Screening and Molecular Identification of Bacteria from the Midgut of Amphimallon solstitiale Larvae Exhibiting Antagonistic Activity against Bacterial Symbionts of Entomopathogenic Nematodes

Entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) are a group of organisms capable of infecting larvae of insects living in soil, including representatives of the family Scarabaeidae. Their insecticidal activity is related to the presence of symbiotic bacteria Xenorhabdus spp. or Photorhabdus spp. in the alimentary tract, which are released into the insect body, leading to its death caused by bacterial toxins and septicemia. Although the antibacterial activities of symbionts of entomopathogenic nematodes have been well described, there is insufficient knowledge of the interactions between these bacteria and microorganisms that naturally inhabit the alimentary tract of insects infested by nematodes. In this study, 900 bacterial strains isolated from midgut samples of Amphimallon solstitiale larvae were tested for their antagonistic activity against the selected five Xenorhabdus and Photorhabdus species. Cross-streak tests showed significant antibacterial activity of 20 isolates. These bacteria were identified as Bacillus [Brevibacterium] frigoritolerans, Bacillus toyonensis, Bacillus wiedmannii, Chryseobacterium lathyri, Chryseobacterium sp., Citrobacter murliniae, Enterococcus malodoratus, Paenibacillus sp., Serratia marcescens and Serratia sp. Since some representatives of the intestinal microbiota of A. solstitiale are able to inhibit the growth of Xenorhabdus and Photorhrhabdus bacteria in vitro, it can be assumed that this type of bacterial interaction may occur at certain stages of insect infection by Steinernema or Heterorhabditis nematodes.

Bacillus promotes invasiveness of exotic Flaveria bidentis by increasing its nitrogen and phosphorus uptake

Aim The effect of exotic plants on Bacillus diversity in the rhizosphere and the role of Bacilli in exotic or native plant species remain poorly understood. Flaveria bidentis is an invasive grass in China. Setaria viridis is a native grass and occurs in areas invaded by F. bidentis. Our objectives were (i) to examine the differences in the Bacillus communities between F. bidentis and S. viridis rhizospheres soil, and (ii) to compare the effects of Bacilli from F. bidentis and S. viridis rhizospheres on the competitiveness of the invasive species. Methods Flaveria bidentis monoculture, mixture of F. bidentis and S. viridis and S. viridis monoculture were designed in the field experiment. Bacillus diversity in their rhizosphere was analyzed using 16S rRNA. One of the dominant Bacilli in the rhizosphere soil of F. bidentis was selected to test its effect on the competitive growth of F. bidentis in a greenhouse experiment. Important Findings Bacillus diversity differed in F. bidentis and S. viridis rhizosphere. Brevibacterium frigoritolerans was the dominant Bacilli in the rhizosphere of both F. bidentis and S. viridis; however, its relative abundance in the F. bidentis rhizosphere was much higher than that in the S. viridis rhizosphere. In addition, B. frigoritolerans in the F. bidentis rhizosphere enhanced the growth of the plant compared to that of S. viridis by improving the nitrogen and phosphorus levels. This study showed that F. bidentis invasion influenced Bacillus communities, especially B. frigoritolerans, which, in turn, facilitated F. bidentis growth by increasing the levels of available nitrogen and phosphorus.

Culturable endophytic bacteria from Phelipanche ramosa (Orobanchaceae) seeds

Endophytic microbiomes play a beneficial role in the development and protection of plants. However, seed-borne endophytic bacteria have not yet been fully explored. Investigation of parasitic plants, whose existence depends on yet poorly understood and complicated relationships with microorganisms and hosts, is particularly crucial. Endophytic bacteria promote seed conservation and facilitate seed germination in soil. Several root holoparasites from the Orobanchaceae family are the most aggressive broomrape species, often causing serious yield losses in important crops. Parasitic plants are characterized by the production of a large number of some of the smallest seeds in the world's flora, allowing them to stay viable in the soil for several dozen years. This study's aim was to isolate and characterize the seed endophyte and surface bacteria of the most aggressive and widespread broomrape weed, Phelipanche ramosa. We isolated two endophytic bacteria from within the seeds which are closely related to Brevibacterium frigoritolerans and Bacillus simplex described as soil bacteria, highly resistant to environmental conditions, and as plant growth-promoting rhizobacteria. Moreover, we isolated three strains from the surface of non-sterile seeds; all three isolates were related to the Bacillus cereus group.

Bacterial endophytes from horseradish (Armoracia rusticana G. Gaertn., B. Mey. & Scherb.) with antimicrobial efficacy against pathogens

The current study aimed to determine the diversity of culturable endophytic bacteria associated with horseradish (Armoracia rusticana G. Gaertn., B. Mey. & Scherb.) grown in Chatkal Biosphere Reserve of Uzbekistan and their antimicrobial potentials. The bacteria were isolated from plant leaves and root tissues using culture-dependent techniques. The 16S rRNA sequences similarities of endophytic bacteria isolated from A. rusticana showed that isolates belong to species Paenibacillus, Raoultella, Stenotrophomonas, Pseudomonas, Serratia, Microbacterium, Enterobacter, Achromobacter, Brevibacterium, Pantoea, and Erwinia. The isolated endophytic bacteria Stenotrophomonas maltophilia KRT1, Serratia ficaria KRT5, and Pantoea agglomerans KLT4 possess antimicrobial activities against human pathogenic bacteria Staphylococcus aureus, Escherichia coli, and Candida albicans. The endophytic bacteria Paenibacillus typhae KRN1, Stenotrophomonas maltophilia KRT1, Pseudomonas kilonensis KRT11, Pseudomonas umsongensis KRT21, Brevibacterium frigoritolerans KLT2 and Pantoea agglomerans KLT4 inhibited phytopathogenic fungi Rhizoctonia solani, Fusarium culmorum, and F. solani. These findings indicate that plant endophytic bacteria with antimicrobial activity could be a source for producing agriculturally and pharmaceutically important antimicrobial compounds.

Efecto de bacterias PGPB, composta y digestato en el rendimiento de materia seca de pasto ovillo

El objetivo fue determinar el efecto de composta, digestato y bacterias plant growth-promoting bacteria (PGPB) en la curva de crecimiento, acumulación de biomasa, tasa de crecimiento, altura de planta y unidades soil plant analysis development (SPAD) en pasto ovillo recién establecido, bajo condiciones de invernadero. Los tratamientos fueron: digestato (60%), composta (10% en base seca del suelo), bacterias: Brevibacterium frigoritolerans, Bacillus simplex, Pseudomonas putida, control positivo (fertilización con triple 17) y el control negativo (suelo sin fertilización). Se utilizó un diseño experimental completamente al azar, la unidad experimental fue una maceta con diez tallos de pasto ovillo, con cuatro repeticiones por tratamiento. Los valores más altos (p< 0.05) de materia seca (6.4 g MS maceta), tasa de crecimiento (0.15 g MS maceta d-1) y altura de forraje (18.3 cm) se registraron en el tratamiento con composta; donde el rendimiento final de materia seca superó 200% al testigo negativo. El tratamiento con digestato evidenció valores inferiores a los obtenidos con composta, pero superó al resto de los tratamientos. Las mejores bacterias PGPB fueron Pseudomonas putida y Bacillus simplex que superaron el rendimiento de materia seca 25 y 37% con respecto a Brevibacterium frigoritolerans y al control negativo, respectivamente. Las bacterias PGPB pueden ser una alternativa de fertilización ya que el rendimiento de materia seca fue mayor que con el control negativo y se igualó al rendimiento obtenido con fertilización química; sin embargo, los dos fertilizantes orgánicos (composta y digestato) favorecieron el mayor rendimiento de materia seca.

Analysis of the complete genome sequence of Brevibacterium frigoritolerans ZB201705 isolated from drought- and salt-stressed rhizosphere soil of maize

Purpose To analyze the complete genome sequence of the Brevibacterium frigoritolerans ZB201705, a Brevibacterium strain was isolated from the maize rhizosphere in drought- and salt-stressed soil, and the activity of the strain under simulated drought and high salt conditions was assessed. Methods We used a combination of the PacBio RS and Illumina sequencing platforms to obtain the complete genome sequence of B. frigoritolerans ZB201705. Results The genome consists of 5,475,560 bp in a linear chromosome with no gaps, 4,391 protein-coding sequences, 39 ribosomal RNAs, and 81 transfer RNAs. The genome analysis revealed many putative gene clusters involved in defense mechanisms. In addition, an activity analysis of the strain under high-salt and simulated drought conditions helped clarify its potential tolerance to these abiotic stresses. Conclusions Our data revealed the complete genome sequence of the new isolated strain, and showed that it produces many proteins involved in drought and salt stress responses, suggesting that B. frigoritolerans ZB201705 may be a potential factor to increase crop yield under abiotic stresses. The information provided here on the genome of B. frigoritolerans ZB201705 provides valuable insight into rhizobacteria-mediated plant salt and drought tolerance and rhizobacteria-based solutions for agriculture under abiotic stress.