improper growth in LB

 hello i did mutation at 5 positions in my gene of interest.gene of interest is in pET23a  vector.mutated plasmid transformed in supercompetent cells XL-10 gold(stratagene).colony inoculated in 10ml luria broth.it is taking too much time to grow that is more than 25 hours even then turbidity was too less. when plasmid was isolated from that culture.everytime plasmid yield was poor. only open circular shown in agarose gel.i dit it around 6 times.same results came.antibiotic i used is fresh lot of carbenicillin