Acinetobacter nematophilus sp. nov., Alcaligenes nematophilus sp. nov., Enterobacter nematophilus sp. nov., and Kaistia nematophila sp. nov., Isolated from Soil-Borne Nematodes and Proposal for the Elevation of Alcaligenes faecalis subsp. faecalis, Alcaligenes faecalis subsp. parafaecalis, and Alcaligenes faecalis subsp. phenolicus to the Species Level.

Four bacterial strains, A-IN1T, A-TC2T, E-TC7T, and K-TC2T, isolated from soil-borne nematodes of the species Oscheius tipulae and Acrobeloides bodenheimeri, were found to represent new species of the genera Acinetobacter, Alcaligenes, Enterobacter, and Kaistia, respectively. In this study, we described these new species using a polyphasic taxonomic approach that included wholegenome and whole-proteome phylogenomic reconstructions, core genome sequence comparisons, and phenotypic characterization. Phylogenomic reconstructions using whole-genome and wholeproteome sequences show that A-IN1T is closely related to Acinetobacter guillouiae DSM 590T and to Acinetobacter bereziniae LMG 1003T. The dDDH values between A-IN1T and these latest strains are 25.1 and 39.6%, respectively, which are below the 70% divergence threshold for prokaryotic species delineation. A-TC2T is closely related to Alcaligenes faecalis subsp. faecalis DSM 30030T and to Alcaligenes faecalis subsp. phenolicus DSM 16503T. The dDDH values between A-TC2T and these latest strains are 47.0 and 66.3%, respectively. In addition, the dDDH values between Alcaligenes faecalis subsp. faecalis DSM 30030T, Alcaligenes faecalis subsp. phenolicus DSM 16503T, and Alcaligenes faecalis subsp. parafaecalis are always lower than 70%, demonstrating that the three strains represent species within the genus Alcaligenes rather than subspecies within Alcaligenes faecalis. E-TC7T is closely related to Enterobacter kobei DSM 13645T, Enterobacter chuandaensis 090028T, and to Enterobacter bugandensis STN0717-56T. The dDDH values between E-TC7T and these strains are 43.5, 42.9, and 63.7%, respectively. K-TC2T is closely related to Kaistia terrae DSM 21341T and to Kaistia defluvii JCM 18034T. The dDDH values between these strains are 29.2 and 30.7%, respectively. Several biochemical tests allow to differentiate the type strains of the newly described species from the type strains of their more closely related species. Based on the results of this polyphasic taxonomic approach, the following new species are proposed: Acinetobacter nematophilus sp. nov. with A-IN1T (=CCM 9231T =CCOS 2018T) as the type strain, Alcaligenes nematophilus sp. nov. with A-TC2T (=CCM 9230T =CCOS 2017T) as the type strain, Enterobacter nematophilus sp. nov. with E-TC7T (=CCM 9232T =CCOS 2020T) as the type strain, and Kaistia nematophila sp. nov. with K-TC2T (=CCM 9239T =CCOS 2022T) as the type strain. In addition, we propose the elevation of Alcaligenes faecalis subsp. faecalis, Alcaligenes faecalis subsp. parafaecalis, and Alcaligenes faecalis subsp. phenolicus to the species level. Therefore, we propose the creation of Alcaligenes parafaecalis sp. nov. with DSM 13975T as the type strain, and Alcaligenes phenolicus sp. nov. with DSM 16503T as the type strain. Our study contributes to a better understanding of the biodiversity and phylogenetic relationships of bacteria associated with soil-borne nematodes

Entomopathogenic potential of bacteria associated with soil-borne nematodes and insect immune responses to their infection

Soil-borne nematodes establish close associations with several bacterial species. Whether they confer benefits to their hosts has been investigated in only a few nematode-bacteria systems. Their ecological function, therefore, remains poorly understood. In this study, we isolated several bacterial species from rhabditid nematodes, molecularly identified them, evaluated their entomopathogenic potential on Galleria mellonella larvae, and measured immune responses of G. mellonella larvae to their infection. Bacteria were isolated from Acrobeloides sp., A. bodenheimeri, Heterorhabditis bacteriophora, Oscheius tipulae, and Pristionchus maupasi nematodes. They were identified as Acinetobacter sp., Alcaligenes sp., Bacillus cereus, Enterobacter sp., Kaistia sp., Lysinibacillus fusiformis, Morganella morganii subsp. morganii, Klebsiella quasipneumoniae subsp. quasipneumoniae, and Pseudomonas aeruginosa. All bacterial strains were found to be highly entomopathogenic as they killed at least 53.33% G. mellonella larvae within 72h post-infection, at a dose of 106 CFU/larvae. Among them, Lysinibacillus fusiformis, Enterobacter sp., Acinetobacter sp., and K. quasipneumoniae subsp. quasipneumoniae were the most entomopathogenic bacteria. Insects strongly responded to bacterial infection. However, their responses were apparently little effective to counteract bacterial infection. Our study, therefore, shows that bacteria associated with soil-borne nematodes have entomopathogenic capacities. From an applied perspective, our study motivates more research to determine the potential of these bacterial strains as biocontrol agents in environmentally friendly and sustainable agriculture

Antifungal lipopeptides from Bacillus strains isolated from rhizosphere of Citrus trees

peer reviewedThe microbial ecology within the rhizosphere of Tylenchulus semipenetrans-infected Citrus L. trees was examined. Sixty bacterial strains were obtained from the roots of infected trees and from the eggs of T. semipenetrans. Among these strains some were obtained from the agar plates of two nematophagous fungi, Dactylellina gephyropaga (Drechsler) Ying Yang & Xing Z. Liu and Arthrobotrys conoides Drechsler. Bacterial strains were identified using 16S rDNA, gyrA and rpoB genes sequence analysis. Bacterial strains identified as Bacillus spp. were examined for their ability to synthesize surfactin, iturin, fengycin, kurstakin and bacillomycin using PCR amplification and sequencing of the encoding genes. Additionally, Bacillus strains were screened for their antifungal activity against F. solani, D. gephyropaga and A. conoides using the dual culture technique. Lipopeptide from whole cells and from supernatants of Bacillus spp. were screened using MALDI-TOF-MS analysis. The majority of the identified bacterial strains belong to the genus Bacillus with the predominance of B. cereus, B. thuringiensis, B. pumilus and B. subtilis. A total of fifteen Bacillus strains demonstrated an antifungal activity against F. solani, D. gephyropaga and A. conoides with the strongest effect found in B. amyloliquefaciens. The analysis of lipopeptides showed a high diversity of molecules, including majorly iturin C, bacillomycin D, fengycin A/B and Kurstakin found especially in B. subtilis strains. Moreover, MALDI-TOF-MS analysis showed that the responsible antibiotics for the antifungal Bacillus strains were associated with the presence of Surfactins/Pumilacidin and Fengycin A/B. Our results demonstrated the wide diversity of lipopeptides among Bacillus strains associated with citrus rhizosphere and demonstrated their antifungal ability. Our results extend the importance of Bacillus strains as potential candidates for antimicrobial activities due to their ability to synthesize and secrete cyclic lipopeptides

Caractérisation de différentes espèces de Pratylenchus associées aux marcottières et aux plants greffés de MM106 en pépinières d’arbres à pépins en Tunisie

Pratylenchus spp. (root-lesion nematodes) are nematodes that can parasitize numerous annual and perennial host plants, such as fruit trees in orchards and nurseries. Nurseries in the five main Tunisian areas of apple production in the regions of Bizerte, Testour (Beja), Jendouba, Kairouan and Kasserine were surveyed. Roots from plants of similar vigor from the MM106 rootstock alone and from the MM106 rootstock grafted to apple varieties were harvested and nematodes were extracted by the double centrifugation technique. Females of different Pratylenchus populations were fixed, mounted in glycerol and measured. Morphometric and morphological characters were used to compare populations to known species. The results obtained by principal compound analysis and discriminate analysis showed regional and host plant effects on biometrical characters of Pratylenchus females. Hierarchical cluster analysis is used to classify different nematode populations in relation to known species. Most specimens, particularly those from the regions of Jendouba and Testour, were similar either to the species P. neglectus and P. brachyurus or to P. vulnus. However, a few isolated specimens obtained from apple roots in Kairouan and Jendouba were similar to P. jordanensis.Les Pratylenchus (nématodes des lésions racinaires) sont des espèces qui peuvent parasiter plusieurs plantes hôtes annuelles et pérennes telles que les arbres fruitiers en vergers et en pépinières. Les pépinières des cinq principales zones de production de plants de pommier situées en Tunisie dans les régions de Bizerte, Testour (Béja), Jendouba, Kairouan et Kasserine sont prospectées. Les racines des plants de même vigueur de marcottes de MM106 ainsi que des plants de MM106 greffés par différentes variétés de pommier sont prélevées et les nématodes sont extraits par la technique de double centrifugation. Les individus femelles de Pratylenchus des différentes populations sont prélevés, fixés, montés dans de la glycérine, mesurés sur la base des caractères morphométriques et comparés aux différentes espèces de ce genre déjà décrites dans la littérature. Les résultats obtenus par l’analyse en composante principale et l’analyse discriminante montrent un effet de la région et de la plante hôte sur les caractères biométriques des femelles de Pratylenchus. L’analyse de la classification hiérarchique a permis de classer les différentes populations de nématodes par rapport aux espèces connues. La plupart des spécimens, notamment ceux provenant des régions de Jendouba et de Testour, se rapprochent soit des espèces P. neglectus et P. brachyurus avec quelques variantes, soit de l’espèce P. vulnus. Cependant, quelques individus isolés des racines de pommier des régions de Kairouan et Jendouba s’apparentent à l’espèce P. jordanensis.Bouali Nesrine, Kallel Sadreddine, Horrigue-Raouani Najet. Caractérisation de différentes espèces de Pratylenchus associées aux marcottières et aux plants greffés de MM106 en pépinières d’arbres à pépins en Tunisie. In: Ecologia mediterranea, tome 40 n°1, 2014. pp. 75-86

Interaction plante-virus-vecteur. Cas du court-noué de la vigne en Tunisie

Cet article est une synthèse bibliographique portant sur la maladie du court-noué illustrée par des travaux conduits en Tunisie. Cette étude se justifie par le caractère destructif de cette maladie et l’interaction entre les souches virales et les différentes espèces de nématodes vecteurs de cette maladie. Deux népovirus sont associés à cette maladie, le grapevine fan leaf virus (GFLV) et l’arabis mosaic virus (ArMV). Les nématodes Xiphinema index et Xiphinema italiae sont les vecteurs du GFLV. Ils ont une reproduction parthénogénétique. Xiphinema diversicaudatum, avec une reproduction majoritairement sexuée, est considéré comme l’unique vecteur de l’ArMV. Les déterminants de la spécificité de transmission de ces népovirus par leurs vecteurs naturels sont localisés sur la protéine de la capside du virus. L’étude de l’incidence du court-noué au nord de la Tunisie montre que la région du Grombalia présente les taux d’infection par le GFLV et l’ArMV les plus élevés (71 % pour les deux virus), suivie par la région du Rafraf (45 et 38 %). La région de Takelsa quoique proche de Grombalia pour ses caractéristiques écologiques, présente un taux d’infestation similaire à celui de la région de Rafraf. Cette même tendance a été observée en analysant la corrélation entre la symptomatologie et la diversité génétique des souches de GFLV. L’étude de l’interaction virus-nématode montre que dans la quasi-totalité des échantillons de Xiphinema analysés en Tunisie, seul le GFLV est isolé. Cela s’explique par l’absence du vecteur spécifique de l’ArMV sur le territoire

Investigations into Physiological, Biochemical, and Histological Modifications in a Vine Decline Associated with Biotic and Abiotic Factors

Tunisian table grape production has significantly increased since two decades due to vineyards regional expansion and yield improvement. But, since several years, decline symptoms on Vitis vinifera have been recorded in some areas. A study case of a vineyard in Naassen area (near to Tunis) was chosen to investigate the disease origin and the physiological, biochemical, and histological modifications associated with vine decline. The investigation revealed characteristic symptoms on leaves, old and young shoots similar to decline symptoms of Grapevine Trunk Diseases. Based on cultural characteristics, laboratory investigations revealed the presence of Phaeomoniella chlamydospora and Phaeoacremonium spp., Diplodia seriata and Botryosphaeria dothidea, from root and shoot samples, respectively. These fungi are known as the main pathogens responsible for the Esca, Black dead arm and Excoriose. Molecular analysis confirmed the identification of Diplodia seriata. Beside morphological alterations on leaves and shoots, symptomatic vines presented significant reductions of 30 and 20% in trunk diameter and bud break rate, respectively, and delayed spring growth compared to healthy ones. Furthermore, roots and stems from declined vines contained 3 times more starch than those from asymptomatic ones. Decline survey revealed a heterogeneous dispersion of symptoms in the vineyard in accordance with water supply. The vines along the edge of vineyards are usually less watered and show more decline symptoms. Decline dynamics in time and space scales have to be considered in order to develop effective management strategies

Comparaison morphologique de deux souches de Monacrosporium salinum, champignon prédateur de nématode, isolées d’un agro-écosystème tunisien et omanais

Monacrosporium salinum strain, MSO03, isolated from Omani horticultural agro-ecosystem in 2003, has been compared to patented strains, MST84, isolated in 1984 from Tunisian soils. Morpho-biometrical characteristics demonstrated that MSO03 was similar to MST84. However, conidia of MSO03 were longer as compared to those of MST84. Furthermore, MSO03 strain produce specifically single chlamydospores rounded, showing thick cell wall, while known M. salinum chlamydospores are flattened, in chains with thin cell wall. Consequently, the Omani strain MSO03 can resist to more severe stress conditions, such as drought and extreme temperature, occurring in Omani agro-ecosystems. Generally, the predatory antagonistic activity toward Tylenchulus semipenetrans and Meloidogyne javanica was similar for both M. salinum strains.La souche de Monacrosporium salinum MSO03, isolée en 2003 d’un agro-écosystème horticole au sultanat d’Oman, a été comparée à la souche tunisienne MST84, brevetée, de la même espèce et isolée depuis 1984. L’utilisation des caractéristiques morpho-biométriques a montré que la souche MSO03 est similaire à la souche MST84. Cependant, les conidies de MSO03 sont plus longues que celles de MST84. En outre, la souche omanaise produit des chlamydospores formées par une seule cellule arrondie à membrane épaisse, contrairement aux chlamydospores de Monacrosporium salinum connues et qui sont formées de cellules aplaties, en chaînes et présentant une membrane mince. Par conséquent, la souche omanaise MSO03 peut résister aux conditions adverses telles que la sécheresse et les températures extrêmes caractérisant les agro-écosystèmes omanais. L’activité prédatrice de ces champignons vis-à-vis de Tylenchulus semipenetrans et de Meloidogyne javanica est similaire pour les deux souches de M. salinum.Elfékih Samia, Kallel Sadreddine, Abdelwahed A., Al-Hinai Sulaiman, B’Chir Mohamed Mouldi. Comparaison morphologique de deux souches de Monacrosporium salinum, champignon prédateur de nématode, isolées d’un agro-écosystème tunisien et omanais. In: Ecologia mediterranea, tome 38 n°1, 2012. pp. 81-88

Occurrence and functional diversity of bacteria in rhizosphere of citrus trees infested by Tylenchulus semipenetrans in a citrus-growing area of Tunisia

Tylenchulus semipenetrans is a major plant-parasitic nematode pest of citrus which readily infests sour orange rootstock Citrus aurantium. In order to examine the bacterial diversity and prevalence in the nematode infested citrus rhizosphere, 282 bacterial strains were isolated from roots of mature citrus trees, from egg masses of T. semipenetrans, and from nematophagous fungi in the orange producing area Cap bon in Tunisia. The rhizosphere of citrus had a high diversity of bacterial strains among the 20 agricultural parcels. According to morphological and biochemical characteristics, sixty bacteria strains were selected to explore the diversity of biological activity. None of the bacterial strains considered in this study have phytopathogenic activity. Each strain was identified and tested as a potential natural antagonist against fungi and against citrus nematode (egg hatching and juvenile mortality). Bacillus cereus, B. mycoides, B. pumilus and B. thuringiensis were the four most abundant species regardless the sampling location. Canonical discriminant analysis grouped the bacteria into five groups of biological activities: Group A, similar to water control, had not specific effect. Group B showed strong effect, and group C caused moderate growth inhibition of the nematophagous fungi Monacrosporium cianopagum CBM. Group C had stronger growth inhibition of the fungus Arthrobotrys conoides RGA than groups B and D. Groups D and E showed a strong activity on nematode egg hatch inhibition.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Characterization of indigenous bacterial strains with antifungal activity from Tunisian Citrus rhizosphere

info:eu-repo/semantics/nonPublishe