88 LABORATORY MANUAL OF MICROBIOLOGY 



C. Nitrogen-fixing bacteria and nitrogen fixation in soil : 



18. The isolation of bacteria from the root nodules of various leguminous 

 plants. 



19. Cultural characteristics of root-nodule bacteria. 



20. The formation of root nodules in agar and sand cultures. 



21. Artificial cultures for the inoculation of leguminous plants. 



22. The structure of root nodules of leguminous plants. 



23. Effect of root-nodule bacteria on the growth and the nitrogen content 

 of alfalfa. 



24. Direct method for demonstrating the occurrence of Azotobacter in 

 soil. 



25. Isolation of Azotobacter from various soils. 



26. Use of silica-gel plate for the isolation of specific bacteria. 



27. Nitrogen fixation by pure cultures of Azotobacter. 



28. Effect of variation in carbohydrates on the growth of Azotobacter. 



29. Anaerobic nitrogen fixation (Clostridium pasteurianum and related 

 organisms). Spore stain- Dorner modified). 



30. Isolation of anaerobic nitrogen-fixing organisms. 



31. Nitrogen-fixing capacity of soil (Winogradsky). 



32. Influence of nitrate on the fixation of nitrogen. 



33. Effect of a soluble carbohydrate on nitrogen assimilation. 



D. Denitrifying bacteria: 



34. Isolation of denitrifying bacteria. 



35. Denitrification by pure cultures of bacteria. 



36. Denitrification in soil. 



E. Nitrification experiments: 



37. Nitrification in impure cultures. 



38. Nitrification in liquid cultures (quantitative). 



39. Isolation of nitrifying organisms. 



40. Nitrification of various substances. 



F. Urea and protein decomposition: 



41. The decomposition of urea with the production of ammonia. 



42. Isolation of urea-decomposing organisms. 



43. Ammonia production from various substances in soil. 



44. Decomposition of an amino acid and a protein by Bac. cereus and 

 Bad. fluorescens. 



G. Sulphate-reducing and sulphur-oxidizing bacteria. 



45. Reduction of sulphates with the formation of hydrogen sulphide. 



46. Isolation of hydrogen sulphide-forming microorganisms. 



47. Crude cultures of higher sulphur bacteria. 



48. Oxidation of sulphur and the dissolving of rock phosphate. 



49. Isolation of pure cultures of higher sulphur bacteria. 



50. Growth and isolation of Thiobacillus thioparus. 



51. Growth of Thiobacillus thiooxidans in liquid medium. 

 H. Iron bacteria: 



52. Iron-precipitating bacteria. 



63. Iron bacteria from drinking water. 



