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S Kjelleberg

Publications and source records attributed to S Kjelleberg.

At least 37 records · Page 2Linked to original sources
PubMed2000

Vibrio vulnificus: a physiological and genetic approach to the viable but nonculturable response.

In this review, we focus on studies of the viable but nonculturable response (VBNC) of Vibrio vulnificus, a significant and aggressive human pathogen, as a model system for the general understanding of the VBNC response. This response is characterized physiologically as the inability to culture an organism on media that normally supports its growth, and yet those cells retain indicators of metabolic activity. Implicit in this definition is that it may be possible to return or resuscitate VBNC cells to active division on laboratory media. Since its original description in 1985, the VBNC response has been recognized in a range of bacteria. Study of the VBNC response has traditionally focused on physiological methods aimed at demonstrating that VBNC cells are indeed viable but have a specific block that prevents them from dividing on laboratory media, and such study has attempted to identify conditions that unequivocally demonstrate the resuscitation of VBNC cells. With the advent of molecular genetics, VBNC studies have begun to focus on genetics as a means to determine whether there are specific genes or regulatory pathways responsible for the development of the VBNC response. Thus, by combining information from physiological and genetic experiments, it is hoped that it can be determined whether the VBNC response represents a genetically programmed physiological adaptation similar to sporulation and outgrowth or whether VBNC represents the slow loss of function on the way to cellular death.

Adaptation, Physiological↗
PubMed2000

Phylogenetic relationship and antifouling activity of bacterial epiphytes from the marine alga Ulva lactuca.

It is widely accepted that bacterial epiphytes can inhibit the colonization of surfaces by common fouling organisms. However, little information is available regarding the diversity and properties of these antifouling bacteria. This study assessed the antifouling traits of five epiphytes of the common green alga, Ulva lactuca. All isolates were capable of preventing the settlement of invertebrate larvae and germination of algal spores. Three of the isolates also inhibited the growth of a variety of bacteria and fungi. Their phylogenetic positions were determined by 16S ribosomal subunit DNA sequencing. All isolates showed a close affiliation with the genus Pseudoalteromonas and, in particular, with the species P. tunicata. Strains of this bacterial species also display a variety of antifouling activities, suggesting that antifouling ability may be an important trait for members of this genus to be highly successful colonizers of animate surfaces and for such species to protect their host against fouling.

Animals↗
PubMed2000

A novel and sensitive method for the quantification of N-3-oxoacyl homoserine lactones using gas chromatography-mass spectrometry: application to a model bacterial biofilm.

A method is reported for the quantification of 3-oxoacyl homoserine lactones (3-oxo AHLs), a major class of quorum-sensing signals found in Gram-negative bacteria. It is based on the conversion of 3-oxo AHLs to their pentafluorobenzyloxime derivatives followed by gas chromatography-mass spectrometry (electron capture-negative ion). The method used [13C16]-N-3-oxo-dodecanoyl homoserine lactone ([13C16]-OdDHL) as the internal standard, and its validity was tested by spiking the supernatant and cell fractions with three levels of 3-oxo AHLs, i.e. 1, 10 and 100 ng per sample. These showed the method to be both sensitive (S/N ratio >10:1 for 1 ng) and accurate. The assay was applied to the biofilm and effluent of a green fluorescent protein (GFP)-expressing strain of Pseudomonas aeruginosa (6294) culture grown in flow cells. Biofilm volume was determined for three replicate flow cells by confocal scanning laser microscopy. OdDHL was detected in the biofilm at 632 +/- 381 microM and the effluent at 14 +/- 3 nM. The biofilm concentration is the highest level so far reported for an AHL in a wild-type bacterial system. The next most abundant 3-oxo AHL in the biofilm and effluent was N-3-oxo-tetradecanoyl homoserine lactone (OtDHL) at 40 +/- 15 microM and 1.5 +/- 0.7 nM respectively. OtDHL is unreported for P. aeruginosa and has an activity equivalent to OdDHL in a lasR bioassay. Two other 3-oxo AHLs were detected at lower concentrations: N3-oxo-decanoyl homoserine lactone (ODHL) in the biofilm (3 +/- 2 microM) and effluent (1 +/- 0.1 nM); and N-3-oxo-octanoyl homoserine lactone (OOHL) in the effluent (0.1 +/- 0.1 nM).

Biofilms↗
PubMed2000

Inhibition of luminescence and virulence in the black tiger prawn (Penaeus monodon) pathogen Vibrio harveyi by intercellular signal antagonists.

Expression of luminescence in the Penaeus monodon pathogen Vibrio harveyi is regulated by an intercellular quorum sensing mechanism involving the synthesis and detection of two signaling molecules, one of which is N-hydroxy butanoyl-L-homoserine lactone and the other of which is uncharacterized. Indirect evidence has suggested that virulence, associated with a toxic extracellular protein, and luminescence in V. harveyi are coregulated. In this study the effects of an acylated homoserine lactone antagonist produced by the marine alga Delisea pulchra on luminescence and toxin production in a virulent strain of V. harveyi were analyzed. Luminescence and toxin production were both inhibited by the signal antagonist at concentrations that had no impact on growth. Toxin production was found to be prematurely induced in V. harveyi cultures incubated in a 10% conditioned medium. Additionally, a significant reduction in the toxicity of concentrated supernatant extracts from V. harveyi cultures incubated in the presence of the signal antagonist, as measured by in vivo toxicity assays in mice and prawns, was observed. These results suggest that intercellular signaling antagonists have potential utility in the control of V. harveyi prawn infections.

Animals↗
PubMed2000

rpoB-based microbial community analysis avoids limitations inherent in 16S rRNA gene intraspecies heterogeneity.

Contemporary microbial community analysis frequently involves PCR-amplified sequences of the 16S rRNA gene (rDNA). However, this technology carries the inherent problem of heterogeneity between copies of the 16S rDNA in many species. As an alternative to 16S rDNA sequences in community analysis, we employed the gene for the RNA polymerase beta subunit (rpoB), which appears to exist in one copy only in bacteria. In the present study, the frequency of 16S rDNA heterogeneity in bacteria isolated from the marine environment was assessed using bacterial isolates from the red alga Delisea pulchra and from the surface of a marine rock. Ten strains commonly used in our laboratory were also assessed for the degree of heterogeneity between the copies of 16S rDNA and were used to illustrate the effect of this heterogeneity on microbial community pattern analysis. The rock isolates and the laboratory strains were also used to confirm nonheterogeneity of rpoB, as well as to investigate the versatility of the primers. In addition, a comparison between 16S rDNA and rpoB PCR-DGGE (denaturing gradient gel electrophoresis)-based community analyses was performed using a DNA mixture of nine isolates from D. pulchra. Eight out of 14 isolates from D. pulchra, all rock isolates, and 6 of 10 laboratory strains displayed multiple bands for 16S rDNA when analyzed by DGGE. There was no indication of heterogeneity for either the rock isolates or the laboratory strains when rpoB was used for PCR-DGGE analysis. Microbial community pattern analysis using 16S rDNA PCR-DGGE showed an overestimation of the number of laboratory strains in the sample, while some strains were not represented. Therefore, the 16S rDNA PCR-DGGE-based community analysis was proven to be severely limited by 16S rDNA heterogeneity. The mixture of isolates from D. pulchra proved to be more accurately described using rpoB, compared to the 16S rDNA-based PCR-DGGE.

Bacteria↗
PubMed2000

Evidence for a role of rpoE in stressed and unstressed cells of marine Vibrio angustum strain S14.

We report the cloning, sequencing, and characterization of the rpoE homolog in Vibrio angustum S14. The rpoE gene encodes a protein with a predicted molecular mass of 19.4 kDa and has been demonstrated to be present as a single-copy gene by Southern blot analysis. The deduced amino acid sequence of RpoE is most similar to that of the RpoE homolog of Sphingomonas aromaticivorans, sigma(24), displaying sequence similarity and identity of 63 and 43%, respectively. Northern blot analysis demonstrated the induction of rpoE 6, 12, and 40 min after a temperature shift to 40 degrees C. An rpoE mutant was constructed by gene disruption. There was no difference in viability during logarithmic growth, stationary phase, or carbon starvation between the wild type and the rpoE mutant strain. In contrast, survival of the mutant was impaired following heat shock during exponential growth, as well as after oxidative stress at 24 h of carbon starvation. The mutant exhibited microcolony formation during optimal growth temperatures (22 to 30 degrees C), and cell area measurements revealed an increase in cell volume of the mutant during growth at 30 degrees C, compared to the wild-type strain. Moreover, outer membrane and periplasmic space protein analysis demonstrated many alterations in the protein profiles for the mutant during growth and carbon starvation, as well as following oxidative stress, in comparison with the wild-type strain. It is thereby concluded that RpoE has an extracytoplasmic function and mediates a range of specific responses in stressed as well as unstressed cells of V. angustum S14.

Amino Acid Sequence↗
PubMed1999

Marine Pseudoalteromonas species are associated with higher organisms and produce biologically active extracellular agents.

The newly established genus Pseudoalteromonas contains numerous marine species which synthesize biologically active molecules. The production of a range of compounds which are active against a variety of target organisms appears to be a unique characteristic for this genus and may greatly benefit Pseudoalteromonas cells in their competition for nutrients and colonization of surfaces. Species of Pseudoalteromonas are generally found in association with marine eukaryotes and display anti-bacterial, bacteriolytic, agarolytic and algicidal activities. Moreover, several Pseudoalteromonas isolates specifically prevent the settlement of common fouling organisms. While a wide range of inhibitory extracellular agents are produced, compounds promoting the survival of other marine organisms living in the vicinity of Pseudoalteromonas species have also been found.

Journal Article↗
PubMed1999

Quorum-sensing cross talk: isolation and chemical characterization of cyclic dipeptides from Pseudomonas aeruginosa and other gram-negative bacteria.

In cell-free Pseudomonas aeruginosa culture supernatants, we identified two compounds capable of activating an N-acylhomoserine lactone (AHL) biosensor. Mass spectrometry and NMR spectroscopy revealed that these compounds were not AHLs but the diketopiperazines (DKPs), cyclo(DeltaAla-L-Val) and cyclo(L-Pro-L-Tyr) respectively. These compounds were also found in cell-free supernatants from Proteus mirabilis, Citrobacter freundii and Enterobacter agglomerans [cyclo(DeltaAla-L-Val) only]. Although both DKPs were absent from Pseudomonas fluorescens and Pseudomonas alcaligenes, we isolated, from both pseudomonads, a third DKP, which was chemically characterized as cyclo(L-Phe-L-Pro). Dose-response curves using a LuxR-based AHL biosensor indicated that cyclo(DeltaAla-L-Val), cyclo(L-Pro-L-Tyr) and cyclo(L-Phe-L-Pro) activate the biosensor in a concentration-dependent manner, albeit at much higher concentrations than the natural activator N-(3-oxohexanoyl)-L-homoserine lactone (3-oxo-C6-HSL). Competition studies showed that cyclo(DeltaAla-L-Val), cyclo(L-Pro-L-Tyr) and cyclo(L-Phe-L-Pro) antagonize the 3-oxo-C6-HSL-mediated induction of bioluminescence, suggesting that these DKPs may compete for the same LuxR-binding site. Similarly, DKPs were found to be capable of activating or antagonizing other LuxR-based quorum-sensing systems, such as the N-butanoylhomoserine lactone-dependent swarming motility of Serratia liquefaciens. Although the physiological role of these DKPs has yet to be established, their activity suggests the existence of cross talk among bacterial signalling systems.

4-Butyrolactone↗
PubMed1999

Carnobacterium inhibens sp. nov., isolated from the intestine of Atlantic salmon (Salmo salar).

Strain K1T, isolated from the gastrointestinal tract of Atlantic salmon (Salmo salar), has the capacity to inhibit the growth of the fish pathogens Vibrio anguillarum and Aeromonas salmonicida. Strain K1T is a motile Gram-positive psychrophilic rod that lacks both catalase and oxidase, which does not grow on acetate containing media, but grows at pH 9 and in TSB with up to 6% sodium chloride content. Strain K1T is facultatively anaerobic and tryptone as a sole source of nutrient promotes growth. The most abundant cellular fatty acid of strain K1T is oleic acid (18:1cis9). Based on 16S rDNA sequence comparisons, it is suggested that strain K1T is phylogenetically closely related to C. alterfunditum. However, the unique phenotypic attributes of strain K1T suggest that it represents a new species. The name Carnobacterium inhibens is proposed, for which the type strain is K1T (= CCUG 31728T).

Aeromonas↗
PubMed1999

Bacterial signals and antagonists: the interaction between bacteria and higher organisms.

It is now well established that bacteria communicate through the secretion and uptake of small diffusable molecules. These chemical cues, or signals, are often used by bacteria to coordinate phenotypic expression and this mechanism of regulation presumably provides them with a competitive advantage in their natural environment. Examples of coordinated behaviors of marine bacteria which are regulated by signals include swarming and exoprotease production, which are important for niche colonisation or nutrient acquisition (e.g. protease breakdown of substrate). While the current focus on bacterial signalling centers on N-Acylated homoserine lactones, the quorum sensing signals of gram-negative bacteria, these are not the only types of signals used by bacteria. Indeed, there appears to be many other types of signals produced by bacteria and it also appears that a bacterium may use multiple classes of signals for phenotypic regulation. Recent work in the area of marine microbial ecology has led to the observation that some marine eukaryotes secrete their own signals which compete with the bacterial signals and thus inhibit the expression of bacterial signalling phenotypes. This type of molecular mimicry has been well characterised for the interaction of marine prokaryotes with the red alga, Delisea pulchra.

4-Butyrolactone↗
PubMed1998

Pseudoalteromonas tunicata sp. nov., a bacterium that produces antifouling agents.

A dark-green-pigmented marine bacterium, previously designated D2, which produces components that are inhibitory to common marine fouling organisms has been characterized and assessed for taxonomic assignment. Based on direct double-stranded sequencing of the 16S rRNA gene, D2T was found to show the highest similarity (93%) to members of the genus Pseudoalteromonas. The G + C content of D2T is 42 mol%, and it is a facultatively anaerobic rod and oxidase-positive. D2T is motile by a sheathed polar flagellum, exhibited non-fermentative metabolism and required sodium ions for growth. The strain was not capable of using citrate, fructose, sucrose, sorbitol and glycerol but it utilizes mannose and maltose and hydrolyses gelatin. The molecular evidence, together with phenotypic characteristics, showed that this bacterium which produces an antifouling agent constitutes a new species of the genus Pseudoalteromonas. The name Pseudoalteromonas tunicata is proposed for this bacterium, and the type strain is D2T (= CCUG 26757T).

Animals↗
PubMed1998

Implications of rRNA operon copy number and ribosome content in the marine oligotrophic ultramicrobacterium Sphingomonas sp. strain RB2256.

Sphingomonas sp. strain RB2256 is a representative of the dominant class of ultramicrobacteria that are present in marine oligotrophic waters. In this study we examined the rRNA copy number and ribosome content of RB2256 to identify factors that may be associated with the relatively low rate of growth exhibited by the organism. It was found that RB2256 contains a single copy of the rRNA operon, in contrast to Vibrio spp., which contain more than eight copies. The maximum number of ribosomes per cell was observed during mid-log phase; however, this maximum content was low compared to those of faster-growing, heterotrophic bacteria (approximately 8% of the maximum ribosome content of Escherichia coli with a growth rate of 1. 5 h-1). The low number of ribosomes per cell appears to correlate with the low rate of growth (0.16 to 0.18 h-1) and the presence of a single copy of the rRNA operon. However, on the basis of cell volume, RB2256 appears to have a higher concentration of ribosomes than E. coli (approximately double that of E. coli with a growth rate of 1.5 h-1). Ribosome numbers reached maximum levels during mid-log-phase growth but decreased rapidly to 10% of maximum during late log phase through 7 days of starvation. The cells in late log phase and at the onset of starvation displayed an immediate response to a sudden addition of excess glucose (3 mM). This result demonstrates that a ribosome content 10% of maximum is sufficient to allow cells to immediately respond to nutrient upshift and achieve maximum rates of growth. These data indicate that the bulk of the ribosome pool is not required for protein synthesis and that ribosomes are not the limiting factor contributing to a low rate of growth. Our findings show that the regulation of ribosome content, the number of ribosomes per cell, and growth rate responses in RB2256 are fundamentally different from those characteristics in fast-growing heterotrophs like E. coli and that they may be characteristics typical of oligotrophic ultramicrobacteria.

Alaska↗
PubMed1998

Extracellular signal molecule(s) involved in the carbon starvation response of marine Vibrio sp. strain S14.

The role of exogenous metabolites as putative signal molecules mediating and/or regulating the carbon starvation adaptation program in Vibrio sp. strain S14 was investigated. Addition of the stationary-phase supernatant extract (SSE) of Vibrio sp. strain S14 to logarithmic-phase cells resulted in a significant number of carbon starvation-induced proteins being up-regulated. Halogenated furanones, putative antagonists of acylated homoserine lactones (AHLs), inhibited the synthesis of proteins specifically induced upon carbon starvation. The effect of the furanone was the opposite of that caused by SSE with respect to the up- and down-regulation of protein expression, indicating that both the furanone and the putative signalling molecules were acting on the same regulatory pathway. Culturability was rapidly lost when Vibrio sp. strain S14 was starved in the presence of the furanone at a low concentration. The furanone also had a negative effect on the ability of carbon-starved cells to mount resistance against UV irradiation and hydrogen peroxide exposure. The SSE of Vibrio sp. strain S14 had the ability to provide cross-protection against the loss in viability caused by the furanone. We have further demonstrated that the SSE taken from low- as well as high-cell-density cultures of Vibrio sp. strain S14 induced luminescence in Vibrio harveyi. Taken together, the results in this report provide evidence that Vibrio sp. strain S14 produces extracellular signalling metabolites during carbon and energy starvation and that these molecules play an important role in the expression of proteins crucial to the development of starvation- and stress-resistant phenotypes.

Bacterial Proteins↗
PubMed1997

Global analysis of physiological responses in marine bacteria.

In this paper, we present results from studies on marine Vibrio species, in which complex adaptive responses have been investigated. The results of two-dimensional polyacrylamide gel electrophoresis serve to illustrate the usefulness of a global approach, and how it can be combined with other methodologies in order to achieve an improved understanding of the means by which bacteria adapt to alterations in environmental conditions. The overall strategies described in this paper are particularly useful for studies of bacteria for which efficient genetic tools, background genotypes and in depth physiological data are not yet available.

Adaptation, Physiological↗
PubMed1997

Plasmid Transfer between Marine Vibrio Strains during Predation by the Heterotrophic Microflagellate Cafeteria roenbergensis.

The effect of grazing by the heterotrophic microflagellate Cafeteria roenbergensis on plasmid transfer between marine Vibrio S14 strains was studied by using artificial seawater. Several factors of potential importance for regulation of the plasmid transfer, such as nutrient release, production of a flagellate-derived substance(s) that may affect plasmid transfer, and the presence of surfaces, were investigated. Only living flagellates gave rise to, at instances, plasmid transfer enhanced more than 2 orders of magnitude. We propose that the activity of grazing flagellates allows for the significant increase in plasmid transfer observed under predation conditions. This may be due to a localized increase in bacterial numbers through filter feeding, thus providing high cell densities with increased possibility for cell-to-cell-contact and hence plasmid transfer.

Journal Article↗