Bacterial Compounds Research Articles

Ginseng polysaccharides enhanced ginsenoside Rb1 and microbial metabolites exposure through enhancing intestinal absorption and affecting gut microbial metabolism

Ethnopharmacological relevancePolysaccharides and small molecules commonly co-exist in decoctions of traditional Chinese medicines (TCMs). Our previous study outlined that ginseng polysaccharides (GP) could interact with co-existing ginsenosides to produce synergistic effect in an over-fatigue and acute cold stress model via gut microbiota involved mechanisms. Aim of the studyThis study aimed to verify the interactions by examining the impact of GP on oral pharmacokinetics of ginsenoside Rb1 (Rb1), the dominant protopanoxadiol (PPD)-type ginsenoside in Ginseng, on a dextran sulphate sodium (DSS) induced experimental colitis model which was characterized by gut dysbiosis, and to delineate the underlying mechanisms in vitro. Materials and MethodsRats received drinking water (normal group), 5% DSS (UC group), or 5% DSS plus daily oral administration of GP (GP group) for 7 days and fecal samples were collected on day −3, 0 and 6. On day 7 all animals received an oral dosage of Rb1 and blood samples were withdrawn for pharmacokinetic study. The in vitro metabolism study of Rb1 in gut microbiota from normal and UC rats and the transport study of Rb1 across Caco-2 cell monolayer were carried out in presence/absence of GP. Rb1 and its bacterial metabolites ginsenoside Rd (Rd), ginsenoside F2 (F2), Compound K (CK) and PPD were determined using LC-MS/MS. Total and target bacteria in fecal samples were determined by using 16S rRNA-based RT-PCR. β-Glucosidase activity was determined by measuring 4-nitrophenol formed from 4-nitrophenyl-β-D-glucopyranoside hydrolysis. ResultsDSS induction did not alter AUC0−t and Cmax of Rb1, which, however, were doubled together with elevated AUC0−t of the metabolites, in particular Rd and CK, in GP group. GP influenced the microbial composition and showed a prebiotic-like effect. Accordingly, GP treatment could partially restore the β-glucosidase activity which was reduced by DSS induction. The presence of GP resulted in quicker microbial metabolism of Rb1 and higher Rd formation in first 8 h of incubation, while the impact on F2 and CK formation/conversion became obvious after 8 h. More interestingly, GP slightly stimulated Caco-2 cell growth and facilitated Rb1 transport across the Caco-2 monolayer in both directions, increasing the Papp of Rb1 from 10−7 cm/s to 10−6 cm/s. Conclusions: GP alleviated DSS-induced colitis-like symptoms and enhanced the systemic exposure of Rb1 through enhancing microbial deglycosylation and intestinal epithelial absorption of Rb1. These findings further demonstrated the important role of gut microbiota in the multifaceted action of polysaccharides in the holistic actions of traditional decoction of TCMs.

Bioactive secondary metabolites from new terrestrial Streptomyces sp. TN82 strain: Isolation, structure elucidation and biological activity

An actinomycete strain designated TN82 was isolated from Tunisian Sahara soil and selected for its interesting antimicrobial activity against Gram positive and Gram negative bacteria and fungi. Based on the results of cultural characteristic, the 16S rRNA gene nucleotide sequence (1434 bp, accession n° LT608133) and the phylogenetic analysis, this new isolate was assigned as Streptomyces sp. TN82 strain. Two active compounds, 3-phenylpyrazin-2(1H)-one (1) and 3-O-methylviridicatin (2), described for the first time as natural product and bacterial compound respectively, together with four known bacterial metabolites; cyclo-(Leu, Pro) (3), anthranilic acid (4), indole-3-carbaldehyde (5) and p-hydroxybenzoic acid (6) were isolated from the culture broth of this strain. Structure of the natural compound (1) was confirmed by extensive 1D and 2D NMR and EI MS and ESI HR mass measurements, and by comparison with literature data. Minimum inhibitory concentrations of the two compounds (1) and (2) against the tested human pathogenic bacteria S. aureus, L. monocytogenes and S. typhimurium were significantly lower than those of kanamycin. For the natural compound 3-phenylpyrazin-2(1H)-one (1), MICs values were very interesting especially that against L. monocytogenes (1.0 μg/mL) which is 2 and 12 times lower than those of ampicillin (2.0 μg/mL) and kanamycin (12.50 μg/mL), respectively.

P094 PROINFLAMMATORY RESPONSES OF THE INTESTINAL EPITHELIUM ARE PREDOMINANTLY FACILITATED BY STEM CELLS

A disturbed balance between reactivity and tolerance of the intestinal epithelium (IE) to bacterial compounds is one of the key contributors to the IBD pathogenesis. To date, research has mainly focused on the epithelial responses in general, whereas individual roles of different epithelial subsets (including stem cells, Paneth-like cells, neuroendocrine cells, enterocytes etc.) and the dynamics of their responses have not been completely addressed. To understand the dynamics of the epithelial immune responses to bacteria and to recognize the individual roles of different cell types in the intestinal epithelium, we used primary intestinal epithelial cultures (intestinal organoids). In contrast to other model systems used before, the organoids contain all the cell types and their progenitors present in the intestinal epithelium and are functionally stable during long term culture. We have characterized the epithelial immune response of intestinal organoids to soluble bacterial lysates using single cell transcriptomics - a method that allows us to measure the expression of all genes in a single cell. Our findings show that: 1. Intestinal organoids retain their capability to respond to stimulation with bacterial lysates by upregulation of pro-inflammatory genes. 2. Prolonged exposure leads to a continuous decline in cytokine production, downregulation of stem cell markers, growth impairment and upregulation of differentiation markers; all of which is reversible after the removal of the bacterial stimulus. 3. Single cell transcriptomics revealed that the cell’s capacity to express pro-inflammatory genes positively correlates with the presence of known stem cell markers and declines with the expression differentiation markers. 4. Expression levels of pro-inflammatory cytokines are highly unequal among individual stem cells. Stem cells are the main source of proinflammatory signals upon epithelial exposure to bacteria.

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.

Oxygenated N-Acyl Alanine Methyl Esters (NAMEs) from the Marine Bacterium Roseovarius tolerans EL-164.

The marine bacterium Roseovarius tolerans EL-164 (Rhodobacteraceae) can produce unique N-acylalanine methyl esters (NAMEs) besides strucutrally related N-acylhomoserine lactones (AHLs), bacterial signaling compounds widespread in the Rhodobacteraceae. The structures of two unprecedented NAMEs carrying a rare terminally oxidized acyl chain are reported here. The compounds (Z)-N-16-hydroxyhexadec-9-enoyl-l-alanine methyl ester (Z9-16-OH-C16:1-NAME, 3) and (Z)-N-15-carboxypentadec-9-enoyl-l-alanine methyl ester (16COOH-C16:1-NAME, 4) were isolated, and the structures were determined by NMR and MS experiments. Both compounds were synthesized to prove assignments and to test their biological activity. Finally, non-natural, structurally related Z9-3-OH-C16:1-NAME (18) was synthesized to investigate the mass spectroscopy of structurally related NAMEs. Compound 3 showed moderate antibacterial activity against microorganisms such as Bacillus, Streptococcus, Micrococcus, or Mucor strains. In contrast to AHLs, quorum-sensing or quorum-quenching activity was not observed.

Myeloid differentiation primary response gene (MyD) 88 signalling is not essential for intestinal fibrosis development

Dysregulation of the immune response to microbiota is associated with inflammatory bowel disease (IBD), which can trigger intestinal fibrosis. MyD88 is a key component of microbiota signalling but its influence on intestinal fibrosis has not been clarified. Small bowel resections from donor-mice were transplanted subcutaneously into the neck of recipients C57BL/6 B6-MyD88tm1 Aki (MyD88−/−) and C57BL/6-Tg(UBC-green fluorescence protein (GFP))30Scha/J (GFP-Tg). Grafts were explanted up to 21 days after transplantation. Collagen layer thickness was determined using Sirius Red stained slides. In the mouse model of fibrosis collagen deposition and transforming growth factor-beta 1 (TGF-β1) expression was equal in MyD88+/+ and MyD88−/−, indicating that MyD88 was not essential for fibrogenesis. Matrix metalloproteinase (Mmp)9 expression was significantly decreased in grafts transplanted into MyD88−/− recipients compared to MyD88+/+ recipients (0.2 ± 0.1 vs. 153.0 ± 23.1, respectively, p < 0.05), similarly recruitment of neutrophils was significantly reduced (16.3 ± 4.5 vs. 25.4 ± 3.1, respectively, p < 0.05). Development of intestinal fibrosis appears to be independent of MyD88 signalling indicating a minor role of bacterial wall compounds in the process which is in contrast to published concepts and theories. Development of fibrosis appears to be uncoupled from acute inflammation.

Mucosal-Associated Invariant T Cells in Regenerative Medicine.

Although antibiotics to inhibit bacterial growth and small compounds to interfere with the productive life cycle of human immunodeficiency virus (HIV) have successfully been used to control HIV infection, the recent emergence of the drug-resistant bacteria and viruses poses a serious concern for worldwide public health. Despite intensive scrutiny in developing novel antibiotics and drugs to overcome these problems, there is a dilemma such that once novel antibiotics are launched in markets, sooner or later antibiotic-resistant strains emerge. Thus, it is imperative to develop novel methods to avoid this vicious circle. Here, we discuss the possibility of using induced pluripotent stem cell (iPSC)-derived, innate-like T cells to control infection and potential application of these cells for cancer treatment. Mucosal-associated invariant T (MAIT) cells belong to an emerging family of innate-like T cells that link innate immunity to adaptive immunity. MAIT cells exert effector functions without priming and clonal expansion like innate immune cells and relay the immune response to adaptive immune cells through production of relevant cytokines. With these characteristics, MAIT cells are implicated in a wide range of human diseases such as autoimmune, infectious, and metabolic diseases, and cancer. Circulating MAIT cells are often depleted by these diseases and often remain depleted even after appropriate remedy because MAIT cells are susceptible to activation-induced cell death and poor at proliferation in vivo, which threatens the integrity of the immune system. Because MAIT cells have a pivotal role in human immunity, supplementation of MAIT cells into immunocompromised patients suffering from severe depletion of these cells may help recapitulate or recover immunocompetence. The generation of MAIT cells from human iPSCs has made it possible to procure MAIT cells lost from disease. Such technology creates new avenues for cell therapy and regenerative medicine for difficult-to-cure infectious diseases and cancer and contributes to improvement of our welfare.

Interaction of Human Enteric Viruses with Microbial Compounds: Implication for Virus Persistence and Disinfection Treatments

Although the interaction between phages and bacteria has already been well described, it only recently emerged that human viruses also interact with bacteria in the mammalian gut. We studied whether this interaction could occur in tap water and thus confer enteric viruses protection against temperature and the classical disinfection treatments used in drinking water production. We demonstrated that the addition of lipopolysaccharide or peptidoglycan of bacterial origin to enterovirus provides thermal protection through stabilization of the viral capsid. This interaction plays a role when viruses are exposed to disinfection that targets the capsid, but less so when the virus genome is directly targeted. The interaction seems to be serotype-specific, suggesting that the capsid protein sequence could be important. The protection is linked to a direct association between viral particles and bacterial compounds as observed by microscopy. These results show that bacterial compounds present in the environment can affect virus inactivation.

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.

The human bitter taste receptor T2R38 is broadly tuned for bacterial compounds

T2R38 has been shown to be a specific bacterial detector implicated in innate immune defense mechanism of human upper airway. Several clinical studies have demonstrated that this receptor is associated with the development of chronic rhinosinusitis (CRS). T2R38 was previously reported to bind to homoserine lactones (HSL), quorum sensing molecules specific of Pseudomonas Aeruginosa and other gram negative species. Nevertheless, these bacteria are not the major pathogens found in CRS. Here we report on the identification of bacterial metabolites acting as new agonists of T2R38 based on a single cell calcium imaging study. Two quorum sensing molecules (Agr D1 thiolactone from Staphylococcus Aureus and CSP-1 from Streptococcus Pneumoniae) and a list of 32 bacterial metabolites from pathogens frequently implicated in CRS were tested. First, we observed that HSL failed to activate T2R38 in our experimental system, but that the dimethylsulfoxide (DMSO), used as a solvent for these lactones may, by itself, account for the agonistic effect previously described. Secondly, we showed that both Agr D1 thiolactone and CSP-1 are inactive but that at least 7 bacterial metabolites (acetone, 2-butanone, 2-pentanone, 2-methylpropanal, dimethyl disulfide, methylmercaptan, γ-butyrolactone) are able to specifically trigger this receptor. T2R38 is thus much more broadly tuned for bacterial compounds than previously thought.

Transcriptional Responses of Creeping Bentgrass to 2,3-Butanediol, a Bacterial Volatile Compound (BVC) Analogue.

Bacterial volatile compounds (BVCs) have been reported to enhance plant growth and elicit plant defenses against fungal infection and insect damage. The objective of this study was to determine transcriptomic changes in response to synthetic BVC that could be associated with plant resistance to Rhizoctonia solani in creeping bentgrass. The 2,3-butanediol (BD) (250 µM) was sprayed on creeping bentgrass leaves grown in jam jars. The result showed that synthetic BD induced plant defense against R. solani for creeping bentgrass. Transcriptomic analysis demonstrated that more genes were repressed by BD while less showed up-regulation. BD suppressed the expression of some regular stress-related genes in creeping bentgrass, such as pheromone activity, calcium channel activity, photosystem II oxygen evolving complex, and hydrolase activity, while up-regulated defense related transcription factors (TFs), such as basic helix-loop-helix (bHLH) TFs, cysteine2-cysteine2-contans-like (C2C2-CO) and no apical meristem TFs (NAC). Other genes related to disease resistance, such as jasmonic acid (JA) signaling, leucine rich repeats (LRR)-transmembrane protein kinase, pathogen-related (PR) gene 5 receptor kinase and nucleotide binding site-leucine rich repeats (NBS-LRR) domain containing plant resistance gene (R-gene) were also significantly up-regulated. These results suggest that BD may induce changes to the plant transcriptome in induced systemic resistance (ISR) pathways.

Intestinal Anti-inflammatory Effects of Outer Membrane Vesicles from Escherichia coli Nissle 1917 in DSS-Experimental Colitis in Mice.

Escherichia coli Nissle 1917 (EcN) is a probiotic strain with proven efficacy in inducing and maintaining remission of ulcerative colitis. However, the microbial factors that mediate these beneficial effects are not fully known. Gram-negative bacteria release outer membrane vesicles (OMVs) as a direct pathway for delivering selected bacterial proteins and active compounds to the host. In fact, vesicles released by gut microbiota are emerging as key players in signaling processes in the intestinal mucosa. In the present study, the dextran sodium sulfate (DSS)-induced colitis mouse model was used to investigate the potential of EcN OMVs to ameliorate mucosal injury and inflammation in the gut. The experimental protocol involved pre-treatment with OMVs for 10 days before DSS intake, and a 5-day recovery period. Oral administration of purified EcN OMVs (5 μg/day) significantly reduced DSS-induced weight loss and ameliorated clinical symptoms and histological scores. OMVs treatment counteracted altered expression of cytokines and markers of intestinal barrier function. This study shows for the first time that EcN OMVs can mediate the anti-inflammatory and barrier protection effects previously reported for this probiotic in experimental colitis. Remarkably, translation of probiotics to human healthcare requires knowledge of the molecular mechanisms involved in probiotic–host interactions. Thus, OMVs, as a non-replicative bacterial form, could be explored as a new probiotic-derived therapeutic approach, with even lower risk of adverse events than probiotic administration.

Selection of Nutrient Used in Biogenic Healing Agent for Cementitious Materials

Biogenic self-healing cementitious materials target on the closure of micro-cracks with precipitated inorganic minerals originating from bacterial metabolic activity. Dormant bacterial spores and organic mineral compounds often constitute a biogenic healing agent. The current paper focuses on the investigation of the most appropriate organic carbon source to be used as component of a biogenic healing agent. It is of great importance to use an appropriate organic source, since it will firstly ensure an optimal bacterial performance in terms of metabolic activity, while it should secondly affect the least the properties of the cementitious matrix. The selection is made among three different organic compounds, namely calcium lactate, calcium acetate and sodium gluconate. The methodology that was used for the research was based on continuous and non-continuous oxygen consumption measurements of washed bacterial cultures and on compressive strength tests on mortar cubes. The oxygen consumption investigation revealed a preference for calcium lactate and acetate, but an indifferent behaviour for sodium gluconate. The compressive strength on mortar cubes with different amounts of either calcium lactate or acetate (up to 2.24% per cement weight) was not or it was positively affected when the compounds were dissolved in the mixing water. In fact, for calcium lactate the increase in compressive strength reached 8%, while for calcium acetate the maximum strength increase was 13.4%.

Biological and chemical strategies for exploring inter- and intra-kingdom communication mediated via bacterial volatile signals.

Airborne chemical signals emitted by bacteria influence the behavior of other bacteria and plants. We present an overview of in vitro methods for evaluating bacterial and plant responses to bacterial volatile compounds (BVCs). Three types of equipment have been used to physically separate the bacterial test strains from either other bacterial strains or plants (in our laboratory we use either Arabidopsis or tobacco plant seedlings): a Petri dish containing two compartments (BI Petri dish); two Petri dishes connected with tubing; and a microtiter-based assay. The optimized procedure for the BI Petri dish system is described in this protocol and can be widely used for elucidation of potential function in interactions between diverse microbes and those plant and chemical volatiles emitted by bacteria that are most likely to mediate bacterial or plant responses to BVCs. We also describe a procedure for metabolome-based BVC profiling via dynamic (i.e., continuous airflow) or static headspace sampling using solid-phase microextraction (SPME). Using both these procedures, bacteria-bacteria communications and bacteria-plant interactions mediated by BVCs can be rapidly investigated (within 1-4 weeks).

Immunostimulatory effects of dietary poly-β-hydroxybutyrate in European sea bass postlarvae

The stable production of high-quality fry in marine aquaculture is still hampered by unpredictable mortality caused by infectious diseases during larval rearing. Consequently, the development of new biocontrol agents is crucial for a viable aquaculture industry. The bacterial energy storage compound poly-β-hydroxybutyrate (PHB) has been shown to exhibit beneficial properties on aquatic organisms such as enhanced survival, growth, disease resistance and a controlling effect on the gastrointestinal microbiota. However, the effect of PHB on the developing immune system of fish larvae has so far not been investigated. In this study, the effect of feeding PHB-enriched Artemia nauplii on survival, growth and immune response in European sea bass (Dicentrarchus labrax) postlarvae was examined. Amorphous PHB was administered to 28-day-old sea bass postlarvae over a period of 10 days. The survival and growth performance were monitored, and the expression of 29 genes involved in immunity, growth, metabolism and stress-response was measured. While the expression of the insulin-like growth factor 1 (igf1), an indicator of relative growth, was upregulated in response to feeding PHB, the larval survival and growth performance remained unaffected. After 10 days of PHB treatment, the expression of the antimicrobial peptides dicentracin (dic) and hepcidin (hep) as well as mhc class IIa and mhc class IIb was elevated in the PHB fed postlarvae. This indicates that PHB is capable of stimulating the immune system of fish early life stages, which may be the cause of the increased resistance to diseases and robustness observed in previous studies.

Effects of 4 Probiotic Strains in Coculture with Traditional Starters on the Flavor Profile of Yogurt.

To study the influence of probiotics on the flavor profile of yogurt, 4 probiotics, including Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus rhamnosus, and Lactobacillus casei, were cofermented with traditional starters. The changes of bacterial growth, acid contents and volatile compounds of yogurt were investigated during fermentation and refrigerated storage. The strains that exhibited a low growth rate in milk did not significantly affect the bacterial population dynamics, acidity, or organic acid content during fermentation and storage. However, high viability and enhancement of postacidification were clearly observed in the samples that contained strains with a high growth rate in milk, particularly L. casei. A total of 45 volatile compounds, detected in most samples, were identified by headspace solid-phase micro-extraction followed by gas chromatography-mass spectrometry. Among these compounds, ketones and aldehydes were the most abundant. The presence of either L. rhamnosus or L. plantarum did not significantly affect the major volatile compounds, while contributions of L. casei and L. acidophilus were found in the formation of minor volatile metabolites. Electronic nose measurements exhibited a good discrimination of samples that contained different probiotics during refrigerated storage.

Akkermansia muciniphila tend to influence experimental non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a growing health-care problem in the western world with limited treatment options. In the recent past, the importance of the gut-liver-axis in the development of NASH came into the centre of attention: bacterial compounds (e.g. endotoxins) are translocated from the gut into the liver and trigger inflammation and hepatic injury. Akkermansia muciniphila, a Gram-negative commensal, reduce endotoxemia by enhancing mucus-thickness, tight-junction expression and thereby restoring barrier function. The aim of this study was to investigate a possible role of Akkermansia muciniphila supplementation in the development of NASH.

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.

Lactobacillus delbrueckii subsp. lactis as a starter culture significantly affects the dynamics of volatile compound profiles of hard cooked cheeses

Lactobacillus delbrueckii (LD) is a species usually found in raw milk hard cooked cheeses. Present in raw milk, it grows in cheeses during ripening, but it can also be added in large concentrations with acidifying starter cultures. Its role in cheese proteolysis has been largely demonstrated, but its role in the formation of volatile compounds in cheeses remains to be documented. For this purpose, 16 experimental hard cooked cheeses were made from raw milk using adjunct cultures made up of Streptococcus thermophilus and Lactobacillus helveticus with the addition or not of LD, and ripened for 184 days. Bacterial populations and volatile compounds were monitored throughout ripening. The LD addition affected the early growth of the starters but not the dynamics of the native microbiota. LD had a major effect on proteolysis and on the composition of volatile compounds. Of the 85 volatile compounds identified in the cheeses, 6 of the 7 acids, 10 of the 16 aldehydes, 11 of the 17 alcohols, 10 of the 17 ketones, 10 of the 23 esters, and 4 of the 5 sulphur compounds were affected by the LD addition at one or more stages of ripening. At the end of ripening, levels of the 31 compounds affected by LD were higher in the cheeses with LD added, except one secondary alcohol and 2 methyl-ketones. The question of the effective involvement of LD in these observations, whether due to the metabolic activity of LD or interactions with other microbial populations, is raised.