Bacterial Volatile Organic Compounds Research Articles

Volatolomics in Bacterial Ecotoxicology, A Novel Method for Detecting Signatures of Pesticide Exposure?

Volatile organic compounds (VOC) produced by microorganisms in response to chemical stressor showed recently increasing attention, because of possible environmental applications. In this work, we aimed to bring the first proof of concept that volatolomic (i.e., VOCs analysis) can be used to determine candidate VOC markers of two soil bacteria strains (Pseudomonas fluorescens SG-1 and Bacillus megaterium Mes11) exposure to pesticides. VOC determination was based on solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Accordingly, we highlighted a set of bacterial VOCs modulated in each strains according to the nature of the pesticide used. Three out these VOCs were specifically modulated in P. fluorescens SG-1 when exposed with two pyrethroid pesticides (deltamethrine and cypermethrine): 2-hexanone; 1,3-ditertbutylbenzene and malonic acid, hexyl 3-methylbutyl ester. Our results thus suggest the possible existence of generic VOC markers of pyrethroids in this strain. Of particular interest, two out of these three VOCs, the 1,3-ditertbutylbenzene and the malonic acid, hexyl 3-methylbutyl ester were found also in B. megaterium Mes11 when exposed with cypermethrine. This result highlighted the possible existence of interspecific VOC markers of pyrethroid in these two bacteria. Altogether, our work underlined the relevance of volatolomic to detect signatures of pesticides exposure in microorganisms and more generally to microbial ecotoxicology. Based on these first results, considerations of volatolomics for the chemical risk assessment in environment such as soils can be indirectly explored in longer terms.

Avocado rhizobacteria emit volatile organic compounds with antifungal activity against Fusarium solani, Fusarium sp. associated with Kuroshio shot hole borer, and Colletotrichum gloeosporioides

Recent studies showed that bacterial volatile organic compounds (VOCs) play an important role in the suppression of phytopathogens. The ability of VOCs produced by avocado (Persea americana Mill.) rhizobacteria to suppress the growth of common avocado pathogens was therefore investigated. We evaluated the antifungal activity of VOCs emitted by avocado rhizobacteria in a first screening against Fusarium solani, and in subsequent antagonism assays against Fusarium sp. associated with Kuroshio shot hole borer, Colletotrichum gloeosporioides and Phytophthora cinnamomi, responsible for Fusarium dieback, anthracnosis and Phytophthora root rot in avocado, respectively. We also analyzed the composition of the bacterial volatile profiles by solid phase microextraction (SPME) gas chromatography coupled to mass spectrometry (GC–MS). Seven isolates, belonging to the bacterial genera Bacillus and Pseudomonas, reduced the mycelial growth of F. solani with inhibition percentages higher than 20%. Isolate HA, related to Bacillus amyloliquefaciens, significantly reduced the mycelial growth of Fusarium sp. and C. gloeosporioides and the mycelium density of P. cinnamomi. Isolates SO and SJJ, also members of the genus Bacillus, reduced Fusarium sp. mycelial growth and induced morphological alterations of fungal hyphae whilst isolate HB, close to B. mycoides, inhibited C. gloeosporioides. The analysis of the volatile profiles revealed the presence of ketones, pyrazines and sulfur-containing compounds, previously reported with antifungal activity. Altogether, our results support the potential of avocado rhizobacteria to act as biocontrol agents of avocado fungal pathogens and emphasize the importance of Bacillus spp. for the control of emerging avocado diseases such as Fusarium dieback.

Volatiles produced by Bacillus mojavensis RRC101 act as plant growth modulators and are strongly culture-dependent

Volatile organic compounds (VOCs) produced by Plant Growth Promoting Rhizobacteria have recently been investigated due to their role in plant growth promotion and defense. Whereas some bacterial VOCs like 3-hydroxy-2-butanone (acetoin) and 2,3-butanediol produced by strains of Bacillus subtilis and Bacillus amyloliquefaciens promote plant growth, others like hydrogen cyanide and 3-phenylpropionic acid are phytotoxic, inhibiting plant growth. Bacillus mojavensis, a close relative of B. subtilis, is an endophytic bacterium of maize that has been shown to have antagonistic activity against the mycotoxigenic phytopathogen Fusarium verticillioides and growth promotion activity on maize seedlings. To investigate the growth promotion activity of B. mojavensis, Arabidopsis thaliana seedlings were grown on 1/2x Murashige & Skoog (MS) medium in divided Petri dishes while bacteria were grown either on 1/2x MS or nutrient agar (NA) medium, so that only microbial volatiles reached the seedlings. Significant plant growth promotion in Arabidopsis seedlings was observed when 1/2x MS medium was used for bacterial growth. In contrast, phytotoxicity was observed with bacterial growth on NA medium. These results indicate that VOCs produced by B. mojavensis may act as plant growth modulators rather than just promoters. Using Solid Phase Microextraction (SPME) coupled with GC–MS, the plant growth promoting compounds acetoin and 2,3-butanediol were both identified as being produced by B. mojavensis on growth promoting 1/2x MS medium. In contrast, while no phytotoxic VOC was conclusively identified from B. mojavensis on NA medium, detection of relatively high levels of acetone/2-propanone indicates its possible contribution to Arabidopsis phytotoxicity.

Volatile organic compound signature from co-culture of lung epithelial cell line with Pseudomonas aeruginosa.

Bacteria are found ubiquitously within and on nearly every site within humans, including the airways. Microbes interact with airway epithelial cells in lung infections such as ventilator-associated pneumonia (VAP). Development of infection results in the production of oxidants such as hydrogen peroxide that may further damage the epithelium. VAP is difficult to diagnose and associated with significant mortality. Current methods are invasive and time consuming impacting on appropriate therapy, antimicrobial resistance and financial costs. Volatile organic compound (VOC) analysis in exhaled breath is proposed as a tool for early detection due to its non-invasive property and potential to facilitate timely diagnosis. To investigate potential early VOC markers, A549 epithelial cells that were originally isolated from human alveoli were cultured with and without Pseudomonas aeruginosa, and the headspace of the culture vessel analysed using sorbent-based capture of VOCs followed by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) in order to identify potential discriminatory VOCs. A549 cells were also cultured with hydrogen peroxide to induce oxidative stress in order to investigate potential biomarkers of epithelial cell damage. Previously reported VOCs including acetone and ethanol were observed from the infection experiment along with novel bacterial markers, which we identified as mostly ether based compounds. Alkanes such as decane and octane were also found to be elevated after hydrogen peroxide treatment of A549 cells, likely as a result of peroxidation of oleic acids.

Seasonal variances in bacterial microbiota and volatile organic compounds in raw milk

The aim of this study was to define the composition of microbiota and the volatile organic compounds (VOCs) in samples of raw milk collected for 22months between 2012 and 2014 originated from north-eastern region of Poland. The results revealed that the VOCs profile changed with respect to the season of milk collection, and milk collected in autumn was characterized by a higher content of acetic acid (C2), propionic acid (C3) and valeric acid (C5), whereas spring was characterized by a frequent presence of acetone (Ac), ethanol (Et) and ethyl acetate (EtAc). Bacterial species composition changed considerably within the tested period and some bacterial species/groups occurred seasonally, e.g. L. helveticus (summer), L. casei (winter). The results show usefulness of the applied techniques (PCR-DGGE and HS-GC) and data analysis (PCA, correlation coefficients) methods in characterizing the raw milk quality intended for dairy production.

Bacterial Detection and Differentiation via Direct Volatile Organic Compound Sensing with Surface Enhanced Raman Spectroscopy

AbstractCurrent methods for detecting bacterial infections, such as culture and morphological analysis of bacterial colonies, are time and labor intensive. Through the direct detection of bacterial volatile organic compounds (VOCs), via surface enhanced Raman spectroscopy (SERS), we report here a reconfigurable assay for the identification and monitoring of bacteria. We demonstrate differentiation between highly clinically relevant organisms: Escherichia coli, Enterobacter cloacae, and Serratia marcescens. This is the first differentiation of bacteria via SERS of bacterial VOC signatures. The assay also detected as few as 10 CFU/ml of E. coli in under 12 hrs, and detected E. coli from whole human blood and human urine in 16 hrs at clinically relevant concentrations of 103 CFU/ml and 104 CFU/ml, respectively. In addition, the recent emergence of portable Raman spectrometers uniquely allows SERS to bring VOC detection to point‐of‐care settings for diagnosing bacterial infections.

Microbial volatile compounds alter the soil microbial community

Volatile organic compounds (VOCs) from soil bacteria are likely to have an important role in the interactions among soil microorganisms. However, their effects on the soil microbial community have not been extensively studied. In this study, the effect of bacterial VOCs generated by growing Bacillus amyloliquefaciens NJN-6 on modified MS medium on soil microbial community was evaluated. B. amyloliquefaciens NJN-6 was able to produce 48 volatile compounds as determined by solid-phase microextraction-GC/MS. MiSeq sequencing data showed that bacterial VOCs could alter the composition of both soil bacterial and soil fungal communities and could decrease the alpha-diversity of the soil microbial community. Taxonomic analysis revealed that bacterial VOCs significantly increased the relative abundance of Proteobacteria, Bacteroidetes, and Firmicutes. Moreover, bacterial VOCs significantly increased the relative abundance of Ascomycota. The qPCR data showed that bacterial VOCs of strain NJN-6 decreased the soil fungal biomass and increased the soil bacterial biomass. Further evaluation of the effect of bacterial VOCs on functional genes revealed that VOCs could reduce the copies of nifH, nirS, and a gene encoding nonribosomal peptide synthase, while increasing the copy number of the ammonium-oxidizing bacteria gene. The effect on gene encoding polyketide synthase was insignificant. Results from this study indicated that bacterial VOCs could influence the soil microbial community as well as functional gene abundance.

Strain-specific variation in plant growth promoting volatile organic compounds production by five different Pseudomonas spp. as confirmed by response of Vigna radiata seedlings.

Analysis of a blend of volatile organic compounds (VOCs) released by Pseudomonas spp. with growth-promoting effect in Vigna radiata seedlings. Plant growth-promoting activity of VOCs produced by five different Pseudomonas spp. was investigated by I-plate technique. VOCs produced by different organisms were extracted by various solvents (methanol, ethyl acetate, hexane and butanol) and were identified by gas chromatography-mass spectrometric analysis. The major VOCs identified were undecane, nonadecane, hexacosane, tetradecane, heptacosane, pentadecane, dodecane and tetratetracontane. The cultural conditions for the production of VOCs with plant growth enhancement effect were optimized and further confirmed using pure pentadecane as a candidate VOC. The study provides insight into plant beneficial effect of VOCs produced by Pseudomonas spp. Remarkable modulation in the production of VOCs with plant growth-promoting effect by rhizobacteria was found to be dependent on the bacterial strain and its concentration. The study describes the requirement to consider bacterial VOC production also for preparing plant probiotic formulations. As VOCs are least considered for preparation of commercial plant growth-promoting rhizobacterial strain formulation, the results of the study is highly significant.

Ketones 2-heptanone, 2-nonanone, and 2-undecanone inhibit DnaK-dependent refolding of heat-inactivated bacterial luciferases in Escherichia coli cells lacking small chaperon IbpB.

Many bacteria, fungi, and plants produce volatile organic compounds (VOCs) emitted to the environment. Bacterial VOCs play an important role in interactions between microorganisms and in bacterial-plant interactions. Here, we show that such VOCs as ketones 2-heptanone, 2-nonanone, and 2-undecanone inhibit the DnaKJE-ClpB bichaperone dependent refolding of heat-inactivated bacterial luciferases. The inhibitory activity of ketones had highest effect in Escherichia coli ibpB::kan cells lacking small chaperone IbpB. Effect of ketones activity increased in the series: 2-pentanone, 2-undecanone, 2-heptanone, and 2-nonanone. These observations can be explained by the interaction of ketones with hydrophobic segments of heat-inactivated substrates and the competition with the chaperones IbpAB. If the small chaperone IbpB is absent in E. coli cells, the ketones block the hydrophobic segments of the polypeptides and inhibit the action of the bichaperone system. These results are consistent with the data on inhibitory effects of VOCs on survival of bacteria. It can be suggested that the inhibitory activity of the ketones indicated is associated with different ability of these substances to interact with hydrophobic segments in proteins.

Growth media affect the volatilome and antimicrobial activity against Phytophthora infestans in four Lysobacter type strains

Bacterial volatile organic compounds (VOCs) play important ecological roles in soil microbial interactions. Lysobacter spp. are key determinants of soil suppressiveness against phytopathogens and the production of non-volatile antimicrobial metabolites has been extensively characterised. However, the chemical composition and antagonistic properties of the Lysobacter volatilome have been poorly investigated. In this work, VOC emission profiles of four Lysobacter type strains grown on a sugar-rich and a protein-rich medium were analysed using solid-phase microextraction gas chromatography–mass spectrometry and proton transfer reaction-time of flight-mass spectrometry. Lysobacter antibioticus, L. capsici, L. enzymogenes and L. gummosus type strains were recognised according to their volatilome assessed using both headspace mass spectrometry methods Moreover, the chemical profiles and functional properties of the Lysobacter volatilome differed according to the growth medium, and a protein-rich substrate maximised the toxic effect of the four Lysobacter type strains against Phytophthora infestans. Antagonistic (pyrazines, pyrrole and decanal) and non-antagonistic (delta-hexalactone and ethanol) VOCs against Ph. infestans or putative plant growth stimulator compounds (acetoin and indole) were mainly emitted by Lysobacter type strains grown on protein- and sugar-rich media respectively. Thus nutrient availability under soil conditions could affect the aggressiveness of Lysobacter spp. and possibly optimise interactions of these bacterial species with the other soil inhabitants.

The antimicrobial volatile power of the rhizospheric isolate Pseudomonas donghuensis P482.

Soil and rhizosphere bacteria produce an array of secondary metabolites including a wide range of volatile organic compounds (VOCs). These compounds play an important role in the long-distance interactions and communication between (micro)organisms. Furthermore, bacterial VOCs are involved in plant pathogens inhibition and induction of soil fungistasis and suppressivenes. In the present study, we analysed the volatile blend emitted by the rhizospheric isolate Pseudomonas donghuensis P482 and evaluated the volatile effect on the plant pathogenic fungi and bacteria as well as one oomycete. Moreover, we investigated the role of the GacS/GacA system on VOCs production in P. donghuensis P482. The results obtained demonstrated that VOCs emitted by P. donghuensis P482 have strong antifungal and antioomycete, but not antibacterial activity. The production of certain volatiles such as dimethyl sulfide, S-methyl thioacetate, methyl thiocyanate, dimethyl trisulfide, 1-undecan and HCN is depended on the GacS/GacA two-component regulatory system. Apparently, these compounds play an important role in the pathogens suppression as the gacA mutant entirely lost the ability to inhibit via volatiles the growth of tested plant pathogens.

Identification of bacteria using volatile organic compounds.

The rapid diagnosis of respiratory infections has always been an important goal for medical professionals, because rapid and accurate diagnosis leads to proper and timely treatment, and consequently, reduces the costs of incorrect and long-term treatments, and antibiotic resistance. The present study was conducted with the aim of detecting volatile organic compounds (VOCs) in three bacteria: Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae. Headspace of the studied bacteria, after separately culturing in two types of liquid medium in three different time-periods, was extracted by solid phase microextraction and analysed by gas chromatography mass spectrometry The analysis results of the VOCs produced by the studied bacteria indicate that some VOCs are common and some are unique in each bacterium. 1-penten-3-ol, levomenthol, and 2-octyl-1-ol for P. aeruginosa, cyclohexene, 4-ethenyl, and cis-Dihydro-α-terpinyl acetate for A. baumannii and 1,3-butadiene, butyraldehyde, longifolene, octyl acetate, tridecanol, dodecenal, (E)-2-hexyl ester, butanoic acid, and 5,5-dodecadinyl-1 12-diol for K. pneumoniae were identified as unique VOCs for each bacterium. Finally, it can be said that an accurate and rapid bacterial detection method can be achieved by using a tool that can detect bacterial VOCs. However, more studies are needed to design a tool for which all aspects have been assessed, so that it can give us a more complete pattern for the use of these compounds as biomarkers.

Plant Growth Promotion by Volatile Organic Compounds Produced by Bacillus subtilis SYST2.

Bacterial volatiles play a significant role in promoting plant growth by regulating the synthesis or metabolism of phytohormones. In vitro and growth chamber experiments were conducted to investigate the effect of volatile organic compounds (VOCs) produced by the plant growth promoting rhizobacterium Bacillus subtilis strain SYST2 on hormone regulation and growth promotion in tomato plants. We observed a significant increase in plant biomass under both experimental conditions; we observed an increase in photosynthesis and in the endogenous contents of gibberellin, auxin, and cytokinin, while a decrease in ethylene levels was noted. VOCs emitted by SYST2 were identified through gas chromatography-mass spectrometry analysis. Of 11 VOCs tested in glass jars containing plants in test tubes, only two, albuterol and 1,3-propanediole, were found to promote plant growth. Furthermore, tomato plants showed differential expression of genes involved in auxin (SlIAA1. SlIAA3), gibberellin (GA20ox-1), cytokinin (SlCKX1), expansin (Exp2, Exp9. Exp 18), and ethylene (ACO1) biosynthesis or metabolism in roots and leaves in response to B. subtilis SYST2 VOCs. Our findings suggest that SYST2-derived VOCs promote plant growth by triggering growth hormone activity, and provide new insights into the mechanism of plant growth promotion by bacterial VOCs.

Microbiota and metabolome during controlled and spontaneous fermentation of Nocellara Etnea table olives

This study is aimed to investigate bacterial community and its dynamics during the fermentation of Nocellara Etnea table olives and to study its effect on metabolome formation. Six different combination of bacterial cultures (BC1-BC6) were used as starters for table olive fermentation and one additional process, conducted without addition of any starters, was used as control (C). The processes were conducted in triplicate and, overall, 21 vessels were performed at industrial scale. The fermentation was monitored for 120 days through culture-dependent and –independent approaches. Microbial counts of the main microbial groups revealed slight differences among brine samples, with the exception of LAB counts and Enterobacteriaceae, which were higher and lower, respectively, in most of the inoculated samples than the control ones. In addition, results demonstrated that the use of bacterial cultures (except the BC1), singly or in different combinations, clearly influenced the fermentation process reducing the final pH value below 4.50. When microbiota was investigated through sequencing analysis, data revealed the presence of halophilic bacteria and, among lactobacilli, the dominance of Lactobacillus plantarum group at the initial stage of fermentation, in all brine samples, except in the BC5 in which dominated Lactobacillus casei group. At 60 and 120 days of fermentation, an overturned bacterial ecology and an increase of biodiversity was observed in all samples, with the occurrence of Lactobacillus paracollinoides, Lactobacillus acidipiscis and Pediococcus parvulus. Correlation between bacterial OTU and volatile organic compounds (VOCs) revealed that, aldehydes and alcohol compounds exhibited a positive correlation with Proteobacteria, while several esters with LAB and Hafnia. In particular, esters, associated with fruity and floral notes, were positively correlated to L. paracollinoides, L. acidipiscis, and P. parvulus species. Although the VOCs amounts were sample-specific, overall aldehydes were mostly produced at the beginning of the fermentation, while acids, alcohols and esters at the end of the process.

Growth promotion of Lactuca sativa in response to volatile organic compounds emitted from diverse bacterial species

Agrochemicals are currently used in horticulture to increase crop production. Nevertheless, their indiscriminate use is a relevant issue for environmental and legal aspects. Alternative tools for reducing fertilizers and synthetic phytohormones are being investigated, such as the use of volatile organic compounds (VOCs) as growth inducers. Some soil bacteria, such as Pseudomonas and Bacillus, stimulate Arabidopsis and tobacco growth by releasing VOCs, but their effects on vegetables have not been investigated. Lactuca sativa was used as model vegetable to investigate bacterial VOCs as growth inducers. We selected 10 bacteria strains, belonging to Bacillus, Staphylococcus and Serratia genera that are able to produce 3-hydroxy-2-butanone (acetoin), a compound with proven growth promoting activity. Two-day old-seedlings of L. sativa were exposed to VOCs emitted by the selected bacteria grown in different media cultures for 7 days. The results showed that the VOCs released from the bacteria elicited an increase in the number of lateral roots, dry weight, root growth and shoot length, depending on the media used. Three Bacillus strains, BCT53, BCT9 and BCT4, were selected according to its their growth inducing capacity. The BCT9 strain elicited the greatest increases in dry weight and primary root length when L. sativa seedlings were subjected to a 10-day experiment. Finally, because acetoin only stimulated root growth, we suggest that other volatiles could be responsible for the growth promotion of L. sativa. In conclusion, our results strongly suggest that bacteria volatiles can be used as growth-inducers as alternative or complementary strategies for application in horticulture species.

Are Bacterial Volatile Compounds Poisonous Odors to a Fungal Pathogen Botrytis cinerea, Alarm Signals to Arabidopsis Seedlings for Eliciting Induced Resistance, or Both?

Biological control (biocontrol) agents act on plants via numerous mechanisms, and can be used to protect plants from pathogens. Biocontrol agents can act directly as pathogen antagonists or competitors or indirectly to promote plant induced systemic resistance (ISR). Whether a biocontrol agent acts directly or indirectly depends on the specific strain and the pathosystem type. We reported previously that bacterial volatile organic compounds (VOCs) are determinants for eliciting plant ISR. Emerging data suggest that bacterial VOCs also can directly inhibit fungal and plant growth. The aim of the current study was to differentiate direct and indirect mechanisms of bacterial VOC effects against Botrytis cinerea infection of Arabidopsis. Volatile emissions from Bacillus subtilis GB03 successfully protected Arabidopsis seedlings against B. cinerea. First, we investigated the direct effects of bacterial VOCs on symptom development and different phenological stages of B. cinerea including spore germination, mycelial attachment to the leaf surface, mycelial growth, and sporulation in vitro and in planta. Volatile emissions inhibited hyphal growth in a dose-dependent manner in vitro, and interfered with fungal attachment on the hydrophobic leaf surface. Second, the optimized bacterial concentration that did not directly inhibit fungal growth successfully protected Arabidopsis from fungal infection, which indicates that bacterial VOC-elicited plant ISR has a more important role in biocontrol than direct inhibition of fungal growth on Arabidopsis. We performed qRT-PCR to investigate the priming of the defense-related genes PR1, PDF1.2, and ChiB at 0, 12, 24, and 36 h post-infection and 14 days after the start of plant exposure to bacterial VOCs. The results indicate that bacterial VOCs potentiate expression of PR1 and PDF1.2 but not ChiB, which stimulates SA- and JA-dependent signaling pathways in plant ISR and protects plants against pathogen colonization. This study provides new evidence for bacterial VOC-elicited plant ISR that protects Arabidopsis plants from infection by the necrotrophic fungus B. cinerea. Our work reveals that bacterial VOCs primarily act via an indirect mechanism to elicit plant ISR, and have a major role in biocontrol against fungal pathogens.

The effects of bacterial volatile emissions on plant abiotic stress tolerance.

Plant growth-promoting rhizobacteria (PGPR) are beneficial plant symbionts that have been successfully used in agriculture to increase seedling emergence, plant weight, crop yield, and disease resistance. Some PGPR strains release volatile organic compounds (VOCs) that can directly and/or indirectly mediate increases in plant biomass, disease resistance, and abiotic stress tolerance. This mini-review focuses on the enhancement of plant abiotic stress tolerance by bacterial VOCs. The review considers how PGPR VOCs induce tolerance to salinity and drought stress and also how they improve sulfur and iron nutrition in plants. The potential complexities in evaluating the effects of PGPR VOCs are also discussed.

Effect of volatile organic compounds from bacteria on nematodes.

The five studied bacterial strains could produce volatile organic compounds (VOCs) that kill nematodes. Based on their 16S rRNA sequences, these strains were identified as Pseudochrobactrum saccharolyticum, Wautersiella falsenii, Proteus hauseri, Arthrobacter nicotianae, and Achromobacter xylosoxidans. The bacterial VOCs were extracted using solid-phase micro-extraction (SPME) and subsequently identified by GC/MS analysis. The VOCs covered a wide range of aldehydes, ketones, alkyls, alcohols, alkenes, esters, alkynes, acids, ethers, as well as heterocyclic and phenolic compounds. Among the 53 VOCs identified, 19 candidates, produced by different bacteria, were selected to test their nematicidal activity (NA) against Caenorhabditis elegans and Meloidogyne incognita. The seven compounds with the highest NAs were acetophenone, S-methyl thiobutyrate, dimethyl disulfide, ethyl 3,3-dimethylacrylate, nonan-2-one, 1-methoxy-4-methylbenzene, and butyl isovalerate. Among them, S-methyl thiobutyrate showed a stronger NA than the commercial insecticide dimethyl disulfide. It was reported for the first time here that the five bacterial strains as well as S-methyl thiobutyrate, ethyl 3,3-dimethylacrylate, 1-methoxy-4-methylbenzene, and butyl isovalerate possess NA. These strains and compounds might provide new insights in the search for novel nematicides.

Effect of electron beam irradiation on bacterial and Ascaris ova loads and volatile organic compounds in municipal sewage sludge

Wastewater treatment plants produce large amounts of biosolids that can be utilized for land applications. However, prior to their use, these biosolids must be treated to eliminate risks of infections and to reduce upsetting odors. In this study, microbiological and chemical analyzes were performed before and after treatment of sewage sludge with 3 MeV of an electron beam accelerator in a pilot processing plant. Thus, we determined that dose 4.5 kGy was required to reduce fecal coliform counts to safe levels for land applications of sludge while, 14.5 kGy was necessary to decrease Ascaris ova counts to safe levels. Furthermore, at low doses, electron beam irradiation showed little effect on the concentrations of volatile organic compounds, while some increase were recorded at high doses. The concentration of dimethyl sulfide was reduced by 50–70% at irradiation doses of 25.7 kGy and 30.7 kGy respectively. By contrast, electron beam irradiation increased dimethyl disulfide concentrations. We also showed that electron beam treatment was less energy-consuming with shorter processing times than conventional techniques used to decontaminate sludge. Hence opening new avenues for large urban agglomerations to save money and time when treating biosolids for land application.

Bioprospecting bacterial and fungal volatiles for sustainable agriculture.

Current agricultural practice depends on a wide use of pesticides, bactericides, and fungicides. Increased demand for organic products indicates consumer preference for reduced chemical use. Therefore, there is a need to develop novel sustainable strategies for crop protection and enhancement that do not rely on genetic modification and/or harmful chemicals. An increasing body of evidence indicates that bacterial and fungal microbial volatile organic compounds (MVOCs) might provide an alternative to the use of chemicals to protect plants from pathogens and provide a setting for better crop welfare. It is well known that MVOCs can modulate the physiology of plants and microorganisms and in this Opinion we propose that MVOCs can be exploited as an ecofriendly, cost-effective, and sustainable strategy for agricultural practices.