Instability of waves formed by motile bacteria

Abstract Cell-free enzyme preparations of the obligately anaerobic halophilic eubacterium Haloanaerobium praevalens synthesize fatty acids from malonyl-CoA. The reaction is stimulated by NaCl and KCl at a concentration of 1 M, and only slightly inhibited by salt concentrations as high as 3 M. Thus, the fatty acid synthetase of H. praevalens is expected to the fully active at the high intracellular salt concentrations present, and it is the first fatty acid synthetase reported to be active in the presence of high salt concentrations.     

Chemotactic responses ofThiobacillus thioparus

A capillary assay was employed to quantify chemotactic responses in the chemoautotrophic bacterium,Thiobacillus thioparus. NH₄Cl, KNO₃, and Na₂S₂O₃ were strong attractants. The minimum concentration of each of these inorganic chemicals needed to elicit an observable response was approximately 10^–4 M.T. thioparus did not respond to carbohydrates or amino acids.     

New motile anaerobic bacteria growing by succinate decarboxylation to propionate

Three strains of new anaerobic, gram-negative bacteria which grew with succinate as sole source of carbon and energy were isolated from anoxic marine and freshwater mud samples. Cells of the three strains were small, non-spore-forming, motile rods or spirilla. The guanine-plus-cytosine content of the DNA of strain US2 was 52.6±1.0 mol%, of strain Ft2 63.5±1.4 mol%, and of strain Ft1 62.6±1.0 mol%. Succinate was fermented stoichiometrically to propionate and carbon dioxide. The growth yields were 1.2–2.6 g dry cell mass per mol succinate degraded. Strains US2 and Ft2 required 0.05% w/v yeast extract in addition to succinate for reproducible growth. Optimal growth occurred at 30°–37°C and pH 6.8–8.0. Addition of acetate as cosubstrate did not stimulate growth with any strain. Strain Ft2 grew only under strictly anaerobic conditions, whereas strains US2 and Ft1 tolerated oxygen up to 20% in the headspace. Strains US2 and Ft2 grew only with succinate. Strain Ft1 also converted fumarate, aspartate, and sugars to propionate and acetate. This strain also oxidized propionate with nitrate to acetate. Very low amounts of a c-type cytochrome were detected in propionate plus nitrate- or glucose-grown cells of this strain (0.4 g x g protein^-1). Moderate activities of avidin-sensitive methylmalonyl-CoA decarboxylase were found in cell-free extracts of all strains.     

Chemotactic responses of Chlamydomonas reinhardtii.

A capillary chemotaxis assay revealed that among a wide range of inorganic and organic chemicals, only ammonium ion (NH4+) could serve as an attractant of Chlamydomonas reinhardtii. NH4+ (10(-2) M) gave the maximum response, with up to a 15-fold increase in accumulated algae being measured. No repellents for the chlorophyte were detected. The response to NH4+ was influenced by exogenous levels of calcium, but not by L-methionine. The optimal pH for positive chemotaxis was 7.0; however, attraction was measurable from pH 4.0 to 9.0. Positive chemotaxis was stimulated by performing the assay under fluorescent illumination rather than in the dark.     

Chemotactic migration of bacteria in porous media

Chemotactic migration of bacteria—their ability to direct multicellular motion along chemical gradients—is central to processes in agriculture, the environment, and medicine. However, current understanding of migration is based on studies performed in bulk liquid, despite the fact that many bacteria inhabit tight porous media such as soils, sediments, and biological gels. Here, we directly visualize the chemotactic migration of Escherichia coli populations in well-defined 3D porous media in the absence of any other imposed external forcing (e.g., flow). We find that pore-scale confinement is a strong regulator of migration. Strikingly, cells use a different primary mechanism to direct their motion in confinement than in bulk liquid. Furthermore, confinement markedly alters the dynamics and morphology of the migrating population—features that can be described by a continuum model, but only when standard motility parameters are substantially altered from their bulk liquid values to reflect the influence of pore-scale confinement. Our work thus provides a framework to predict and control the migration of bacteria, and active matter in general, in complex environments.     

Microbial hitchhiking: how Streptomyces spores are transported by motile soil bacteria

Streptomycetes are sessile bacteria that produce metabolites that impact the behavior of microbial communities. Emerging studies have demonstrated that Streptomyces spores are distributed through various mechanisms, but it remains unclear how spores are transported to their preferred microenvironments, such as plant roots. Here, we show that Streptomyces spores are capable of utilizing the motility machinery of other soil bacteria. Motility assays and microscopy studies reveal that Streptomyces spores are transported to plant tissues by interacting directly with the flagella of both gram-positive and gram-negative bacteria. Genetics experiments demonstrate that this form of motility is facilitated by structural proteins on the spore coat. These results demonstrate that nonmotile bacteria are capable of utilizing the motility machinery of other microbes to complete necessary stages of their lifecycle.Subject terms: Bacteria, Cellular microbiology     

Dispersal of motile bacteria from a plane layer.

The dispersal of an initially well-defined concentration of the motile bacterium Escherichia coli was measured under nonchemotactic conditions. The distribution of bacteria along a glass observation cell was measured by recording the intensity of light scattered by the organisms. For comparison, the diffusion of fluorescein was also measured by determining the distribution of fluorescence throughout the observation cell. The dispersal of bacteria from a plane layer, under nonchemotactic conditions, can be adequately described by the Gaussian solution of the diffusion equation.     

The dispersal of an initial concentration of motile bacteria.

The dispersal of an initial concentration of identical Brownian particles is accurately described by the solution of the conventional diffusion equation, and a diffusion coefficient can be assigned to the assembly of particles. However, the dispersal of an initial concentration of motile bacteria is not well described by the same solution, in spite of the similarity between the random motion of a bacterium and a Brownian particle. Reasons for the failure of the Gaussian solution of the diffusion equation to describe the dispersal of Escherichia coli are discussed. An equation is formulated which gives the concentration of dispersing organisms as a function of space and time if the speed distribution function of the assembly of organism is known and reproduction is suppressed. For three assumed speed distributions the results are compared with concentrations measured by previous authors.     

Chemotactic responses of Vibrio alginolyticus to algal extracellular products.

A capillary assay was used to evaluate the chemotactic responses of Vibrio alginolyticus to three common algal extracellular products. Acrylate and glycolate attracted the motile marine bacterium. The peak response occurred with 10(-2) M of each chemical. Acrylic and glycolic acid also attracted V. alginolyticus, with the peak response occurring at 5 x 10(-4) M of each chemical. Higher concentrations of the organic acids resulted in a decreased response. The bacteria also displayed positive chemotaxis to dimethyl sulfide.     

Commensalism of methane-producing and motile aerobic bacteria in certain freshwater wetlands

It is pointed out that the methane flux measured experimentally for certain ponds and swamps is quantitatively consistent with a commensal dependence of Methanobacteria on O₂-chemotactic motile aerobic bacteria. The Methano species is thereby shielded from oxygen and provided with carbon dioxide for the anaerobic production of methane.     

Chemotactic Signaling by Single-Chain Chemoreceptors

Bacterial chemoreceptors of the methyl-accepting chemotaxis protein (MCP) family operate in commingled clusters that enable cells to detect and track environmental chemical gradients with high sensitivity and precision. MCP homodimers of different detection specificities form mixed trimers of dimers that facilitate inter-receptor communication in core signaling complexes, which in turn assemble into a large signaling network. The two subunits of each homodimeric receptor molecule occupy different locations in the core complexes. One subunit participates in trimer-stabilizing interactions at the trimer axis, the other lies on the periphery of the trimer, where it can interact with two cytoplasmic proteins: CheA, a signaling autokinase, and CheW, which couples CheA activity to receptor control. As a possible tool for independently manipulating receptor subunits in these two structural environments, we constructed and characterized fused genes for the E. coli serine chemoreceptor Tsr that encoded single-chain receptor molecules in which the C-terminus of the first Tsr subunit was covalently connected to the N-terminus of the second with a polypeptide linker. We showed with soft agar assays and with a FRET-based in vivo CheA kinase assay that single-chain Tsr~Tsr molecules could promote serine sensing and chemotaxis responses. The length of the connection between the joined subunits was critical. Linkers nine residues or shorter locked the receptor in a kinase-on state, most likely by distorting the native structure of the receptor HAMP domain. Linkers 22 or more residues in length permitted near-normal Tsr function. Few single-chain molecules were found as monomer-sized proteolytic fragments in cells, indicating that covalently joined receptor subunits were responsible for mediating the signaling responses we observed. However, cysteine-directed crosslinking, spoiling by dominant-negative Tsr subunits, and rearrangement of ligand-binding site lesions revealed subunit swapping interactions that will need to be taken into account in experimental applications of single-chain chemoreceptors.     

Chemotactic responses of Rhodobacter sphaeroides in the absence of apparent adaptation

Rhodobacter sphaeroides, which lacks methyl accepting chemotaxis proteins, showed a strong response to gradients of either pyruvate or propionate. If cells were placed in a saturating background of pyruvate they no longer responded to a gradient of propionate but they still responded to potassium or ammonia. This demonstrates that pyruvate saturated the response to another carbon source, but not to other classes of compound. The total movement of cells in a pyruvate background was maintained at a high level relative to a buffer control, indicating an apparent lack of adaptation to saturating pyruvate. The response of R. sphaeroides to a saturating background of pyruvate was weak in cells grown on limiting ammonia although these cells showed a strong response to ammonia. These data suggest that cells show a strong response to the class of compound that currently limits motility. Two hypotheses to explain these results are presented. Firstly, cells show a chemotactic response to a gradient of the limiting compound until saturated by it, they then respond to a gradient of the new compound that has then become limiting. The chemotactic response is the result of a decrease in stopping frequency as cells move up a gradient and an increase as they move down. Secondly, the behavioural response may have two components, a short term chemotactic response and a long term excitation of motility.Abbreviations MCP methyl accepting chemotaxis protein     

Chemotactic responses of Escherichia coli to small jumps of photoreleased L-aspartate

Computer-assisted motion analysis coupled to flash photolysis of caged chemoeffectors provides a means for time-resolved analysis of bacterial chemotaxis. Escherichia coli taxis toward the amino acid attractant L-aspartate is mediated by the Tar receptor. The physiology of this response, as well as Tar structure and biochemistry, has been studied extensively. The beta-2, 6-dinitrobenzyl ester of L-aspartic acid and the 1-(2-nitrophenyl)ethyl ether of 8-hydroxypyrene-1,3,6-tris-sulfonic acid were synthesized. These compounds liberated L-aspartate and the fluorophore 8-hydroxypyrene 1,3,6-tris-sulfonic acid (pyranine) upon irradiation with near-UV light. Photorelease of the fluorophore was used to define the amplitude and temporal stability of the aspartate jumps employed in chemotaxis experiments. The dependence of chemotactic adaptation times on aspartate concentration, determined in mixing experiments, was best fit by two Tar aspartate-binding sites. Signal processing (excitation) times, amplitudes, and adaptive recovery of responses elicited by aspartate jumps producing less than 20% change in receptor occupancy were characterized in photorelease assays. Aspartate concentration jumps in the nanomolar range elicited measurable responses. The response threshold and sensitivity of swimming bacteria matched those of bacteria tethered to glass by a single flagellum. Stimuli of similar magnitude, delivered either by rapid mixing or photorelease, evoked responses of similar strength, as assessed by recovery time measurements. These times remained proportional to change in receptor occupancy close to threshold, irrespective of prior occupancy. Motor excitation responses decayed exponentially with time. Rates of excitation responses near threshold ranged from 2 to 7 s-1. These values are consistent with control of excitation signaling by decay of phosphorylated pools of the response regulator protein, CheY. Excitation response rates increased slightly with stimulus size up to values limited by the instrumentation; the most rapid was measured to be 16 +/- 3 (SE) s-1. This increase may reflect simultaneous activation of CheY dephosphorylation, together with inhibition of its phosphorylation.     

Comparison of the relative concentration of motile and non-motile bacteria in small pores

The effect of small pores (similar in size to the stomata of plants) on the diffusion constants and relative concentrations of non-motile, randomly motile and chemotactic bacteria is considered. It is shown that although the Brownian diffusion constant of non-motile bacteria is a couple of orders of magnitude lower than the diffusion constant of motile bacteria, non-motile bacteria will still be present in both short (100 microns) and long (0.5 cm) pores in similar numbers to motile bacteria. It is postulated that this is due, at least in part, to the smaller amount of excluded volume for non-flagellated bacteria.     

Pathogenicity of live bacteria and extracellular products of motile Aeromonas isolated from eels

The pathogenic activities in vitro and in vivo of live bacteria and extracellular products (ECP) of 24 motile Aeromonas strains were investigated. Most Aer. hydrophila and Aer. jandaei isolates were pathogenic for eels (LD₅₀ 10^5·4-10^7·6 cfu fish^-1) but no Aer. sobria , Aer. caviae and Aer. allosaccharophila caused mortality in eels at doses of > 10^8·4 cfu fish^-1. Of these Aeromonas strains, Aer. hydrophila and Aer. jandaei in particular produced elastases and haemolysins against fish erythrocytes. ECP from Aer. hydrophila and Aer. jandaei caused degenerative changes in fish cell lines and were strongly toxic for eels (LD⁵⁰ 1·0–3·2 μg (g fish)^-1) reproducing the symptoms associated with natural disease. ECP from non-pathogenic species were inactive on fish cell lines as well as being poorly lethal for eels (LD⁵⁰ > 9·2 μg (g fish)^-1). All these biological activities of Aeromonas ECP were lost after heat treatment. These findings indicate differences between pathogenic and non-pathogenic Aeromonas species with respect to the expression of virulence factors, and show that elastases, haemolysins and exotoxins play a leading role in the pathogenicity of motile Aeromonas for eels.