| Huanglong, well known for its unique depositional physiognomy and colorful travertine landscape, was chosen by UNESCO as a World Natural Heritage site in1992. The physical and hydrochemistry effects are believed to be the key causes for the formation of travertine landscape and biological factor also plays a role in the formation process. Based on the previous research, we found that the number of psychrophilic bacteria in Huanglong water was surprisingly high and the populations of culturable bacteria reached about106cfu/mL. As a result, they inevitably participate in the formation of travertine. In this study,2typical strains isolated from Huanglong water were used as the experimental strains. The extracellular matrix component including organic acids, amimo acids and polysaccharides obtained at stable phase were determined by high performance liquid chromatography(HPLC). By simulating the low-temperature sedimentary environments in Huanglong.water, we investigated the effects of extracellular matrix component, native cells and extracellular polymeric substances (EPS) on the calcium carbonate deposition process as well as the deposited products. And possible formation mechanism were suggested at the same time. Inductively coupled plasma(ICP), Scanning electron microscope(SEM), Fourier transform infrared spectroscopy(FT-IR)and X-ray diffraction(XRD) were used to characterize the morphology and polymorphs of CaCO3precipitation. The results will be of great significance in making clear the microbial factor in Huanglong travertine deposition and proposing protective measures to prevent the degradation of Huanglong travertine. The main results are list as follows:(1) By sequencing the16s rDNA of strains, the strain20-18and21-3were identified as Pseudomonas sp. The extracellular matrix component including organic acids, amimo acids and polysaccharides were determined by HPLC. The results showed that extracellular organic acids consisted of lactic acid, citric acid and succinic acid; extracellular amino acids consisted of histidine, tyrosine, valine, methionine, cysteine, phenylalanine and lysine; Glucose, ribose, rhamnose, glucuronic acid, galactose were the main components in the hydrolysate of extracellular polysaccharides. (2) The effects of2organic acids on the calcification kinetics, polymorphism and morphology of CaCO3were investigated. The results showed that organic acids inhibited the calcification to a certain extent. Rod-like calcite with a length of5-10μm in long-axis and3-5μm in short-axis were obtained in the presence of citric acid. High concentration of succinic acid (160mg·L-1) induced the formation of vaterite.(3) The effects of3amino acids on the calcification kinetics, polymorphism and morphology of CaCO3were investigated. The results showed that L-tyrosine, L-phenylalanine and L-cystine could induce the precipitation of CaCO3. Imperfect calcite rhombohedral were obtained in the presence of L-tyrosine and L-phenylalanine; L-cystine induced the synthesis of aragonite clusters.(4) The effects of2monosaccharide on the calcification kinetics, polymorphism and morphology of CaCO3were investigated. The results showed that glucose and ribose induced the calcification to a certain extent; High concentration of glucose (80,160mg·L-1) induced the formation of spindle-like and cluster-like aragonite.(5) The interactive effects of organic acids, amino acids and monosaccharide on the calcification kinetics, polymorphism and morphology of CaCO3were investigated. The results showed that the interactions between amino acids and monosaccharides induced the precipitation of CaCO3to a certain extent, while organic acids involved interactive systems inhibited the calcificationt. Amino acids-monosaccharides system induced the synthesis of cake-like aragonite, these cake-like structures might be stacked with ring-like crystals layer by layer.(6) The effects of EPS, native cells and cell secretions of strains on the calcification kinetics, polymorphism and morphology of CaCO3were investigated. The results showed that EPS solution and native cells weakly promoted the CaCO3precipitation. Conversely, EPS-free cells and cell secretions slightly inhibited the calcification. Spherical particles assembled by slices were obtained in the presence of native cells of strain20-18. Complex structure of ring-like crystal(5-10μm) and cubic crystal(5-20μm) were formed in EPS solution of strain21-3. These superlattice structures might be related to the adsorption and stability effects of the charged groups on cell surface, as well as the oriented assembly of amphiphilic molecules in EPS.In conclusion, Characteristic component, native cells and EPS of psychrophilic bacteria in Huanglong had multiple regulations on the calcium carbonate deposition process as well as the morphology and polymorphs of CaCO3precipitation. The promotion or inhibition of organic components will be of great importance in revealing the degradation reason of Huanglong travertine and proposing protection measures. The explanation of possible promation mechanism of morphology and polymorphs under the control of organic components revealed the participating role of microorganism in Huanglong travertine to a certain extent。... |
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