Today I resuspended 2 ml "before" sample (=OD590 was about 0,5) in 50 ul of loading buffer and 2 ml "after" sample in 90 ul if I remember right. Then I centrifuged 15 min 13 000 g and loaded on gel about 20 ul of the supernatant. Bands weren't that strong - but the blue background caused difficulties. Should I load less and/or resuspend in larger volume? The background is perhaps because of DNA?
I would not do it like you did...just pellet the cells and resuspend them in SDS loading buffer. If it it still "gloopy" you can also add more loading buffer. Try it the way I wrote in the first comment...so far it always worked
I guess your "backround" is because you overload the....20 µl is too much. Do you destain your gel with water properly after Coomassie-staining?