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| 2. |
- Amlinger, Lina, et al.
(författare)
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Fluorescent CRISPR Adaptation Reporter for rapid quantification of spacer acquisition
- 2017
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- CRISPR-Cas systems are adaptive prokaryotic immune systems protecting against horizontally transferred DNA or RNA such as viruses and other mobile genetic elements. Memory of past invaders is stored as spacers in CRISPR loci in a process called adaptation. Here we developed a novel assay where spacer integration results in fluorescence, enabling detection of memory formation in single cells and quantification of as few as 0.05% cells with expanded CRISPR arrays in a bacterial population. Using this fluorescent CRISPR Adaptation Reporter (f-CAR), we quantified adaptation of the two CRISPR arrays of the type I-E CRISPR-Cas system in Escherichia coli, and confirmed that more integration events are targeted to CRISPR-II than to CRISPR-I. The f-CAR conveniently analyzes and compares many samples, allowing new insights into adaptation. For instance, we show that in an E. coli culture the majority of acquisition events occur in late exponential phase.
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| 3. |
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| 4. |
- Andersson, Dan I., et al.
(författare)
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Biological roles of translesion synthesis DNA polymerases in eubacteria
- 2010
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 77:3, s. 540-548
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Forskningsöversikt (refereegranskat)abstract
- Biological systems are strongly selected to maintain the integrity of their genomes by prevention and repair of external and internal DNA damages. However, some types of DNA lesions persist and might block the replication apparatus. The universal existence of specialized translesion synthesis DNA polymerases (TLS polymerases) that can bypass such lesions in DNA implies that replication blockage is a general biological problem. We suggest that the primary function for which translesion synthesis polymerases are selected is to rescue cells from replication arrest at lesions in DNA, a situation that, if not amended, is likely to cause an immediate and severe reduction in cell fitness and survival. We will argue that the mutagenesis observed during translesion synthesis is an unavoidable secondary consequence of this primary function and not, as has been suggested, an evolved mechanism to increase mutation rates in response to various stresses. Finally, we will discuss recent data on additional roles for translesion synthesis polymerases in the formation of spontaneous deletions and in transcription-coupled TLS, where the coupling of transcription to TLS is proposed to allow the rescue of the transcription machinery arrested at DNA lesions.
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| 5. |
- Baldanzi, Gabriel, et al.
(författare)
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OSA Is Associated With the Human Gut Microbiota Composition and Functional Potential in the Population-Based Swedish CardioPulmonary bioImage Study
- 2023
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Ingår i: Chest. - : Elsevier. - 0012-3692 .- 1931-3543. ; 164:2, s. 503-516
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Obstructive sleep apnea (OSA) is a common sleep-breathing disorder linked to increased risk of cardiovascular disease. Intermittent hypoxia and intermittent airway obstruction, hallmarks of OSA, have been shown in animal models to induce substantial changes to the gut microbiota composition and subsequent transplantation of fecal matter to other animals induced changes in blood pressure and glucose metabolism.RESEARCH QUESTION: Does obstructive sleep apnea in adults associate with the composition and metabolic potential of the human gut microbiota?STUDY DESIGN AND METHODS: We used respiratory polygraphy data from up to 3,570 individuals aged 50-64 from the population-based Swedish CardioPulmonary bioImage Study combined with deep shotgun metagenomics of fecal samples to identify cross-sectional associations between three OSA parameters covering apneas and hypopneas, cumulative sleep time in hypoxia and number of oxygen desaturation events with gut microbiota composition. Data collection about potential confounders was based on questionnaires, on-site anthropometric measurements, plasma metabolomics, and linkage with the Swedish Prescribed Drug Register.RESULTS: We found that all three OSA parameters were associated with lower diversity of species in the gut. Further, the OSA-related hypoxia parameters were in multivariable-adjusted analysis associated with the relative abundance of 128 gut bacterial species, including higher abundance of Blautia obeum and Collinsela aerofaciens. The latter species was also independently associated with increased systolic blood pressure. Further, the cumulative time in hypoxia during sleep was associated with the abundance of genes involved in nine gut microbiota metabolic pathways, including propionate production from lactate. Lastly, we observed two heterogeneous sets of plasma metabolites with opposite association with species positively and negatively associated with hypoxia parameters, respectively.INTERPRETATION: OSA-related hypoxia, but not the number of apneas/hypopneas, is associated with specific gut microbiota species and functions. Our findings lay the foundation for future research on the gut microbiota-mediated health effects of OSA.
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| 6. |
- Edelbroek, Bart, et al.
(författare)
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Chromosome-level genome assembly and annotation of the social amoeba Dictyostelium firmibasis
- 2024
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Ingår i: Scientific Data. - : Springer Nature. - 2052-4463. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Dicytostelium firmibasis is a member of Dictyostelia, a group of social amoebae that upon starvation display aggregative multicellularity where the amoebae transition from uni- to multicellular life. The D. firmibasis genome assembly that is currently available is of limited use due to its low contiguity, large number of undetermined bases, and lack of annotations. Here we used Nanopore long read sequencing, complemented with Illumina sequencing, and developmental transcriptomics as well as small RNA-sequencing, to present a new, fully annotated, chromosome-level D. firmibasis genome assembly. The new assembly contains no undetermined bases, and consists mainly of six large contigs representing the chromosomes, as well as a complete mitochondrial genome. This new genome assembly will be a valuable tool, allowing comprehensive comparison to Dictyostelium discoideum, the dictyostelid genetically tractable model. Further, the new genome will be important for studies of evolutionary processes governing the transition from unicellular to multicellular organisms and will aid in the sequencing and annotation of other dictyostelids genomes, many of which are currently of poor quality.
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| 7. |
- Ghosh, Anirban, et al.
(författare)
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Contact-dependent growth inhibition induces high levels of antibiotic-tolerant persister cells in clonal bacterial populations
- 2018
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Ingår i: EMBO Journal. - : WILEY. - 0261-4189 .- 1460-2075. ; 37:9
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial populations can use bet-hedging strategies to cope with rapidly changing environments. One example is non-growing cells in clonal bacterial populations that are able to persist antibiotic treatment. Previous studies suggest that persisters arise in bacterial populations either stochastically through variation in levels of global signalling molecules between individual cells, or in response to various stresses. Here, we show that toxins used in contact-dependent growth inhibition (CDI) create persisters upon direct contact with cells lacking sufficient levels of CdiI immunity protein, which would otherwise bind to and neutralize toxin activity. CDI-mediated persisters form through a feedforward cycle where the toxic activity of the CdiA toxin increases cellular (p)ppGpp levels, which results in Lon-mediated degradation of the immunity protein and more free toxin. Thus, CDI systems mediate a population density-dependent bet-hedging strategy, where the fraction of non-growing cells is increased only when there are many cells of the same genotype. This may be one of the mechanisms of how CDI systems increase the fitness of their hosts.
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| 8. |
- Jones, Allison M., et al.
(författare)
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Genetic Evidence for SecY Translocon-Mediated Import of Two Contact-Dependent Growth Inhibition (CDI) Toxins
- 2021
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Ingår i: mBio. - : American Society for Microbiology. - 2161-2129 .- 2150-7511. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The C-terminal (CT) toxin domains of contact-dependent growth inhibition (CDI) CdiA proteins target Gram-negative bacteria and must breach both the outer and inner membranes of target cells to exert growth inhibitory activity. Here, we examine two CdiA-CT toxins that exploit the bacterial general protein secretion machinery after delivery into the periplasm. A Ser281Phe amino acid substitution in transmembrane segment 7 of SecY, the universally conserved channel-forming subunit of the Sec translocon, decreases the cytotoxicity of the membrane depolarizing orphan10 toxin from enterohemorrhagic Escherichia coli EC869. Target cells expressing secY(S281F) and lacking either PpiD or YfgM, two SecY auxiliary factors, are fully protected from CDI-mediated inhibition either by CdiA-CTo10EC869 or by CdiA-CTGN05224, the latter being an EndoU RNase CdiA toxin from Klebsiella aerogenes GN05224 that has a related cytoplasm entry domain. RNase activity of CdiA-CTGN05224 was reduced in secY(S281F) target cells and absent in secY(S281F) Delta ppiD or secY(S281F) Delta yfgM target cells during competition co-cultures. Importantly, an allele-specific mutation in secY (secY(G313W)) renders DppiD or Delta yfgM target cells specifically resistant to CdiA-CTGN05224 but not to CdiA-CTo10EC869, further suggesting a direct interaction between SecY and the CDI toxins. Our results provide genetic evidence of a unique confluence between the primary cellular export route for unfolded polypeptides and the import pathways of two CDI toxins. IMPORTANCE Many bacterial species interact via direct cell-to-cell contact using CDI systems, which provide a mechanism to inject toxins that inhibit bacterial growth into one another. Here, we find that two CDI toxins, one that depolarizes membranes and another that degrades RNA, exploit the universally conserved SecY translocon machinery used to export proteins for target cell entry. Mutations in genes coding for members of the Sec translocon render cells resistant to these CDI toxins by blocking their movement into and through target cell membranes. This work lays the foundation for understanding how CDI toxins interact with the protein export machinery and has direct relevance to development of new antibiotics that can penetrate bacterial cell envelopes.
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| 9. |
- Kjellin, Jonas, et al.
(författare)
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Colicins and T6SS-based competition systems enhance enterotoxigenic E. coli (ETEC) competitiveness
- 2024
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Ingår i: Gut microbes. - : Taylor & Francis. - 1949-0976 .- 1949-0984. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Diarrheal diseases are still a significant problem for humankind, causing approximately half a million deaths annually. To cause diarrhea, enteric bacterial pathogens must first colonize the gut, which is a niche occupied by the normal bacterial microbiota. Therefore, the ability of pathogenic bacteria to inhibit the growth of other bacteria can facilitate the colonization process. Although enterotoxigenic Escherichia coli (ETEC) is one of the major causative agents of diarrheal diseases, little is known about the competition systems found in and used by ETEC and how they contribute to the ability of ETEC to colonize a host. Here, we collected a set of 94 fully assembled ETEC genomes by performing whole-genome sequencing and mining the NCBI RefSeq database. Using this set, we performed a comprehensive search for delivered bacterial toxins and investi-gated how these toxins contribute to ETEC competitiveness in vitro. We found that type VI secretion systems (T6SS) were widespread among ETEC (n = 47). In addition, several closely related ETEC strains were found to encode Colicin Ia and T6SS (n = 8). These toxins provide ETEC compe-titive advantages during in vitro competition against other E. coli, suggesting that the role of T6SS as well as colicins in ETEC biology has until now been underappreciated.
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| 10. |
- Koskiniemi, Sanna, et al.
(författare)
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Activation of cryptic aminoglycoside resistance in Salmonella enterica
- 2011
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 80:6, s. 1464-1478
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Tidskriftsartikel (refereegranskat)abstract
- Aminoglycoside resistance in bacteria can be acquired by several mechanisms, including drug modification, target alteration, reduced uptake and increased efflux. Here we demonstrate that increased resistance to the aminoglycosides streptomycin and spectinomycin in Salmonella enterica can be conferred by increased expression of an aminoglycoside adenyl transferase encoded by the cryptic, chromo-somally located aadA gene. During growth in rich medium the wild-type strain was susceptible but mutations that impaired electron transport and conferred a small colony variant (SCV) phenotype or growth in glucose/glycerol minimal media resulted in activation of the aadA gene and aminoglycoside resistance. Expression of the aadA gene was positively regulated by the stringent response regulator guanosine penta/tetraphosphate ((p) ppGpp). SCV mutants carrying stop codon mutations in the hemA and ubiA genes showed a streptomycin pseudo-dependent phenotype, where growth was stimulated by streptomycin. Our data suggest that this phenotype is due to streptomycin-induced readthrough of the stop codons, a resulting increase in HemA/UbiA levels and improved electron transport and growth. Our results demonstrate that environmental and mutational activation of a cryptic resistance gene can confer clinically significant resistance and that a streptomycin-pseudo-dependent phenotype can be generated via a novel mechanism that does not involve the classical rpsL mutations.
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