Plasmid inheritability and biomass production: comparison between free and immobilized cell cultures of Escherichia coli BZ18(pTG201) without selection pressure

Abstract

Maintenance of the plasmid pTG201 in Escherichia coli BZ18 was studied for both free and immobilized cells during chemostat culture, in the absence of the antibiotic against which resistance was plasmid encoded. Electron microscopic observations of immobilized proliferant cells within carrageenan gel beads showed high cell concentrations and growth into distinct cavities. The plasmid which coded for the catechol 2,3-dioxygenase activity was stably maintained during 80 generations in the case of immobilized cells. A theoretical analysis founded on the compartmentalization resulting from the immobilized growth conditions was described. However, the model still showed a plasmid stability inferior to that determined experimentally. Hypotheses dealing with physiological changes of immobilized cells were presented. In addition, the high cell concentrations obtained in the outer 50 microns of the carrageenan gel beads gave a biomass productivity within this useful volume which was 20 times higher than in free-cell cultures.

Improvement in segregational stability of recombinant plasmids by retransformation of E. coli host cells

“…, cell immobilization (de Taxis du Poet et al, 1986), and insertion of the par (Meacock and Cohen, 1980) and cer (Summers and Sherratt, 1984) sequences into plasmids.…”

Production of alkaline phosphatase by immobilized growing cells of Escherichia coli excretory mutants

“…Total AP activity As already described for immobilized cell cultures (De Taxis du PoEt et al 1986;Nasri et al 1987), cells principally grew in the outer 100 ~tm of gel beads for a limited number of generations before the clone escaped from the matrix. Cell leakage occurred after 5-6 h of growth and a steady state was achieved after 10-12 h of culture.…”

“…This medium was supplemented with 0.1 M KCI to ensure mechanical stability of the gel beads. Continuous cultures were carried out in a small chemostat described previously (De Taxis du PoEt et al 1986), which was modified in order to withdraw samples of the beads. Chemostat growth conditions were: 40 ml working volume, air supply rate of 170 ml/min and temperature control at 37 ° C. For free cell cultures, 1 ml preculture (10 9 cells) was transferred to the chemostat and after growth in batch mode for 4 h, the flow of fresh medium was initiated.…”

Evidence that enzymes of a novel aerobic 2‐amino‐benzoate metabolism in denitrifying Pseudomonas are coded on a small plasmid

“…The data suggest that the average copy number changes depending on the growth conditions rather than the number of plasmid-bearing individuals since we were unable to isolate plasmid-less clones; however, this point needs further investigation. In E. coli the copy number of certain plasmids, even under selective conditions, may change depending on the growth rate, the medium composition, the oxygen supply and other factors [33].…”