Three strains of strictly aerobic, Gram-negative, naphthalene-degrading bacteria isolated from polychlorinated-dioxin-contaminated soil and sediment were characterized. These isolates grew well with naphthalene as the sole carbon and energy source, degrading it completely within 24 h of incubation. The isolates also degraded dibenzofuran co-metabolically in the presence of naphthalene with the concomitant production of yellow intermediate metabolite(s). A 16S rRNA gene sequence analysis revealed that the isolates affiliated to the genus Novosphingobium with Novosphingobium pentaromativorans and Novosphingobium subarcticum as their nearest phylogenetic neighbors (97.4–97.5% similarity). The isolates had a genomic DNA G+C ratio of 64.5–64.6 mol% and formed a genetically coherent group distinguishable from any established species of the genus Novosphingobium at a DNA-DNA hybridization level of less than 46%. The cellular fatty acids were characterized by the predominance of 18 : 1ω7c with significant proportions of 16 : 0, 16 : 1ω7c, 17 : 1ω6c and 2-OH 14 : 0. Sphingoglycolipids were present. The major respiratory quinone was ubiquinone-10. Spermidine was detected as the major polyamine. The distinct taxonomic position of the isolates within the Novosphingobium was also demonstrated by physiological and biochemical testing. Based on these phylogenetic and phenotypic data, we propose Novosphingobium naphthalenivorans sp. nov. to accommodate the novel isolates. The type strain is strain TUT562T (DSM 18518T, JCM 13951T, NBRC 102051T).
Toxigenic Vibrio cholerae, the cause of cholera, is a native flora of the aquatic environment which is transmitted through drinking water and still remains the leading cause of morbidity and mortality in many developing countries including Thailand. The culture method (CM), which is routinely used for assessing water quality, has not proven as efficient as molecular methods because the notorious pathogen survives in water mostly in a non-culturable state. We employed duplex-polymerase chain reaction (duplex-PCR) for detection of tcpA and ctxA genes in toxigenic V. cholerae, and compared PCR detection with CM in various waters of Khon Kaen Municipality, Thailand. We also evaluated the effect of different pre-PCR conditions on the results of ctxA and tcpA detection including: 1) water filtered and enriched in alkaline peptone water (APW) for 3 h before PCR, 2) water filtered without enrichment before PCR, and 3) use of only enrichment in APW for 6 h before PCR. Of the 96 water samples (taken from waste-water, potable and waste-water from patients' houses, and from rivers) tested, 48 (50%) were positive for ctxA and tcpA by duplex-PCR, whereas only 29 (30%) were positive for V. cholerae by CM. Of the 29 V. cholerae isolated by CM, 2 (7%) were toxigenic V. cholerae belonging to serovar O1, while the rests were non-O1/ non-O139. Results revealed, therefore, that ctxA and tcpA-targeted duplex PCR is more sensitive than CM for detection of toxigenic V. cholerae from water samples because CM detected much less toxigenic V. cholerae than the non-toxigenic V. cholerae. Template DNA as low as 100 fg or 23 cells of V. cholerae in the water sample was detected in duplex PCR. Pre-PCR filtration followed by enrichment for 3 h significantly increase in the efficiency of duplex-PCR detection of toxigenic V. cholerae.
Two strains of anamorphic yeasts isolated from insect frass collected in southern Thailand were assigned to the genus Candida based on the conventional taxonomic criteria used for yeast classification. In the phylogenetic tree based on the D1/D2 domain of the 26S rDNA, these strains are distant from the known species of yeasts and considered to represent two different new species. They are named Candida kazuoi sp. nov. and Candida hasegawae sp. nov.
A novel mixed substrate solid-state fermentation (SSF) process has been developed for Aspergillus niger MTCC 2594 using wheat bran (WB) and gingelly oil cake (GOC) and the results showed that addition of GOC to WB (WB : GOC, 3 : 1, w/w) increased the lipase activity by 36.0% and the activity was 384.3±4.5 U/g dry substrate at 30°C and 72 h. Scale up of lipase production to 100 g and 1 kg tray-level batch fermentation resulted in 95.0% and 84.0% of enzyme activities respectively at 72 h. A three-stage multiple contact counter-current extraction yielded 97% enzyme recovery with a contact time of 60 min. However, extraction by simple percolation and plug-flow methods resulted in decreased enzyme recoveries. The mixed substrate SSF process has resulted in a significant increase in specific activity (58.9%) when compared to a submerged fermentation (SmF) system. Furthermore, an efficient process of extraction has been standardized with this process. Use of GOC along with WB as potential raw materials for enzyme production could be of great commercial significance. This is the first report on the production and extraction of lipase from Aspergillus niger using mixed solid substrates, WB and GOC, which are potential raw materials for the production of enzymes and other value-added products.