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| 2. |
- Adlerberth, Ingegerd, 1959, et al.
(författare)
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A mannose-specific adherence mechanism in Lactobacillus plantarum conferring binding to the human colonic cell line HT-29.
- 1996
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Ingår i: Applied and environmental microbiology. - 0099-2240. ; 62:7, s. 2244-51
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Tidskriftsartikel (refereegranskat)abstract
- Two Lactobacillus plantarum strains of human intestinal origin, strains 299 (= DSM 6595) and 299v (= DSM 9843), have proved to be efficient colonizers of the human intestine under experimental conditions. These strains and 17 other L. plantarum strains were tested for the ability to adhere to cells of the human colonic cell line HT-29.L.plantarum 299 and 299v and nine other L. plantarum strains, including all six strains that belong to the same genetic subgroup as L. plantarum 299 and 299v, adhered to HT-29 cells in a manner that could be inhibited by methyl-alpha-D-mannoside. The ability to adhere to HT-29 cells correlated with an ability to agglutinate cells of Saccharomyces cerevisiae and erythrocytes in a mannose-sensitive manner and with adherence to D-mannose-coated agarose beads. L. plantarum 299 and 299v adhered to freshly isolated human colonic and ileal enterocytes, but the binding was not significantly inhibited by methyl-alpha-D-mannoside. Periodate treatment of HT-29 cells abolished mannose-sensitive adherence, confirming that the cell-bound receptor was of carbohydrate nature. Proteinase K treatment of the bacteria also abolished adherence, indicating that the binding involved protein structures on the bacterial cell surface. Thus, a mannose-specific adhesin has been identified in L. plantarum; this adhesin could be involved in the ability to colonize the intestine.
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| 3. |
- Aertsen, A., et al.
(författare)
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Heat shock protein-mediated resistance to high hydrostatic pressure in Escherichia coli
- 2004
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 70:5, s. 2660-2666
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Tidskriftsartikel (refereegranskat)abstract
- A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i) the expression of rpoH, encoding the heat shock-specific sigma factor {sigma}32, was also induced by high pressure; (ii) heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii) basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels.
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| 4. |
- Agervald, Åsa, et al.
(författare)
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CalA, a cyanobacterial AbrB protein, interacts with the upstream region of hypC and acts as a repressor of its transcription in the cyanobacterium Nostoc sp. strain PCC 7120
- 2010
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 76:3, s. 880-890
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Tidskriftsartikel (refereegranskat)abstract
- The filamentous, heterocystous, nitrogen-fixing cyanobacterium Nostoc sp. strain PCC 7120 may contain, depending on growth condition, up to two hydrogenases directly involved in hydrogen metabolism. HypC is one out of at least seven auxiliary gene products required for synthesis of a functional hydrogenase, specifically involved in the maturation of the large subunit. In this study we present a protein, Alr0946, belonging to the transcription regulator family AbrB, which in protein-DNA assays was found to interact with the upstream region of hypC. Transcriptional investigations showed that alr0946 is co-transcribed with the downstream gene alr0947, which encodes a putative protease from the abortive infection superfamily, Abi. Alr0946 was shown to interact specifically not only with the upstream region of hypC but also with its own upstream region, acting as a repressor on both. The bidirectional hydrogenase activity was significant down-regulated when Alr0946 was over-expressed demonstrating a correlation to the transcription factor, either direct or indirect. In silico studies showed that homologues to both Alr0946 and Alr0947 are highly conserved proteins within cyanobacteria with a very similar physical organisation of the corresponding structural genes. Possible functions of the co-transcribed downstream protein Alr0947 are presented. In addition, we present a 3D model of the CyAbrB domain of Alr0946 and putative DNA-binding mechanisms are discussed.
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| 5. |
- Ahlstrom, Christina A. A., et al.
(författare)
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Exchange of Carbapenem-Resistant Escherichia coli Sequence Type 38 Intercontinentally and among Wild Bird, Human, and Environmental Niches
- 2023
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Ingår i: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 89:6
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Tidskriftsartikel (refereegranskat)abstract
- Carbapenem-resistant bacteria are a threat to public health globally and have been found in the environment as well as the clinic. Some bacterial clones are associated with carbapenem resistance genes, such as Escherichia coli sequence type 38 (ST38) and the carbapenemase gene bla(OXA-48). Carbapenem-resistant Enterobacteriaceae (CRE) are a global threat to human health and are increasingly being isolated from nonclinical settings. OXA-48-producing Escherichia coli sequence type 38 (ST38) is the most frequently reported CRE type in wild birds and has been detected in gulls or storks in North America, Europe, Asia, and Africa. The epidemiology and evolution of CRE in wildlife and human niches, however, remains unclear. We compared wild bird origin E. coli ST38 genome sequences generated by our research group and publicly available genomic data derived from other hosts and environments to (i) understand the frequency of intercontinental dispersal of E. coli ST38 clones isolated from wild birds, (ii) more thoroughly measure the genomic relatedness of carbapenem-resistant isolates from gulls sampled in Turkey and Alaska, USA, using long-read whole-genome sequencing and assess the spatial dissemination of this clone among different hosts, and (iii) determine whether ST38 isolates from humans, environmental water, and wild birds have different core or accessory genomes (e.g., antimicrobial resistance genes, virulence genes, plasmids) which might elucidate bacterial or gene exchange among niches. Our results suggest that E. coli ST38 strains, including those resistant to carbapenems, are exchanged between humans and wild birds, rather than separately maintained populations within each niche. Furthermore, despite close genetic similarity among OXA-48-producing E. coli ST38 clones from gulls in Alaska and Turkey, intercontinental dispersal of ST38 clones among wild birds is uncommon. Interventions to mitigate the dissemination of antimicrobial resistance throughout the environment (e.g., as exemplified by the acquisition of carbapenem resistance by birds) may be warranted.IMPORTANCE Carbapenem-resistant bacteria are a threat to public health globally and have been found in the environment as well as the clinic. Some bacterial clones are associated with carbapenem resistance genes, such as Escherichia coli sequence type 38 (ST38) and the carbapenemase gene bla(OXA-48). This is the most frequently reported carbapenem-resistant clone in wild birds, though it was unclear if it circulated within wild bird populations or was exchanged among other niches. The results from this study suggest that E. coli ST38 strains, including those resistant to carbapenems, are frequently exchanged among wild birds, humans, and the environment. Carbapenem-resistant E. coli ST38 clones in wild birds are likely acquired from the local environment and do not constitute an independent dissemination pathway within wild bird populations. Management actions aimed at preventing the environmental dissemination and acquisition of antimicrobial resistance by wild birds may be warranted.
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| 6. |
- Ahmed Osman, Omneya, et al.
(författare)
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Interactions of Freshwater Cyanobacteria with Bacterial Antagonists
- 2017
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 83:7
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Tidskriftsartikel (refereegranskat)abstract
- Cyanobacterial and algal mass development, or blooms, have severe effects on freshwater and marine systems around the world. Many of these phototrophs produce a variety of potent toxins, contribute to oxygen depletion, and affect water quality in several ways. Coexisting antagonists, such as cyanolytic bacteria, hold the potential to suppress, or even terminate, such blooms, yet the nature of this interaction is not well studied. We isolated 31 cyanolytic bacteria affiliated with the genera Pseudomonas, Stenotrophomonas, Acinetobacter, and Delftia from three eutrophic freshwater lakes in Sweden and selected four phylogenetically diverse bacterial strains with strong-to-moderate lytic activity. To characterize their functional responses to the presence of cyanobacteria, we performed RNA sequencing (RNA-Seq) experiments on coculture incubations, with an initial predator-prey ratio of 1: 1. Genes involved in central cellular pathways, stress-related heat or cold shock proteins, and antitoxin genes were highly expressed in both heterotrophs and cyanobacteria. Heterotrophs in coculture expressed genes involved in cell motility, signal transduction, and putative lytic activity. L, D-Transpeptidase was the only significantly upregulated lytic gene in Stenotrophomonas rhizophila EK20. Heterotrophs also shifted their central metabolism from the tricarboxylic acid cycle to the glyoxylate shunt. Concurrently, cyanobacteria clearly show contrasting antagonistic interactions with the four tested heterotrophic strains, which is also reflected in the physical attachment to their cells. In conclusion, antagonistic interactions with cyanobacteria were initiated within 24 h, and expression profiles suggest varied responses for the different cyanobacteria and studied cyanolytes. IMPORTANCE Here, we present how gene expression profiles can be used to reveal interactions between bloom-forming freshwater cyanobacteria and antagonistic heterotrophic bacteria. Species-specific responses in both heterotrophs and cyanobacteria were identified. The study contributes to a better understanding of the interspecies cellular interactions underpinning the persistence and collapse of cyanobacterial blooms.
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| 7. |
- Albertsen, L., et al.
(författare)
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Diversion of Flux toward Sesquiterpene Production in Saccharomyces cerevisiae by Fusion of Host and Heterologous Enzymes
- 2011
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Ingår i: Applied and Environmental Microbiology. - 1098-5336 .- 0099-2240. ; 77:3, s. 1033-1040
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Tidskriftsartikel (refereegranskat)abstract
- The ability to transfer metabolic pathways from the natural producer organisms to the well-characterized cell factory Saccharomyces cerevisiae is well documented. However, as many secondary metabolites are produced by collaborating enzymes assembled in complexes, metabolite production in yeast may be limited by the inability of the heterologous enzymes to collaborate with the native yeast enzymes. This may cause loss of intermediates by diffusion or degradation or due to conversion of the intermediate through competitive pathways. To bypass this problem, we have pursued a strategy in which key enzymes in the pathway are expressed as a physical fusion. As a model system, we have constructed several fusion protein variants in which farnesyl diphosphate synthase (FPPS) of yeast has been coupled to patchoulol synthase (PTS) of plant origin (Pogostemon cablin). Expression of the fusion proteins in S. cerevisiae increased the production of patchoulol, the main sesquiterpene produced by PTS, up to 2-fold. Moreover, we have demonstrated that the fusion strategy can be used in combination with traditional metabolic engineering to further increase the production of patchoulol. This simple test case of synthetic biology demonstrates that engineering the spatial organization of metabolic enzymes around a branch point has great potential for diverting flux toward a desired product.
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| 8. |
- Aldén, Louise, et al.
(författare)
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Rapid method of determining factors limiting bacterial growth in soil
- 2001
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 67:4, s. 1830-1838
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Tidskriftsartikel (refereegranskat)abstract
- A technique to determine which nutrients limit bacterial growth in soil was developed. The method was based on measuring the thymidine incorporation rate of bacteria after the addition of C, N, and P in different combinations to soil samples. First, the thymidine incorporation method was tested in two different soils: an agricultural soil and a forest humus soil. Carbon (as glucose) was found to be the limiting substance for bacterial growth in both of these soils. The effect of adding different amounts of nutrients was studied, and tests were performed to determine whether the additions affected the soil pH and subsequent bacterial activity. The incubation time required to detect bacterial growth after adding substrate to the soil was also evaluated. Second, the method was used in experiments in which three different size fractions of straw (1 to 2, 0.25 to 1, and <0.25 mm) were mixed into the agricultural soil in order to induce N limitation for bacterial growth. When the straw fraction was small enough (<0.25 mm), N became the limiting nutrient for bacterial growth after about 3 weeks. After the addition of the larger straw fractions (1 to 2 and 0.25 to 1 mm), the soil bacteria were C limited throughout the incubation period (10 weeks), although an increase in the thymidine incorporation rate after the addition of C and N together compared with adding them separately was seen in the sample containing the size fraction from 0.25 to 1 mm. Third, soils from high-pH, limestone-rich areas were examined. P limitation was observed in one of these soils, while tendencies toward P limitation were seen in some of the other soils.
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| 9. |
- Almstrand, Robert, et al.
(författare)
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New methods for analysis of spatial distribution and co-aggregation of microbial populations in complex biofilms.
- 2013
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 79:19, s. 5978-5987
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Tidskriftsartikel (refereegranskat)abstract
- In biofilms, microbial activities form gradients of substrates and electron acceptors, creating a complex landscape of microhabitats, often resulting in structured localization of the microbial populations present. To understand the dynamic interplay between and within these populations, quantitative measurements and statistical analysis of their localization patterns within the biofilms are necessary, and adequate automated tools for such analyses are needed. We have designed and applied new methods for fluorescence in situ hybridization (FISH) and digital image analysis of directionally dependent (anisotropic) multispecies biofilms. A sequential-FISH approach allowed multiple populations to be detected in a biofilm sample. This was combined with an automated tool for vertical-distribution analysis by generating in silico biofilm slices and the recently developed Inflate algorithm for coaggregation analysis of microbial populations in anisotropic biofilms. As a proof of principle, we show distinct stratification patterns of the ammonia oxidizers Nitrosomonas oligotropha subclusters I and II and the nitrite oxidizer Nitrospira sublineage I in three different types of wastewater biofilms, suggesting niche differentiation between the N. oligotropha subclusters, which could explain their coexistence in the same biofilms. Coaggregation analysis showed that N. oligotropha subcluster II aggregated closer to Nitrospira than did N. oligotropha subcluster I in a pilot plant nitrifying trickling filter (NTF) and a moving-bed biofilm reactor (MBBR), but not in a full-scale NTF, indicating important ecophysiological differences between these phylogenetically closely related subclusters. By using high-resolution quantitative methods applicable to any multispecies biofilm in general, the ecological interactions of these complex ecosystems can be understood in more detail.
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| 10. |
- Alriksson, Björn, et al.
(författare)
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Cellulase production from spent lignocellulose hydrolysates by recombinant aspergillus niger
- 2009
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Ingår i: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 75:8, s. 2366-2374
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Tidskriftsartikel (refereegranskat)abstract
- A recombinant Aspergillus niger strain expressing the Hypocrea jecorina endoglucanase Cel7B was grown on spent hydrolysates (stillage) from sugarcane bagasse and spruce wood. The spent hydrolysates served as excellent growth media for the Cel7B-producing strain, A. niger D15[egI], which displayed higher endoglucanase activities in the spent hydrolysates than in standard medium with a comparable monosaccharide content (e.g., 2,100 nkat/ml in spent bagasse hydrolysate compared to 480 nkat/ml in standard glucose-based medium). In addition, A. niger D15[egI] was also able to consume or convert other lignocellulose-derived compounds, such as acetic acid, furan aldehydes, and phenolic compounds, which are recognized as inhibitors of yeast during ethanolic fermentation. The results indicate that enzymes can be produced from the stillage stream as a high-value coproduct in secondgeneration bioethanol plants in a way that also facilitates recirculation of process water.
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