Microscopiclife:From chaos to classification

Microorganisms constitute a very antique group of living organisms which appeared on the Earth's surface almost 3000 million years ago.

- TAPAN KUMAR MAITRA

The questions arising from the study of the origin and evolution of microorganisms are extremely complex. Some scientists assumed that microbes were the first living organisms on Earth.Others maintained that non-cellular forms of living matter (photobionts, protobionts, etc.) appeared prior to the microbes. It is now generally believed that organisms evolved along the following lines: viruses containing RNA, viruses containing DNA, mycoplasmas, chlamydias, rickettsiae, bacteria, blue-green algae, lower and higher fungi, plants, and animals.

Medical microbiology is mainly concerned with the study of pathogenic bacteria, actinomycetes, spirochaetes, rickettsiae, viruses, fungi, and common protozoa, all grouped under the name of microbes or microorganisms.

The great majority of microbes are invisible to the naked eye. They comprise multicellular organisms (the blue-green algae, some fungi and chlamydobacteria, possibly some corynebacteria, mycobacteria, cocci), unicellular organisms (bacteria, actinomycetes, spirochaetes, and protozoa), and non-cellular organisms (viruses).

The great Swedish naturalist C. Linnaeus, who had never used a microscope, was unable to identify the numerous and diverse forms in the minute world of microorganisms, and classified all the microbes into one genus, which he originally named Chaos.

The first attempts to classify microorganisms were based solely on morphological properties. The Danish naturalist O. Miiller (1786) subdivided the bacteria into two genera, Monas and Vibrio.

In 1827, the Russian zoologist A. Lovetsky, while studying different organisms, identified three genera of microbes: Bacillus, Vibrio, and Proteus, and described a number of other bacteria.

In 1838, the German scientist C. Ehrenberg subdivided the microorganisms into bacteria, vibrios, spirilla, and spirochaetes.