Bacteria

Bacteria

• Bacterial Structure Function :
• Plasmid : Ring of DNA
• Capsule : Protective covering made up of polysaccharides (complex sugars). Keeps the bacteria from drying out and protect it from being engulfed by larger microorganism.
• Cell Wall : Gives cell its shape and surrounds the cytoplasm protecting it from the environment.
• Plasma Membrane : A layer of phospholipids and proteins, which allows certain materials in and out of the cell
• Ribosomes : Only type of cell organelle found in bacteria.
• Small factories : that translate the genetic code into proteins.
• Fimbriae : Small hair like projections that emerge from the cell membrane. These help the bacteria attach to their host.
• Cytoplasm : Or protoplasm. This is where the functions of cell growth, cellular metabolism and replication are carried out. It is a gel like material that is composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as the ribosomes, chromosomes, and plasmids.
• Nucleoid : A region of the cytoplasm where the chromosomal DNA is located.
• Flagella : Hair like structures that provide locomotion. Not all bacteria have flagella.

• Classification of Bacteria: Bacteria are mainly classified into phylums (phylum is a scientific classification of organisms). For simplification, bacteria can be grouped into the following groups: Bacteria classification based on shapes: As already mentioned, before the advent of DNA sequencing, bacteria were classified based on their shapes and biochemical properties. Most of the bacteria belong to three main shapes: rod (rod shaped bacteria are called bacilli), sphere (sphere shaped bacteria are called cocci) and spiral (spiral shaped bacteria are called spirilla). Some bacteria belong to different shapes, which are more complex than the above mentioned shapes. Aerobic and anaerobic bacteria: Bacteria are also classified based on the requirement of oxygen for their survival. Bacteria those need oxygen for their survival are called Aerobic bacteria and bacteria those do not require oxygen for survival. Anaerobic bacteria cannot bear oxygen and may die if kept in oxygenated environment (anaerobic bacteria are found in places like under the surface of earth, deep ocean, and bacteria which live in some medium). Gram Positive and Gram Negative bacteria: Bacteria are grouped as ‘Gram Positive’ bacteria and ‘Gram Negative’ bacteria, which is based on the results of Gram Staining Method (in which, an agent is used to bind to the cell wall of the bacteria) on bacteria. Autotrophic and heterotrophic bacteria: This is one of the most important classification types as it takes into account the most important aspect of bacteria growth and reproduction. Autotrophic bacteria (also known as autotrophs) obtain the carbon it requires from carbon-dioxide. Some autotrophs directly use sun-light in order to produce sugar from carbon-dioxide whereas other depend on various chemical reactions. Heterotrophic bacteria obtain carob and/or sugar from the environment they are in (for example, the living cells or organism they are in). Classification based on Phyla: Based on the morphology, DNA sequencing, conditions required and biochemistry, scientists have classified bacteria into phyla: 1) Aquificae 2) Xenobacteria 3) Fibrobacter 4) Bacteroids 5) Firmicutes 6) Planctomycetes 7) Chrysogenetic 8) Cyanobacteria 9) Thermomicrobia 10) Chlorobia 11) Proteobacteria 12) Spirochaetes 13) Flavobacteria 14) Fusobacteria 15) Verrucomicrobia

• Reproduction of Bacteria :

• Binary Fission Bacteria reproduce by a way of asexual reproduction called binary fission. In one bacterium, the single circular chromosome duplicates. Then, the two resulting chromosomes attach to the inside of the plasma membrane. The cell elongates and separates into two strands. Finally, the cell membrane grows inward, the cell wall forms separating two daughter cells each with a chromosome.

• Exchange of genetic material.
Bacteria also reproduce with the exchange of DNA. When bacteria exchange DNA, it has a similar effect to sexual reproduction, in that, there is a blending of genes between two organisms. There are three was in which bacteria exchange DNA.
• Conjugation – male cell passes DNA to female cell by means of a conjugation tube (sex pilus).
• Transformation – bacterium takes up DNA released by dead bacteria.
• Transduction – bacteriophages carry DNA from one cell to another.

• The importance of bacteria to humans:

• Bacteria in food :

• Milk from a healthy cow initially contains very few bacteria, which primarily come from the skin of the cow and the procedures for handling the milk. Milk is an excellent growth medium for numerous bacteria, and the bacteria can increase rapidly in numbers unless the milk is properly processed. Bacterial growth can spoil the milk or even pose a serious health hazard if pathogenic bacteria are present. Diseases that can be transmitted from an infected cow include tuberculosis (Mycobacterium tuberculosis), undulant fever (Brucella abortus), and Q fever (Coxiella burnetii). In addition, typhoid fever (Salmonella typhi) can be transmitted through milk from an infected milk handler. Pasteurization procedures increase the temperature of the milk to 63 °C (145 °F) for 30 minutes or to 71 °C (160 °F) for 15 seconds, which kills any of the pathogenic bacteria that might be present, although these procedures do not kill all microorganisms.

• Certain bacteria convert milk into useful dairy products, such as buttermilk, yogurt, and cheese. Commercially cultured buttermilk is prepared from skim milk inoculated with a starter culture of Streptococcus lactis or S. cremoris, together with Leuconostoc citrovorum or L. dextranicum. The combined action of Streptococcus and Leuconostoc consumes the milk sugar, produces lactic acid, and precipitates milk protein (casein). Yogurt and other fermented milk products are produced in a similar manner using different cultures of bacteria. Many cheeses are likewise made through the action of bacteria. Growth in milk of an acid-producing bacterium such as S. lactis causes the casein to precipitate as curd. Following the removal of moisture and the addition of salt, the curd is allowed to ripen through the action of other microorganisms. Lactobacilli, streptococci, and propionibacteria are important for the ripening of Swiss cheese and the production of its characteristic taste and large gas bubbles. In addition, Brevibacterium linens is responsible for the flavour of Limburger cheese, and molds (Penicillium species) are used in the manufacture of Roquefort and Camembert cheeses. Other types of bacteria have long been used in the preparation and preservation of various foods produced through bacterial fermentation, including pickled products, sauerkraut, and olives.
  
• The toxins of many pathogenic bacteria that are transmitted in foods can cause food poisoning when ingested. These include a toxin produced by Staphylococcus aureus, which causes a rapid, severe, but limited gastrointestinal distress, or the toxin of Clostridium botulinum, which is often lethal. Production of botulism toxin can occur in canned nonacidic foods that have been incompletely cooked before sealing. C. botulinum forms heat-resistant spores that can germinate into vegetative bacterial cells that thrive in the anaerobic environment, which is conducive to the production of their extremely potent toxin. Other food-borne infections are actually transmitted from an infected food handler, including typhoid fever, salmonellosis (Salmonella species), and shigellosis (Shigella dysenteriae).

• Substances contributing to the virulence of pathogenic bacteriasubstanceactionhyaluronidaseincreases permeability of tissue spaces to bacterial cellscoagulaseincreases resistance of bacteria to phagocytosis (engulfment by defense cells, or phagocytes)hemolysinsdestroy red blood cellscollagenasedissolves collagen, a connective tissue proteinleucocidinkills white blood cells (specifically leucocytes) and hence decreases phagocytic actionexotoxins and endotoxinsinterfere with normal metabolic processes.

By: Mia Nugraha (Edited from Biology grade X)