Microbial mats in two hot springs in South China were sampled for the research of mineralization of microbes and its mechanism by the methods of geology and modern biology. The results show that hot spring microbes have the key capability for enrichment of Si, Al, Fe, Ca and other elements, and the microbes are also crucial for the formation of SiO2, CaCO3, clay and so on. The extracellular polymeric substances (EPS) play important roles in the process of mineralization of hot spring microbes, which mainly takes place in the layer of EPS outside cell wall or sheath of cyanobacteria. The sheath outside cell wall, which keeps the normal metabolism of cyanobacteria during the process of mineralization on its surface, is also considerable for the biomineralization of cyanobacteria. According to structure and mineralization characteristics of two microbial mats, the process of mineralization can be divided into three stages, namely, early surface mineralization, middle degradation mineralization, and late des- quamation of mineral. The above conclusions are significant for comprehension of the process of mineralization, the process of deposition and the preservation of microfossil in modern and ancient extreme environments.
PENG XiaoTong ZHOU HuaiYang WU ZhiJun JIANG Lei TANG Song YAO HuiQiang
Microbial mats are ecosystems that can control or induce the precipitation of calcium（Ca） carbonate on Earth through geological time.In the present study,we report on a novel accumulation of Ca,together with iron（Fe）,in a microbial mat collected from a slight acidic hot spring（pH=5.9） in south China.Combining an array of approaches,including environmental scanning electron microscopy,X-ray microanalysis,transmission electron microscopy,and selected area electron diffraction,we provide ultrastructral evidence for amorphous acicular aggregates containing Ca and Fe associated with cyanobacteria precipitating in the microbial mats.Cyanobacterial photosynthesis and exopolymeric organic matrixes are considered to be responsible for the precipitation of Ca.These amorphous acicular aggregates might imply the early stage of calcification occurring in microbial mats.Ca and Fe coprecipitation indicates another potential important way of inorganic element precipitation in hot spring microbial mats.Our results provide insight into the possible mechanism of cyanobacterial calcification and microfossil preservation in slight acidic hot spring environments.
PENG Xiaotong ZHOU Huaiyang YAO Huiqiang, LI Jiangtao WU Zijun
This paper deals with the bio-oxidation of galena particles （-80 meshes） using Acidithiobacillus ferrooxidans and compares it with Fe^3＋ oxidation. Experimental results show that, at least, 0.00197 mol galena was leached from lOOmL pulp （density of 3.8%） with 39 days＇ bio-oxidation, as compared to 0.00329 mol galena by Fe^3＋ with 9 days＇ oxidation. Because Fe^3＋ was constantly consumed, leaching by Fe^3＋ almost stopped after 9 days. Large amounts of lead sulfate were detected in both bio-oxidation and Fe^3＋ oxidation of galena. A. ferrooxidans followed a unique growth pattern during the bio-oxidation of galena. In the initial 15 days, the bacteria attached themselves to the galena surface with the formation of erosion pits similar in shape and length to those of the bacteria, and there were hardly any bacteria suspended in the solution. After 15 days, suspended bacteria increased. It is thus suggested that A. ferrooxidans may directly oxidize galena.
Microbial mats, several millimeters thick and brown-yellow to white in color, were collected in hollow inside of chimney structure from Edmond hydrothermal field on the Central Indian Ridge. Microbes with shapes of rod and helical stalk-like filaments were observed in the microbial mats, and are com- monly characterized by their cells completely encrusted by thick mineralized layers, made up of large amounts of amorphous silica and minor amounts of iron oxides. Transmission Electron Microscope observation has demonstrated that the acicular Fe-bearing matter was not only heterogenously dis- tributed on the surface of the cell wall, but also deposited in the inside of cell, suggesting that bio-precipitation of Fe had occurred both on the surface and in the interior of cell. Microbial silicification was also commonly found in the mats. Silica usually precipitated homogeneously on the surface of the microbes and forms micro-laminated layers, which might be controlled by the inorganic process of precipitation in hydrothermal environment. The biomineralization phenomenon in the mi- crobial mats showed that the precipitation of Fe and Si was closely related to microbes in hydrothermal environment. Considering that hydrothermal activities provided required chemical elements for miner- alization, it is suggested that this biomineralization process also might be driven by hydrothermal ac- tivities at the sea floor to some extent.
Based on structural and mineralogical characteristics of four hydrothermal chimney samples collected by submersible Alvin, growth history and formation environment of hydro-thermal chimney at EPR 9―10°N are established. It is shown that there occur two types of hydrothermal chimney with different deposition environments at EPR 9―10°N according to dif-ferences in their shape, structure and mineral assemblage: type I chimney forms in an environ-ment with high temperature, low pH and strong reducing hydrothermal focus flow and type II chimney forms in a relatively low temperature, high pH and rich Zn hydrothermal environment. Growth of type I chimney begins with the formation of anhydrite. Subsequently deposition of Cu-Fe-Zn sulphide in various directions of chimneys decides the final structure of this type of chimney. According to observation and analysis of mineral assemblages, the formation process of type I chimney could be divided into three stages from early, middle to late. Changes of tem-perature and major chemical reaction type in the process of hydrothermal chimney formation are also deduced. Different from type I chimney, quenching crystalline of pyrite and/or crystalline of sphalerite provide the growth foundation of type II chimney in the early stage of chimney forma-tion.
During DY105-17 cruise onboard the R/V "Da Yang Yi Hao" in 2005,methane concentrations in the wa-ter column above Logachev hydrothermal vent field were measured by applying stripping/trapping-gas chromatographic (GC) and the distinct methane plumes were detected. Results show that the back-ground methane concentration within the Logachev area is from 1.05 nmol/L to 1.68 nmol/L,signifi-cantly higher than the background level of the Atlantic abyssal plain of 0.4―0.5 nmol/L,suggesting that hydrothermal venting is a major source of dissolved methane to the ocean. The highest anomalies of methane concentrations in the water column range from 7.14 nmol/L to 113.9 nmol/L and occur just at 180―500 m above the seafloor. The distribution of methane concentration and the structural charac-teristics of hydrothermal plumes are strongly influenced by the supply of underlying hydrothermal fluids,the mixing process of ocean bottom currents and the microbial oxidation. Furthermore,the dif-ferences in distribution of methane plume between the station MAR-CTD3 and the other stations indi-cate a probable unknown hydrothermal vent site nearby. There occurs high concentration of methane along with temperature and nephelometry anomalies,which strongly confirms that the subtle meas-urement of methane concentration in water column is one of the effective ways to locate active sites of hydrothermal venting.
ZHOU HuaiYangWU ZiJunPENG XiaoTongJIANG LeiTANG Song
