Dead cells release a ‘necrosignal’ that activates antibiotic survival pathways in bacterial swarms

Abstract

Swarming is a form of collective bacterial motion enabled by flagella on the surface of semisolid media. Swarming populations exhibit non-genetic or adaptive resistance to antibiotics, despite sustaining considerable cell death. Here, we show that antibiotic-induced death of a sub-population benefits the swarm by enhancing adaptive resistance in the surviving cells. Killed cells release a resistance-enhancing factor that we identify as AcrA, a periplasmic component of RND efflux pumps. The released AcrA interacts on the surface of live cells with an outer membrane component of the efflux pump, TolC, stimulating drug efflux and inducing expression of other efflux pumps. This phenomenon, which we call 'necrosignaling', exists in other Gram-negative and Gram-positive bacteria and displays species-specificity. Given that adaptive resistance is a known incubator for evolving genetic resistance, our findings might be clinically relevant to the rise of multidrug resistance.

New Functional Criterion for Evaluation of Homologous MDR Pumps

“…Thus, significant substitutions in the sequences may lead to the loss of important functions in cell physiology of E. coli bacteria. This observation was confirmed in a recent work (Bhattacharyya et al, 2020 ), which demonstrated the key role of individual amino acid residues of AcrA and TolC in “necrosignal” recognition that activates swarm-specific resistance in an E. coli population. Thus, it can be assumed that the AcrAB-TolC pump may not only remove certain molecules from the cell, but also is a keystone element in regulatory processes important for the physiology of bacteria.…”

Swarming bacteria undergo localized dynamic phase transition to form stress-induced biofilms

“…Swarming bacteria can also collectively tolerate antibiotic treatments that are lethal to planktonic cells – albeit only to a lesser degree than biofilms – through motility-induced mixing and reduced small-molecule absorption ( Bhattacharyya et al, 2020 ; Butler et al, 2010 ; Lai et al, 2009 ). As a rapid mode of surface colonization ( Kearns, 2010 ), a swarm’s ability to withstand high antibiotic concentrations could therefore lead to the subsequent establishment of highly resilient biofilms in regions that could not have been reached otherwise.…”

Cytochrome bd promotes Escherichia coli biofilm antibiotic tolerance by regulating accumulation of noxious chemicals

“…The increased ethidium bromide accumulation represents a net increase in uptake and could be explained by alterations to the rate of influx, efflux, or both. To differentiate these possibilities, we quantified influx kinetics using resazurin-based PrestoBlue, a dye that becomes fluorescent after import into the cytosol 46 . In planktonic cells we observe a small, but statistically significant increase in the rate of dye influx in ∆ cydAB relative to wild-type (slope: 2.6 and 3.0 for wild-type and ∆ cydAB , respectively) (Fig.…”

“…Uptake of PrestoBlue (Invitrogen) was performed as previously described 46 . Planktonic cultures were grown to mid-logarithmic phase and normalized to OD 600 = 1.0 in PBS.…”