| The nanoscale surface analysis of microbial cells is an important research field of current microbiology. Using atomic force microscope (AFM), researchers can visualize the ultrastructure of microbial cell surface and their appendages, thus they can research microbial subtle modifications upon cell growth or treatment with drugs. Besides structural imaging, AFM can be used in the force spectroscopy mode to detect the nanomechanical property of the microbial cells.In this thesis, using AFM as the main technique, we carried out a series of microbiology researches:1. Establishing the method of capsular observation and detection of capsules under delinquent water.Previous work with AFM has revealed liquid-like substances surrounding the bacterial cells under ambient conditions, and these substances used to be considered bacterial capsules. However, recent advances have pointed out that these liquid-like structures are in fact deliquescent water instead of real bacterial capsules. Thus, identification of the real bacterial capsule under AFM remains elusive. Using the deep-sea bacteria Zunongwangia profunda SM-A87as the expetimental subject, we observed the real capsule structure, thus we established the method of capsular observation. What is more, we found that using the "ScanAsyst" imaging mode, the capsules could be detected even with deliquescent water covering the capsule. So we establish the technology of detecting the capsules under delinquent water. 2. The process of individual bacterial exopolysaccharide yield and capsular structure of Zunongwangia profunda SM-A87under different culture temperatureWe detected the growth and polysaccharide yield changes of Z. profunda SM-A87under10℃and30℃. And based on the AFM imaging technology for observing bacteria and capsule, we detected the capsular structure of the bacteria during different growth phage. We found that the bacteria can secret large quantity of polysaccharide under10℃When the bacteria reached the logarithmic phage, the capsule became thicker, and when the bacteria reached the stationary phage, the value of the capsule thickness reached the maximum When the culture temperature is30℃the majority of the bacteria are groth in a line, and most of the bacteria are in rod shape, the shape of the bacteria capsule is the sheet and net structure coexisted, and the polysaccharide yield of the bacteria is minimal3. The structure changes of the capsule polysaccharide under different incubation temperatureAfter separation and purification, we obtained the purified capsule polysaccharide from Z. profunda SM-A87(EPS-A87), and we captured the high resolution topographic images of them under different incubation temperatures. According to our observation, the polysaccharide aggregation happened for different level after incubated at different temperatures4. The surface structure and the mechanical changes of the bacteria during the interaction of the bacteria and antibiotic Trichokonin ⅥWe examined the interaction between Trichokonin Ⅵ, a peptaibol isolated from Trichoderma pseudokoningii SMF2, and Bacillus subtilis, a representative Gram-positive bacterium Trichokonin Ⅵ was effective against B. subtilis with a minimal inhibitory concentration of25mM Trichokonin Ⅵ exhibited a concentration-and time-dependent effect against B. subtilis, which was studied using AFM. The cell wall of B. subtilis collapsed and the roughness increased upon treatment with Trichokonin Ⅵ. Furthermore, the membrane permeabilization effect of Trichokonin Ⅵ on B. subtilis was monitored, and the results suggested that the leakage of intracellular materials was a possible mechanism of Trichokonin Ⅵ on B. suhlilis. |
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