Intriguing Microbiology

Tomorrow is my Microbiology practical examination and as I leaf through pages of MICROBIOLOGY by Tortora, Funke and Case, some questions repeatedly drift my mind to pleasurable confusion.

Microbiology is central to the study of life as life (the definition varies with your perception) originally arose from microbes. A lot of our genome, both functional and idle, was acquired as endosymbionts conquered prokaryotes to give rise to eukaryotes. Appearance of cyanobacteria was a critical event in the history of life as it facilitated the increase in atmospheric oxygen from negligible to the current levels, 21%, within a few million years.

Microbiomes of soil, water, air and that within us work in tandem to ensure proper cycling of essential elements like carbon, nitrogen, oxygen, phosphorus etc. The fate of the two world wars was shaped by microbiologists, with the first giving Israel and the second, penicillin. The “ancient” biotechnology benefitted from the then unrecognised microbes at work and the “modern” biotechnology is driven through discoveries made in the characterised microbes.

The following are the questions that are intriguing me. The questions are basic and may seem as much as evolutionary as they are microbiological.


Microbial colonies are reported to grow as a unit. In colonies, the cells have been shown to interact and exhibit multicellular organisation. Also, most microbes reproduce by asexual means wherein variations are rare and the whole colony can be said to be clones of the original cell.

In such case, is it right to say that a microbial cell is immortal and is it the colony which is the individual being? Or, each microbe is an individual in self?

Quorum sensing?

It refers to alteration of gene expression in bacterial cells depending on the cell density in the bacterial colony. What are the minimum conditions for quorum sensing to initiate? Why would quorum sensing evolve at the first place, if evolution is not gene-centric?

I think Richard Dawkin’s concept of evolution at the replicator (genes) level, rather than at the individual level, is an answer. Why, or why not, it could be so?

Bonnie Bassler sheds some light on how bacteria talk in this TED video (bit old, posted April ‘09)

Sexual reproduction?

Most bacteria reproduce asexually. Asexual reproduction copies the genome with remarkable infidelity. The sexual reproduction has the critical advantage of producing variations. But, why did sexual reproduction ever arise given the advantage the replicators had in the absence of variations?

Variations guarantee that a number of mutants would exist in the population who would proliferate in case selective conditions arise. Selective pressures don’t produce mutations, but select them. Did the vigorously dynamic environmental conditions favour evolution of sexual reproduction? Or was there any other major factor/event?

Mechanism of prions?

Prion is a term for proteinaceous infectious protein associated with some neurodegenerative diseases such as the mad cow disease. How can a protein, with no solid evidence of genetic inheritance, misfold and turn so deadly? Why do they only cause neurodegenerative diseases?

Here is another TED talk (posted July’12) by Jonathan Eisen. Meet your microbes. Eisen’s work focuses on the origin of novelty, that is, how new processes and functions originate during evolution.



7 thoughts on “Intriguing Microbiology

  1. as pr my knowledge a microbe is an individual in itself since it prepares all sch proteins and biomolecules necessary fr its existence. and the cell-cell interaction (if any) does not play any sch role fr d individual existence of a cell that is d reason whn any prokaryote is engineered a single cell z taken nd not d whole colony….

    1. Studies have shown that in a colony, not all the individual cells manufacture all the proteins which indicates multicellular organisation.. explain lichens! they are 2 cells but one living individual.

      1. the “one-living individual” case fr lichen is bcoz dey won’t exist in each others absnce nd hence z beneficial fr only dm and fr any 3rd membr in d envirnmnt (only if u don’t consdr plants)….

          1. expression, is a cell’s response to the surroundings…you cannot expect an individual to behave same in two different situations. cells behave “heterogenously” as they hav enough supply of proteins from their neighbouring cells.
            though the colony seems to be microscopically small it may have different resources at different positions nd the cells will behave according to their immidiate surroundings.

            BTW Can u tell me what is the use of Bioluminicence in V. harveyi population??

  2. Bioluminescence ensures that no one eats V. harveyi. Anyone who eats their colony is then more susceptible to be eaten up as they are visible easily in the darkness of the bottom ocean. Plus, they were used for the particular experiment as in them the gene for luminescence is regulated by quorum sensing itself.

  3. bt d que stil remains as it is about individuality…..howevr we’ll b usng only dose microbes wch hv a successfl individual exstnce since as pr rDNA tchnq we’ll insrt a type of gene in jst one cell of a microbe nd dn will allow it to proliferate rahr dn intrdncng d gene in colony of cells………….

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