Spotlight
Environmental Microbiology
Environmental MicrobiologyIn Planta Sporulation of Frankia spp. as a Determinant of Alder-Symbiont InteractionsMost Frankia-actinorhiza plant symbioses are capable of high rates of nitrogen fixation comparable to those found on legumes. Yet, our understanding of the ecology and distribution of Frankia spp. is still very limited. Several studies have focused on the distribution patterns of...
Environmental MicrobiologyChronic Airway Colonization by Achromobacter xylosoxidans in Cystic Fibrosis Patients Is Not Sustained by Their Domestic EnvironmentAchromobacter spp. are worldwide emerging opportunistic pathogens in CF patients, able to chronically colonize the respiratory tract. Apart from regular consultations at the hospital CF center, patients spend most of their time at home. Colonization from nonhuman sources has been suggested, but the presence of...
Environmental MicrobiologyMethanogens and Iron-Reducing Bacteria: the Overlooked Members of Mercury-Methylating Microbial Communities in Boreal LakesDespite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the...
Environmental Microbiology | SpotlightRediscovering Zygorhizidium affluens Canter: Molecular Taxonomy, Infectious Cycle, and Cryopreservation of a Chytrid Infecting the Bloom-Forming Diatom Asterionella formosaDespite their ecological relevance, parasitic aquatic chytrids are understudied, especially due to the challenges associated with their isolation and maintenance in culture. Here we isolated and established a culture of a chytrid parasite infecting the bloom-forming freshwater diatom Asterionella formosa. The chytrid morphology suggests that it corresponds to the...
Environmental MicrobiologySurvival of Extremophilic Yeasts in the Stratospheric Environment during Balloon Flights and in Laboratory SimulationsStudies of eukaryotic microorganisms under conditions of astrobiological relevance, as well as the aerial dispersion potential of extremophilic yeasts, are still lacking in the literature compared to works with bacteria. Using stratospheric balloon flights and a simulation chamber, we demonstrate that yeasts isolated from an extreme environment are capable of surviving all stressors found in the stratosphere, including intense UV...
Environmental MicrobiologyToxicity of Potential Fungal Defense Proteins towards the Fungivorous Nematodes Aphelenchus avenae and Bursaphelenchus okinawaensisOur results support the hypothesis that cytoplasmic proteins abundant in fungal fruiting bodies are involved in fungal resistance against predation. The toxicity of these proteins toward stylet-feeding nematodes, which are also capable of feeding on plants, and the abundance of these proteins in edible mushrooms, may open possible avenues for biological crop protection against parasitic nematodes, e.g., by expression of these proteins...
Environmental Microbiology | SpotlightChromate Resistance Mechanisms in Leucobacter chromiiresistensChromate is a highly toxic oxyanion. Extensive industrial use and inadequate waste management has caused the toxic pollution of several field sites. Understanding the chromate resistance mechanisms that enable organisms to thrive under these conditions is fundamental to develop (micro)biological strategies and applications aiming at bioremediation of contaminated soils or waters. Potential detoxifying microorganisms are often not...
Enzymology and Protein Engineering
Enzymology and Protein EngineeringVersatile Fungal Polyphenol Oxidase with Chlorophenol Bioremediation Potential: Characterization and Protein EngineeringA novel fungal PPO was heterologously expressed and biochemically characterized. Construction of single and double mutants led to the generation of variants with altered specificity against CPs. Through this work, knowledge is gained regarding the effect of mutations on the substrate specificity of PPOs. This work also demonstrates that more potent biocatalysts for the bioremediation of harmful CPs can be developed by applying site-...
Enzymology and Protein EngineeringA New Group of Modular Xylanases in Glycoside Hydrolase Family 8 from Marine BacteriaXylanases play a crucial role in natural xylan degradation and have been extensively used in industries such as food processing, animal feed, and kraft pulp biobleaching. Some marine bacteria have been found to secrete xylanases. Characterization of novel xylanases from marine bacteria has significance for both the clarification of xylan degradation mechanisms in the sea and the development of new enzymes for industrial application....
Enzymology and Protein Engineering | SpotlightFilling the Void: Introducing Aromatic Interactions into Solvent Tunnels To Enhance Lipase Stability in MethanolEnzymatic synthesis in organic solvents holds increasing industrial opportunities in many fields; however, one major obstacle is the limited stability of biocatalysts in such a denaturing environment. Aromatic interactions play a major role in protein folding and stability, and we were inspired by this to redesign enzyme voids. The rational protein engineering of solvent tunnels of lipase from...
Food Microbiology
Food MicrobiologyCell Wall Glycans Mediate Recognition of the Dairy Bacterium Streptococcus thermophilus by BacteriophagesStreptococcus thermophilus is widely used in starter cultures for cheese and yoghurt production. During dairy fermentations, infections of bacteria with bacteriophages result in acidification failures and a lower quality of the final products. An understanding of the molecular factors involved in phage-host interactions, in particular, the phage receptors in dairy...
Food MicrobiologyTranscriptional and Functional Analysis of Bifidobacterium animalis subsp. lactis Exposure to TetracyclineBifidobacterium animalis subsp. lactis is widely used in human food and dietary supplements. Although well documented to be safe, B. animalis subsp. lactis strains must not contain transferable antibiotic resistance...
Genetics and Molecular Biology
Genetics and Molecular BiologyCatalase Expression in Azospirillum brasilense Sp7 Is Regulated by a Network Consisting of OxyR and Two RpoH Paralogs and Including an RpoE1→RpoH5 Regulatory CascadeIn silico analysis of the A. brasilense genome showed the presence of multiple paralogs of genes involved in oxidative stress response, which included 2 OxyR transcription regulators and 3 catalases. So far, Deinococcus radiodurans and...
Genetics and Molecular BiologyEfficient Counterselection for Methylococcus capsulatus (Bath) by Using a Mutated pheS GeneMethanotrophs have long been considered promising strains for biologically reducing methane from the environment and converting it into valuable products, because they can oxidize methane at ambient temperatures and pressures. Although several methodologies and tools for the genetic manipulation of methanotrophs have been developed, their mutagenic efficiency remains lower than that of tractable strains such as...
Genetics and Molecular BiologyA Cotransformation Method To Identify a Restriction-Modification Enzyme That Reduces Conjugation Efficiency in Campylobacter jejuniConjugation is an important horizontal gene transfer mechanism contributing to the evolution of bacterial pathogenesis and antimicrobial resistance. Campylobacter jejuni, the leading foodborne bacterial organism, displays significant strain diversity due to horizontal gene transfer; however, the molecular components influencing conjugation efficiency in...
Methods
Methods | SpotlightBioaerosol Sampler Choice Should Consider Efficiency and Ability of Samplers To Cover Microbial DiversityAssociating bioaerosol exposure and health problems is challenging, and adequate exposure monitoring is a priority for scientists in the field. Conclusions that can be drawn from bioaerosol exposure studies are highly dependent on the design of the study and the methodologies used. The air sampling strategy is the first methodological step leading to an accurate interpretation of what is present in the air. Applying new molecular...
MethodsSingle Nucleotide Polymorphism Genotyping Analysis Shows That Vaccination Can Limit the Number and Diversity of Recombinant Progeny of Infectious Laryngotracheitis Viruses from the United StatesRecombination allows alphaherpesviruses to evolve over time and become more virulent. Historically, characterization of viral vaccines in poultry have mainly focused on limiting clinical disease, rather than limiting virus replication, but such approaches can allow field viruses to persist and evolve in vaccinated populations. In this study, we vaccinated chickens with Gallid alphaherpesvirus 1 vaccines that are commercially...
MethodsCRISPR-Cas9 and CRISPR-Assisted Cytidine Deaminase Enable Precise and Efficient Genome Editing in Klebsiella pneumoniaeGenetics is a key means to study bacterial physiology. However, the highly desirable scarless genetic manipulation is often time-consuming and laborious for the major human pathogen K. pneumoniae. We developed a CRISPR-Cas9-mediated genome-editing method and a cytidine base-editing system, enabling rapid, highly efficient, and iterative genome editing in both...
Methodscis-Acting Determinant Limiting Expression of Sphingomyelinase Gene sph2 in Leptospira interrogans, Identified with a gfp Reporter PlasmidGenetic tools are needed to examine gene expression in the pathogen Leptospira interrogans. We developed a reporter plasmid that replicates in L. interrogans with green fluorescent protein (GFP) as the readout of promoter activity. We demonstrated an application of the new reporter plasmid by...
Microbial Ecology
Microbial EcologyDiversity of Active Viral Infections within the Sphagnum MicrobiomeSphagnum-dominated peatlands play an important role in maintaining atmospheric carbon dioxide levels by modifying conditions in the surrounding soil to favor the growth of Sphagnum over that of other plant species. This lowers the rate of decomposition and facilitates the accumulation of fixed...
Microbial EcologyMetagenomic Insights into the Degradation of Resistant Starch by Human Gut MicrobiotaManipulation of gut microbiota is increasingly recognized as a promising approach to reduce various noncommunicable diseases, such as obesity and type 2 diabetes. Specific dietary supplements, including resistant starches (RS), are often a focus, yet comprehensive insights into functional responses of microbiota are largely lacking. Furthermore, unresponsiveness in certain individuals is poorly understood. Our data indicate that...
Physiology
PhysiologyAlanine, a Novel Growth Substrate for the Acetogenic Bacterium Acetobacterium woodiiPeptides and amino acids are widespread in nature, but there are only a few reports that demonstrated use of amino acids as carbon and energy sources by acetogenic bacteria, a central and important group in the anaerobic food web. Our finding that A. woodii can perform alanine oxidation coupled to reduction of carbon dioxide not only increases the number of substrates...
PhysiologyFunctional Redundancy in the Hydroxycinnamate Catabolism Pathways of the Salt Marsh Bacterium Sagittula stellata E-37Hydroxycinnamates (HCAs) are essential components of lignin and are involved in various plant functions, including defense. In nature, microbial degradation of HCAs is influential to global carbon cycling. HCA degradation pathways are also of industrial relevance, as microbial transformation of the HCA, ferulate, can generate vanillin, a valuable flavoring compound. Yet, surprisingly little is known of the genetics underlying bacterial...
Physiology | SpotlightDivergent Nrf Family Proteins and MtrCAB Homologs Facilitate Extracellular Electron Transfer in Aeromonas hydrophilaMetal-reducing microorganisms are used for electricity production, bioremediation of toxic compounds, wastewater treatment, and production of valuable compounds. Despite numerous microorganisms being reported to reduce metals, the molecular mechanism has primarily been studied in two model systems, Shewanella oneidensis and...
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Applied and Environmental Microbiology® (AEM) publishes study results that make significant contributions to applied microbial research, basic microbial ecology research, and genetic and molecular investigations of microbial topics of practical value.
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Dr. Harold L. Drake, Editor in Chief