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The small size of bacterial cells necessitates rapid adaption to sudden environmental changes. In Bdellovibrio bacteriovorus, an obligate predator of bacteria common in oligotrophic environments, the non-replicative, highly motile attack phase (AP) cell must invade a prey to ensure replication. AP cells swim fast and respire at high rates, rapidly consuming their own contents. How the predator survives in the absence of prey is unknown. We show that starvation for prey significantly alters swimming patterns and causes exponential decay in prey-searching cells over hours, until population-wide swim-arrest. Swim-arrest is accompanied by changes in energy metabolism, enabling rapid swim-reactivation upon introduction of prey or nutrients, and a sweeping change in gene expression and gene regulation that largely differs from those of the paradigmatic stationary phase. Swim-arrest is costly as it imposes a fitness penalty in the form of delayed growth. We track the control of the swim arrest-reactivation process to cyclic-di-GMP (CdG) effectors, including two motility brakes. CRISPRi transcriptional inactivation, and in situ localization of the brakes to the cell pole, demonstrated their essential role for effective survival under prey-induced starvation. Thus, obligate predators evolved a unique CdG-controlled survival strategy, enabling them to sustain their uncommon lifestyle under fluctuating prey supply.

The small size of bacterial cells necessitates rapid adaption to sudden environmental changes. In Bdellovibrio bacteriovorus, an obligate predator of bacteria common in oligotrophic environments, the non-replicative, highly motile attack phase (AP) cell must invade a prey to ensure replication. AP cells swim fast and respire at high rates, rapidly consuming their own contents. How the predator survives in the absence of prey is unknown. We show that starvation for prey significantly alters swimming patterns and causes exponential decay in prey-searching cells over hours, until population-wide swim-arrest. Swim-arrest is accompanied by changes in energy metabolism, enabling rapid swim-reactivation upon introduction of prey or nutrients, and a sweeping change in gene expression and gene regulation that largely differs from those of the paradigmatic stationary phase. Swim-arrest is costly as it imposes a fitness penalty in the form of delayed growth. We track the control of the swim arrest-reactivation process to cyclic-di-GMP (CdG) effectors, including two motility brakes. CRISPRi transcriptional inactivation, and in situ localization of the brakes to the cell pole, demonstrated their essential role for effective survival under prey-induced starvation. Thus, obligate predators evolved a unique CdG-controlled survival strategy, enabling them to sustain their uncommon lifestyle under fluctuating prey supply.

This study aimed at testing the application of nano-composites of micelle–montmorillonite for removal of bacteria and parasites from water. The suitability of these complexes for efficient adsorption of microorganisms was expected on account of their large surface areas, large excess of positive charge, and existence of large hydrophobic domains. Tests included removal from water of bacteria: Gram negative (Escherichia coliK-12), Gram positive (Bacillus megaterium), and a protozoan parasite, Cryptosporidium parvum. Micelles of the organic cations Benzyldimethylhexadecylammonium (BDMHDA), or Octadecyltrimethylammonium complexed with the clay-mineral montmorillonite were shown to reduce by 3–6 orders of magnitude the numbers of microorganisms in water as tested in suspension and by filters (20 cm in length) packed with the complexes mixed with excess sand (100:1, w/w). Respiration tests demonstrated that E. coliK-12 cells adsorbed to micelle (BDMHDA)–montmorillonite complex lost their viability. Kinetics of filtration of E. coliby two filters in series was adequately simulated by a model which considers convection, adsorption. and desorption. Filtration of E. coliK-12 cells demonstrated that they stayed adsorbed and inactivated by the complex within the column filter without re-growth in water. These results suggest that filters including micelle–montmorillonite composites can secure the safety of drinking water in case of threatening increases in the number of pathogenic microorganisms in the water.

AbstractThis study aimed at testing the application of nano-composites of micelle–montmorillonite for removal of bacteria and parasites from water. The suitability of these complexes for efficient adsorption of microorganisms was expected on account of their large surface areas, large excess of positive charge, and existence of large hydrophobic domains. Tests included removal from water of bacteria: Gram negative (Escherichia coliK-12), Gram positive (Bacillus megaterium), and a protozoan parasite, Cryptosporidium parvum. Micelles of the organic cations Benzyldimethylhexadecylammonium (BDMHDA), or Octadecyltrimethylammonium complexed with the clay-mineral montmorillonite were shown to reduce by 3–6 orders of magnitude the numbers of microorganisms in water as tested in suspension and by filters (20 cm in length) packed with the complexes mixed with excess sand (100:1, w/w). Respiration tests demonstrated that E. coliK-12 cells adsorbed to micelle (BDMHDA)–montmorillonite complex lost their viability. Kinetics of filtration of E. coliby two filters in series was adequately simulated by a model which considers convection, adsorption. and desorption. Filtration of E. coliK-12 cells demonstrated that they stayed adsorbed and inactivated by the complex within the column filter without re-growth in water. These results suggest that filters including micelle–montmorillonite composites can secure the safety of drinking water in case of threatening increases in the number of pathogenic microorganisms in the water.