Isolation and description of a non-motile,fusiform, stalked bacterium,a representatieve of a new genus

A single strain representing the fusiform group of caulobacters first described by Henrici and Johnson has been isolated from a freshwater pond. Like the genusCaulobacter this is a chemo-organotrophic bacterium that has one polar prostheca, a stalk in the sense that its apical holdfast permits the cell to attach to solid substrates. Fine structure studies reveal, however, that the prostheca of this organism contains typical cellular constituents, not the membranous material found in the stalks ofCaulobacter andAsticcacaulis. The organism also differs from the other caulobacters in having no motile stage and no dimorphic life cycle (both daughter cells are stalked at the time of division). Because only one strain has been isolated no nomenclatural proposals are made, but sufficient evidence is presented to indicate that this is a representative of a new genus of the Schizomycetes.     

Peculiarities of fatty acid composition of the genusCaulobacter

The fatty acid composition of 35 strains of stalked bacteria belonging to 17 of the hitherto described 19 species and 10 unidentified strains of the genusCaulobacter was studied. ll-Methyl-cis-octadec-11-enoic acid presumably synthesized fromcis-vaccenic acid was detected in all the strains in amounts of 0.4 – 34.7 % and was considered as a chemotaxonomic marker of the genus. During growth on a peptone-yeast medium, the caulobacters synthesized, along with the fatty acids which are typical of gram-negative bacteria, some normal and branched fatty acids with 15 and 17 carbon atoms (1–49 %). The synthesis of these acids was inhibited by glucose. The cell shape of stalked bacteria (fusiform, vibrioid or bacteroid) is not obviously associated with the contents of individual fatty acids.     

In Situ Reproductive Rate of Freshwater Caulobacter spp.

Electron microscope grids were submerged in Lake Washington, Seattle, Wash., in June 1996 as bait to which Caulobacter sp. swarmers would attach and on which they would then reproduce in situ. Enumeration of bands in the stalks of attached cells implied that the caulobacters were completing approximately three reproductive cycles per day. A succession of morphological types of caulobacters occurred, as well as an episode of bacteriovore grazing that slowed the accumulation of caulobacters and prevented the aging of the population.     

Plant growth enhancement is not a conserved feature in the Caulobacter genus

Aims

Species within the Caulobacter genus have been termed ‘hub species’ in the plant microbiome. To understand these interactions, we assessed the interactions between several Caulobacter strains and a common host plant.

Methods

We identified a set of 11 Caulobacter strains that range in genetic diversity and tested them for their ability to increase the growth of Arabidopsis thaliana. In addition, biochemical assays were employed to determine if these Caulobacter strains produce common plant growth promoting (PGP) biosynthates. To identify potential PGP-related genes, genomic analyses were performed to compare the genomes of PGP Caulobacter strains to those of non-PGP Caulobacter strains.

Results

For the PGP Caulobacter strains, we observed that common PGP biosynthates did not contribute to the observed Caulobacter-mediated plant growth stimulation. Genomic analyses suggested that the genomes of PGP strains maintain similar metabolic pathways compared to those of non-PGP strains, and that common genes related to PGP factors do not explain the PGP mechanisms for the Caulobacter strains we analyzed.

Conclusions

Plant growth enhancement is not a conserved feature in the Caulobacter genus, and some Caulobacter strains even inhibit plant growth. Moreover, common PGP factors do not fully explain Caulobacter-mediated plant growth enhancement.

     

Evolutionary relationship of some stalked and budding bacteria (genera Caulobacter, “Hyphobacter”, Hyphomonas and Hyphomicrobium) as studied by the new integral taxonomical method

A new approach was developed for the determination of taxonomic and evolutional relationships among four genera of oligotrophic bacteria. The main idea of this approach is the algorithmized integrative analysis of the morphological and physiological specificity of these bacteria, their 5S rRNA sequences, fatty acid and lipid composition of their membranes, as well as their sensitivity to a large variety of antibiotics. It was shown that the genera Caulobacter and Hyphomonas are closely related to each other, but they are both distant from Hyphomicrobium species. The new genus, Hyphobacter, is placed between Caulobacter and Hyphomonas. Taxonomic heterogeneity was found to exist within the genera Caulobacter and Hyphomicrobium. Evolutional pathways from Caulobacter to Hyphomicrobium are proposed on the basis of the present data. No correlations were found between the cell morphology of the organisms and their geno-and chemotaxonomy.Abbreviations C-1 one-carbon - kB kilobases     

Isolation and Characterization of Marine Caulobacters and Assessment of Their Potential for Genetic Experimentation

A total of 25 marine caulobacters were isolated from littoral marine sources. Several aspects of their physiology and morphology were examined, as well as their suitability for genetic manipulation in laboratory cultivation. Caulobacters were readily isolated from all sources, including samples from areas containing pollution-related organic compounds. All isolates grew best in media containing seawater, but eight strains grew if sea salts were replaced with NaCl alone, three strains grew at 1/10 the normal sea salt concentration, and one isolate grew, albeit poorly, in freshwater medium. Of the marine isolates, 12 strains grew under anaerobic conditions, indicating that some caulobacters are not obligately aerobic bacteria, as they are currently categorized. Although some freshwater caulobacters are able to oxidize manganese, this capability was not found in these marine caulobacters. Of the marine isolates, 10 strains were resistant to mercury chloride concentrations 10- to 20-fold greater than that tolerated by sensitive bacteria. However, a mercury reductase gene comparable with that found in R100-type plasmids was not detected by gene hybridization. With respect to the potential for genetic experimentation, most strains grew rapidly (3- to 4-h generation time at 30°C), producing colonies on solid media in 2 to 3 days. The isolates were sensitive to antibiotics commonly used in recombinant DNA experiments, and spontaneous drug-resistant mutants were selectable. Conjugal transfer of plasmids from Escherichia coli to several marine caulobacters was demonstrated for four broad-host-range plasmid incompatibility groups, by using both self-transmissible plasmids and cloning-oriented plasmids that require a helper plasmid. Conjugal transfer of broad-host-range plasmids between freshwater and marine caulobacters was also demonstrated in both directions. Native plasmids of approximately 100- to 150-kilobase sizes were found in 2 of the 25 marine Caulobacter strains. The native plasmids were present in relatively high copy number and appeared stable in laboratory culture. In short, the marine caulobacters appeared appropriate as candidates for genetic manipulation and the expression of selected genes in the marine environment.     

The effect of light on the number of chloroplast nucleoids in daughter cells of the algaScenedesmus quadricauda

Summary Synchronous cultures of the green algaScenedesmus quadricauda (Turp.) Bréb. grown at mean irradiances 25Wm^–2, 75Wm^–2, and 130Wm^–2 PhAR were exposed to different illumination regimes (ratio of light to dark interval varied from 2:22 to 24:0 hours). The populations of daughter cells released under these conditions differed markedly in their progress in the cell cycle. The cells from these populations were stained with DAPI and the shape, localization and number of chloroplast nucleoids were examined. The nucleoids were of spherical shape, divided asynchronously having dumbbell shape during fission. In the chloroplast, nucleoids were located symmetrically about the transverse axis of the cells. The mean number of nucleoids varied from two in the least developed daughter cells to 16 in the daughter cells of the highest developmental stage. The progress of these cells and thus also the number of nucleoids were proportional to the portion of the light energy amount which these daughter cells shared from the total light energy amount obtained by their mother cells.Abbreviations DAPI 4, 6-diamidino-2-diphenylindole - PhAR photosynthetically active radiation (400–700 nm)     

Tightly regulated and heritable division control in single bacterial cells

The robust surface adherence property of the aquatic bacterium Caulobacter crescentus permits visualization of single cells in a linear microfluidic culture chamber over an extended number of generations. The division rate of Caulobacter in this continuous-flow culture environment is substantially faster than in other culture apparati and is independent of flow velocity. Analysis of the growth and division of single isogenic cells reveals that the cell cycle control network of this bacterium generates an oscillatory output with a coefficient of variation lower than that of all other bacterial species measured to date. DivJ, a regulator of polar cell development, is necessary for maintaining low variance in interdivision timing, as transposon disruption of divJ significantly increases the coefficient of variation of both interdivision time and the rate of cell elongation. Moreover, interdivision time and cell division arrest are significantly correlated between mother and daughter cells, providing evidence for epigenetic inheritance of cell division behavior in Caulobacter. The single-cell growth/division results reported here suggest that future predictive models of Caulobacter cell cycle regulation should include parameters describing the variance and inheritance properties of this system.     

Vertical distribution in and isolation of bacteria from Lake Vanda: an Antarctic lake

Vertical distribution of bacteria in Lake Vanda, an Antarctic meromictic lake, was examined by the acridine orange epifluorescence direct count method. Total bacteria were 10⁴–10⁵ cells · ml^–1 in the water at 55 m depth and above, and increased drastically to 10⁷ cells · ml^–1 in the bottom water. Filamentous or long rodshaped bacteria occurred at a high frequency in the upper layers, but in the bottom layers most bacteria were coccoidal or short rods. Mean bacterial cell volume in water of between 10 m and 60 m deep was fairly large compared with common bacterial populations in seawater and lake water. Aerobic heterotrophic bacteria were recovered from the water of a depth of 30 m and above, and were assumed to belong to Caulobacter. Viable heterotrophic bacteria were not recovered from the high salinity deep water by media prepared with the same deep water. Phototrophic purple non-sulphur bacteria were isolated by enrichment cultures from water at 55 m depth.     

Influence of the incubation temperature on the reaction of oligotrophic bacteria to stress

Representatives of five genera of psychroactive oligotrophic bacteria, Arcocella, Renobacter, Spirosoma, Caulobacter, and Methylobacterium, were for the first time shown to be capable of growing at a negative temperature (–2°C). Long-term cultivation (for 116 days) at a low temperature under limitation by the carbon source is stressful for oligotrophic bacteria and leads to the death of a part of the cell population. The number of viable cells of Caulobacter crescentus decreased by two to three orders of magnitude. Over the studied period of time, Renobacter vacuolatum cells retained viability at a low temperature, whereas, at room temperature, the titer of colony-forming cells decreased by two orders of magnitude under starvation stress.Translated from Mikrobiologiya, Vol. 73, No. 6, 2004, pp. 758–762.Original Russian Text Copyright © 2004 by Slabova, Nikitin.     

Evaluation of the taxonomic diversity of prosthecate bacteria belonging to the genera <Emphasis Type="Italic">Brevundimonas</Emphasis> and <Emphasis Type="Italic">Caulobacter</Emphasis> isolated from various eurasian ecosystems by analysis of the 16S rRNA genes

A taxonomic study of 35 cultures of prosthecate bacteria of the genera Brevundimonas and Caulobacter isolated from various soil and aquatic ecosystems of Eurasia was performed by amplified ribosomal DNA restriction analysis (ARDRA) and 16S rRNA gene sequencing. The most widespread groups of prosthecate bacteria belonging to these genera were revealed; at least two new species belonging to the genus Brevundimonas were found. The genus Brevundimonas includes both prosthecate and non-prosthecate species; however, it is quite possible that some Brevundimonas species may exhibit heterogeneity in such an important taxonomic characteristics as the ability to form prosthecae.     

The phylogeny of marine and freshwater caulobacters reflects their habitat.

Caulobacter is a distinctive genus of prosthecate bacteria. Because caulobacters adhere to surfaces and are found in diverse locales, their role in oligotrophic environments and bacterial biofilm communities is of interest. The phylogenetic relationships of a group of marine and freshwater caulobacters were examined in part to address whether the taxonomic grouping of these bacteria (based primarily on morphological characters) was consistent with 16S rRNA sequence divergence. The caulobacters examined (9 marine and 11 freshwater species or strains) were affiliated with the alpha proteobacteria. They made up a diverse yet, with the possible exception of a strain of Caulobacter subvibrioides, coherent assemblage. The diversity was most apparent in a comparison of freshwater and marine isolates; an early divergence within the main caulobacter lineage generally corresponded to strains isolated from freshwater and marine habitats. The marine caulobacter assemblage was not exclusive; it also embraced strains of marine hyphomonads and Rhodobacter capsulatus. We hypothesize that these genera are derived from more ancestral caulobacters. Overall, the data are consistent with the interpretation that all of the caulobacters examined, with the possible exception of C. subvibrioides, are ancestrally related, albeit anciently, and that most often division by terrestrial and marine habitats corresponds to an early evolutionary divergence within the genus.     

Morphology and phylogeny of <Emphasis Type="Italic">Botryosphaeria dothidea</Emphasis> causing fruit rot of olives

The taxonomic position of the causal agent of fruit rot of olives was determined from fresh collections of the fungus from central Greece. In culture it formed two types of conidia, namely fusiform, hyaline, aseptate conidia typical of the genus Fusicoccum, and dark-walled, ovoid, ellipsoid or fusiform, 1–2 septate conidia that are not typically observed in Fusicoccum. A phylogenetic analysis based on ITS and EF1- sequences placed the fungus within the same clade as Fusicoccum aesculi, which is the anamorph of Botryosphaeria dothidea, and the type of the genus Fusicoccum.     

Fermentation of methoxyacetate to glycolate and acetate by newly isolated strains of Acetobacterium sp.

Three strains of new mesophilic homoacetogenic bacteria were enriched and isolated from sewage sludge and from marine sediment samples with methoxyacetate as sole organic substrate in a carbonate-buffered medium under anoxic conditions. Two freshwater isolates were motile, Gram-positive, non-sporeforming rods. The marine strain was an immotile, Gram-positive rod with a slime capsula. All strains utilized only the methyl residue of methoxyacetate and released glycolic acid. They also fermented methyl groups of methoxylated aromatic compounds and of betaine to acetate with growth yields of 6–10 g dry matter per mol methyl group. H₂/CO₂, formate, methanol, hexamethylene tetramine, as well as fructose, numerous organic acids, glycerol, ethylene glycol, and glycol ethers were fermented to acetate as well. High activities of carbon monoxide dehydrogenase (0.4–2.2 U x mg protein^–1) were detected in all three isolates. The guanine-plus-cytosine-content of the DNA of the freshwater isolates was 42.7 and 44.4 mol %, with the marine isolate it was 47.7 mol %. The freshwater strains were assigned to the genus Acetobacterium as new strains of the species A. carbinolicum. One freshwater isolate, strain KoMac1, was deposited with the Deutsche Sammlung von Mikroorganismen GmbH, Braunschweig, under the number DSM 5193.     

Characterization of the Adhesive Holdfast of Marine and Freshwater Caulobacters

Caulobacters are prosthecate (stalked) bacteria that elaborate an attachment organelle called a holdfast at the tip of the cellular stalk. We examined the binding of lectins to the holdfasts of 16 marine Caulobacter strains and 10 freshwater species or strains by using a panel of fluorescein-conjugated lectins and fluorescence microscopy. The holdfasts of all the marine isolates bound to only wheat germ agglutinin (WGA) and other lectins that bind N-acetylglucosamine (GlcNac) residues. The freshwater caulobacters showed more variability in holdfast composition. Some bound only to WGA and comparable lectins as the marine strains did. Others bound additional or other lectins, and some did not bind to the lectins tested. The binding of WGA appeared to involve the regions of the holdfast involved with adhesion; a holdfast bound to WGA was significantly less adhesive to glass. Competition experiments with WGA-binding holdfasts and oligomers of GlcNac demonstrated that trimers of GlcNac (the preferred substrate for WGA binding) were more effective than dimers or monomers in preventing WGA binding to holdfasts, suggesting that stretches of contiguous GlcNac residues occur in the WGA-binding holdfasts. In addition, differences between freshwater and marine holdfasts in the strength of WGA binding were noted. The effect of a number of proteolytic and glycolytic enzymes on holdfast integrity was examined; the proteases had no effect for all caulobacters. None of the glycolytic enzymes had an effect on marine caulobacter holdfasts, but chitinase and lysozyme (both attack oligomers of GlcNac) disrupted the holdfasts of those freshwater caulobacters that bound WGA. Despite some similarity to chitin, holdfasts did not bind Calcofluor and no measurable effects on holdfast production were detectable after cell growth in the presence of diflubenzuron or polyoxin D, inhibitors of chitin synthesis in other systems. Finally, the holdfasts of all caulobacters bound to colloidal gold particles, without regard to the coating used to stabilize the gold particles. This binding was stronger or more specific than WGA binding; treatment with colloidal gold particles prevented WGA binding, but the reverse was not the case.     

Novel root nodule bacteria belonging to the genus Caulobacter

Aims: Aim of this study is to determine the genetic variation of rhizobia associated with horse gram [Macrotyloma uniflorum (Lam.) Verdc.] plants grown in different regions of Andhra Pradesh, India. Methods and Results: Four representative isolates having most representative characters from the previous characterization were selected for 16S rRNA sequence. The sequences were submitted to the NCBI GenBank and Ribosomal Database Project (RDP). The isolates HGR‐4, 6 and 13 showed more than 99% homology between them and they were grouped with Rhizobium reference strains where as the isolate HGR‐25 showed 87·1, 87·4 and 87·2% homology with the isolates HGR‐4, 6 and 13, respectively, and were grouped with reference strains for Caulobacter. The nodulation ability of these isolates on horse gram was confirmed by inoculation tests. Conclusions: The isolate HGR‐25 was identified as Caulobacter isolated from the plants growing in soil samples collected from Khareemnagar district, Andhra Pradesh, India. Inoculation tests revealed that Caulobacter formed nodules on horse gram. It was also confirmed by RDP. Significance and Impact of the Study: This is the first report that a legume was nodulated by a member of the genus Caulobacter, which belongs to the family Caulobacteriaceae in the order Caulobacterales of Alphaproteobacteria.     

Ectothiorhodospira vacuolata sp. nov., a new phototrophic bacterium from soda lakes

A new phototrophic bacterium was isolated from Jordanian and Kenyan alkaline salt lakes. Cells are rod shaped, 1.5 m wide and 2–4 m long, and motile by polar flagella. They divide by binary fission, and possess photosynthetic membranes as lamellar stacks similar to those in the other species of the genus Ectothiorhodospira and the brown colored Rhodospirillum species. The presence of bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series is indicated by the absorption spectra of living cells. Under certain growth conditions the cells form gas vacuoles, may become immotile and float to the top of the culture medium. Sulfide and thiosulfate are used as photosynthetic electron donors. During the oxidation of sulfide to sulfate, elemental sulfur is formed, which is accumulated outside the cells. The organisms are strictly anaerobic, do not require vitamins, are moderately halophilic and need alkaline pH-values for growth. The new species Ectothiorhodospira vacuolata is proposed.     

Bacterial filaments recover by successive and accelerated asymmetric divisions that allow rapid post-stress cell proliferation

Filamentation is a reversible morphological change triggered in response to various stresses that bacteria might encounter in the environment, during host infection or antibiotic treatments. Here we re-visit the dynamics of filament formation and recovery using a consistent framework based on live-cells microscopy. We compare the fate of filamentous Escherichia coli induced by cephalexin that inhibits cell division or by UV-induced DNA-damage that additionally perturbs chromosome segregation. We show that both filament types recover by successive and accelerated rounds of divisions that preferentially occur at the filaments' tip, thus resulting in the rapid production of multiple daughter cells with tightly regulated size. The DNA content, viability and further division of the daughter cells essentially depends on the coordination between chromosome segregation and division within the mother filament. Septum positioning at the filaments' tip depends on the Min system, while the nucleoid occlusion protein SlmA regulates the timing of division to prevent septum closure on unsegregated chromosomes. Our results not only recapitulate earlier conclusions but provide a higher level of detail regarding filaments division and the fate of the daughter cells. Together with previous reports, this work uncovers how filamentation recovery allows for a rapid cell proliferation after stress treatment.     

Taxonomic Characterization of New Alkaliphilic and Alkalitolerant Methanotrophs from Soda Lakes of the Southeastern Transbaikal Region and description of Methylomicrobium buryatense sp.nov.

Five strains of obligate methanotrophic bacteria (4G, 5G, 6G, 7G and 5B) isolated from bottom sediments of Southeastern Transbaikal soda lakes (pH 9.5–10.5) are taxonomically described. These bacteria are aerobic, Gram-negative monotrichous rods having tightly packed cup-shaped structures on the outer cell wall surface (S-layers) and Type I intracytoplasmic membranes. All the isolates possess particulate methane monooxygenase (pMMO) and one strain (5G) also contains soluble methane monooxygenase (sMMO). They assimilate methane and methanol via the ribulose monophosphate pathway (RuMP). The isolates are alkalitolerant or facultatively alkaliphilic, able to grow at pH 10.5–11.0 and optimally at pH 8.5–9.5. These organisms are obligately dependent on the presence of sodium ions in the growth medium and tolerate up to 0.9–1.4 M NaCl or 1 M NaHCO₃. Although being mesophilic, all the isolates are resistant to heating (80 °C, 20 min), freezing and drying. Their cellular fatty acids profiles primarily consist of C_16:1. The major phospholipids are phosphatidylethanolamine and phosphatidylglycerol. The main quinone is Q-8. The DNA G+C content ranges from 49.2–51.5 mol%. Comparative 16S rDNA sequencing showed that the newly isolated methanotrophs are related to membres of the Methylomicrobium genus. However, they differ from the known members of this genus by DNA-DNA relatedness. Based on pheno- and genotypic characteristics, we propose a new species of the genus Methylomicrobium - Methylomicrobium buryatense sp. nov.     

Snow algae of the Windmill Islands, continental Antarctica 3. Chloromonas polyptera (Volvocales, Chlorophyta)

A new name, Chloromonas hohamii, is proposed to accommodate a common North American snow alga previously incorrectly referred to as Chloromonas polyptera. Chloromonas hohamii differs in having the motile vegetative cells with a cup-shaped chloroplast opening in the anterior end of the cell, shorter, narrower, ellipsoidal to elongate to somewhat fusiform, sexual spores with non-spiralled wall flanges, shorter and narrower daughter cells derived from the spores, and it grows in snow of significantly lower pH and conductivity. Received: 29 August 1997 / Accepted: 24 April 1998