DYNAMICS OF Pseudomonas aeruginosa AGGREGATE FORMATION ON APOPTOTIC CELLS

CELESTE DEA; MARÍA VICTORIA PEPE; FERNANDO PERUANI; ARLINET KIERBEL

virutal

Congreso; Congreso Conjunto SAIB-SAMIGE 2021; 2021

SAIB SAMIGE

The formation of bacterial multicellular structures (such as biofilms and biofilms-like aggregates) is an essential precursor of many infectious diseases. Bacteria within these structures are difficult to eliminate due to their tolerance to the immune system and antibiotics. Such is the case of cystic fibrosis (CF), where Pseudomonas aeruginosa ?an opportunistic pathogen ? forms bacterial aggregates in the lungs that lead to chronic infections, increasing the concomitant mortality of CF patients. Understanding the early steps of the formation of bacterial multicellular structures is critical for developing strategies against chronic infections. The emergence of bacterial aggregates involves the transition from a free-swimming to a multicellular and sessile state, but this transition is not well understood. Former studies suggest that irreversible adhesion of individual bacterial cells occurs first, and then the multicellular state is achieved. We have previously shown that P. aeruginosa attaches to monolayers of polarized epithelial cells mainly in the form of aggregates, on sites of apical extrusion of apoptotic cells. In the span of minutes, free-swimming bacteria are recruited on the surface of these apoptotic cells. Once the aggregates reach their final size, they remain stable for at least several hours. In time-lapse confocal experiments, we observed that free-swimming P. aeruginosa attaches to apoptotic cells for a period of time and then detaches and swims away. By tracking individual bacteria (using a plugin from the ImageJ software) we were able to establish the attachment and detachment times. Then we analyzed the distribution of dwelling times in wild-type bacteria and in two Type IV pili (T4P) mutants. T4P are multifunctional surface appendages that elongate and retract and can be important adhesins. Experimental data were used to establish a mathematical model. We concluded that aggregate formation occurs via a stochastic, two-step, reversible process involving transient adhesion mediated by fully functional-T4P. Thus, in our biotic model system, the emergence of permanent multicellular structures does not involve irreversible adhesion. To better describe the dynamics of aggregate formation, we are currently studying the frequency with which the different strains contact the apoptotic surface as well as their swimming capacity.