Definition of bacteria:
Bacteria are single-celled microscopic organisms discovered by Leeuwenhoek in 1676 through his microscope. He first called them animalcules. Bacteria are prokaryotic microbes and, therefore, have no nucleus or membrane bound organelles. They have simple cell structure and varied in shape.They are huge in number approximately 5×1030 on earth.
Bacteria are sometimes maligned because of human and animal disease like Leptospira, that causes serious disease in livestock. However, several bacteria, the actinomycetes, produce antibiotics such as streptomycin and nocardicin; others live symbiotically in the guts of animals or elsewhere within their bodies, or on the roots of certain plants, converting nitrogen in a usable form. Bacteria help to break down dead organic matter, bacteria make up the base of the food web in numerous environments. Bacteria are of such immense importance for their extreme flexibility, ability to rapid growth and reproduction, and great age - the oldest fossils were known, nearly 3.5 billion years old, are fossils of bacteria-like microorganisms.
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