E. coli culture contamination - (Nov/19/2004 )
i am just wondering is souce of the contamination in my E. Coli culture. the big yellow cell clusters are around. those clusters could be distroied by votex and then the whole liquid turn to yellow. the miniprep give a abnormally big pellet but there are only very small amount DNA inside. OD 280 is also low and the ratio 260/280 is normal.
Sounds like Staphylococcus aureus to me. I'd streak your E.coli out, get a single white colony and start again. You may have preped a mixed E.coli / staph culture which would explain your low plasmid yeild.
yellow clusters might even be micrococcus contamination. it ur e.coli is recA u can screen by mutagenesis with uv and purify the colonies.