BSC 314 Lecture Notes - Lecture 43: Saprotrophic Nutrition, Nitrification, Lichen
27 Jun 2018
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Reproduction
The principal mode of reproduction is an asexual separation of one bacterium into two.
There are, in addition, several mechanisms that make possible the exchange of genetic
material, the DNA, among and between bacterial cells. None, however, are as elaborate
as the mitosis—meiosis choreography of gene exchange in the eukaryotes.
Asexual
Three common types of asexual reproduction are present:
Binary fission(the most common): The “chromosome” replicates and the two
genomes move to opposite ends of the cell. The old cell walls then grow inward
between the two, pinching the cell apart—no mitosis, no microtubules. The whole
process is over within 30 minutes to three hours.
Fragmentation: This occurs when filaments of cells break into separate pieces
or fragments.
Budding: An outgrowth ( bud) pushes out from the cell, pinches off, and then
enlarges into a new cell.
Gene exchange
With no nuclei, there can be no sexual reproduction in the prokaryotes, but there is an
exchange of DNA. In one type, conjugation, conjugation (“sex”) pili(bridges of
cytoplasm) form between cells, and some DNA is passed from the donor to the recipient
cell.
In bacterial communities some DNA exists outside of cells, presumably left when the
cells die, or more probably, excreted into the environment by living cells. This “free”
DNA is picked up bacterial cells in another kind of gene exchange, transformation.
A third type of exchange— transduction—results when bacteriophages (special kinds
of viruses) bring into bacterial cells the DNA from their previous viral host.
(Researchers in biotechnologyuse the same method to introduce new genes into host
organisms.)
Mutation
Random changes in the DNA are common. These mutations of the genetic code alter
the response of the individual to its environment. If the mutation is deleterious, the
individual dies, but favorable mutations spread rapidly as the cells divide repeatedly and
often.
Prokaryote Metabolism
The prokaryotes are the most metabolically diverse of all organisms and have some
exotic ways to obtain and channel their needs. Organisms need carbon for building cells
and energy to fuel the process; eukaryotes, in general, all follow the same basic
metabolic pathways whereas prokaryotes use a variety of materials and pathways—
some employed by no other organisms. The terms for energy and carbon acquisition
are not standardized among biologists and microbiologists, and to make matters worse,
are inconsistently used concerning the separation of energy and carbon acquisition.
Table lists some basic terms frequently used by plant biologists.
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Document Summary
The principal mode of reproduction is an asexual separation of one bacterium into two. There are, in addition, several mechanisms that make possible the exchange of genetic material, the dna, among and between bacterial cells. None, however, are as elaborate as the mitosis meiosis choreography of gene exchange in the eukaryotes. Three common types of asexual reproduction are present: Binary fission(the most common): the chromosome replicates and the two genomes move to opposite ends of the cell. The old cell walls then grow inward between the two, pinching the cell apart no mitosis, no microtubules. The whole process is over within 30 minutes to three hours. Fragmentation: this occurs when filaments of cells break into separate pieces or fragments. Budding: an outgrowth ( bud) pushes out from the cell, pinches off, and then enlarges into a new cell. With no nuclei, there can be no sexual reproduction in the prokaryotes, but there is an exchange of dna.
