Lysogenic phages have more turbid plaques and they look cloudy rather than a complete clearing in the agar, but it varies between different phages, between very turbid (almost invisible) plaques, to almost clear plaques.

Here, you can see plaque produced by lytic somatic coliphages.

My one is this. Can anyone let me know whether they are lytic or lysogenic phages?

Something you can try to do... touch a loop or toothpick to the centre of the plaque and streak out the bacteria... from a lytic plaque you should get few colonies, but from a lysogenic phage you will get many. If you take individual isolates from the streak plate, and streak across a line of the same phage on a second plate, some of the streaks should grow before and after crossing the phage line, whereas others will only grow before and will be killed by the phage line. This is because a bacterial lysogen will be resistant to superinfection by its own prophage. You can look up a protocol for this - it's called cross-streaking.

All of the phages I work with are lysogenic and look very similar to yours. But I work with a collection of over 100 Pseudomonas phages and there is quite a lot of variability in the way they look.

I mainly work with lytic phages (somatic coliphages or F-specific RNA phages), and your plaques are very similar of that produced by a lytic phages, especially the F-RNA phages (small clear plaques).

For this phage, It happened like this. In the liquid culture of its host, this phage inhibits the growth of the host quite fast, Just after 3 hours of incubation and you can clearly see lysis in culture tube (bacterial cell debris, clear culture broth). But in the end (overnight incubation), culture tube show re-growth of its host (turbis culture broth).

Probably you could streak some cells from the overnight grown broth. Pick up a few colonies and grow them again in whatever culture broth you are using and do an ultraviolet induction. If the cells that you streaked originally contained a prophage, you should observe cell lysis in some time.

To know if these are lytic or temperate phages you can take the single plaques, make more lysates with these until you get a lawn of complete lysis. When you see that there are colonies growing in this lawn, they can be phage resistant mutants or lysogens. You can purifiy these colonies and check if they carry the phage by a marker (if you have) or by a phage specific PCR. You can also try to induce these colonies again and to see if these generate new phages by üplaque formation. I hope this was useful

kind regards

I suppose you have noc contaminants. so in this case your nice looking colonies are either lysogens or phage resistant by another mutation (for example receptor lossed). For testing this you have to streak out single colonies from the lysis plate to isolate pure cultures. Then, you induce these again. If you generate phages with a given colony/culture than it is a lysogen yielding viable phages. If not it can be resitant or a lysogen carrying a defective phage. You can screen you colonies with a phage specific PCR (if you have) to see if you have some of these colonies transduced with the phage.

Thanks Professor Lothar Beutin, It is a great honor for me to hear your comment. I know that you are extremely expertise in Shiga toxin producing Escherichia coli researches and must say that the bacterial host used in this my pic was STEC O26. It means that I surely will have shiga toxin bacteriophages if induce these colonies. Am I right ? Best regards

If you use wildtype O26 as a host you might certainly have prophages in this strain. So, before testing your colonies for lysogeny you should test if you can induce phages from your recipient O26 strain you have used for your experiment. Otherwise, you may get confused as it is not clear if phages are generate by lysogenization or were present already in this strain. I think the most clearest answer would be a PCR for your phage. This should be negative with the recipient strain and positive with a least some of the colonies you have obtained after lysogenization. Best regards

Lothar Beutin

Thank you Prof Lothar Beutin, If a PCR assay is the best choice for this situation so which gene(s) should I focus on? would you mind to recommend me some critical ones or even better, some PCR primer sequences ?. Best regards

It depends what kind of phage you have. If you have no idea about its genes than its difficult. In this case it would be good to have some sequencing first. Or you make a gene probe from a fragment of the phage DNA and do colony hybridization.