Prokaryotic organisms are that in which nucleus is primitive type and nuclear material is not enclosed within the nuclear membrane.
Bacteria are placed in the kingdom “Prokaryotae” because of the prokaryotic cellular organization of the members. However, extremely diverse groups of microorganisms differing in morphological, physiological and ecological properties are found within this kingdom. In the beginning, description and information of bacterial systematics or classification was being published in the comprehensive volumes of “Bergey’s Manual of Determinative Bacteriology” (1923, first edition). The 8 th edition of Bergey’s Manual, published in 1974 was the last of such comprehensive manual and from 1984 onwards it was renamed as “Bergey’s Manual of Systematic Bacteriology”. It is the most widely accepted and used reference document or book for classification and identification of bacteria. Begey’s manual consists of four separate volumes and each volume is further divided into different sections ( Ist Volume : 1-11 sections, IInd volume : 12-17 sections, III rd volume : 18-25 sections and Iv th volume: 26-33 sections. )