Antimicrobial Activity of Metabolites Secreted by the Endophytic Bacterium Frateuria defendens

Odorant receptors for floral- and plant-derived volatiles in the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae)

Adult mosquitoes require regular sugar meals, including nectar, to survive in natural habitats. Both males and females locate potential sugar sources using sensory proteins called odorant receptors (ORs) activated by plant volatiles to orient toward flowers or honeydew. The yellow fever mosquito, Aedes aegypti (Linnaeus, 1762), possesses a large gene family of ORs, many of which are likely to detect floral odors. In this study, we have uncovered ligand-receptor pairings for a suite of Aedes aegypti ORs using a panel of environmentally relevant, plant-derived volatile chemicals and a heterologous expression system. Our results support the hypothesis that these odors mediate sensory responses to floral odors in the mosquito's central nervous system, thereby influencing appetitive or aversive behaviors. Further, these ORs are well conserved in other mosquitoes, suggesting they function similarly in diverse species. This information can be used to assess mosquito foraging behavior and develop novel control strategies, especially those that incorporate mosquito bait-and-kill technologies.

Bois noir management in vineyard: a review on effective and promising control strategies

Among grapevine yellows, Bois noir (BN), associated with 'Candidatus Phytoplasma solani', represents the biggest threat in the main wine-growing areas worldwide, causing significant losses in berry quality and yields. BN epidemiology involves multiple plant hosts and several insect vectors, making considerably complex the development of effective management strategies. Since application of insecticides on the grapevine canopy is not effective to manage vectors, BN management includes an integrated approach based on treatments to the canopy to make the plant more resistant to the pathogen and/or inhibit the vector feeding, and actions on reservoir plants to reduce possibilities that the vector reaches the grapevine and transmit the phytoplasma. Innovative sustainable strategies developed in the last twenty years to improve the BN management are reviewed and discussed.

Odorant receptors for floral- and plant-derived volatiles in the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae)

Adult mosquitoes require regular sugar meals, usually floral nectar, to survive and flourish in natural habitats. Both males and females locate potential sugar sources using sensory proteins called odorant receptors activated by plant volatiles that facilitate orientation toward flowers or honeydew. The Yellow Fever mosquito, Aedes aegypti (Linnaeus, 1762), possesses a large repertoire of odorant receptors, many of which are likely to support floral odor detection and nectar-seeking. In this study, we have employed a heterologous expression system and the two-electrode voltage clamping technique to identify environmentally relevant chemical compounds that activate specific odorant receptors. Importantly, we have uncovered ligand-receptor pairings for a suite of Aedes aegypti odorant receptors likely to mediate appetitive or aversive behavioral responses, thus shaping a critical aspect of the life history of a medically important mosquito. Moreover, the high degree of conservation of these receptors in other disease-transmitting species suggests common mechanisms of floral odor detection. This knowledge can be used to further investigate mosquito foraging behavior to either enhance existing, or develop novel, control strategies, especially those that incorporate mosquito bait-and-kill or attractive toxic sugar bait technologies.

Frateuria soli sp. nov. and Frateuria edaphi sp. nov., isolated from greenhouse soil

Two bacterial strains, designated 5GH9-11^T and 5GH9-34^T, were isolated from greenhouse soil sampled in Wanju-gun, Jeollabuk-do, Republic of Korea. Both strains formed yellow colonies and were aerobic, rod-shaped and flagellated. The 16S rRNA gene sequence similarity between 5GH9-11^T and 5GH9-34^T was 98.6 %. Strain 5GH9-11^T showed the highest sequence similarities to Dyella thiooxydans ATSB10^T (98.1 %) and Frateuria aurantia DSM 6220^T (97.7 %) while strain 5GH9-34^T revealed the highest sequence similarity to F. aurantia DSM 6220^T (98.3 %) and D. thiooxydans ATSB10^T (98.3 %). Phylogenetic analysis on the basis of the 16S rRNA gene sequence showed that strains 5GH9-11^T and 5GH9-34^T formed a robust cluster with Frateuria flava MAH-13^T and Frateuria terrea NBRC 104236^T. The phylogenomic tree also showed that strains 5GH9-11^T and 5GH9-34^T formed a robust cluster with F. terrea DSM 26515^T and F. flava MAH-13^T. Strain 5GH9-11^T showed the highest orthologous average nucleotide identity (OrthoANI; 88.5 %) and digital DNA-DNA hybridization (dDDH) values (35.5 %) with F. flava MAH-13^T, and strain 5GH9-34^T revealed highest OrthoANI (88.1 %) and dDDH (34.2 %) values with F. flava MAH-13^T. The orthoANI and dDDH values between strain 5GH9-11^T and 5GH9-34^T were 87.7 and 33.9 %, respectively. Their major respiratory quinone was ubiquinone 8, and the major cellular fatty acids were iso-C_16 : 0, summed feature 9 (iso-C_17 : 1 ω9c and/or C_16 : 0 10-methyl) and iso-C_15 : 0. The major polar lipids of both strains were composed of large or moderate amounts of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, an unidentified aminolipid and an unidentified aminophospholipid. Based on these data, strains 5GH9-11^T and 5GH9-34^T should represent two independent novel species of Frateuria, for which the names Frateuria soli sp. nov. (type strain 5GH9-11^T=KACC 16943^T=JCM 35197^T) and Frateuria edaphi sp. nov. (type strain 5GH9-34^T=KACC 16945^T=JCM 35198^T) are proposed.

Evaluation of the biocontrol activity of Frateuria defendens-derived metabolites against mollicutes

Frateuria defendens is a candidate biocontrol agent that has been shown to reduce phytoplasma-related disease symptoms in grapevines and periwinkle plants. While a crude filtrate prepared from F. defendens can inhibit mollicute growth, the specific growth parameters for this bacterium, necessary to enhance this protective inhibitory response, remain unknown. Moreover, the separation of filtrate preparations from bacterial cells via centrifugation and filtration is laborious and time-consuming. As such, the present study was conducted to define the optimal growth conditions associated with maximal inhibitory activity of F. defendens and to establish a better approach to separating these bacterial cells from their secreted metabolites. To conduct these analyses, F. defendens was cultured in a range of media types, while associated inhibitory effects were tested in vitro using Spiroplasma melliferum as a model mollicute bacterium, and in planta using phytoplasma-infected periwinkle plantlets. These analyses revealed F. defendens growth patterns change based upon media composition, with filtrates prepared from a specific rich medium (S-medium) exhibiting beneficial activities, including the inhibition of S. melliferum and enhanced plant growth. When F. defendens cells were grown within semi-permeable, membrane-coated Small Bioreactor Platform (SBP) capsules, they could be more readily separated from the secreted metabolite fraction, obviating the need for filtration and/or centrifugation. This study is the first to have reported the use of SBP capsules to separate bacterial cells from their secreted metabolites under sterile conditions while retaining the ability of these metabolites to inhibit S. melliferum growth and to benefit the host plant. The results highlight promising new approaches to the effective biocontrol of phytoplasma-driven diseases in grapevines and other economically important plant species.

Bioprospecting of a novel endophytic Bacillus velezensis FZ06 from leaves of Camellia assamica: Production of three groups of lipopeptides and the inhibition against food spoilage microorganisms

Food contamination caused by microorganisms has become a threat to consumers' health. Exploring antagonistic endophytes from plants of food raw-material and applying bioactive metabolites to inhibit the contamination has been an alternative and safer solution. In this study, we isolated and screened potential antagonistic endophytes from fresh Camellia assamica leaves, which were widely used in tea beverage production. We focused on a strain that showed visible inhibitory activity to Gram-positive bacteria, Gram-negative bacteria, and fungi. It was identified as a member of Bacillus velezensis and named FZ06. The results of genome analysis showed the strain FZ06 had 167 single-copy specific genes, much higher than those of most related strains. Also, 11 potential gene clusters of antimicrobial metabolites were found. Three groups of lipopeptides (surfactin, iturin, and fengycin) were identified by UPLC-MS/MS in purified antimicrobial methanol fraction of strain FZ06. The results of minimum inhibitory concentration (MIC) test proved the lipopeptide extract showed significant inhibitory effect on food spoilage bacteria (MIC 512-2048 μg/mL) and toxigenic fungi (MIC 128-256 μg/mL). In conclusion, this study suggests that the endophytic B. velezensis FZ06 and its lipopeptide extract hold great potential applications in the inhibition of food spoilage bacteria and toxic fungi in food industry.