After transformation of Dh5alpha cells by heat shock I grew them at 37 in 200microlitre Terrific Broth (because I had it at hand) and then before plating I found cloudy white ppt in the cell tubes. I still went ahead with the plating, but any idea what these could mean?
It is hard to tell from a single picture but my best guess would be that you had a lot of cell lysis and this is genomic DNA bound to membrane. Was the sample very thick and viscous? If so then that would confirm it.
I agree with Michael for Genomic DNA sticking together and with some degraded bacterial membrane after the heat shock. But, your bacteria looks like grew in the media since it looks cloudy. I assume you grew your bacteria at 30 degrees not at 37 degree before plating since they need to recover from the heat shock.
I agree with Michael Benedik. The clump most likely arises from lysed cells. As to proceeding with the cells after the heat shock before before plating, most protocols, including those described by commercial providers of competent cells, recommend leaving the cells for 5 min on ice after the heat shock followed by 1 h in broth at 37 °C.
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