Microbial Volatiles Research Articles

Bio-fumigants as grain protectants in storage-A review

Agriculture is a global lifeline, especially in developing nations like India, where over 70% of the population relies on it. Protecting food grains from insect pests during post-harvest storage is crucial, particularly in regions lacking advanced storage technologies, leading to significant losses. Fumigation is still a key strategy for safeguarding stored grains. Methyl bromide (MBr) and aluminium phosphide (AlP) are the widely used chemical fumigants. Phosphine is used to a greater extent today, but there are frequent reports that several storage pests have developed resistance to this fumigant. The United Nations World Meteorological Organization declared methyl bromide as an ozone-depleting chemical in 1995, and hence, most of the developed countries have phased out its use. Therefore, there is an urgent requirement to develop alternatives having a possible replacement for these fumigants. Biofumigants are organic compounds derived from various plant sources, including essential oils, botanical powders, and plant residues or from microbial volatiles. They release volatile compounds toxic to pests but safe for humans and the environment, offering a sustainable pest management approach. Plants such as mustard and radish produce glucosinolates that release isothiocyanates, known for their pesticidal properties. Essential oils from eucalyptus, clove, and mint and volatiles from certain fungi and bacteria also exhibit fumigant properties. Biofumigants disrupt insect physiological and biochemical processes, leading to mortality or reduced reproduction. Studies showed their efficacy against pests like red flour beetle, lesser grain borer, and rice weevil. Unlike chemical fumigants, biofumigants do not leave harmful residues, preserving grain quality and aligning with organic farming practices. Shifting to biofumigants offers a promising, eco-friendly, and effective alternative for post-harvest pest management, ensuring food safety and sustainability

Grape Endophytic Microbial Community Structures and Berry Volatile Components Response to the Variation of Vineyard Sites

Vitis vinifera L. is a commercially important horticultural plant with abundant microbial resources. However, the impact of grape-associated microbiota on grape quality and flavor has been largely overlooked. We integrated volatomics and microbiomics to explore temporal variations in berry volatiles and microbial diversity of ‘Cabernet Sauvignon’ in Ningxia (NX) and Shanxi (SX), and the correlation between microbial communities and volatiles. A total of 38 and 35 free and bound aroma compounds, respectively, were identified in NX berries and SX berries. For free aroma, these 38 compounds were classified into aldehydes (69%), alcohols (22%), acids (4%), aromatics (4%), terpenes (0.6%), esters (0.37%), and norisoprenoids (0.3%). Similarly, the 35 bound aromas were attributed to aromatics (58%), acids (29%), terpenes (4%), esters (3%), alcohols (2.82%), aldehydes (2.78%), and norisoprenoids (0.4%). Additionally, a total of 616 bacterial genera and 254 fungal genera were detected in all samples from both regions. The results demonstrated that vineyard sites significantly shaped the characteristics of berry volatiles and microbial biogeographic patterns. SX berries exhibited more abundant free aroma and higher microbial diversity than NX berries, with three key taxa (Sphingomonas, Massilia, and Bacillus) identified in the bacterial network. Correlation analysis results highlighted that these key taxa might play an important role in berry-free aroma. This study reveals the crucial role of microbes in shaping grape flavor and uncovers the link between microbial diversity and the regional attributes of grapes and wine.

Metagenomic and metatranscriptomic analyses of microbial genera and volatiles produced during the fermentation of doubanjiang meju

Fermented broad beans (Vicia faba L.), commonly known as meju, serve as a crucial raw material for producing Pixian Doubanjiang (DBJ), a traditional condiment in Chinese cuisine. However, there is limited information on the dynamics of fungal populations and the activity shifts of key enzymes during DBJ meju fermentation. This study aimed to elucidate the microbial composition, active genera, expressed genes and pathways during the DBJ meju fermentation. The general chemical components, free amino acids, enzymes and volatile compounds were also investigated; the correlations between active genera and physicochemical factors were analyzed, at different fermentation stages. The results demonstrated that protease was the predominant enzyme during meju fermentation. A total of 32 major volatile compounds were identified, with most alcohols and aldehydes showing a sharp increase from the early to the middle stages, followed by stabilization until the end of fermentation. Significant shifts in metatranscriptomic composition at the genus level were observed, with Aspergillus, Staphylococcus, and Tulasnella emerging as the core active genera in the process. Notably, cellulase activity was positively correlated with the presence of Tulasnella. Additionally, Aspergillus and Tulasnella were found to play a crucial role in developing the unique aroma of DBJ meju. Our findings on the succession of active genera and their correlation with physicochemical factors are expected to provide substantial evidence for potential quality control and enhancement of this renowned Chinese condiment.

Impact of Seasonal Variation in Pasture on Rumen Microbial Community and Volatile Fatty Acids in Grazing Yaks: Insights from High-Altitude Environments.

The environment is one of the most important factors influencing the variation and diversity of the host gut microbiome in plateau areas. It is well-established that dietary variations substantially alter the rumen microbiota. However, there is limited research on the response of the rumen microbiota of grazing yaks to changes in seasonal diet composition under high-altitude environments. This study investigates the seasonal variations in rumen fermentation parameters, bacterial, and fungal communities in yaks, with a focus on the cold and warm seasons. Quantitative data revealed that in the cold season, yaks had an increased acetic acid proportion (p < 0.05) and acetic acid/propionic acid ratio (p < 0.05) compared to the warm season. The relative abundance of Bacteroidetes and Firmicutes were 64.67% and 25.82% in the cold season, respectively, and 66.77% and 26.87% in the warm season. The fungal community showed a higher abundance of Ascomycetes (58.72% to 76.91%) and Neocallimastigomycota in the cold season. These findings highlight the adaptation mechanisms of yaks to seasonal dietary changes and their implications for optimizing yak husbandry practices.

EVALUATION OF THE EFFICIENCY OF BEETROOT PEEL (BETA VULGARIS) IN OVITRAPS AS AN ATTRACTANT FOR SURVEILLANCE OF ARBOVIRUS VECTORS IN THE MUNICIPALITY OF AGRESTINA, STATE OF PERNAMBUCO, BRAZIL.

It is estimated that there are over 500 species of arboviruses worldwide, with more than 150 of them directly associated with human diseases, the majority of which are zoonotic. Among the main arboviruses circulating in Brazil, dengue, Zika, and chikungunya stand out, all transmitted through a common vector, Aedes aegypti. Given this scenario, the development and implementation of more efficient surveillance strategies become urgent. This study aims to compare and evaluate the efficiency of beetroot peel, Beta vulgaris, as an attractant for Ae. aegypti oviposition under field conditions in the municipality of Agrestina, State of Pernambuco, Brazil. Beetroot peel extract is a cheap and accessible source of geosmin, which holds significant potential as an attractant for mosquitoes due to its resemblance to microbial volatiles found in water bodies rich in organic material. During the study period (November 2023 to April 2024), 40 traps were set in each neighborhood, with 20 of each attractant. Two traps were used per property, one following the traditionally used model (beer yeast infusion) and another containing beetroot peel. Overall, in both analyzed neighborhoods (Campo Novo and Cohab), beetroot peel appeared to be a more efficient attractant for the oviposition of culicids. Beetroot peel showed the highest values in egg abundance and in the analyzed indices.

Biopurification using non-growing microorganisms to improve plant protein ingredients

Securing a sustainable global food supply for a growing population requires a shift toward a more plant-based diet. The application of plant-based proteins is therefore increasing, but unpleasant off-flavors complicate their use. Here, we screened 97 microorganisms for their potential to remove off-flavors in a process with limiting amounts of fermentable sugar. This allowed the production of a more neutral-tasting, purified food ingredient while limiting microbial growth and the production of typical fermentation end products. We demonstrate that various lactic acid bacteria (LAB) and yeasts remove “green” aldehydes and ketones. This conversion can be carried out in less than one hour in almond, pea, potato, and oat proteins. Heterofermentative LAB was best at aldehyde and ketone neutralization with minimum de novo formation of microbial volatiles such as ethylacetate (sweet, fruity) or alpha-diketones (butter- and cheese-like). While sensory properties were improved, changes in protein solubility, emulsification, foaming, and in vitro digestibility were limited.

Disruption of pollination by herbivores is rescued by nectar yeasts

Abstract Attracting pollinators to achieve successful reproduction is a key challenge for wild plants that may be disturbed by complex multispecies interactions in nature. Pairwise plant–pollinator interactions have traditionally been studied for decades, while ignoring other ecological players may obscure a comprehensive understanding on how plants recruit partners or combat enemies in the pollination process. Hence, integrated studies considering the inherent complexity of ecological interactions are needed, which may open up new perspectives for deciphering intricate systems and predicting ecological consequences. We examined the presence of nectar yeasts using a combination of high‐throughput sequencing, cultivation and microscopy and quantified floral herbivory by evaluating the incidence of flowers with visible holes in 13 natural populations of Iris bulleyana in the Hengduan Mountains of southwest China during 2017–2022. We combined yeast inoculation and herbivore manipulation treatments to illustrate the isolated and combined impacts of two contrasting nectarivorous organisms, the ascomycetous yeast Metschnikowia reukaufii and adult sawflies, on pollinator visitation and plant reproductive success in two populations. In the lab, we first employed gas chromatography–mass spectrometry to profile the volatile metabolites of yeast‐inoculated nectar relative to control, followed by a behavioural bioassay to test the preference of honeybees for these microbial volatiles. Yeasts commonly inhabited floral nectar and insect herbivores frequently bit holes in the perianth tube to consume nectar and nectaries. Nectar yeasts indirectly facilitated plant reproduction through increased pollinator visits, probably because of microbial metabolism as honeybees preferred nectar volatiles produced by yeasts in behavioural bioassays. Insect herbivores increased total floral visits but reduced legitimate visits by inducing legitimate‐to‐robbing behavioural changes of honeybees, thus leading to lower seed production. The detrimental effect of herbivory was mitigated by the presence of yeasts, which diminished the relative proportion of robbing visits and thereby ‘rescued’ flowers from reproductive failure. Synthesis: Overall, we found contrasting effects of non‐pollinator species, including both micro‐ and macro‐organisms, on plant–pollinator interactions in a biodiversity hotspot, where pollination deficit may be a ubiquitous phenomenon. Our findings suggest that both microbial and herbivory effects are likely to be important in explaining the exact causes of pollen limitation in species‐rich areas, highlighting the biological context dependence of species interactions in natural ecosystems.

Novel Pseudomonas Species Prevent the Growth of the Phytopathogenic Fungus Aspergillus flavus.

In response to the escalating demand for sustainable agricultural methodologies, the utilization of microbial volatile organic compounds (VOCs) as antagonists against phytopathogens has emerged as a viable eco-friendly alternative. Microbial volatiles exhibit rapid diffusion rates, facilitating prompt chemical interactions. Moreover, microorganisms possess the capacity to emit volatiles constitutively, as well as in response to biological interactions and environmental stimuli. In addition to volatile compounds, these bacteria demonstrate the ability to produce soluble metabolites with antifungal properties, such as APE Vf, pyoverdin, and fragin. In this study, we identified two Pseudomonas strains (BJa3 and MCal1) capable of inhibiting the in vitro mycelial growth of the phytopathogenic fungus Aspergillus flavus, which serves as the causal agent of diseases in sugarcane and maize. Utilizing GC/MS analysis, we detected 47 distinct VOCs which were produced by these bacterial strains. Notably, certain volatile compounds, including 1-heptoxydecane and tridecan-2-one, emerged as primary candidates for inhibiting fungal growth. These compounds belong to essential chemical classes previously documented for their antifungal activity, while others represent novel molecules. Furthermore, examination via confocal microscopy unveiled significant morphological alterations, particularly in the cell wall, of mycelia exposed to VOCs emitted by both Pseudomonas species. These findings underscore the potential of the identified BJa3 and MCal1 Pseudomonas strains as promising agents for fungal biocontrol in agricultural crops.

Unraveling symbiotic microbial communities, metabolomics and volatilomics profiles of kombucha from diverse regions in China

Kombucha is a natural fermented beverage (mixed system). This study aimed to unravel the signatures of kombucha in China to achieve tailor-made microbial consortium. Here, biochemical parameters, microbiome, metabolite production and volatile profile were comprehensively compared and characterized across four regions (AH, HN, SD, SX), both commonalities and distinctions were highlighted. The findings revealed that yeast species yeast Starmerella, Zygosaccharomyces, Dekkera, Pichia and bacterium Komagataeibacter, Gluconobacter were the most common microbes. Additionally, the composition, distribution and stability of microbial composition in liquid phase were superior to those in biofilm. The species diversity, differences, marker and association were analyzed across four areas. Metabolite profiles revealed a total of 163 bioactive compounds (23 flavonoids, 13 phenols), and 68 differential metabolites were screened and identified. Moreover, the metabolic pathways of phenylpropanoids biosynthesis were closely linked with the highest number of metabolites, followed by flavonoid biosynthesis. Sixty-five volatile compounds (23 esters) were identified. Finally, the correlation analysis among the microbial composition and volatile and functional metabolites showed that Komagataeibacter, Gluconolactone, Zygosacchaaromycess, Starmerella and Dekkera seemed closely related to bioactive compounds, especially Komagataeibacter displayed positive correlations with 1-hexadecanol, 5-keto-D-gluconate, L-malic acid, 6-aminohexanoate, Starmerella contributed greatly to gluconolactone, thymidine, anabasine, 2-isopropylmalic acid. Additionally, Candida was related to β-damascenone and α-terpineol, and Arachnomyces and Butyricicoccus showed the consistency of associations with specific esters and alcohols. These findings provided crucial information for creating a stable synthetic microbial community structure, shedding light on fostering stable kombucha and related functional beverages.

Interaction analysis of tobacco leaf microbial community structure and volatiles flavor compounds during cigar stacking fermentation.

Cigar stacking fermentation is a key step in tobacco aroma enhancement and miscellaneous gas reduction, which both have a great influence on increasing cigar flavor and improving industrial availability. To analyze the effect of cigar tobacco leaf (CTLs) microbial community on volatiles flavor compounds (VFCs), this study used multi-omics technology to reveal the changes in microbial community structure and VFCs of different cigar varieties during stacking fermentation, in addition to exploring the interaction mechanism of microbiome and VFCs. The results showed that the dominant microbial compositions of different CTL varieties during stacking fermentation were similar, which included Staphylococcus, Corynebacterium 1, Aerococcus, and Aspergillus. These dominant microbes mainly affected the microbial community structure and characteristic microorganisms of CTLs through microbial interactions, thereby influencing the transformation of VFCs. Characteristic microorganisms of different CTLs varieties such as Trichothecium, Trichosporon, Thioalkalicoccus and Jeotgalicoccus, were found to positively correlate with characteristic VFCs like megastigmatrienone 4, pyrazine, tetramethyl-, geranyl acetone, and 2-undecanone, 6,10-dimethyl-, respectively. This in turn affected the aroma and sensory quality of the CTLs. This study provides theoretical support for the analysis of the mechanism of microorganisms on VFCs and aroma, and development of microbial agents during cigar stacking fermentation.

Electrophysiological and Behavioral Responses of Virgin Female Bactrocera tryoni to Microbial Volatiles from Enterobacteriaceae.

The Queensland fruit fly (Bactrocera tryoni) is a major polyphagous pest widespread in Australia and several Pacific Islands. Bacteria present on the host plant phyllosphere supply proteins, essential for egg development and female sexual maturity. We investigated the role of microbial volatile organic compounds (MVOCs) emitted by Enterobacteriaceae commonly found on the host plant and in the fly gut in attracting virgin females. Bacteria were cultured on artificial media and natural fruits, at various pH, and MVOCs were collected using different headspace volatile absorbent materials. The olfactory responses of virgin females to bacterial MVOCs were assessed via electrophysiology and behavioral assays. The production of MVOCs was strongly influenced qualitatively by the bacterial strain and the type of media, and it semi-quantitatively varied with pH and time. MVOCs emitted by Klebsiella oxytoca invoked the strongest antennal response and were the most attractive. Among the identified compounds triggering an olfactory response, D-limonene and 2-nonanone were both significantly behaviorally attractive, whereas phenol, nonanal, isoamyl alcohol, and some pyrazines appeared to be repulsive. This study deepens our understanding of the chemical ecology between fruit flies and their bacterial symbionts and paves the way for novel synthetic lures based on specifically MVOCs targeting virgin females.

Deciphering the mechanism of Trichoderma spp. consortia possessing volatile organic compounds and antifungal metabolites in the suppression of Sclerotium rolfsii in groundnut

Groundnut, one of the oilseed crops is severely infected with necrotropic pathogen Sclerotium rolfsii, incurring huge economic loss to farmers. In the present study, the microbial volatiles (mVOCs) produced by six different Trichoderma spp. was tested for its in vitro efficacy against S. rolfsii IS (BDI)-8 infecting groundnut. Among the six isolates, Trichoderma longibrachiatum T (SP)-20 exhibited the maximum percentage inhibition (84.44%) followed by T (AR)-10 (75.44%) and TNAU TA (75.33%) in dual culture assay against S. rolfsii. Besides, volatiles of T. longibrachiatum T (SP)-20 and T. asperellum T (AR)-10 effectively reduced the mycelial growth of S. rolfsii by 61.11 and 54.44% respectively in paired plate assay. Co culturing of Trichoderma spp. with S. rolfsii produced specific antimicrobial mVOCs viz., Isolongifolan-7-ol and Trans-sesquisabinene hydrate, which could induce plant growth promotion and inhibited the growth of S. rolfsii. Application of consortia of Trichoderma longibrachiatum T (SP)-20 + Trichoderma asperellum T (AR)-10 as seed treatment at 4 g/kg and soil application at 50 g/pot before sowing and at 30 DAS (Days After Sowing), along with mahua oil cake as soil application at 100 g/pot recorded least stem rot disease incidence of 11.34% in pot culture. Besides, upregulation of a novel antifungal metabolite 6-pentyl-2H-pyran-2-one (6-PP) was also noticed in groundnut through GC-MS analysis. Thus, it is concluded that microbial volatiles and metabolites from Trichoderma spp. play an important role in resistance to S. rolfsii in groundnut.

Effect of combined treatments of electron beam irradiation with antioxidants on the microbial quality, physicochemical characteristics and volatiles of vacuum-packed fresh pork during refrigerated storage

In this study, the effects of combined treatments of electron beam irradiation (3 kGy) with antioxidants (tea polyphenols, grape seed extract, and D-sodium erythorbate) on the microbial quality, physicochemical characteristics and volatiles of vacuum-packed fresh pork during refrigerated storage were evaluated. The results indicate that irradiation treatment significantly suppressed the increases in total plate count, total volatile basic-nitrogen and pH of the samples during storage . Furthermore, these effects were enhanced by the combination of irradiation with antioxidant treatments. However, the increases in thiobarbituric acid reactive substances and protein carbonyl content, and the decrease in sulfhydryl content of the samples were significantly accelerated by irradiation treatment, indicating a higher degree of lipid and protein oxidation. Interestingly, these adverse effects of combined treatments were significantly lower than those of irradiation treatment. The amounts of hydrocarbons, aldehydes and esters in radiation-treated samples were higher than that in control during the whole storage time, however, these phenomena were diminished by the use of irradiation in combination with antioxidants treatments. • Antioxidants enhanced bactericidal effects of irradiation on fresh pork. • Irradiation in combination with antioxidants retarded lipid and protein oxidation. • The generation of volatiles in irradiated pork could be reduced by antioxidants. • Irradiation combine with antioxidants could improve meat safety and quality.

Bacterial Volatiles (mVOC) Emitted by the Phytopathogen Erwinia amylovora Promote Arabidopsis thaliana Growth and Oxidative Stress

Phytopathogens are well known for their devastating activity that causes worldwide significant crop losses. However, their exploitation for crop welfare is relatively unknown. Here, we show that the microbial volatile organic compound (mVOC) profile of the bacterial phytopathogen, Erwinia amylovora, enhances Arabidopsis thaliana shoot and root growth. GC-MS head-space analyses revealed the presence of typical microbial volatiles, including 1-nonanol and 1-dodecanol. E. amylovora mVOCs triggered early signaling events including plasma transmembrane potential Vm depolarization, cytosolic Ca2+ fluctuation, K+-gated channel activity, and reactive oxygen species (ROS) and nitric oxide (NO) burst from few minutes to 16 h upon exposure. These early events were followed by the modulation of the expression of genes involved in plant growth and defense responses and responsive to phytohormones, including abscisic acid, gibberellin, and auxin (including the efflux carriers PIN1 and PIN3). When tested, synthetic 1-nonanol and 1-dodecanol induced root growth and modulated genes coding for ROS. Our results show that E. amylovora mVOCs affect A. thaliana growth through a cascade of early and late signaling events that involve phytohormones and ROS.

Seed priming by application of Microbacterium spp. strains for control of Botrytis cinerea and growth promotion of lettuce plants

The abusive use of chemical pesticides to control plant diseases has caused the loss of soil biodiversity as well as the emergence of resistance by plant pathogens. This effect has forced an urgent search for other environmentally sustainable alternatives that serve to control plant pathogens safely and efficiently. In this sense, the search for new biopesticides is currently a booming field within the field of agro-biotechnology. Volatile compounds produced by plant-associated microorganisms represent a diverse resource to promote plant growth and health. In this work, a collection of 29 strains of the genus Microbacterium from the composting of plant remains was studied. The objective was to determine whether the production of volatile compounds of microbial origin could contribute to the mitigation of symptoms caused by the fungus Botrytis cinerea (gray mold) as well as contribute to the lettuce plant growth in seedbeds. It should be noted that in both the B. cinerea inhibition and seed priming assays, the microorganisms did not come into direct contact with either the pathogen or the seeds. In all cases, incubation was carried out in a closed environment to expose the seeds to the microbial volatiles. Five strains capable of inhibiting the in vitro growth of B. cinerea at levels greater than 30% were pre-selected. Only 3 of these 5 strains, identified as M. aerolatum, M. foliorum and M. profundi showed positive results in the in vitro germination promotion test in lettuce seeds, increasing the radicle weight at levels close to 45%. These strains finally were tested in planta, showing two of them significant palliative effects of B. cinerea and promoting the development of lettuce seedlings both at aerial and root levels.

Malodorous volatile organic compounds (MVOCs) formation after dewatering of wastewater sludge: Correlation with the extracellular polymeric substances (EPS) and microbial communities

Malodorous volatile organic compounds (MVOCs) are often the key odorants in determining sludge odor character and odor impact. However, the emission characterization and generation mechanisms of MVOCs from various dewatered sludge have not been sufficiently understood partly due to the diverse and complex composition and low concentration of odorants. In this study, waste activated sludge (WAS) was collected to examine the variation of MVOC emission from sludge after different dewatering treatment in lab-scale trials. The MVOCs were measured using the electronic nose (eNose), headspace gas chromatography-coupled ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC–MS). The results showed that centrifugation treatment promoted the generation of various odorous volatiles. The identified key odorants included dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), geosmin, and p-cresol according to their odor activity values (OAVs). The effects of the enhanced dewatering on volatile production were greater than thickening, however, the key odorants of dewatered sludge using gravity thickening varied more greatly than sludges from centrifuge thickening. The distribution of extracellular polymeric substances (EPS) and variation of microbial community showed correlations with the production of key odorants. Tryptophan-like substances in the inner layer of EPS (LB-EPS and TB-EPS) were better correlated with the key odorants. The bound EPS released by centrifugation may play the role of precursor for odorous microbial volatiles. According to the predicted functions of differential microbial genera, Desulfobulbus (Desulfobacterota), Gordonia (Actinobacteriota), and Hyphomicrobium (Proteobacteria) were associated with the production of DMS, DMDS, and DMTS, while Gordonia and Hyphomicrobium were related to p-cresol production.

Elucidating the mechanism underlying volatile and non-volatile compound development related to microbial amino acid metabolism during golden pomfret (Trachinotus ovatus) fermentation

Golden pomfret (Trachinotus ovatus) is an important farmed fish in Asia, often consumed following salting and natural microbial fermentation. Flavor development in fermented foods depends on the metabolism of fermenting microbes, especially amino acid metabolism. However, the microbes involved in golden pomfret fermentation and the mechanism by which they regulate flavor development are largely unknown. Accordingly, in this study, we investigated the microbial community and volatile and non-volatile compounds during the traditional fermentation of golden pomfret, focusing on amino acid metabolism. Thirty-five volatile compounds were detected. Glutamate, alanine, and leucine were the main amino acids responsible for the development of the characteristic taste of fermented golden pomfret. Metagenomic analyses were performed, and microbial genes for amino acid metabolism were functionally annotated, revealing the underlying mechanisms of flavor development during fish fermentation. Halobacterium, Clostridium, Natrinema, Alkalibacillus, Natrialba, and Vibrio were the dominant microbial genera with a major contribution to amino acid metabolism during fermentation and were strongly correlated with the majority of volatile compounds. The study provides a theoretical reference for the mechanism of flavor formation and important information on the microbial sources of volatile compounds derived from amino acids.

Metabolic phenotyping of acquired ampicillin resistance using microbial volatiles from Escherichia coli cultures.

This study sought to assess the volatile organic compound (VOC) profiles of ampicillin-resistant and -susceptible Escherichia coli to evaluate whether VOC analysis may be utilized to identify resistant phenotypes. An E. coli BL21 (DE3) strain and its pET16b plasmid transformed ampicillin-resistant counterpart were cultured for 6h in drug-free, low- and high-concentrations of ampicillin. Headspace analysis was undertaken using thermal desorption-gas chromatography-mass spectrometry. Results revealed distinct VOC profiles with ampicillin-resistant bacteria distinguishable from their susceptible counterparts using as few as six compounds. A minimum of 30 compounds (fold change >2, p ≤ 0.05) were differentially expressed between the strains across all set-ups. Furthermore, three compounds (indole, acetoin and 3-methyl-1-butanol) were observed to be significantly more abundant (fold change >2, p ≤ 0.05) in the resistant strain compared to the susceptible strain both in the presence and in the absence of drug stress. Results indicate that E. coli with acquired ampicillin resistance exhibit an altered VOC profile compared to their susceptible counterpart both in the presence and in the absence of antibiotic stress. This suggests that there are fundamental differences between the metabolisms of ampicillin-resistant and -susceptible E. coli which may be detected by means of VOC analysis. Our findings suggest that VOC profiles may be utilized to differentiate between resistant and susceptible bacteria using just six compounds. Consequently, the development of machine-learning models using VOC signatures shows considerable diagnostic applicability for the rapid and accurate detection of antimicrobial resistance.

Microbial volatiles as mediators of eco-evolutionary dynamics

Microbial volatiles as mediators of eco-evolutionary dynamics

The involvement of AtMKK1 and AtMKK3 in plant-deleterious microbial volatile compounds-induced defense responses.

Plant-deleterious microbial volatiles activate the transactivation of hypoxia, MAMPs and wound responsive genes in Arabidopsis thaliana. AtMKK1 and AtMKK3 are involved in the plant-deleterious microbial volatiles-induced defense responses. Microbial volatile compounds (mVCs) are a collection of volatile metabolites from microorganisms with biological effects on all living organisms. mVCs function as gaseous modulators of plant growth and plant health. In this study, the defense events induced by plant-deleterious mVCs were investigated. Enterobacter aerogenes VCs lead to growth inhibition and immune responses in Arabidopsis thaliana. E. aerogenes VCs negatively regulate auxin response and transport gene expression in the root tip, as evidenced by decreased expression of DR5::GFP, PIN3::PIN3-GFP and PIN4::PIN4-GFP. Data from transcriptional analysis suggests that E. aerogenes VCs trigger hypoxia response, innate immune responses and metabolic processes. In addition, the transcript levels of the genes involved in the synthetic pathways of antimicrobial metabolites camalexin and coumarin are increased after the E. aerogenes VCs exposure. Moreover, we demonstrate that MKK1 serves as a regulator of camalexin biosynthesis gene expression in response to E. aerogenes VCs, while MKK3 is the regulator of coumarin biosynthesis gene expression. Additionally, MKK1 and MKK3 mediate the E. aerogenes VCs-induced callose deposition. Collectively, these studies provide molecular insights into immune responses by plant-deleterious mVCs.