The following are the answers or suggestions given according to my personal understanding:
First, the purpose of microscopic examination should be to familiarize you with the individual morphology and spore characteristics of Bacillus subtilis, which is the need for further strain classification and state identification.
Second, the purpose of physiological and biochemical experiments is the same as above, which should mainly identify the classification status of strains, or familiarize you with the process of strain identification. It does not rule out the need to study the specific function of this strain.
3. Colony morphology is an important basis for strain identification, but it is not a sufficient and necessary condition. If the taxonomic status of strains is strictly identified, it is necessary to adopt multiple classifications, analyze strains from multiple angles, and make comprehensive judgments by using various methods and technologies with different principles. There are three general steps:
1. Morphological identification: individual morphology, group morphology, Gram staining, basic structure, special structure, etc.
2. Molecular identification: pure bacterial DNA samples were extracted, amplified 16SrDNA and sequenced. The sequencing results were published on the NCBI website, and the first-class taxon of the genus was initially determined.
3. Physical and chemical analysis: identification characteristics such as utilization of carbon and nitrogen sources, enzyme production characteristics and metabolites. It should be tested according to the results of the previous two analyses and Berger's Handbook of Systematic Bacteriology. Generally, it is necessary to detect at least 20 physical and chemical indexes, many of which can reach more than 100. Generally, the first taxon of "species" can be identified.
If the above three steps still cannot determine the taxonomic status of the strain, further analysis is needed, such as DNA hybridization and chemical composition analysis. , if necessary, you can determine the entire sequence.
4. Physiology and biochemistry commonly used for bacteria identification include starch hydrolysis test, sugar fermentation test, methyl red (MR) test, vp test, gelatin liquefaction test and hydrogen sulfide production test. It is suggested to refer to Berger's Handbook of Systematic Bacteriology or Dong Xiuzhu's Handbook of Systematic Identification of Common Bacteria. In addition, for general teaching or confirmatory experiments, you can refer to the Handbook of General Microbiology Experiments.