• Question: How do pathogens develop and get their characteristics if they are only one bacteria?

    Asked by to Hannah, Bethany on 19 Jun 2014. This question was also asked by .
    • Photo: Hannah Tanner

      Hannah Tanner answered on 19 Jun 2014:


      Good question. As you have correctly worked out, there’s not much development you can do if you are a single solitary bacterial cell.

      For a single celled bacteria genetic changes (mutations) can happen as it copies it’s DNA and divides. Sometimes the copy process makes mistakes, that leads to the daughter cell being different genetically.

      Some bacteria can take up little bits of DNA from other organisms from the environment they are in (called transformation). This DNA might get destroyed but sometimes it’s compatible with the cell and becomes part of it. If it encodes useful genes that help the bacterium survive it will be kept.

      Bacteria can also have a kind of sex (called conjugation) where they share bits of DNA between different cells. This also helps mix up the genes and create diversity.

      Viruses of bacteria can also help move bits of bacteria DNA as well as viral DNA from on bacterium to another (called transduction).

    • Photo: Bethany Dearlove

      Bethany Dearlove answered on 22 Jun 2014:


      This is a really great question! There are a number of way bacteria can diversify, allowing a single species to have many different characteristics such as resistance to different antibiotics.

      Mutation – A mutation is a change from one nucleotide base to a different one, for example C to T. If this falls into a part of the genome that codes for a protein, this might affect the shape of the protein, and how it works.

      Selection – Mutations that are beneficial (for example, a mutation conferring resistance against the antibiotic being used as treatment) will tend to increase in frequency in the population. Equally, mutations that are harmful are likely die before reproduction, therefore leaving fewer copies in the population, and over time these mutations will tend to be lost from the population. In microbes, one of the strongest sources of selective pressure is the host immune system.

      Genetic drift – This is the random amount of genetic change from one generation. It can cause the loss of good characteristics purely down to luck – for example, bacteria with a really awesome resistance gene but that didn’t get to reproduce because they all dried out first.

      Horizontal gene transfer – Horizontal gene transfer is the movement of genetic material from one bacterial cell to another, not through direct copying. This can happen in three ways:
      Transformation – uptake of DNA in the environment.
      Conjugation – transfer of circular DNA called plasmids via the pili.
      Transduction – transfer via a virus that only infects bacteria (known as a bacteriophage).
      Once the genetic material has entered the cell, it can be integrated into the genome so it can be copied when the cell next duplicates. Horizontal gene transfer is the mechanism through which antibiotic resistance can rapidly spread through a bacterial population.

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