The 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.

检查了Tylenchulus semipenetrans感染的柑橘树根际内的微生物生态学。从受感染树木的根部和T. semipenetrans的卵中获得了60 株细菌菌株。其中一些菌株是从两种食线虫真菌Dactylellina gephyropaga (Drechsler) Ying Yang & Xing Z. Liu 和Arthrobotrys conoides Drechsler的琼脂平板中获得的。使用16S rDNA、gyrA和rpoB基因序列分析鉴定细菌菌株。细菌菌株鉴定为芽孢杆菌属 使用 PCR 扩增和编码基因的测序检查了它们合成表面活性素、伊图林、芬奇素、库斯塔金和杆菌霉素的能力。此外，芽孢杆菌属菌株筛选它们的抗真菌活性茄病镰刀菌，D. gephyropaga和A. conoides使用双培养技术。来自全细胞和芽孢杆菌属上清液的脂肽。使用 MALDI-TOF-MS 分析进行筛选。大多数已鉴定的细菌菌株属于芽孢杆菌属，主要是蜡样芽孢杆菌、苏云金芽孢杆菌、短小芽孢杆菌和枯草芽孢杆菌。共十五个芽孢杆菌菌株表现出对F. solani、D. gephyropaga和A. conoides的抗真菌活性，在B. amyloliquefaciens 中发现的效果最强。脂肽的分析显示了高度多样性的分子，主要包括伊图林 C、杆菌霉素 D、芬奇素 A/B 和尤其在枯草芽孢杆菌菌株中发现的 Kurstakin 。此外，MALDI-TOF-MS 分析表明，抗真菌芽孢杆菌菌株的负责抗生素与 Surfactins/Pumilacidin 和 Fengycin A/B 的存在有关。我们的结果证明了芽孢杆菌中脂肽的广泛多样性与柑橘根际相关的菌株并证明了它们的抗真菌能力。我们的结果扩展了芽孢杆菌菌株作为抗菌活性潜在候选者的重要性，因为它们具有合成和分泌环状脂肽的能力。