The widely distributed Acidithiobacillus ferrooxidans (A. ferrooxidans)
lives in extremely acidic conditions by fixing CO2 and nitrogen, and by obtaining energy from Fe2+ oxidation with either downhill or uphill electron transfer pathway and from reduced sulfur oxidation. A. ferrooxidans exists as different genomovars and its genome size is 2.89–4.18 Mb. The chemotactic movement of A. ferrooxidans is regulated by quorum sensing. A. ferrooxidans shows weak magnetotaxis due to formation of 15–70 nm magnetite magnetosomes with surface functional groups. The room- and low-temperature magnetic features of A. ferrooxidans are different from other magnetotactic bacteria. A. ferrooxidans has potential for removing sulfur from solids and gases, metals recycling from metal-bearing ores, electric wastes and sludge, biochemical production synthesizing, and metal workpiece machining.
Due to a long-term transgression since the Early Cambrian, an extensive shallow-water carbonate platform was developed in the entire Tarim Basin (NW China). During the deposition of the Yingshan Formation (Early-Middle Ordovician), a carbonate ramp system was formed in the intrashelf basin in the Bachu-Keping area of the western basin. Four well-exposed outcrop sections were selected to investigate their depositional facies, cycles, and sequences, as well as the depositional evolution. Detailed facies analyses permit the recognition of three depositional facies associations, including peritidal, semi-restricted subtidal, and open-marine subtidal facies, and eleven types of lithofacies. These are vertically arranged into meter-scale, shallowing-upward peritidal, semi-restricted subtidal, and open-marine subtidal cycles, in the span of Milankovitch frequency bands, suggesting a dominant control of Earth’s orbital forcing on the cyclic sedimentation on the platform. On the basis of vertical facies (or lithofacies) and cycle stacking patterns, as well as accommodation changes illustrated graphically by Fischer plots at all studied sections, six third-order depositional sequences are recognized and consist of lower transgressive and upper regressive parts. In shallow depositional settings, the transgressive packages are dominated by thicker-than-average, shallow subtidal cycles, whereas the regressive parts are mainly represented by thinner-than-average, relatively shallow subtidal to peritidal cycles. In relatively deep environments, however, the transgressive and regressive successions display the opposite trends of cycle stacking patterns, i.e., thinner-than-average subtidal cycles of transgressive packages. Sequence boundaries are mainly characterized by laterally traceable, transitional zones without apparent subaerial exposure features. Good correlation of the long-term changes in accommodation space inferred from vertical facies and cycle stacking patterns with sea-level fluctuations elsewhere around the world suggests an overriding eustatic control on cycle origination, platform building-up and evolution during the Early-Middle Ordovician, although with localized influences of syndepositional faulting and depositional settings. 相似文献
Heavy metal pollution has become one of the most serious environmental pollution problems. This study aimed to determine the adsorption and desorption characteristics of Ni2+ and Cu2+ by bio-mineral which was induced by Bacillus subtilis, and to explore the effect of pH on adsorption characteristics. The results showed that the Langmuir model gave a better fit to the experimental data than the Freundlich model, which demonstrated the adsorption was of a single-molecule layer form. The maximum adsorption capacities of the bio-mineral for Ni2+ and Cu2+ were determined as 67.114 mg/g and 69.930 mg/g, respectively. The desorption rates of Ni2+ and Cu2+ were very low, especially for Ni2+ which was almost 0. Besides, the bio-mineral maintained high adsorption capability for metals ions within a wide pH range (pH ≥ 3). It did not show any new phases after adsorption of Ni2+ and Cu2+ tested by FTIR, indicating that the bio-mineral and heavy metal ions might mainly physically be adsorbed. The bio-mineral has a larger internal and external specific surface area, pore volume and colloidal properties which are beneficial for the adsorption of metals ions, but shows limits in desorption. This study provides a theoretical basis for the utilization of bio-mineral and opens a new perspective for the remediation of heavy metals pollution. 相似文献
A bacterial strain secreting potent chitinolytic activity was isolated from shrimp-pond water by enrichment culture using colloidal crab-shell chitin as the major carbon source. The isolated bacterium, designated asAeromonas sp No. 16 exhibited a rod-like morphology with a polar flagellum. Under optimal culture conditions in 500-ml shaker flasks, it produced a chitinolytic activity of 1.4 U ml–1. A slightly higher enzymatic activity of 1.5 U ml–1 was obtained when cultivation was carried out in a 5-liter jar fermentor using a medium containing crystalline chitin as the carbon source. The secretion of the enzyme(s) was stimulated by several organic nitrogenous supplements. Most carbon sources tested (glucose, maltose, N-acetylglucosamine, etc) enhanced cell growth, but they slightly inhibited enzyme secretion. Glucosamine (0.5% w/v) severely inhibited cell growth (16% of the control), but it did not significantly affect enzyme secretion. The production of chitinolytic enzymes was pH sensitive and was enhanced by increasing the concentration of colloidal chitin to 1.5%. The observed chitinolytic activity could be attributed to the presence of -N-acetylglucosaminidase and chitinase. Chitinase was purified by ammonium sulfate fractionation and preparative gel electrophoresis to three major bands on SDS-PAGE. An in-gel enzymatic activity assay indicated that all three bands possessed chitinase activity. Analysis of the enzymatic products indicated that the purified enzyme(s) hydrolyzed colloidal chitin predominantly to N,N-diacetyl-chitobiose and, to a much lesser extent, the mono-, tri, and tetramer of N-acetylglucosamine, suggesting that they are mainly endochitinases. 相似文献
The production of dissolved organic carbon (DOC) in culturesof the diatoms Chaetoceros gracilis and Phaeodactylum tricornutum,the flagellate Isochrysis galbana, the dinoflagellate Alexandriumtamarense and a natural algal assemblage from the NorthwestArm, Halifax, Nova Scotia, Canada, was followed using a high-temperaturecatalytic oxidation (HTCO) and a UV photo-oxidation method.Molecular weight fractionation of the DOC was performed fortwo cultures: C.gracilis and I.galbana. While the DOC in theculture medium increased significantly during log-phase growthfor all organisms except the dinoflagellate, this increase wasproportional to the increase in cell numbers; the increase inDOC per cell was either small or zero. In all cultures, maximumrelease took place during stationary and senescent phases, usuallyafter cell numbers had started to decrease. In both C.gracilisand I.galbana, a major portion (>65%) of the organic matterreleased to the medium during log-phase growth had mol. wtsof <10 000 Da. The increase in DOC in the I.galbana culturein stationary and senescent phases was due to the release ofhigh-molecular-weight materials. The differences in extracellularrelease of DOC between species and between different growthstages in the same species suggest that both the species compositionand physiological state of phytoplankton populations must beknown before interpretations and predictions based on fielddata can be made. In order to determine whether the differencesin DOC values found by the HTCO and UV oxidation methods arecaused by the resistance to UV oxidation of some compounds producedby phytoplankton, rather than by less than optimum efficiencyof the UV unit used, standards must be based on naturally occurringcompounds, rather than the pure compounds normally used. 相似文献