Biosurfactant production maintains viability in anoxic conditions by depolarizing the membrane inBacillus subtilis

Abstract

20membrane potential, membrane energetics, LytC 21 35 depolarizes the B. subtilis membrane, and that other known membrane-potential 36 disruptors restore viability to 168. These findings highlight the importance of surfactin for 37 survival during oxygen-depleted conditions and demonstrate that antimicrobials normally 38 considered harmful can instead benefit cells in stressful conditions when the terminal 39 electron acceptor in respiration is limiting. 40 following a rain [12]. Early observations of B. subtilis culture lysis upon a shift to anoxic 64 environments have yet to be further characterized [13], and it remains a mystery whether 65 B. subtilis has strategies to cope with oxygen limitation. 66 B. subtilis has long been domesticated in the lab, leading to a multitude of genetic 67 tools, strain libraries, and online databases and resources [14][15][16]. The high level of genetic 68 relatedness between biofilm-forming "wild" strains and derivative non-biofilm-forming 69 laboratory strains has been exploited to identify genetic differences that underlie biofilm 70 community behaviors [17]. For instance, the commonly studied laboratory strain 168, 71 which is derived from the biofilm-forming strain 3610, lacks an extrachromosomal plasmid 72 and harbors several point mutations that reduce or abolish social behaviors such as matrix 73 production [18]. Notably, 3610 produces the small molecule surfactin, a powerful 74 surfactant that has previously been implicated in swarming motility [19][20][21]. Surfactin has 75 also been shown to kill fungi [22] and some bacteria in vitro [22][23][24][25][26]. However, fitness 76 benefits of surfactin production in the context of planktonic cultures have yet to be 77 identified, although some surfactants can accelerate oxygen diffusion through the air-water 78 interface [27]. 79 Here, we characterize the interplay between oxygen availability and surfactin 80 production during the growth and death of B. subtilis cultures. We show that oxygen 81 becomes limiting in the culture during the transition to stationary phase and that surfactin 82 secretion improves growth yield in stationary phase by increasing oxygen availability. 83 During a shift to anoxic conditions, we demonstrate that the majority of B. subtilis cells die 84 and lyse due to the activity of the LytC autolysin and surfactin. Finally, we discover that 85 surfactin maintains the viability of the remaining cells by causing membrane 86 depolarization that allows these cells to survive until oxygen is restored. 87 131 hour (Fig. 1D). Since the lysis behavior varied with initial OD, we standardized all further 132 experiments by growing 3610 cells to an OD600 of ~0.9-1.1 before cutting off oxygen 133

Selection of sponge-associated bacteria with high potential for the production of antibacterial compounds

“…The debate on the antimicrobial effect of surfactins remains active, but may be accounted to the non-specific mode of action on the cell layer, e.g. cation transport through the bilipid layer 57 , pore-formation on the cell wall 58 , and distortion of the membrane integrity by detergent-like properties of surfactins that induce membrane depolarization events in the host 59 . In consequence the cell's energy balance is affected by compromising the cell wall potential, which results in reduced cell proliferation fitness and inactivation of transport processes into and out of the cell.…”