Abstract
Using optical tweezers the motility of a single outer membrane protein in E. coli bacteria, the λ-receptor, was studied. The λ-receptor is a porin that transports nutrients (maltodextrins) across the bacterial membrane. By poisoning the cells with arsenate and azide the bacterial metabolism was stopped. The motility of the exact same λ-receptor was measured before and after energy depletion. After energy depletion there was a significant decrease in the spread of positions visited. We have thus established that there is a difference in the movement of membrane proteins in living and dead cells. The active component of the motion of the λ-receptor in living cells has been modeled as an artificial temperature, which estimates the energy necessary for this active motion. The influence of antimicrobial peptides (AMPs) on the outer membrane of bacteria was investigated using the mobility of the λ-receptor as a membrane marker. With the growing resistance to antibiotics AMPs are gaining increased interested. Using the AMPs polymyxin B (PMB), and the non toxic derivate polymyxin B nonapeptide (PMBN), we have investigated the influence of AMPs on the outer bacterial membrane. Cells exposed to PMB showed a decrease in the spread of position visited by the λ-receptor upon poisoning. PMBN is known to increase the permeability of the outer membrane with out killing the cells. Exposure to PMBN did, however, not influence the mobility of the λ-receptor.
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