Epiphytic Bacteria from Sweet Pepper Antagonistic In Vitro to Ralstonia solanacearum BD 261, a Causative Agent of Bacterial Wilt

Antagonistic potential of endophytic fungal isolates of tomato (Solanum lycopersicum L.) fruits against post-harvest disease-causing pathogens of tomatoes: An in vitro investigation

Post-harvest decay of fresh agricultural produce is a major threat to food security globally. Synthetic fungicides, commonly used in practice for managing the post-harvest losses, have negative impacts on consumers' health. Studies have reported the effectiveness of fungal isolates from plants as biocontrol agents of post-harvest diseases, although this is still poorly established in tomatoes (Solanum lycopersicum L. cv. Jasmine). In this study, 800 endophytic fungi were isolated from mature green and ripe untreated and fungicide-treated tomato fruits grown in open soil and hydroponics systems. Of these, five isolates (Aureobasidium pullulans SUG4.1, Coprinellus micaceus SUG4.3, Epicoccum nigrum SGT8.6, Fusarium oxysporum HTR8.4, Preussia africana SUG3.1) showed antagonistic properties against selected post-harvest pathogens of tomatoes (Alternaria alternata, Fusarium solani, Fusarium oxysporum, Geotrichum candidum, Rhizopus stolonifera, Rhizoctonia solani), with Lactiplantibacillus plantarum as a positive control. P. africana SUG3.1 and C. micaceus SUG4.3 significantly inhibited growth of all the pathogens, with antagonistic capabilities comparable to that exhibited by L. plantarum. Furthermore, the isolates produced an array of enzymes, including among others, amylase, cellulose and protease; and were able to utilize several carbohydrates (glucose, lactose, maltose, mannitol, sucrose). In conclusion, P. africana SUG3.1 and C. micaceus SUG4.3 may complement L. plantarum as biocontrol agents against post-harvest pathogens of tomatoes.

Genome Assembly of a Putative Plant Growth-Stimulating Bacterial Sweet Pepper Fruit Isolate, Enterobacter hormaechei SRU4.4

Here, we report the draft genome sequence of Enterobacter hormaechei SRU4.4. This bacterium (genome size = 4,440,516 bp; coding sequences = 4,100; G+C content = 56%) encodes for genes attributed to plant growth promotion (PGP).

De novo Genome Assessment of Serratia marcescens SGT5.3, a Potential Plant Growth-Promoting Bacterium Isolated from the Surface of Capsicum annuum Fruit

Serratia marcescens SGT5.3, a potential plant growth-promoting strain with a wide range of functions, was isolated from the surface of Capsicum annuum fruit. Here, we report the whole-genome sequence of this bacterium. Gene prediction revealed various functional genes potentially involved in plant growth promotion and development.

Xanthomonas Infection Transforms the Apoplast into an Accessible and Habitable Niche for Salmonella enterica

Bacterial spot disease caused by Xanthomonas species devastates tomato production worldwide. Salmonellosis outbreaks from consumption of raw produce have been linked to the arrival of Salmonella enterica on crop plants in the field via contaminated irrigation water.

Antifungal Activities of Bacillus mojavensis BQ-33 towards the Kiwifruit Black Spot Disease Caused by the Fungal Pathogen Didymella glomerata

‘Hongyang’ kiwifruit (Actinidia chinensis, cultivar ‘Hongyang’) black spot disease is caused by the fungal pathogen Didymella glomerata, and is a serious disease, causing considerable losses to the kiwifruit industry during growth of the fruit. Hence, we aimed to identify a potential biocontrol agent against D. glomerata. In this study, bacterial isolates from the rhizosphere soil of kiwifruit were tested for their potential antifungal activity against selected fungal pathogens. Based on a phylogenetic tree constructed using sequences of 16S rDNA and the gyrA gene, BQ-33 with the best antifungal activity was identified as Bacillus mojavensis. We evaluated the antagonistic activity and inhibitory mechanism of BQ-33 against D. glomerata. Confrontation experiments showed that both BQ-33 suspension and the sterile supernatant (SS) produced by BQ-33 possessed excellent broad-spectrum antifungal activity. Furthermore, the SS damaged the cell membrane and cell wall of the mycelia, resulting in the leakage of a large quantity of small ions (Na⁺, K⁺), soluble proteins and nucleic acids. Chitinase and β-1,3-glucanase activities in SS increased in correlation with incubation time and remained at a high level for several days. An in vivo control efficacy assay indicated that 400 mL L⁻¹ of SS completely inhibited kiwifruit black spot disease caused by D. glomerata. Therefore, BQ-33 is a potential biocontrol agent against kiwifruit black spot and plant diseases caused by other fungal pathogens. To our knowledge, this is the first report of the use of a rhizosphere microorganism as a biocontrol agent against kiwifruit black spot disease caused by D. glomerata.

Purification and characterization of a Metschnikowia pulcherrima killer toxin with antagonistic activity against pathogenic microorganisms

Yeasts can produce toxins in protein or glycoprotein structures that can act as an inhibitor on some bacteria and yeast species. The effects of those toxins on the growth of pathogenic and food spoilage microorganisms are subject to various studies. Metschnikowia pulcherrima was determined to be a killer toxin-producing yeast that was tested against three selected microorganisms, namely Escherichia coli Type-I, Micrococcus luteus and Candida albicans. The killer toxin only showed inhibitory activity against M. luteus. Different pH (5-6-7-8), temperature (20-25-30-35 °C) and carbon source (glucose-glycerol-ethanol-acetate) combinations were applied to stimulate the growth and toxin production of the killer yeast. The greatest increase among the different combinations was obtained at 20 °C and pH 7 when glycerol was used as the main carbon source. It was then also tested against other pathogen indicators or pathogens under these conditions. The killer toxin was partially purified by ethanol precipitation and showed inhibitory activity against M. luteus (36 mm). According to the protein profile obtained by SDS-PAGE, the molecular weight of the inhibitor toxin was measured about 7.4 kDa. The molecular weight with amino acid sequence of the killer toxin was 10.3 kDa and determined by MALDI-TOF mass spectrometry.

Draft Genome Sequence of Sweet Pepper Fruit Epiphyte-Associated Bacillus cereus HRT7.7

This study reports the whole-genome sequence of Bacillus cereus HRT7.7, an epiphyte isolated from red sweet pepper fruits that is capable of stimulating plant growth and development. The genome assembly is 5,109,010 bp in length, with a G+C content of 35.2%.

Whole-Genome Sequence of Paenibacillus polymyxa Strain SRT9.1, a Promising Plant Growth-Promoting Bacterium

Paenibacillus polymyxa SRT9.1 is an epiphytic bacterium capable of inhibiting plant-pathogenic bacteria. The strain has potential for development as a biocontrol agent for use in agriculture. We report the whole-genome sequence of Paenibacillus polymyxa SRT9.1, consisting of 6,754,470 bp and 7,878 coding sequences, with an average G+C content of 45%.