Social Cooperativity of Bacteria during Reversible Surface Attachment in Young Biofilms: a Quantitative Comparison of Pseudomonas aeruginosa PA14 and PAO1

Abstract

What are bacteria doing during “reversible attachment,” the period of transient surface attachment when they initially engage a surface, besides attaching themselves to the surface? Can an attaching cell help any other cell attach? If so, does it help all cells or employ a more selective strategy to help either nearby cells (spatial neighbors) or its progeny (temporal neighbors)? Using community tracking methods at the single-cell resolution, we suggest answers to these questions based on how reversible attachment progresses during surface sensing for Pseudomonas aeruginosa strains PAO1 and PA14. Although PAO1 and PA14 exhibit similar trends of surface cell population increase, they show unanticipated differences when cells are considered at the lineage level and interpreted using the quantitative framework of an exactly solvable stochastic model. Reversible attachment comprises two regimes of behavior, processive and nonprocessive, corresponding to whether cells of the lineage stay on the surface long enough to divide, or not, before detaching. Stark differences between PAO1 and PA14 in the processive regime of reversible attachment suggest the existence of two surface colonization strategies. PAO1 lineages commit quickly to a surface compared to PA14 lineages, with early c-di-GMP-mediated exopolysaccharide (EPS) production that can facilitate the attachment of neighbors. PA14 lineages modulate their motility via cyclic AMP (cAMP) and retain memory of the surface so that their progeny are primed for improved subsequent surface attachment. Based on the findings of previous studies, we propose that the differences between PAO1 and PA14 are potentially rooted in downstream differences between Wsp-based and Pil-Chp-based surface-sensing systems, respectively. IMPORTANCE The initial pivotal phase of bacterial biofilm formation known as reversible attachment, where cells undergo a period of transient surface attachment, is at once universal and poorly understood. What is more, although we know that reversible attachment culminates ultimately in irreversible attachment, it is not clear how reversible attachment progresses phenotypically, as bacterial surface-sensing circuits fundamentally alter cellular behavior. We analyze diverse observed bacterial behavior one family at a time (defined as a full lineage of cells related to one another by division) using a unifying stochastic model and show that our findings lead to insights on the time evolution of reversible attachment and the social cooperative dimension of surface attachment in PAO1 and PA14 strains.

Smartphone-Based Whole-Cell Biosensor Platform Utilizing an Immobilization Approach on a Filter Membrane Disk for the Monitoring of Water Toxicants

“…These findings are supported by previously reported results that showed evidence for enhanced sensitivity in surface-bound E. coli strain AB725 as compared to suspended ones when tested with genotoxicant nalidixic acid [ 12 ]. The explanation behind this higher sensitivity might be the cooperativity between the immobilized bacteria cells, which maximizes the bioluminescence signal output when exposed to environmental toxicants [ 15 , 44 , 45 ]. It was previously reported that the transition of bacterial cells from a free-swimming state to adsorption on surfaces might lead to changes in their cellular responses as well as to cooperative behavior between the bacteria cells, due to the limitation of nutrients [ 44 ].…”

Blue‐light perception by epiphytic Pseudomonas syringae drives chemoreceptor expression, enabling efficient plant infection

“…Another of the blue‐light activated MCPs (PSPTO_1493) is homologous to the WspA chemoreceptor of P. aeruginosa and belongs to the Wsp chemosensory pathway. In P. aeruginosa PAO1, this pathway is involved in surface sensing, causing an increase in c‐di‐GMP levels that facilitates bacterial attachment (Lee et al ., 2020). Moreover, it has been suggested that the undefined surface signal is recognized by the WspA chemoreceptor (O'Connor et al ., 2012).…”

Fine tuning cyclic-di-GMP signaling inPseudomonas aeruginosausing the type 4 pili alignment complex

“…All strains were routinely grown in 5 ml lysogeny broth (LB) medium and maintained on 1.5% LB agar plates with appropriate antibiotics, as necessary [6,10]. Biofilm, swarming and twitching assays [26][27][28], as well as flow cells [18][19][20] and bacterial adenylate cyclase two hybrid assays [29][30][31] were performed and quantified as reported with additional details outlined in the Supplementary Methods.…”

“…We tracked single cell levels of cyclic-di-GMP in the WT and mutant strain using a reporter wherein GFP was fused to the cyclic-di-GMP-responsive P cdrA promoter. We tracked single cells in a flow cell immediately before and after the initiation of exponential surface cell growth, as reported [18][19][20], and aggregated the data across blocks of time of ~6 hrs each (Fig. S4).…”