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6.2.2.3. Bacteria Physiology

Nutrition functions

Bacteria can have different types of nutrition, since they can carry out all types of metabolism. Thus, bacteria can be:

  • Photoautotrophs.
  • Photoheterotrophs.
  • Chemoautotrophs.
  • Chemoheterotrophs.

Relationship functions

Many bacteria can move by creeping, with contraction and dilation movements , or by the movement of their flagella.

They respond to environmental stimuli, such as light (phototactic photosynthetic bacteria) and chemicals (chemotacticism).

When environmental conditions are adverse, the bacterium's response consists of the formation of spores, where they reduce their metabolism, resisting temperatures of up to 80 ºC, periods of water shortage, toxic substances, etc. that would end his life. When conditions are favorable again, the spores germinate and the bacteria can already carry out their functions.

Reproduction functions

Bacterial reproduction is asexualDNA is duplicated and bipartition takes place, in which each daughter bacterium carries its identical DNA molecule.

The mesosomes are responsible for directing the DNA replication and create the membrane will separate the two daughter cells. In bacterial colonies, all bacteria are genetically the same.

In addition, bacteria have parasexual mechanisms with which they can exchange genetic material with other bacteria of their species or even others. These processes are:

Conjugation

The conjugation process occurs when a donor bacterium transmits DNA, through the pili, to another recipient bacterium.

There are two types of donor bacteria: F+ and Hfr (of the English high frequency of recombination or high frequency of recombination). The receptor bacteria are the -.

Donor bacteria have plasmids, small DNA molecules that they can transmit by conjugation, called F factors or episomes.

The F+ bacteria have a free episome in the hyaloplasm, transferring only the F factor, which does not recombine with their DNA, to the recipient bacteria. This bacterium transforms into F+.

The bacteria Hfr have episome included in the DNA of the bacterial chromosome. Before conjugation, they have to duplicate their DNA, including the factor F. They transfer a copy of DNA that will recombine with the DNA of the recipient bacteria.

By Asignatura de Microbiología (Odontología) de la Universidad de Oviedo (España) [CC BY-SA 2.5], via Wikimedia Commons

Transduction

In transduction, genetic exchange also occurs, but the intervention of a transmitting agent, a bacteriophage virus, is necessary, which provides DNA fragments from the last bacterium that has parasitized.

The genetic material of the virus is integrated into the chromosome of the donor bacteria, and it follows a lysogenic cycle. When a lytic cycle begins, it will separate from the bacterial DNA but will carry some genes that it will pass on to the recipient bacteria.

By Asignatura de Microbiología (Odontología) de la Universidad de Oviedo (España) [CC BY-SA 2.5], via Wikimedia Commons

Transformation

In the transformation process, the bacterium introduces DNA fragments from the lysis of other bacteria.

These parasexual mechanisms, in which genetic exchange occurs between bacteria, allow bacteria to become resistant to antibiotics, as some pathogenic bacteria coexist with symbiotic bacteria that resist them.

By Asignatura de Microbiología (Odontología) de la Universidad de Oviedo (España) [CC BY-SA 2.5], via Wikimedia Commons

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Canarias, July 2010, question 9

Nutrition is one of the processes that define all living things. Bacteria are especially versatile when it comes to nutrition.

a.- Name the different nutritional processes that occur in bacteria, both in terms of the carbon source and the energy source.
b.- Another vital function is reproduction. What type of reproduction do bacteria have?
c.- Where is the genome in bacteria?

Extremadura, June 2019, option A, question 4

A. Name and briefly describe the mechanisms of gene exchange or transfer that can occur between bacteria. (1.5 points)
B. Habitual microbiota (normal flora) of the human body. Concept. Functions. (0.5 pts)

Canary Islands, June 2021, question 18

18. An artist exhibits bacterial cultures on paper money to raise awareness about biological processes and denounce world conflicts. The fact that a bacterium consumed the figure of the Queen of England or that of George Washington printed on a banknote was what most surprised and inspired Ken Rinaldo. (Source: Elpais.com)

a. Indicates where the bacterial genome is located.
b. It indicates what type of biomolecules the plasmids present in many bacterial types are made up.
c. What type of reproduction do bacteria have?
d. What do bacterial transformation and transduction have in common?

Galicia, July 2021, question 8b

With respect to bacteria, what is the mechanism of gene transfer called transduction?