Signatures of a globally optimal searching strategy in the three-dimensional foraging flights of bumblebees

Simulated annealing is a powerful stochastic search algorithm for locating a global maximum that is hidden among many poorer local maxima in a search space. It is frequently implemented in computers working on complex optimization problems but until now has not been directly observed in nature as a searching strategy adopted by foraging animals. We analysed high-speed video recordings of the three-dimensional searching flights of bumblebees (Bombus terrestris) made in the presence of large or small artificial flowers within a 0.5 m3 enclosed arena. Analyses of the three-dimensional flight patterns in both conditions reveal signatures of simulated annealing searches. After leaving a flower, bees tend to scan back-and forth past that flower before making prospecting flights (loops), whose length increases over time. The search pattern becomes gradually more expansive and culminates when another rewarding flower is found. Bees then scan back and forth in the vicinity of the newly discovered flower and the process repeats. This looping search pattern, in which flight step lengths are typically power-law distributed, provides a relatively simple yet highly efficient strategy for pollinators such as bees to find best quality resources in complex environments made of multiple ephemeral feeding sites with nutritionally variable rewards

A Salmonella toxin promotes persister formation through acetylation of tRNA

The recalcitrance of many bacterial infections to antibiotic treatment is thought to be due to the presence of persisters that are non-growing, antibiotic-insensitive cells. Eventually, persisters resume growth, accounting for relapses of infection. Salmonella is an important pathogen that causes disease through its ability to survive inside macrophages. After macrophage phagocytosis, a significant proportion of the Salmonella population forms non-growing persisters through the action of toxin-antitoxin modules. Here we reveal that one such toxin, TacT, is an acetyltransferase that blocks the primary amine group of amino acids on charged tRNA molecules, thereby inhibiting translation and promoting persister formation. Furthermore, we report the crystal structure of TacT and note unique structural features, including two positively charged surface patches that are essential for toxicity. Finally, we identify a detoxifying mechanism in Salmonella wherein peptidyl-tRNA hydrolase counteracts TacT-dependent growth arrest, explaining how bacterial persisters can resume growth

Mechanism of regulation and neutralization of the AtaR–AtaT toxin–antitoxin system

GCN5-related N-acetyl-transferase (GNAT)-like enzymes from toxin–antitoxin modules are strong inhibitors of protein synthesis. Here, we present the bases of the regulatory mechanisms of ataRT, a model GNAT-toxin–antitoxin module, from toxin synthesis to its action as a transcriptional de-repressor. We show the antitoxin (AtaR) traps the toxin (AtaT) in a pre-catalytic monomeric state and precludes the effective binding of ac-CoA and its target Met-transfer RNA fMet .In the repressor complex, AtaR intrinsically disordered region interacts with AtaT at two different sites, folding into different structures, that are involved in two separate functional roles, toxin neutralization and placing the DNA-binding domains of AtaR in a binding-compatible orientation. Our data suggests AtaR neutralizes AtaT as a monomer, right after its synthesis and only the toxin–antitoxin complex formed in this way is an active repressor. Once activated by dimerization, later neutralization of the toxin results in a toxin–antitoxin complex that is not able to repress transcription.SCOPUS: ar.jinfo:eu-repo/semantics/publishe