Comparison of microbial community assemblages in the rhizosphere of three Amaranthus spp.

Weed management remains a major challenge in cropping systems worldwide, with rising interest in ecological based approaches that can be integrated with herbicide use. Soil microbial communities may play important, yet undiscovered, roles in weed success. Little is known about the rhizosphere communities associated with weeds like Amaranthus, commonly known as pigweeds, and considered some of the most problematic weeds in agricultural systems.

Tropical lacustrine sediment microbial community response to an extreme El Niño event.

Salinity can influence microbial communities and related functional groups in lacustrine sediments, but few studies have examined temporal variability in salinity and associated changes in lacustrine microbial communities and functional groups. To better understand how microbial communities and functional groups respond to salinity, we examined geochemistry and functional gene amplicon sequence data collected from 13 lakes located in Kiritimati, Republic of Kiribati (2° N, 157° W) in July 2014 and June 2019, dates which bracket the very large El Niño event of 2015-2016 and a period of extremely high precipitation rates. Lake water salinity values in 2019 were significantly reduced and covaried with ecological distances between microbial samples.

Stable carbon isotope values of syndepositional carbonate spherules and micrite record spatial and temporal changes in photosynthesis intensity.

Marine and lacustrine carbonate minerals preserve carbon cycle information, and their stable carbon isotope values (δ C) are frequently used to infer and reconstruct paleoenvironmental changes. However, multiple processes can influence the δ C values of bulk carbonates, confounding the interpretation of these values in terms of conditions at the time of mineral precipitation. Co-existing carbonate forms may represent different environmental conditions, yet few studies have analyzed δ C values of syndepositional carbonate grains of varying morphologies to investigate their origins.

Differential structure and functional gene response to geochemistry associated with the suspended and attached shallow aquifer microbiomes from the Illinois Basin, IL.

Despite the clear ecological significance of the microbiomes inhabiting groundwater and connected ecosystems, our current understanding of their habitats, functionality, and the ecological processes controlling their assembly have been limited. In this study, an efficient pipeline combining geochemistry, high-throughput Fluidigm functional gene amplification and sequencing was developed to analyze the suspended and attached microbial communities inhabiting five groundwater monitoring wells in the Illinois Basin, USA. The dominant taxa in the suspended and the attached microbial communities exhibited significantly different spatial and temporal changes in both alpha- and beta-diversity.

Beyond denitrification: The role of microbial diversity in controlling nitrous oxide reduction and soil nitrous oxide emissions.

Many biotic and abiotic processes contribute to nitrous oxide (N O) production in the biosphere, but N O consumption in the environment has heretofore been attributed primarily to canonical denitrifying microorganisms. The nosZ genes encoding the N O reductase enzyme, NosZ, responsible for N O reduction to dinitrogen are now known to include two distinct groups: the well-studied Clade I which denitrifiers typically possess, and the novel Clade II possessed by diverse groups of microorganisms, most of which are non-denitrifiers. Clade II N O reducers could play an important, previously unrecognized role in controlling N O emissions for several reasons, including: (1) the consumption of N O produced by processes other than denitrification, (2) hypothesized non-respiratory functions of NosZ as an electron sink or for N O detoxification, (3) possible differing enzyme kinetics of Clade II NosZ compared to Clade I NosZ, and (4) greater nosZ gene abundance for Clade II compared to Clade I in soils of many ecosystems.

Hierarchical detection of diverse Clade II (atypical) nosZ genes using new primer sets for classical- and multiplex PCR array applications.

The reduction of nitrous oxide (NO) to N represents the key terminal step in canonical denitrification. Nitrous oxide reductase (NosZ), the enzyme associated with this biological step, however, is not always affiliated with denitrifying microorganisms. Such organisms were shown recently to possess a Clade II (atypical) nosZ gene, in contrast to Clade I (typical) nosZ harbored in more commonly studied denitrifiers.

Comparing DNA, RNA and protein levels for measuring microbial dynamics in soil microcosms amended with nitrogen fertilizer.

To what extent multi-omic techniques could reflect in situ microbial process rates remains unclear, especially for highly diverse habitats like soils. Here, we performed microcosm incubations using sandy soil from an agricultural site in Midwest USA. Microcosms amended with isotopically labeled ammonium and urea to simulate a fertilization event showed nitrification (up to 4.

Consumption of NO and other N-cycle intermediates by strain T-27.

Bacteria affiliated with the phylum Gemmatimonadetes are found in high abundance in many terrestrial and aquatic environments, yet little is known about their metabolic capabilities. Difficulty in their cultivation has prompted interest in identifying better growth conditions for metabolic studies, especially related to their ability to reduce NO, a potent greenhouse gas. T-27 is one of few cultivated strains of Gemmatimonadetes available for physiological studies.

Effects of triclosan and triclocarban on denitrification and NO emissions in paddy soil.

Triclosan (TCS) and triclocarban (TCC) are two common antimicrobial compounds, which are widely used as ingredients in pharmaceuticals and personal care products. They occur ubiquitously in soil due to biosolid application as agricultural fertilizers, but their influence on microbially mediated soil biogeochemical processes is poorly understood. We tested the effects of varying concentrations of TCS and TCC applied both individually and together on denitrification and NO emissions in paddy soil.

Influence of the geophagous earthworm Aporrectodea sp. on fate of bisphenol A and a branched 4-nonylphenol isomer in soil.

Large amounts of endocrine disrupting chemicals (EDCs) including bisphenol A (BPA) and nonylphenol (NP) are released into the soil due to the application of biosolids. Earthworms are the predominant biomass in many terrestrial ecosystems and profoundly influence the physico-chemical and biological properties of soils. However, information about the effects of earthworm activities on the behaviors of EDCs in soil is still limited.

Sequence alignments and validation of PCR primers used to detect phylogenetically diverse genes associated with dissimilatory nitrate reduction to ammonium (DNRA).

PCR primer sets were designed to target , the gene encoding the pentaheme nitrite reductase NrfA that catalyzes the nitrite ammonification step in the process of dissimilatory nitrate reduction to ammonium (DNRA). Details of the nucleotide alignments of the primer target regions of 271 sequences from reference genomes representing 18 distinct clades of NrfA are shown here along with validation of application to PCR-based methodology including the use of amplified fragment length polymorphism (AFLP) profiling and Illumina platform amplicon-based sequencing of environmental samples and selected reference strains. Summary data tables illustrate the specificity of forward primers nrfAF2awMOD and nrfAF2awMODgeo when paired with the new reverse primer nrfAR1MOD in relation to consensus target reference sequences associated with members of 18 NrfA clades.

Water-soluble exudates from seeds of Kochia scoparia exhibit antifungal activity against Colletotrichum graminicola.

Plant seed exudates are composed of complex mixtures of chemicals with potential for bioactive compounds with antimicrobial properties. This study focused on kochia (Kochia scoparia), one of many weedy plant species considered invasive in many agricultural systems. Extraction of compounds in water yielded an exudate mass equivalent to 7% of the original seed mass used.

Optimization of PCR primers to detect phylogenetically diverse nrfA genes associated with nitrite ammonification.

Dissimilatory nitrate reduction to ammonium (DNRA) is now known to be a more prevalent process in terrestrial ecosystems than previously thought. The key enzyme, a pentaheme cytochrome c nitrite reductase NrfA associated with respiratory nitrite ammonification, is encoded by the nrfA gene in a broad phylogeny of bacteria. The lack of reliable and comprehensive molecular tools to detect diverse nrfA from environmental samples has hampered efforts to meaningfully characterize the genetic potential for DNRA in environmental systems.

Year-Round Shotgun Metagenomes Reveal Stable Microbial Communities in Agricultural Soils and Novel Ammonia Oxidizers Responding to Fertilization.

The dynamics of individual microbial populations and their gene functions in agricultural soils, especially after major activities such as nitrogen (N) fertilization, remain elusive but are important for a better understanding of nutrient cycling. Here, we analyzed 20 short-read metagenomes collected at four time points during 1 year from two depths (0 to 5 and 20 to 30 cm) in two Midwestern agricultural sites representing contrasting soil textures (sandy versus silty loam) with similar cropping histories. Although the microbial community taxonomic and functional compositions differed between the two locations and depths, they were more stable within a depth/site throughout the year than communities in natural aquatic ecosystems.

Detection and Diversity of Fungal Nitric Oxide Reductase Genes (p450nor) in Agricultural Soils.

Unlabelled: Members of the Fungi convert nitrate (NO3 (-)) and nitrite (NO2 (-)) to gaseous nitrous oxide (N2O) (denitrification), but the fungal contributions to N loss from soil remain uncertain. Cultivation-based methodologies that include antibiotics to selectively assess fungal activities have limitations, and complementary molecular approaches to assign denitrification potential to fungi are desirable. Microcosms established with soils from two representative U.

Detecting nitrous oxide reductase (NosZ) genes in soil metagenomes: method development and implications for the nitrogen cycle.

Unlabelled: Microbial activities in soils, such as (incomplete) denitrification, represent major sources of nitrous oxide (N2O), a potent greenhouse gas. The key enzyme for mitigating N2O emissions is NosZ, which catalyzes N2O reduction to N2. We recently described "atypical" functional NosZ proteins encoded by both denitrifiers and nondenitrifiers, which were missed in previous environmental surveys (R.

Refined NrfA phylogeny improves PCR-based nrfA gene detection.

Dissimilatory nitrate reduction to ammonium (DNRA) and denitrification are contrasting microbial processes in the terrestrial nitrogen (N) cycle, in that the former promotes N retention and the latter leads to N loss (i.e., the formation of gaseous products).

Unexpected nondenitrifier nitrous oxide reductase gene diversity and abundance in soils.

Agricultural and industrial practices more than doubled the intrinsic rate of terrestrial N fixation over the past century with drastic consequences, including increased atmospheric nitrous oxide (N(2)O) concentrations. N(2)O is a potent greenhouse gas and contributor to ozone layer destruction, and its release from fixed N is almost entirely controlled by microbial activities. Mitigation of N(2)O emissions to the atmosphere has been attributed exclusively to denitrifiers possessing NosZ, the enzyme system catalyzing N(2)O to N(2) reduction.

Characterization of bromate-reducing bacterial isolates and their potential for drinking water treatment.

The objective of the current study was to isolate and characterize several bromate-reducing bacteria and to examine their potential for bioaugmentation to a drinking water treatment process. Fifteen bromate-reducing bacteria were isolated from three sources. According to 16S rRNA gene sequencing, the bromate-reducing bacteria are phylogenetically diverse, representing the Actinobacteria, Bacteroidetes, Firmicutes, and α-, β-, and γ-Proteobacteria.

Molecular ecology of macrolide-lincosamide-streptogramin B methylases in waste lagoons and subsurface waters associated with swine production.

RNA methylase genes are common antibiotic resistance determinants for multiple drugs of the macrolide, lincosamide, and streptogramin B (MLS(B)) families. We used molecular methods to investigate the diversity, distribution, and abundance of MLS(B) methylases in waste lagoons and groundwater wells at two swine farms with a history of tylosin (a macrolide antibiotic structurally related to erythromycin) and tetracycline usage. Phylogenetic analysis guided primer design for quantification of MLS(B) resistance genes found in tylosin-producing Streptomyces (tlr(B), tlr(D)) and commensal/pathogenic bacteria (erm(A), erm(B), erm(C), erm(F), erm(G), erm(Q)).

Fate and transport of antibiotic residues and antibiotic resistance genes following land application of manure waste.

Antibiotics are used in animal livestock production for therapeutic treatment of disease and at subtherapeutic levels for growth promotion and improvement of feed efficiency. It is estimated that approximately 75% of antibiotics are not absorbed by animals and are excreted in waste. Antibiotic resistance selection occurs among gastrointestinal bacteria, which are also excreted in manure and stored in waste holding systems.

Monitoring and source tracking of tetracycline resistance genes in lagoons and groundwater adjacent to swine production facilities over a 3-year period.

To monitor the dissemination of resistance genes into the environment, we determined the occurrence of tetracycline resistance (Tc(r)) genes in groundwater underlying two swine confinement operations. Monitoring well networks (16 wells at site A and 6 wells at site C) were established around the lagoons at each facility. Groundwater (n = 124) and lagoon (n = 12) samples were collected from the two sites at six sampling times from 2000 through 2003.

Tetracycline residues and tetracycline resistance genes in groundwater impacted by swine production facilities.

Antibiotics are used at therapeutic levels to treat disease; at slightly lower levels as prophylactics; and at low, subtherapeutic levels for growth promotion and improvement of feed efficiency. Over 88% of swine producers in the United States gave antimicrobials to grower/finisher pigs in feed as a growth promoter in 2000. It is estimated that ca.

DNA buoyant density shifts during 15N-DNA stable isotope probing.

DNA-based stable isotope probing (SIP) is a novel technique for the identification of organisms actively assimilating isotopically labeled compounds. Herein, we define the limitations to using 15N-labeled substrates for SIP and propose modifications to compensate for these shortcomings. Changes in DNA buoyant density (BD) resulting from 15N incorporation were determined using cultures of disparate GC content (Escherichia coli and Micrococcus luteus).