– they have both beneficial and harmful effects in the life of man
– bacteria like Rhizobium species symbiotically fix atmospheric nitrogen into soils
– free living N-fixing bacteria include Clostridiums and Azotobacter
– Bacteria decomposes dead organic matter
– All these processes enhance soil fertility
– thus increase agricultural productivity
– some bacteria live in mammalian intestines
– helps in the manufacture of certain vitamins, antibiotics and enzymes
– others help in digestion of cellulose in the intestines of ruminants
– useful in the manufacture of organic acids such as acetic acid
– useful in curring of tea and tobacco leaves
– useful in retting of fibers
– some bacteria are useful in sewage disposal
– useful in decomposition of/breakdown of oil spill
– certain bacteria are used in butter and cheese making
– useful as research materials/tools
– many bacteria and all viruses are harmful
– causes disease of plants, man and other animals e.g cassava mosaic, typhoid, HIV