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Pseudomonas chlororaphis strain PA23 is a biocontrol agent able to suppress growth of the fungal pathogen Sclerotinia sclerotiorum. This bacterium produces an arsenal of exometabolites including pyrrolnitrin (PRN), phenazine (PHZ), hydrogen cyanide (HCN), and degradative enzymes. Production of these compounds is controlled at both the transcriptional and posttranscriptional levels by the Gac-Rsm system, RpoS, PsrA, and the Phz quorum-sensing system. Beyond pathogen-suppression, the success of a biocontrol agent is dependent upon its ability to establish itself in the environment where predation by bacterivorous organisms, including nematodes, may threaten persistence. The focus of this study was to investigate whether PA23 is able to resist grazing by Caenorhabditis elegans and to define the role played by exoproducts in the bacterial-nematode interaction. We discovered that both PRN and HCN contribute to fast- and slow-killing of C. elegans. HCN is well-established as having lethal effects on C. elegans; however, PRN has not been reported to be nematicidal. Exposure of L4 stage nematodes to purified PRN reduced nematode viability in a dose-dependent fashion and led to reduced hatching of eggs laid by gravid adults. Because bacterial metabolites can act as chemoattractants or repellents, we analyzed whether PA23 exhibited attractant or repulsive properties towards C. elegans. Both PRN and HCN were found to be potent repellents. Next we investigated whether the presence of C. elegans would elicit changes in PA23 gene activity. Co-culturing the two organisms increased expression of a number of genes associated with biocontrol, including phzA, hcnA, phzR, phzI, rpoS and gacS. Exoproduct analysis showed that PHZ and autoinducer signals were upregulated, consistent with the gene expression profiles. Collectively, these findings indicate that PA23 is able to sense the presence of C. elegans and it is able to both repel and kill the nematodes, which should facilitate environmental persistence and ultimately biocontrol.

The effect of Plant Growth Promoting Rhizobacteria ( Bacillus sp.) and silver nanoparticles on Zea mays was evaluated. The silver nanoparticles were synthesized from Tagetes erecta (Marigold) leaf and flower extracts, whereas PGPR isolated from spinach rhizosphere. The silver nanoparticles (AgNPs) were purified using ultra centrifugation and were characterized using UV–Vis spectroscopy at gradient wavelength and also by High Resolution Transmission Electron microscopy (HRTEM). The average particles size of AgNPs was recorded approximately 60 nm. Almost all potential isolates were able to produce Indole Acetic Acid (IAA), ammonia and Hydrogen cyanide (HCN), solubilized tricalcium phosphate and inhibited the growth of Macrophomina phaseolina in vitro but the isolate LPR2 was found the best among all. On the basis of 16S rRNA gene sequence, the isolate LPR2 was characterized as Bacillus cereus LPR2. The maize seeds bacterized with LPR2 and AgNPs individually showed a significant increase in germination (87.5%) followed by LPR2 + AgNPs (75%). But the maximum growth of root and shoot of maize plant was observed in seeds coated with LPR2 followed by AgNPs and a combination of both. Bacillus cereus LPR2 and silver nanoparticles enhanced the plant growth and LPR2 strongly inhibited the growth of deleterious fungal pathogen. Therefore, LPR2 and AgNPs could be utilized as bioinoculant and growth stimulator, respectively for maize.

Bacterial volatile compounds have emerged as important chemical messengers between bacteria themselves as well as in their interactions with other organisms. One of the earliest examples of bioactive volatiles emitted by bacteria is hydrogen cyanide (HCN), which was long considered a mere respiratory toxin conferring competitive advantage to cyanide-producing strains. Using cyanide-deficient mutants in two Pseudomonas strains and global transcriptome analysis, we demonstrate that the impact of HCN is much more global than previously thought. We first observed that the lack of cyanogenesis (i.e., the ability to produce HCN) in emitting strains led to massive transcriptome reprogramming affecting diverse traits such as motility and biofilm formation (respectively inhibited vs promoted by HCN), or the production of siderophores, phenazines, and other antimicrobial compounds (repressed by HCN). We then exposed non-cyanogenic strains to biogenically emitted HCN from neighboring cells and observed similar transcriptome modulations and phenotypic changes, suggesting that HCN not only acts endogenously but also exogenously, remotely manipulating important traits involved in competition and virulence, e.g., siderophore production, in other organisms. Cyanogenesis in Pseudomonas has long been known to play a role in both the virulence of opportunistic pathogens and the efficient biocontrol activity of plant-beneficial strains; however, this impact was so far thought to occur solely through the inhibition of respiration. We demonstrate here new ecological roles for a small and fast-diffusing volatile compound, which opens novel avenues in our understanding of and ability to interfere with important processes taking place in pathogenic and beneficial Pseudomonas strains. Bacteria communicate by exchanging chemical signals, some of which are volatile and can remotely reach other organisms. HCN was one of the first volatiles discovered to severely impact exposed organisms by inhibiting their respiration. Using HCN-deficient mutants in two Pseudomonas strains, we demonstrate that HCN’s impact goes beyond the sole inhibition of respiration and affects both emitting and receiving bacteria in a global way, modulating their motility, biofilm formation, and production of antimicrobial compounds. Our data suggest that bacteria could use HCN not only to control their own cellular functions, but also to remotely influence the behavior of other bacteria sharing the same environment. Since HCN emission occurs in both clinically and environmentally relevant Pseudomonas , these findings are important to better understand or even modulate the expression of bacterial traits involved in both virulence of opportunistic pathogens and in biocontrol efficacy of plant-beneficial strains.

The demand for agricultural crops continues to escalate with an increasing population. To meet this demand, marginal land can be used as a sustainable source for increased plant productivity. However, moisture stress not only affects crop growth and productivity but also induces plants' susceptibility to various diseases. The positive role of plant growth hormone, salicylic acid (SA), on the defence systems of plants has been well documented. With this in mind, a combination of plant growth promoting rhizobacteria (PGPR) and SA was used to evaluate its performance on wheat grown under rainfed conditions (average moisture 10-14%). The selected bacterial strains were characterized for proline production, indole-3-acetic acid (IAA), hydrogen cyanide (HCN), ammonia (NH3), and exopolysaccharides (EPS). Wheat seeds of two genotypes, Inqilab-91 (drought tolerant) and Shahkar-2013 (drought sensitive), which differed in terms of their sensitivity to drought stress, were soaked for three hours prior to sowing in 24-hour old cultures of the bacterial strains Planomicrobium chinense strain P1 (accession no. MF616408) and Bacillus cereus strain P2 (accession no. MF616406). SA was applied (150 mg/L), as a foliar spray on one-month-old wheat seedlings. A significant reduction in the physiological parameters was noted in the plants grown in rainfed conditions but the PGPR and SA treatment effectively ameliorated the adverse effects of moisture stress. The wheat plants treated with PGPR and SA showed significant increases in leaf protein and sugar contents and maintained higher chlorophyll content, chlorophyll fluorescence (fv/fm) and performance index (PI) under rainfed conditions. Leaf proline content, lipid peroxidation, and antioxidant enzyme activity were higher in the non-inoculated plants grown in rainfed conditions but significantly reduced in the inoculated plants of both genotypes. Integrative use of a combination of PGPR strains and SA appears to be a promising and eco-friendly strategy for reducing moisture stress in plants.

The four gases, nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H₂S) and hydrogen cyanide (HCN) all readily inhibit oxygen consumption by mitochondrial cytochrome oxidase. This inhibition is responsible for much of their toxicity when they are applied externally to the body. However, recently these gases have all been implicated, to greater or lesser extents, in normal cellular signalling events. In this review we analyse the chemistry of this inhibition, comparing and contrasting mechanism and discussing physiological consequences. The inhibition by NO and CO is dependent on oxygen concentration, but that of HCN and H₂S is not. NO and H₂S are readily metabolised by oxidative processes within cytochrome oxidase. In these cases the enzyme may act as a physiological detoxifier of these gases. CO oxidation is much slower and unlikely to be as physiologically important. The evidence for normal physiological levels of these gases interacting with cytochrome oxidase is equivocal, in part because there is little robust data about their steady state concentrations. A reasonable case can be made for NO, and perhaps CO and H₂S, inhibiting cytochrome oxidase in vivo, but endogenous levels of HCN seem unlikely to be high enough.

Little is known about how pharmacological and toxicological knowledge evolves. The aim of this study was to investigate the changes in the presentation of the poison hydrogen cyanide in sixteen German-language pharmacology and toxicology textbooks from 1878 to 2020. The categories of structure, molecular mechanism of action, occurrence, effects, resorption, areas of application, lethal dose, acute symptoms of intoxication, treatment of hydrogen cyanide poisoning, and recommended therapeutic preparations were evaluated. The knowledge on the structure, lethal dosage, and occurrence of hydrogen cyanide has remained constant. In contrast, knowledge on molecular mechanism of action and recommended preparations of the poison has changed dramatically. Until 1944, the binding of hydrogen cyanide to hemoglobin was considered the mechanism of action, whereas from 1951 onwards, the interaction of hydrogen cyanide with the Fe 3+ of cytochrome oxidase was described. The number of preparations containing hydrogen cyanide decreased into obsolescence until 1951. The areas of application of hydrogen cyanide also show a change, as from 1919 onwards, mainly industrial areas of application of the poison are described instead of medical ones, and from 1951 onwards, criminalistic areas of application are also mentioned. Thus, pharmacological and toxicological knowledge develops non-linearly, molecular mechanism and uses being the most dynamic areas, whereas the knowledge about hydrogen cyanide’s chemical structure, lethal dose, and occurrence remained constant. Older pharmacology and toxicology textbooks were better than newer ones at discussing changes in scientific concepts. Pharmacology and toxicology textbooks also mostly failed to discuss the misuse of hydrogen cyanide (Zyklon B) during the Nazi regime, missing an important opportunity to showcase the ethical responsibility of pharmacology and toxicology. Thus, future pharmacology and toxicology textbooks should improve on discussing the development of pharmacological and toxicological concepts and the ethical responsibility of the discipline.

The use of plant tissue analysis as a tool for attaining low cyanogenic glucoside levels in cassava roots, has hardly been investigated. Just as the quality of crops is improved through the use of plant tissue analysis, the same can probably be done to consistently attain the lowest possible cyanogenic glucoside levels in cassava roots. High levels of cyanogenic glucosides in consumed fresh cassava roots or in their products have the potential of causing cyanide intoxication, hence the need to lower them. An experiment was thus conducted to assess the occurrence of meaningful relationships between plant nutritional status and cyanogenic glucoside production in cassava roots. Total hydrogen cyanide (HCN) levels in cassava roots were used to assess cyanogenic glucoside production. Using NPK fertiliser application to induce changes in plant nutritional status, the main objective of the study was investigated using the following sub-objectives; (1) to determine the effects of increased NPK fertiliser application on cassava root HCN levels; (2) and to show the occurrence of relationships between changes in nutrient levels in plant 'indicator tissue' and HCN levels in cassava roots. The study was a field experiment laid out as a split-plot in a randomized complete block design with three replicates. It was repeated in two consecutive years, with soil nutrient deficiencies only being corrected in the second year. The varieties Salanga, Kalinda, Supa and Kiroba were used in the experiment, while the NPK fertiliser treatments included; a control with no fertiliser applied; a moderate NPK treatment (50 kg N + 10 kg P + 50 kg K /ha); and a high NPK treatment (100 kg N + 25 kg P + 100 kg K /ha). A potassium only treatment (50 kg K/ha) was also included, but mainly for comparison. The root HCN levels of Salanga, Kalinda and Kiroba were significantly influenced by NPK fertiliser application in at least one of the two field experiments, while those of Supa remained uninfluenced. Changes in plant nutritional status in response to fertiliser application were thus shown to influence cyanogenic glucoside production. The results of the multiple linear regression analysis for the first field experiment, generally showed that the root HCN levels of some cassava varieties could have been 'reduced' by decreasing concentrations of nitrogen, potassium and magnesium in plants, or by improving plant calcium concentrations along with NPK fertiliser application. However, in the second field experiment (with corrected soil nutrient deficiencies) the regression analysis generally showed that the root HCN levels of some cassava varieties could have been 'reduced' by improving either one or a combination of the nutrients phosphorous, zinc and potassium in plants along with NPK fertiliser application. Although the results obtained in the two experiments had been contradicting due to slight differences in how they were conducted, the study had nonetheless demonstrated the occurrence of meaningful relationships between plant nutritional status and cyanogenic glucoside production; confirming the possible use of plant tissue analysis in predicting fertiliser needs for the consistent attainment of low cyanogenic glucosides in cassava roots.

Over the past few years, evidence has accrued that demonstrates that terrestrial photochemical reactions could have provided numerous (proto)biomolecules with implications for the origin of life. This chemistry simply relies on UV light, inorganic sulfur species and hydrogen cyanide. Recently, we reported that, under the same conditions, reduced phosphorus species, such as those delivered by meteorites, can be oxidized to orthophosphate, generating thiophosphate in the process. Here we describe an investigation of the properties of thiophosphate as well as additional possible means for its formation on primitive Earth. We show that several reported prebiotic reactions, including the photoreduction of thioamides, carbonyl groups and cyanohydrins, can be markedly improved, and that tetroses and pentoses can be accessed from hydrogen cyanide through a Kiliani–Fischer-type process without progressing to higher sugars. We also demonstrate that thiophosphate allows photochemical reductive aminations, and that thiophosphate chemistry allows a plausible prebiotic synthesis of the C5 moieties used in extant terpene and terpenoid biosynthesis, namely dimethylallyl alcohol and isopentenyl alcohol.The streamlined synthesis of multiple (proto)biomolecules from common starting materials is a key goal of prebiotic chemistry. Now, a one-pot synthesis of ribo-aminooxazoline (a precursor for prebiotic nucleotide synthesis) from HCN has been achieved. Additionally, the two moieties used in extant terpenoid biosynthesis have been accessed, with all carbon atoms also originating from HCN.

Recent results in prebiotic chemistry implicate hydrogen cyanide (HCN) as the source of carbon and nitrogen for the synthesis of nucleotide, amino acid and lipid building blocks. HCN can be produced during impact events by reprocessing of carbonaceous and nitrogenous materials from both the impactor and the atmosphere; it can also be produced from these materials by electrical discharge. Here we investigate the effect of high energy events on a range of starting mixtures representative of various atmosphere-impactor volatile combinations. Using continuously scanning time–resolved spectrometry, we have detected ·CN radical and excited CO as the initially most abundant products. Cyano radicals and excited carbon monoxide molecules in particular are reactive, energy-rich species, but are resilient owing to favourable Franck–Condon factors. The subsequent reactions of these first formed excited species lead to the production of ground-state prebiotic building blocks, principally HCN.

Larvae and adults of the Colorado potato beetle ( Leptinotarsa decemlineata ), a major pest of potato crops, display conspicuous coloration to advertise their toxicity to predators. However, the identity of the toxic compounds remains unclear. Here, we show that larvae and adults release toxic hydrogen cyanide (HCN) from the degradation of mandelonitrile and other cyano-compounds, which are produced by commensal bacteria. We isolate the bacterium Proteus vulgaris Ld01 from the insect’s gut, and show that it produces HCN and a mandelonitrile-producing cyanoglucoside, amygdalin. Knockout of a gene ( hcnB ) encoding putative hydrogen cyanide synthase impairs HCN production in P. vulgaris Ld01. Antibiotic treatment of larvae, to eliminate their commensal bacteria, leads to a substantial reduction of HCN emission in larvae and adults. HCN release by bacteria-deprived beetles can be restored by addition of mandelonitrile or by re-infection with P. vulgari s Ld01 (but not with its ∆ hcnB1 or ∆ hcnB2  mutants). Finally, we use dual-choice experiments to show that domestic chicks prefer to eat bacteria-deprived larvae over control larvae, larvae re-colonized with P. vulgaris Ld01, or mandelonitrile-injected larvae. Our work highlights the role of the beetle’s intestinal bacteria in the production of the cyanoglucoside amygdalin and its derived metabolites, including mandelonitrile and HCN, which protect the insect from predation. The Colorado potato beetle, a major pest of potato crops, displays conspicuous coloration to advertise their toxicity to predators, but the identity of the toxic compounds is unclear. Here, Kang et al. show that the insect releases toxic hydrogen cyanide, which results from the degradation of cyano-compounds produced by commensal bacteria.