Differences in colony size of bacteria on agar plates

[SFSF]

Bacterial colonies will differ in size due to the metabolic differences because of different genomes. I would expect XDR colonies to be smaller because it takes a lot of energy to produce and maintain those XDR phenotypes (whether gene is chromosomal or plasmid etc). A DS strain has no such extra metabolic burden and will grow faster on non-selective media. Sometimes a gene will be somewhat toxic to the cell and slow down growth thus producing a slower-growing colony. Also, a marker may be gotten rid of and those cells which no longer have it will grow faster resulting in a petri plate of small and big colonies...and of course in general growth will be inhibited depending on how many other colonies are nearby.

[Jorge1907]

I doubt many recognized the codes for these strains that are in any case different clones. The question was asked after colonies of the same clone or strain.

[SFSF]

Charissa explained the strain names.

My last sentence gives the example of 2 different cases where the colonies are the same clone.

To expand-

Example 1: Clone contains a plasmid containing direct or inverted repeats like the 6 base pair repeat of the human telomer sequence. Lets say it has 200 repeats of the 6 bp sequence for a total of 1200 bp. Such repeats are "irritable" to E Coli and such sequences are frequently lost or reduced in size (even in cell lines engineered to tolerate such repeats like SURE) Cells containing plasmids with reduced or absent repeats will grow faster and can take over the population (due to less energy used to make repeats and/or less "toxicity" to the E coli cell). On an isolation streak plate then one can see 2 general sizes of colonies, especially if plating from a liquid prep.

Example 2: Simple crowding of colonies will reduce nutrients to all except colonies far away from the majority of colonies in the 1st and 2nd quadrants etc. So these isolated colonies will be bigger even though they are the same clone because they have greater nutritional resources to exploit.

Both conditions summarized in Example 1 and 2 can act at the same time. Usually though you can see a good example in the 3rd or 4th quadrant of an isolation streak plate where it will be easy to see that some colonies are small and some are large not because of nutrition but because of different metabolism due to different genomes.

[Jorge1907]

Example 1 is a pedantic contrivance and #2 is obtuse - we all recognize minor differences of that nature - growth in 3rd and 4th quadrant will also differ from confluent growth in 1st.

[SFSF]

Don't be embarrassed when you don't understand something Jorge. Its a learning opportunity.

[Jorge1907]

Good to offer the insult when you've lost the point. Nice dancing but glad you admit you lost.

[Jorge1907]

Pity the poor pedant neither understand the term "clone" nor read the request for perspective re. major differences in colonies.

[admin]

Thank you both for the discussions here, I think both of you had good points but the original topic was split into two questions making it confusing for everyone.

I remind Charisa to post a question in a new topic, not hijack an original question/topic.

thank you for your understanding

[Jorge1907]

Thanks admin. The other poster referred to genetic change (so no longer the same clone) establishing the mentioned "major" change in colony morphology - see the classic work with smooth and rough pneumococci ([Only registered users see links. ] ). Much more complex is the "sectoring" of fungal colonies where pie-shaped sections of mycelial colony can appear substantially different - these can result from frank genetic change or mechanisms arguablly of the same clone such as "phenotypic switching" or heterokaryon formation ([Only registered users see links. ]) .