Introduction

Introduction to Microbiology

Microbiology is the study of microorganisms. Microorganisms are all single-celled microscopic organisms and include the viruses, which are microscopic but not cellular.

Microbial cells differ in a fundamental way from the cells of plants and animals in that microorganisms are independent entities that carry out their life processes independently of other cells. By contrast, plant and animal cells are unable to live alone in nature and instead exist only as parts of multicellular structures, such as the organ systems of animals or the leaves of plants.

One of the first things to realise about the microbial world is that microorganisms are everywhere. Almost every natural surface is colonized by microbes (including your skin). Some microorganisms can live quite happily in boiling hot springs, whereas others form complex microbial communities in frozen sea ice.

Most microorganisms are harmless to humans. You swallow millions of microbes every day with no ill effects. In fact, we are dependent on microbes to help us digest our food and to protect our bodies from pathogens. Microbes also keep the biosphere running by carrying out essential functions such as decomposition of dead animals and plants. Microbes are the dominant form of life on planet Earth. More than half the biomass on Earth consists of microorganisms, whereas animals constitute only 15% of the mass of living organisms on Earth.

Microbiology is about microbial cells and how they work, especially the bacteria, a very large group of very small cells that, collectively, have enormous basic and practical importance. Microbiology is about diversity and evolution of microbial cells, about how different kinds of microorganisms arose and why. It is also about what microorganisms do in the world at large, in soils and waters, in the human body, and in animals and plants. One way or another, microorganisms affect and support all other forms of life, and thus microbiology can be considered the most fundamental of the biological sciences.

In brief, the Microbiology deals with How and where they live? How they look like? How they derive food? How they reproduce? What are their relationships with plant and animals?

Microorganisms

The microorganisms can be divided into two distinct groups based on the nucleus structure:

Prokaryotes – The organism lacking true nucleus (membrane enclosed chromosome and nucleolus) and other organelles like mitochondria, golgi body, entoplasmic reticulum etc. are referred as Prokaryotes. (Ex : Bacteria, archaea)

Eukaryotes - The organism possessing membrane enclosed nucleus and other cell organelles are referred as Eukaryotes (Ex : algae, fungi, protozoa)

Microbial Cells

A basic tenet of biology is that the cell is the fundamental unit of life. A single cell is an entity isolated from other such entities by a membrane; many cells also have a cell wall outside the membrane. The membrane defines the compartment that is the cell, maintains the correct proportions of internal constituents, and prevents leakage, while the wall lends structural strength to the cell. But the fact that a cell is a compartment does not mean that it is a sealed compartment. Instead, the membrane is semipermeable and thus the cell is an open, dynamic structure. Cells can communicate, move about, and exchange materials with their environments, and so they are constantly undergoing change.

Properties of Cellular Life

All cells show some form of metabolism. That is, they take up nutrients from the environment and transform them into new cell materials and waste products. During these transformations, energy is conserved in a form that can be drawn upon by the cell to support the synthesis of key structures. Production of the new structures culminates in the division of the cell to form two cells. The metabolic capabilities of cells can differ dramatically, but the final result of any cell’s metabolic activities is to form two cells. In microbiology, we typically use the term growth, rather than “reproduction,” to refer to the increase in cell number from cell division.

All cells undergo evolution, the process of descent with modification in which genetic variants are selected based on their reproductive fitness. Evolution is typically a slow process but can occur rapidly in microbial cells when selective pressure is strong. For example, we can witness today the selection for antibiotic resistance in pathogenic (disease-causing) bacteria by the indiscriminate use of antibiotics in human and veterinary medicine.

Although all cells metabolize, grow, and evolve, the possession of other common properties varies from one species of cell to another. Many cells are capable of motility, typically by self propulsion. Motility allows cells to move away from danger or unfavourable conditions and to exploit new resources or opportunities.

Cells as Biochemical Catalysts and genetic entities

The routine activities of cells can be viewed in two ways. On one hand, cells can be viewed as biochemical catalysts, carrying out the chemical reactions that constitute metabolism. On the other hand, cells can be viewed as genetic coding devices, replicating DNA and then processing it to form the RNAs and proteins needed for maintenance and growth under the prevailing conditions. DNA processing includes two main events, the production of RNAs (transcription) and the production of proteins (translation). Cells coordinate their catalytic and genetic functions to support cell growth. In the events that lead up to cell division, all constituents in the cell double. This requires that a cell’s catalytic machinery, its enzymes, supply energy and precursors for the biosynthesis of all cell components, and that its entire complement of genes (its genome) replicates. The catalytic and genetic functions of the cell must therefore be highly coordinated.

The microorganisms were divided into 6 distinct groups based on the phylogenic, morphological and physiological characters.

The major groups of microorganisms are

Bacteria
Archaea (or Archaeobacteria)
Fungi
Algae
Protozoa
Viruses

1. Bacteria are phylogenetically related group of unicellar prokaryotic organisms distinct from archeae

2. Archaea are phylogenetically related group of prokaryotes which are primitive and distinct from bacteria

3. Fungi are group of eukaryotic organisms lack of chlorophyll. They range in size and shape from single celled yeast to multicellular mushrooms.

4. Algae refers the group of eukaryotic organisms with chlorophyll. They range in size and shape from single celled algae (Ex: Chlorella) to complex cellular structured plant like algae (Ex. Kelp)

5. Protozoa are group of eukaryotic organisms lack of cell wall. The morphology, nutrition and physiology is different from other groups

6. Viruses are group of non-cellular organisms, parasite or pathogen to plant, animals and other microorganisms. They are too small and cab be visualized only under electron microscopes

Necessary for Microbiology

The microorganisms are research tool to understand the chemical and physical basis of life
They are tool to analyze the biochemical and genetic background of living things
They are excellent model for understanding the cell functions
They play important role in the field of medicine, agriculture and industry

Branches of Microbiology

Medical Microbiology – deals with the microorganisms associated with human body; diseases; diagnostic procedures; preventive measures
Aquatic microbiology – deals with water purification; microbiological examination; biological degradation of wastes and ecology
Aeromicrobiology - deals with the microbes in air; contaminations; spoilage; dissemination of diseases
Food microbiology – deals with the microorganisms associated with foods; food borne pathogens; food spoilage; food preservation and food safety
Agricultural Microbiology – deals with plant associated microbes; soil fertility; plant and animal diseases; microbial degradation of organic matter; soil nutrients transformation
Industrial microbiology – deals with production of antibiotics and vaccines using microorganisms; fermentation and fermented products such as beverages, bread, milk products; production of protein and hormones by genetically modified organisms.
Exomicrobiology – Exploitation for life in outer space
Geochemical microbiology – Coal, gas and mineral formation; mineral recovery through microbes from ore (bioleaching)

Youtube vedio by Eric Row - Introduction to Microbiology

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