Dominguez Jessica, Jayachandran Krishnaswamy, Stover Ed, Krystel Joseph, Shetty Kateel G
Department of Earth and Environment, Florida International University, Miami, FL 33199, USA.
United States Department of Agriculture/Agricultural Research Service, Ft. Pierce, FL 34945, USA.
Microorganisms. 2023 Jun 8;11(6):1529. doi: 10.3390/microorganisms11061529.
Huanglongbing (HLB), also known as citrus greening, is an insidious disease in citrus and has become a threat to the sustainability of the citrus industry worldwide. In the U.S., Liberibacter asiaticus (Las) is the pathogen that is associated with HLB, an unculturable, phloem-limited bacteria, vectored by the Asian Citrus Psyllid (ACP, ). There is no known cure nor treatment to effectively control HLB, and current control methods are primarily based on the use of insecticides and antibiotics, where effectiveness is limited and may have negative impacts on beneficial and non-target organisms. Thus, there is an urgent need for the development of effective and sustainable treatment options to reduce or eliminate Las from infected trees. In the present study, we screened citrus-derived endophytes, their cell-free culture supernatants (CFCS), and crude plant extracts for antimicrobial activity against two culturable surrogates of Las, and . Candidates considered high-potential antimicrobial agents were assessed directly against Las in vitro, using a propidium monoazide-based assay. As compared to the negative controls, statistically significant reductions of viable Las cells were observed for each of the five bacterial CFCS. Subsequent 16S rRNA gene sequencing revealed that each of the five bacterial isolates were most closely related to ns, a species dominating the market of biological control products. As such, the aboveground endosphere of asymptomatic survivor citrus trees, grown in an organic orchard, were found to host bacterial endophytes capable of effectively disrupting Las cell membranes. These results concur with the theory that native members of the citrus microbiome play a role in the development of HLB. Here, we identify five strains of demonstrating notable potential to be used as sources of novel antimicrobials for the sustainable management of HLB.
黄龙病（HLB），又称柑橘绿变病，是柑橘类作物中的一种隐匿性病害，已对全球柑橘产业的可持续发展构成威胁。在美国，亚洲韧皮杆菌（Las）是与黄龙病相关的病原体，这是一种不可培养的、韧皮部受限的细菌，由亚洲柑橘木虱（ACP）传播。目前尚无已知的治愈方法或有效控制黄龙病的治疗手段，当前的控制方法主要基于使用杀虫剂和抗生素，但效果有限，且可能对有益生物和非目标生物产生负面影响。因此，迫切需要开发有效且可持续的治疗方案，以减少或消除受感染树木中的Las。在本研究中，我们筛选了柑橘来源的内生菌、它们的无细胞培养上清液（CFCS）以及植物粗提物对Las的两种可培养替代菌的抗菌活性。被认为具有高潜力抗菌剂的候选物使用基于单叠氮丙锭的测定法直接在体外针对Las进行评估。与阴性对照相比，观察到五种细菌CFCS中的每一种对存活的Las细胞均有统计学上显著的减少。随后的16S rRNA基因测序显示，这五种细菌分离株中的每一种与ns关系最为密切，ns是一种主导生物防治产品市场的物种。因此，发现在有机果园中生长的无症状存活柑橘树的地上内生菌层含有能够有效破坏Las细胞膜的细菌内生菌。这些结果与柑橘微生物组的天然成员在黄龙病发展中起作用的理论一致。在这里，我们鉴定出五株ns菌株，它们具有显著潜力，可作为用于黄龙病可持续管理的新型抗菌剂来源。
