Bacterial strains and culture
Bacterial strain E. coli JM109 and plasmid pUC19 were obtained
from Sangon Biotech (Shanghai, China). Plasmid vector pUC19 has
one ampR gene (ampicillin resistance gene) which encodes TEM-1
β-lactamase. A single colony of E. coli JM109 or ampicillin-resistant
JM109/pUC19 on a solid Luria-Bertani (LB) (10 g tryptone, 5 g yeast
extract, and 15 g agar per liter) agar plate was transferred to a
2 mL liquid LB culture medium without or with 100 μg/mL carbenicillin, respectively. The bacterial samples were cultured overnight in an incubator shaker at 37 °C and 220 rpm. Then 150 μL E.
coli JM109 or E. coli JM19/pUC109 were inoculated in 15 mL fresh
LB medium without or with 100 μg/mL carbenicillin, respectively.
The samples were grown at 37 °C and 220 rpm until the extinction
at 600 nm (OD600) reached 0.8–1.0 (∼3.5 h) to the mid log phase.
The E. coli samples were harvested by centrifugation at 10,000 rpm
for 5 min, resuspended in PBS with OD600 adjusted to 1.2
(concentration ∼1 109 cells/mL). The harvested bacterial samples
were stored at 4 °C and analyzed on the HSFCM within 24 h.