▪ Abstract Agricultural soils suppressive to soilborne plant pathogens occur worldwide, and for several of these soils the biological basis of suppressiveness has been described. Two classical types of suppressiveness are known. General suppression owes its activity to the total microbial biomass in soil and is not transferable between soils. Specific suppression owes its activity to the effects of individual or select groups of microorganisms and is transferable. The microbial basis of specific suppression to four diseases, Fusarium wilts, potato scab, apple replant disease, and take-all, is discussed. One of the best-described examples occurs in take-all decline soils. In Washington State, take-all decline results from the buildup of fluorescent Pseudomonas spp. that produce the antifungal metabolite 2,4-diacetylphloroglucinol. Producers of this metabolite may have a broader role in disease-suppressive soils worldwide. By coupling molecular technologies with traditional approaches used in plant patholog...

Microbial populations responsible for specific soil suppressiveness to plant pathogens.

https://escholarship.org/content/qt7vr6q81m/qt7vr6q81m.pdf?t=qlsxxe

Update of the LIPID MAPS comprehensive classification system for lipids

Actinobacteria are Gram-positive bacteria with high G+C DNA content that constitute one of the largest bacterial phyla, and they are ubiquitously distributed in both aquatic and terrestrial ecosystems. Many Actinobacteria have a mycelial lifestyle and undergo complex morphological differentiation. They also have an extensive secondary metabolism and produce about two-thirds of all naturally derived antibiotics in current clinical use, as well as many anticancer, anthelmintic, and antifungal compounds. Consequently, these bacteria are of major importance for biotechnology, medicine, and agriculture. Actinobacteria play diverse roles in their associations with various higher organisms, since their members have adopted different lifestyles, and the phylum includes pathogens (notably, species of Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, and Tropheryma), soil inhabitants (e.g., Micromonospora and Streptomyces species), plant commensals (e.g., Frankia spp.), and gastrointestinal commensals (Bifidobacterium spp.). Actinobacteria also play an important role as symbionts and as pathogens in plant-associated microbial communities. This review presents an update on the biology of this important bacterial phylum.

/pdf/taxonomy-physiology-and-natural-products-of-actinobacteria-1arwsidgil.pdf

Taxonomy, Physiology, and Natural Products of Actinobacteria

Trichothecene mycotoxins are a group of structurally similar fungal metabolites that are capable of producing a wide range of toxic effects. Deoxynivalenol (DON, vomitoxin), a trichothecene, is prevalent worldwide in crops used for food and feed production, including in Canada and the United States. Although DON is one of the least acutely toxic trichothecenes, it should be treated as an important food safety issue because it is a very common contaminant of grain. This review focuses on the ability of DON to induce toxicologic and immunotoxic effects in a variety of cell systems and animal species. At the cellular level, the main toxic effect is inhibition of protein synthesis via binding to the ribosome. In animals, moderate to low ingestion of toxin can cause a number of as yet poorly defined effects associated with reduced performance and immune function. The main overt effect at low dietary concentrations appears to be a reduction in food consumption (anorexia), while higher doses induce vomiting (emesis). DON is known to alter brain neurochemicals. The serotoninergic system appears to play a role in mediation of the feeding behavior and emetic response. Animals fed low to moderate doses are able to recover from initial weight losses, while higher doses induce more long-term changes in feeding behavior. At low dosages of DON, hematological, clinical, and immunological changes are also transitory and decrease as compensatory/adaptation mechanisms are established. Swine are more sensitive to DON than mice, poultry, and ruminants, in part because of differences in metabolism of DON, with males being more sensitive than females. The capacity of DON to alter normal immune function has been of particular interest. There is extensive evidence that DON can be immunosuppressive or immunostimulatory, depending upon the dose and duration of exposure. While immunosuppression can be explained by the inhibition of translation, immunostimulation can be related to interference with normal regulatory mechanisms. In vivo, DON suppresses normal immune response to pathogens and simultaneously induces autoimmune-like effects which are similar to human immunoglobulin A (IgA) nephropathy. Other effects include superinduction of cytokine production by T helper cells (in vitro) and activation of macrophages and T cells to produce a proinflammatory cytokine wave that is analogous to that found in lipopolysaccharide-induced shock (in vivo). To what extent the elevation of cytokines contributes to metabolic effects such as decreased feed intake remains to be established. Although these effects have been largely characterized in the mouse, several investigations with DON suggest that immunotoxic effects are also likely in domestic animals. Further toxicology studies and an assessment of the potential of DON to be an etiologic agent in human disease are warranted.

Toxicology of deoxynivalenol (vomitoxin).

Summary: Nitroaromatic compounds are relatively rare in nature and have been introduced into the environment mainly by human activities. This important class of industrial chemicals is widely used in the synthesis of many diverse products, including dyes, polymers, pesticides, and explosives. Unfortunately, their extensive use has led to environmental contamination of soil and groundwater. The nitro group, which provides chemical and functional diversity in these molecules, also contributes to the recalcitrance of these compounds to biodegradation. The electron-withdrawing nature of the nitro group, in concert with the stability of the benzene ring, makes nitroaromatic compounds resistant to oxidative degradation. Recalcitrance is further compounded by their acute toxicity, mutagenicity, and easy reduction into carcinogenic aromatic amines. Nitroaromatic compounds are hazardous to human health and are registered on the U.S. Environmental Protection Agency's list of priority pollutants for environmental remediation. Although the majority of these compounds are synthetic in nature, microorganisms in contaminated environments have rapidly adapted to their presence by evolving new biodegradation pathways that take advantage of them as sources of carbon, nitrogen, and energy. This review provides an overview of the synthesis of both man-made and biogenic nitroaromatic compounds, the bacteria that have been identified to grow on and completely mineralize nitroaromatic compounds, and the pathways that are present in these strains. The possible evolutionary origins of the newly evolved pathways are also discussed.

Nitroaromatic Compounds, from Synthesis to Biodegradation

/pdf/plant-pathogenicity-in-the-genus-streptomyces-39b322iwjp.pdf

Plant pathogenicity in the genus streptomyces.

Two phytotoxins capable of inducing scab-like lesions on immature potato tubers were isolated from field grown and aseptically cultured potato tubers that had been infected by Streptomyces scabies; the compounds were characterized by spectral methods and partial syntheses as unique 2,5-dioxopiperazines.

Isolation and characterization of phytotoxins associated with Streptomyces scabies

Transformation of deoxynivalenol (vomitoxin) by rumen microorganisms

The thaxtomin phytotoxins: Sources, synthesis, biosynthesis, biotransformation and biological activity

A total of 23 isolates obtained from scab infected potato tubers representative of six sampling areas in Eastern and Central Canada and five ATCCStreptomyces strains were screened for pathogenicity on the basis of their ability to initiate scab development on aseptically cultured minitubers and plant generated tubers. The results were then correlated with any associated generation of the scab inducing phytotoxin, Thaxtomin A. In all cases a positive correlation was demonstrated between the pathogenicity of variousStreptomyces scabies isolates and their ability to produce the phytotoxin.

Russell R. King

Papers

Plant pathogenicity in the genus streptomyces.

Isolation and characterization of phytotoxins associated with Streptomyces scabies

Transformation of deoxynivalenol (vomitoxin) by rumen microorganisms

The thaxtomin phytotoxins: Sources, synthesis, biosynthesis, biotransformation and biological activity

Correlation of phytotoxin production with pathogenicity of Streptomyces scabies isolates from scab infected potato tubers