A very versatile molecular machine.

In this issue (J Bacteriol. 206: e0014024, https://doi.org/10.

Rotary Nanomotors in the Rear View Mirror.

Rotation is part of our everyday lives. For most of human history, rotation was considered a uniquely human invention, something beyond the anatomical capabilities of organisms. In 1973, Howard Berg made the audacious proposal that the common gut bacterium swims by rotating helical flagellar filaments.

Howard Berg (1934-2021).

David Blair and Michael Manson commemorate the late Howard Berg, who studied, among other things, the biophysics of bacterial motion.

Mechanosensitive recruitment of stator units promotes binding of the response regulator CheY-P to the flagellar motor.

Reversible switching of the bacterial flagellar motor between clockwise (CW) and counterclockwise (CCW) rotation is necessary for chemotaxis, which enables cells to swim towards favorable chemical habitats. Increase in the viscous resistance to the rotation of the motor (mechanical load) inhibits switching. However, cells must maintain homeostasis in switching to navigate within environments of different viscosities.

Howard Berg's Random Walk through Biology.

This minireview presents the career of biophysicist Howard Berg from his first interest in bacterial chemotaxis and motility through the present. After a summary of some of his early work, a series of reminiscences of students, postdocs, colleagues, and family members is presented. In sum, these recollections capture the effect that Howard's scientific life has had on the field of bacterial chemotaxis and motility and on the careers and lives of those who have interacted with him.

Biphasic chemotaxis of to the microbiota metabolite indole.

Bacterial chemotaxis to prominent microbiota metabolites such as indole is important in the formation of microbial communities in the gastrointestinal (GI) tract. However, the basis of chemotaxis to indole is poorly understood. Here, we exposed to a range of indole concentrations and measured the dynamic responses of individual flagellar motors to determine the chemotaxis response.

Molecular Mechanism for Attractant Signaling to DHMA by E. coli Tsr.

The attractant chemotaxis response of Escherichia coli to norepinephrine requires that it be converted to 3,4-dihydroxymandelic acid (DHMA) by the monoamine oxidase TynA and the aromatic aldehyde dehydrogenase FeaB. DHMA is sensed by the serine chemoreceptor Tsr, and the attractant response requires that at least one subunit of the periplasmic domain of the Tsr homodimer (pTsr) has an intact serine-binding site. DHMA that is generated in vivo by E.

pH Sensing in Bacillus subtilis: a New Path to a Common Goal.

pH is one of the most fundamental properties of the environments in which microorganisms live. It is, therefore, not surprising that bacteria have evolved mechanisms to sense and respond to pH. One aspect of this response for motile bacteria is to migrate to areas of optimal pH.

One Basic Blueprint, Many Different Motors.

The cytoplasmic C ring of the bacterial flagellum is known as the switch complex. It binds the response regulator phospho-CheY to control the direction of flagellar rotation. The C ring of enteric bacteria is well characterized.

Transmembrane Signal Transduction in Bacterial Chemosensing.

Like all living organisms, bacteria must communicate with the world around them. As they typically live as single cells, the communication with their environment must occur at the cell membrane, both in moving molecules in and out and in transmitting information about their surroundings to response elements within the cell. This volume is devoted primarily to methods used to study either the behavior of bacteria in response to their environment or methods used to study events that involve signaling pathways that are initiated by events at the cell membrane.

The Diversity of Bacterial Chemosensing.

Bacteria have a continuous and urgent need to inform themselves about the chemistry of their surroundings. They must rapidly adjust their patterns of gene expression, their metabolic and transport functions, and their behavior to cope with every challenge and opportunity with which they are presented. This volume collates the most recent methods developed to monitor and manipulate the processes by which bacteria sense and respond to their chemical environment.

Chemotaxis to self-generated AI-2 promotes biofilm formation in .

Responses to the interspecies quorum-sensing signal autoinducer-2 (AI-2) regulate the patterns of gene expression that promote biofilm development. also senses AI-2 as a chemoattractant, a response that requires the periplasmic AI-2-binding protein LsrB and the chemoreceptor Tsr. Here, we confirm, as previously observed, that under static conditions highly motile cells self-aggregate and form surface-adherent structures more readily than cells lacking LsrB and Tsr, or than Δ cells unable to produce AI-2.

Conversion of Norepinephrine to 3,4-Dihdroxymandelic Acid in Escherichia coli Requires the QseBC Quorum-Sensing System and the FeaR Transcription Factor.

The detection of norepinephrine (NE) as a chemoattractant by strain K-12 requires the combined action of the TynA monoamine oxidase and the FeaB aromatic aldehyde dehydrogenase. The role of these enzymes is to convert NE into 3,4-dihydroxymandelic acid (DHMA), which is a potent chemoattractant sensed by the Tsr chemoreceptor. These two enzymes must be induced by prior exposure to NE, and cells that are exposed to NE for the first time initially show minimal chemotaxis toward it.

The Norepinephrine Metabolite 3,4-Dihydroxymandelic Acid Is Produced by the Commensal Microbiota and Promotes Chemotaxis and Virulence Gene Expression in Enterohemorrhagic Escherichia coli.

Enterohemorrhagic (EHEC) is a commonly occurring foodborne pathogen responsible for numerous multistate outbreaks in the United States. It is known to infect the host gastrointestinal tract, specifically, in locations associated with lymphoid tissue. These niches serve as sources of enteric neurotransmitters, such as epinephrine and norepinephrine, that are known to increase virulence in several pathogens, including enterohemorrhagic The mechanisms that allow pathogens to target these niches are poorly understood.

Chemotaxis of Escherichia coli to norepinephrine (NE) requires conversion of NE to 3,4-dihydroxymandelic acid.

Norepinephrine (NE), the primary neurotransmitter of the sympathetic nervous system, has been reported to be a chemoattractant for enterohemorrhagic Escherichia coli (EHEC). Here we show that nonpathogenic E. coli K-12 grown in the presence of 2 μM NE is also attracted to NE.

Cryoelectron tomography reveals the sequential assembly of bacterial flagella in Borrelia burgdorferi.

Periplasmic flagella are essential for the distinctive morphology, motility, and infectious life cycle of the Lyme disease spirochete Borrelia burgdorferi. In this study, we genetically trapped intermediates in flagellar assembly and determined the 3D structures of the intermediates to 4-nm resolution by cryoelectron tomography. We provide structural evidence that secretion of rod substrates triggers remodeling of the central channel in the flagellar secretion apparatus from a closed to an open conformation.

Residues at the cytoplasmic end of transmembrane helix 2 determine the signal output of the TarEc chemoreceptor.

Baseline signal output and communication between the periplasmic and cytoplasmic domains of the Escherichia coli aspartate chemoreceptor Tar(Ec) are both strongly influenced by residues at the C-terminus of transmembrane helix 2 (TM2). In particular, the cytoplasmic aromatic anchor, composed of residues Trp-209 and Tyr-210 in wild-type Tar(Ec), is important for determining the CheA kinase-stimulating activity of the receptor and its ability to respond to chemoeffector-induced stimuli. Here, we have studied the effect on Tar(Ec) function of the six-residue sequence at positions 207-212.

Molecular architecture of chemoreceptor arrays revealed by cryoelectron tomography of Escherichia coli minicells.

The chemoreceptors of Escherichia coli localize to the cell poles and form a highly ordered array in concert with the CheA kinase and the CheW coupling factor. However, a high-resolution structure of the array has been lacking, and the molecular basis of array assembly has thus remained elusive. Here, we use cryoelectron tomography of flagellated E.

The residue composition of the aromatic anchor of the second transmembrane helix determines the signaling properties of the aspartate/maltose chemoreceptor Tar of Escherichia coli.

Repositioning of the tandem aromatic residues (Trp-209 and Tyr-210) at the cytoplasmic end of the second transmembrane helix (TM2) modulates the signal output of the aspartate/maltose chemoreceptor of Escherichia coli (Tar(Ec)). Here, we directly assessed the effect of the residue composition of the aromatic anchor by studying the function of a library of Tar(Ec) variants that possess all possible combinations of Ala, Phe, Tyr, and Trp at positions 209 and 210. We identified three important properties of the aromatic anchor.

Not too loose, not too tight--just right. Biphasic control of the Tsr HAMP domain.

HAMP domains communicate between input and output signalling modules in a wide variety of bacterial sensor proteins. In the Tsr chemoreceptor, they convert a signal initiated by binding of serine to the periplasmic domain of the protein into regulation of receptor control of the CheA kinase, and ultimately of the direction of flagellar rotation. In this issue, Zhou et al.

Chemotaxis to the quorum-sensing signal AI-2 requires the Tsr chemoreceptor and the periplasmic LsrB AI-2-binding protein.

AI-2 is an autoinducer made by many bacteria. LsrB binds AI-2 in the periplasm, and Tsr is the l-serine chemoreceptor. We show that AI-2 strongly attracts Escherichia coli.

Mutational analysis of the transmembrane helix 2-HAMP domain connection in the Escherichia coli aspartate chemoreceptor tar.

Transmembrane helix 2 (TM2) of the Tar chemoreceptor undergoes an inward piston-like displacement of 1 to 3 Å upon binding aspartate. This signal is transmitted to the kinase-control module via the HAMP domain. Within Tar, the HAMP domain forms a parallel four-helix bundle consisting of a dimer of two amphipathic helices connected by a flexible linker.