a Bacillus-fermented alkaline food, with respect to a minimum level of antinutrients

AIMS

Optimization of traditional processing of soybeans using response surface methodology (RSM) to achieve a minimum level of antinutritional factors (ANFs) in kinema.

METHODS AND RESULTS

Central composite rotatable designs were used to optimize the processing stages of kinema preparation. In each stage, the linear or quadratic effects of independent variables were significant in minimizing ANF levels. The predicted optimum condition for soaking was when the raw beans-water ratio was 1 : 10, and the soaking temperature, time and pH were 10°C, 20 h and 8·0 respectively. Here, tannins content (TC), phytic acid content (PAC) and trypsin inhibitor activity (TIA) decreased (P < 0·05). While haemagglutinating activity (HA) level remained unchanged (P < 0·05), total biogenic amines content (TBAC) increased. The optimum condition for cooking was optimally soaked beans-water ratio of 1 : 5, and cooking pressure and time were 1·10 kg cm(-2) and 20 min respectively. Here, TC, PAC, TIA and HA decreased (P < 0·05), but TBAC remained unchanged compared to optimally soaked beans. TC and HA went below the level of detection. The optimum condition for fermentation was obtained when inoculum load was 10(3) total cells g(-1) grits, and fermentation temperature and time were 37°C and 48 h respectively. Fermentation of optimally cooked beans caused a reduction (P < 0·05) of PAC. While TIA remained unchanged (P < 0·05), TBAC increased. In kinema, TC, PAC, TIA and HA decreased (P < 0·05) over raw beans by 100, 61, 71 and 100% respectively. Good agreement was observed between predicted values and experimental values.

CONCLUSIONS

The processing treatments significantly minimized the level of ANFs in soybeans.

SIGNIFICANCE AND IMPACT OF THE STUDY

RSM was successfully deployed to obtain the optimum condition for kinema-making with a minimum level of ANFs without impairing sensory attributes of the product. The results are useful for commercial production of kinema.

Use of Bacillus subtilis isolates from Tua-nao towards nutritional improvement of soya bean hull for monogastric feed application

Soya bean hull (SBH) is a cheap and high-fibre content feed ingredient that obtained after soya bean oil extraction. Microbial fermentation was expected to improve SBH qualities before applying to animals, especially monogastric animals. Two bacterial strains, Bacillus subtilis MR10 and TK8 that were isolated from Tua-nao, a traditional fermented soya bean in northern Thailand, were used for fermented soya bean hull (FSBH) production. Both could easily grow at 37°C in SBH as the sole substrate. MR10 produced the highest β-mannanase activity (400 U g(-1) SBH) on day 2, while TK8 produced the highest cellulase activity (14·5 U g(-1) SBH) on day 3. After fermentation, the nutritional quality of SBH was obviously improved by an increase in soluble sugars, soluble proteins, crude protein and crude lipid, and a decrease in the content of raffinose family oligosaccharides. Scavenging activity (%) of SBH against ABTS radical cation was also increased from 14 to 27 and 20% by MR10 and TK8 fermentation, respectively. According to the GRAS property of these both strains and various improvements of nutritional values, the fermented SBH proved to be a potential feed ingredient, especially for the monogastric animals.

SIGNIFICANCE AND IMPACT OF THE STUDY

Normally, soya bean hull has been recognized as only a worthless by-product from soya bean oil production process because of its low utilizable nutrients. Our study introduced an alternative way to utilize this worthless residue using biotechnological knowledge. The nutritional quality of soya bean hull was improved by microbial fermentation. Fermented soya bean hull can be used as a cheap, safe and high-nutrient feed ingredient for livestock production, especially monogastric animals, to promote their growth performances, instead of using antibiotics in some regions of the world.

Screening and selection of Bacillus spp. for fermented corticate soybean meal production

AIMS

To screen and select the Bacillus spp. from Tua-nao of northern Thailand for fermented corticate soybean meal (FCSBM) production.

METHODS AND RESULTS

After isolation of Bacillus spp. from Tua-nao was carried out, cellulase, hemicellulases (i.e., β-mannanase and xylanase) and phytase production by isolated Bacillus spp. were determined. B. subtilis isolate MR10 showed the highest β-mannanase, xylanase and phytase production at 280, 41 and 16 U g(-1) substrate, respectively, while the highest cellulase production was found in TK8 at 25 U g(-1) substrate. FCSBMs produced by single starter and mixed starter of both isolates showed the better properties than those of corticate soybean meal (CSBM), i.e., higher in soluble sugar, protein and phosphate content, smaller sugar molecules and better digestibility and absorbability than those of CSBM. Moreover, FCSBMs had no toxicity effect on mouse fibroblast cell line (3T3) but had an inhibitory effect on lung cancer cell line (CorL23).

CONCLUSIONS

B. subtilis isolate MR10 and TK8 were selected for FCSBMs production because of their role as nutritional enhancer for CSBM and their safety.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study were useful for FCSBM production process that can be applied as feed ingredient for monogastric animals.