The bacteria which do not synthesize their own food but depend on other organisms or dead organic matter are called heterotrophic bacteria.
They depend upon other organisms (living/dead) for their food as they cannot synthesize their own food. They may be:
saprotrophic e.g (Bacillus subtilis),
parasitic e.g. Plant parasite-(Xanthomonas citrii)
animal parasite e.g.(Bacillusanthracis) ,
human parasite e.g (Vibrio cholerae) or
symbiotic in association with roots of the family Leguminosae. e.g. (Rhizobium)
Heterotrophic bacteria are most plentiful in nature.
The majority are responsible for the decomposition of organic matter.
Many of them have a very important impact on human affairs.
They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc.
Some are pathogens which causes damages to human beings, crops, farm animals and pets.
Cholera, typhoid, tetanus, citrus canker are well known diseases caused by different bacteria.