[Chemical Speciation, Influencing Factors, and Regression Model of Heavy Metals in Farmland of Typical Carbonate Area with High Geological Background, Southwest China].

The speciation of heavy metals in soil is an important factor determining their bioavailability and toxicity, and it is crucial for the scientific assessment of ecological risks posed by heavy metals in soils of typical carbonate areas with high geological background in southwest China. In order to investigate the distribution of speciation of heavy metals in soils of carbonate rock with high geological background, we selected a typical carbonate rock distribution area in Guizhou Province and used the second national soil survey plots as sampling units. A total of 309 topsoil samples were collected from farmland. The improved Tessier seven-step sequential extraction method was used to analyze the seven chemical forms of heavy metals:water-soluble (F1); exchangeable (F2); carbonate-bound (F3); weakly organic-bound (F4); iron-manganese oxide-bound (F5); strongly organic-bound (F6); and residual (F7) forms of arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn). The study found that the residual forms of heavy metals As, Cu, Hg, Ni, Pb, and Zn in the soil accounted for more than 50%, the effective components (F1-F3) accounted for less than 5%, and the potential biological effective components (F4-F6) were less than 45%, indicating low reactivity and low ecological risk. The effective and potentially bioavailable components of Cd accounted for 55.49% and 29.37%, respectively, which were much higher than those of other heavy metals. The ecological risk based on the speciation of heavy metals in the soil was much lower than that based on the total content of heavy metals. The stepwise regression equations could effectively establish the relationship between the bioavailable and potentially bioavailable fractions of Cd, Cu, and Pb and their influencing factors. Total heavy metal contents and pH value were important factors influencing the speciation of heavy metals in soils of carbonate rock with high geological background areas. The enrichment of heavy metal elements in the residual fraction was influenced by long-term zinc smelting activities and the weathering of carbonate rocks into soil. Soil organic matter (OM) and oxide content had a relatively small influence on the speciation of heavy metals in the soil.

Disruption of the gene encoding ß-1, 3-glucanase in marine-derived Williopsis saturnus WC91-2 enhances its killer toxin activity.

As the ß-1, 3-glucanase produced by the marine-derived Williopsis saturnus WC91-2 could inhibit the activity of the killer toxin produced by the same yeast, the WsEXG1 gene encoding exo-ß-1, 3-glucanase in W. saturnus WC91-2 was disrupted. The disruptant WC91-2-2 only produced a trace amount of ß-1, 3-glucanase but had much higher activity of killer toxin than W. saturnus WC91-2. After the disruption of the WsEXG1 gene, the expression of the gene was significantly decreased from 100% in the cells of W. saturnus WC91-2 to 27% in the cells of the disruptant WC91-2-2 while the expression of the killer toxin gene in W. saturnus WC91-2 and the disruptant WC91-2-2 was almost the same. During 2-l fermentation, the disruptant WC91-2-2 could produce the highest amount of killer toxin (the size of the inhibition zone was 22 ± 0.7 mm) within 36 h when the cell growth reached the middle of the log phase.

Enhanced ß-galactosidase production from whey powder by a mutant of the psychrotolerant yeast Guehomyces pullulans 17-1 for hydrolysis of lactose.

In order to isolate ß-galactosidase overproducers of the psychrotolerant yeast Guehomyces pullulans 17-1, its cells were mutated by using nitrosoguanidine (NTG). One mutant (NTG-133) with enhanced ß-galactosidase production was obtained. The mutant grown in the production medium with 30.0 g/l lactose and 2.0 g/l glucose could produce more ß-galactosidase than the same mutant grown in the production medium with only 30.0 g/l lactose while ß-galactosidase production by its wild type was sensitive to the presence of glucose in the medium. It was found that 40.0 g/l of the whey powder was the most suitable for ß-galactosidase production by the mutant. After optimization of the medium and cultivation conditions, the mutant could produce 29.2 U/ml of total ß-galactosidase activity within 132 h at the flask level while the mutant could produce 48.1 U/ml of total ß-galactosidase activity within 144 h in 2-l fermentor. Over 77.1% of lactose in the whey powder (5.0% w/v) was hydrolyzed in the presence of the ß-galactosidase activity of 280 U/g of lactose within 9 h while over 77.0% of lactose in the whey was hydrolyzed in the presence of ß-galactosidase activity of 280 U/g of lactose within 6 h. This was the first time to show that the ß-galactosidase produced by the psychrotolerant yeast could be used for hydrolysis of lactose in the whey powder and whey.

A GH57 family amylopullulanase from deep-sea Thermococcus siculi: expression of the gene and characterization of the recombinant enzyme.

The gene encoding a new extracellular amylopullulanase (type II pullulanase) was cloned from an extremely thermophilic anaerobic archaeon Thermococcus siculi strain HJ21 isolated previously from a deep-sea hydrothermal vent. The functional hydrolytic domain of the amylopullulanase (TsiApuN) and its MalE fusion protein (MTsiApuN) were expressed heterologously. The complete amylopullulanase (TsiApu) was also purified from fermentation broth of the strain. The pullulanase and amylase activities of the three enzymes were characterized. TsiApu had optimum temperature of 95°C for the both activities, while MTsiApuN and TsiApuN had a higher optimum temperature of 100°C. The residual total activities of MTsiApuN and TsiApuN were both 89% after incubation at 100°C for 1 h, while that of TsiApu was 70%. For all the three enzymes the optimum pHs for amylase and pullulanase activities were 5.0 and 6.0, respectively. By analyzing enzymatic properties of the three enzymes, this study suggests that the carboxy terminal region of TsiApu might interfere with the thermoactivity. The acidic thermoactive amylopullulanases MTsiApuN and TsiApuN could be further employed for industrial saccharification of starch.

Hymenobacter daecheongensis sp. nov., isolated from stream sediment.

A Gram-negative, strictly aerobic, non-spore-forming, rod-shaped, red-pink bacterium, designated strain Dae14(T), was isolated from stream sediment collected near Daecheong Dam, South Korea, and its taxonomic position was investigated by using a polyphasic approach. Phylogenetic analysis of 16S rRNA gene sequences showed that strain Dae14(T) belonged to the genus Hymenobacter. Sequence similarities between strain Dae14(T) and the type strains of Hymenobacter species with validly published names ranged from 91.3 to 94.3 %. The predominant cellular fatty acids of strain Dae14(T) were iso-C(15 : 0), C(16 : 1)omega5c, summed feature 5 (iso-C(17 : 1) I and/or anteiso-C(17 : 1) B) and iso-C(16 : 0). The DNA G+C content was 62.2 mol%. Results of phylogenetic, chemotaxonomic and phenotypic characterization indicated that strain Dae14(T) can be distinguished from all known Hymenobacter species and represents a novel species, for which the name Hymenobacter daecheongensis sp. nov. is proposed, with Dae14(T) (=KCTC 22258(T)=LMG 24498(T)) as the type strain.

Spirosoma panaciterrae sp. nov., isolated from soil.

A Gram-negative, yellowish bacterial strain, designated Gsoil 1519(T), was isolated from soil of a ginseng field in Pocheon province (South Korea) and characterized using a polyphasic approach to determine its taxonomic position. Comparative 16S rRNA gene sequence analysis showed that strain Gsoil 1519(T) belongs to the family 'Flexibacteraceae' and is related to Spirosoma rigui KCTC 12531(T) (91.8 % similarity) and Spirosoma linguale LMG 10896(T) (91.5 % similarity). Phylogenetic distances from any other recognized species within the family 'Flexibacteraceae' were greater than 14.7 %. The G+C content of the genomic DNA of strain Gsoil 1519(T) was 50.1 %. The detection of MK-7 as the predominant menaquinone and a fatty acid profile with C(16 : 1)omega5c, summed feature 4 (C(16 : 1)omega7c and/or iso-C(15 : 0) 2-OH), iso-C(15 : 0) and C(16 : 0) as the major acids supported the affiliation of strain Gsoil 1519(T) to the genus Spirosoma. On the basis of its phenotypic properties and phylogenetic distinctiveness, strain Gsoil 1519(T) should be classified in the genus Spirosoma as a representative of a novel species, for which the name Spirosoma panaciterrae sp. nov. is proposed. The type strain is Gsoil 1519(T) (=KCTC 22263(T)=DSM 21099(T)).