Glucose transport in isolated prosthecae of Asticcacaulis biprosthecum

Complete genome sequence of Hirschia baltica type strain (IFAM 1418(T))

The family Hyphomonadaceae within the Alphaproteobacteria is largely comprised of bacteria isolated from marine environments with striking morphologies and an unusual mode of cell growth. Here, we report the complete genome sequence Hirschia baltica, which is only the second a member of the Hyphomonadaceae with a published genome sequence. H. baltica is of special interest because it has a dimorphic life cycle and is a stalked, budding bacterium. The 3,455,622 bp long chromosome and 84,492 bp plasmid with a total of 3,222 protein-coding and 44 RNA genes were sequenced as part of the DOE Joint Genome Institute Program CSP 2008.

Genome sequences of eight morphologically diverse Alphaproteobacteria

The Alphaproteobacteria comprise morphologically diverse bacteria, including many species of stalked bacteria. Here we announce the genome sequences of eight alphaproteobacteria, including the first genome sequences of species belonging to the genera Asticcacaulis, Hirschia, Hyphomicrobium, and Rhodomicrobium.

Complex regulatory pathways coordinate cell-cycle progression and development in Caulobacter crescentus

Caulobacter crescentus has become the predominant bacterial model system to study the regulation of cell-cycle progression. Stage-specific processes such as chromosome replication and segregation, and cell division are coordinated with the development of four polar structures: the flagellum, pili, stalk, and holdfast. The production, activation, localization, and proteolysis of specific regulatory proteins at precise times during the cell cycle culminate in the ability of the cell to produce two physiologically distinct daughter cells. We examine the recent advances that have enhanced our understanding of the mechanisms of temporal and spatial regulation that occur during cell-cycle progression.

Out on a limb: how the Caulobacter stalk can boost the study of bacterial cell shape

Understanding the mechanisms underlying the establishment of different bacterial cell shapes and the advantage that a particular shape imparts is one of the most fascinating and challenging areas of study in microbiology. One remarkable example of bacterial morphogenesis is the elaboration of long, tubular extensions of the cell envelope of certain aquatic bacteria. These appendages (also called prosthecae or stalks) possess features that make them particularly amenable models for experiments designed to uncover general principles of cell morphogenesis and of cell shape function. Recent evidence supports the hypothesis that stalk synthesis in Caulobacter crescentus is a specialized form of cell elongation that confers to the cell substantial advantages in nutrient uptake. Further insights into the mechanisms and function of stalk synthesis will require a multidisciplinary systems biology approach using principles and methodologies from ecology and evolutionary biology to biophysics and mathematical modelling.

The selective value of bacterial shape

Why do bacteria have shape? Is morphology valuable or just a trivial secondary characteristic? Why should bacteria have one shape instead of another? Three broad considerations suggest that bacterial shapes are not accidental but are biologically important: cells adopt uniform morphologies from among a wide variety of possibilities, some cells modify their shape as conditions demand, and morphology can be tracked through evolutionary lineages. All of these imply that shape is a selectable feature that aids survival. The aim of this review is to spell out the physical, environmental, and biological forces that favor different bacterial morphologies and which, therefore, contribute to natural selection. Specifically, cell shape is driven by eight general considerations: nutrient access, cell division and segregation, attachment to surfaces, passive dispersal, active motility, polar differentiation, the need to escape predators, and the advantages of cellular differentiation. Bacteria respond to these forces by performing a type of calculus, integrating over a number of environmental and behavioral factors to produce a size and shape that are optimal for the circumstances in which they live. Just as we are beginning to answer how bacteria create their shapes, it seems reasonable and essential that we expand our efforts to understand why they do so.

Proteomic analysis of the Caulobacter crescentus stalk indicates competence for nutrient uptake

Caulobacter crescentus, a Gram-negative alpha-purple proteobacterium, is an oligotroph that lives in aquatic environments dilute in nutrients. This bacterium divides asymmetrically. Part of this asymmetric cell division involves the formation of a prosthecum at one pole, referred to as the stalk, which replaces the flagellum of the motile swarmer cell. Little is known about the synthesis or function of the stalk. The stalk is an extension of the cell membranes and peptidoglycan layer, and stalk elongation is stimulated by phosphate starvation. In this study, we have taken advantage of two-dimensional gel (2D gel) electro-phoresis as well as the fully sequenced genome of Caulobacter to study the proteome of the stalk. We modified a stalk-shedding mutant strain of Caulobacter crescentus to increase the yield of stalk material shed and performed 2D gel electrophoresis of purified stalks and cellular fractions. Comparison of the stalk 2D gel with the 2D gels of cell membrane and soluble fractions showed that the stalk is mostly free of cytoplasmic proteins and has a profile very similar to that of the cell membrane. Of the 172 proteins on a stalk 2D gel, we report the identification of 64 spots, corresponding to 39 different proteins present in the stalk of Caulobacter. The identifications include several TonB-dependent receptors, two OmpA family proteins, a dipeptidase, GlpQ, two alkaline phosphatases, 3-phytase, a putative TolC protein and 11 proteins of unknown function. These identifications are consistent with the hypothesis that the stalk plays a role in nutrient uptake.

Use of diaminobenzidine to stain for cytochrome c oxidase activity in Caulobacter crescentus and Escherichia coli

Caulobacter crescentus is an aerobic Gram negative bacterium found in bacterial biofilms. C. crescentus produces a sessile stalked cell during its life cycle that allows it to attach to surfaces. Due to the oxygen gradient found in the bacterial biofilm, we postulated that C. crescentus would localize the terminal cytochrome to the cell body that remains in the aerobic portion of the biofilm. The terminal electron acceptor in the electron transport system was determined using Kovac's oxidase test to be cytochrome c oxidase. We are able to use diaminobenzidine to locate the oxidase histochemically using transmission electron microscopy. Upon examination of sectioned bacteria, we determined that cytochrome c oxidase of C. crescentus is found only in the cell body.

Decreased glucose metabolism causes separation of hoof lamellae in vitro: a trigger for laminitis?

Explants of horses' hooves remained intact for up to 8 days when incubated in Dulbecco's modified Eagle medium (D-MEM) containing 25 mmol/l glucose but separated within 36 h when incubated in saline. The separation occurred between the basal epidermal cells and their basement membrane which is characteristic of the hoof separation that occurs in laminitis. Separation of hoof explants was prevented by addition of glucose to saline and was induced by adding 2-deoxyglucose or aminophenylmercuric acetate to D-MEM. Glucose consumption by the hoof explants was inhibited by 2-deoxyglucose and aminophenylmercuric acetate. The explants consumed relatively large amounts of glucose during the first 2 days of incubation and then little over the next 6 days. Despite the reduced glucose consumption, the hoof explants did not separate over 8 days of incubation. The results indicated that the integrity of the hoof explants was initially dependent on consumption of glucose and provide a possible explanation for the development of laminitis caused by conditions such as carbohydrate overload, acute inflammatory conditions, corticosteroid therapy and hyperlipidaemia. It would be expected that these conditions would induce a major hormonally-mediated metabolic shift away from glucose consumption by many peripheral tissues. It is suggested, therefore, that if the metabolic change occurred faster than the hoof tissue could adapt to an alternative energy substrate, then hoof separation and laminitis would occur.

Physiological bases of oligotrophy of microorganisms and the concept of microbial community

Three groups of physiological processes in microorganisms are considered the physiological basis of oligotrophy: the greater substrate affinity of the oligotrophs' transport systems, efficient or "economical" metabolism, and existence of a "master reaction" or "rate-determining steps" controlling the rate of metabolism. Heterotrophic microorganisms are divided into three unequal groups according to "reaction norma." Two groups representing the extremes are small groups with the "narrow" reaction norma, regarding the concentrations and structure of the assimilated organic compounds and variability limits of the physiological characteristics mentioned above. The third, intermediate group includes the majority of microorganisms with the "wide" reaction norma.

Effect of Na + Concentration and Nutritional Factors on the Lag Phase and Exponential Growth Rates of the Marine Bacterium Deleya aesta and of Other Marine Species

Growth of the marine bacterium Deleya aesta in a succinate minimal medium showed increasingly long lag phases as Na + was decreased below the optimum (200 to 500 mM). The minimum Na + concentration permitting growth consistently was 15 mM. Supplementation of the medium with KHCO 3 (as a source of CO 2 ) or yeast extract, especially in combination, reduced the lag phase, increased the rate of exponential growth, and allowed growth at 8 mM Na + . KHCO 3 did not reduce the lag period but did increase the rate of exponential growth of Deleya venusta, Deleya pacifica , and Alteromonas haloplanktis 214. Yeast extract was active for all three. The effect of yeast extract on D. aesta could be reproduced by a mixture of amino acids approximating its amino acid composition. l -Alanine, l -aspartate, and l -methionine, in combination, were the most effective in reducing the lag phase, although not as effective as the complete mixture. Succinate, l -aspartate, and l -alanine were transported into the cells by largely independent pathways and oxidized at rates which were much lower at 10 than at 200 mM Na + . l -Methionine was transported at a low rate in the absence of Na + and at a higher rate at 10 mM but was not oxidized. Above 25 mM Na + , the rate of transport of the carbon source was not the rate-limiting step for growth. It is concluded that a combination of transportable carbon sources reduced the lag period and increased the rate of exponential growth because they can be taken up independently and at low Na + utilized simultaneously.

Structure of the porin from a bacterial stalk

The stalks (hyphae) of a prosthecate bacterium, directly sampled from the water surface of a hot pond, show extended regular patterns on their envelope in the electron microscope. Image processing revealed a structure of the crystalline complexes which is very similar to the gross morphology of the Escherichia coli porins OmpC and OmpF. The natural two-dimensional crystal of the outer membrane protein has p3 symmetry and a lattice constant of 7.95 nm. The three-dimensional structure of the stalk porin has been determined to an almost isotropic resolution of 1.7 nm. The reconstruction revealed a complex network of channels within the membrane matrix with a triplet of pores merging into a common outlet, similar to the structure of the E. coli porin OmpF in reconstituted membranes. In addition, a blindly ending pore exists which appears to be connected to the continuous pores via small channels. The significance of the regularly arrayed porin cylinders with respect to the shape and function of the stalks is discussed.

The caulobacters: ubiquitous unusual bacteria

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