Immunoblot detection of proteins released in free-soluble form by planktonic E. coli strain IHE3034, using polyclonal antisera raised against OmpA, GroEL, and CRP (lysis marker), respectively. Proteins released to PBS through the 20 nm filters of the inserts were collected after 6 h of incubation and a concentrated sample (denoted 1) equal to 0.75 ml filtrate was applied on the gels where indicated. Whole cell preparation samples (denoted 2; 10 μg protein each) of strain IHE3034 were loaded as controls where indicated. The sizes of the proteins (kDa) in the prestained molecular weight marker (M) are indicated. The reactive band corresponding to each protein is indicated with an arrow.