Bacterial Growth, Genetics, and Virulence

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Chapter 7

Bacterial Growth, Genetics, and Virulence

Proliferation of Bacterial Cells

Bacterial growth curve

Growth requirements

1. Overview

2. Oxygen requirement

3. Nutrient requirements

4. Temperature requirements

Cell division

Bacterial spores (endospores)

• Spores, formed by some gram-positive bacteria, represent a dormant state that is resistant to heat, drying, and chemicals.

1. Spore formation, a variant type of cell division, is induced by depletion of essential nutrients needed for normal growth.

2. Germination of spores into vegetative cells is initiated by damage to the spore coat by trauma, water, or aging and requires specific nutrients.

II Bacterial Genetics

• Important definitions are given in Table 7-1.

TABLE 7-1

Bacterial Genetics Terminology

Term Definition
Allele A particular example of a gene. Each variant of a given gene is a different allele of that gene. Genes that are represented by multiple alleles in a population are said to be polymorphic.
Cistron Region of DNA that codes for a single protein; a complementation unit
Operator Nucleotide sequence, located between the promoter and first structural gene of an operon, that binds a repressor protein
Operon Bacterial transcription unit comprising a promoter, operator, and one or more structural genes
Plasmid Small extrachromosomal DNA molecule capable of autonomous replication in bacteria
Promoter Nucleotide sequence in an operon that is recognized by RNA polymerase
Replicon Replication unit, consisting of a replication origin, a replication terminus, and the intervening coding sequence

Bacterial chromosome

1. Single, double-stranded, circular molecule of DNA, containing about 5 million base pairs (or 5000 kilobase pairs)

2. Operons provide coordinated control of protein-coding (structural) genes. A bacterial chromosome contains many operons.

• The enzymes in many bacterial metabolic pathways are encoded by polycistronic operons, which contain multiple structural genes.

• All the genes in a polycistronic operon are transcribed as a unit, producing a single messenger RNA (mRNA) that is translated into multiple proteins.

• Transcription of the lac operon and many other operons is controlled by presence or absence of metabolites to meet the needs of the cell (Fig. 7-2).

Other genetic elements

1. Plasmids

2. Bacteriophages

3. Transposons