Root-knot nematodes (Meloidogyne spp.) have garnered significant attention from researchers owing to the substantial damage they cause to crops and their worldwide distribution. However, controlling these nematodes is challenging because a limited number of chemical pesticides and biocontrol agents are effective against them. Here, we demonstrate that pepper rotation markedly reduces Meloidogyne incognita infection in cucumber and diminishes the presence of p-hydroxybenzoic acid in the soil, a compound known to exacerbate M. incognita infection. Pepper rotation also restructures the rhizobacterial community, leading to the colonization of the cucumber rhizosphere by two Pseudarthrobacter oxydans strains (RH60 and RH97), facilitated by enrichment of palmitic acid in pepper root exudates. Both strains exhibit high nematocidal activity against M. incognita and have the ability to biosynthesize indoleacetic acid and biodegrade p-hydroxybenzoic acid. RH60 and RH97 also induce systemic resistance in cucumber plants and promote their growth. These data suggest that the pepper root exudate palmitic acid alleviates M. incognita infection by recruiting beneficial P. oxydans to the cucumber rhizosphere. Our analyses identify a novel chemical component in root exudates and reveal its pivotal role in crop rotation for disease control, providing intriguing insights into the keystone function of root exudates in plant protection against root-knot nematode infection.

The genus Arthrobacter is a source of many natural products that are critical in the development of new medicines. Here, we isolated a novel carotenoid from Arthrobacter sp. QL17 and characterized its properties. The carotenoid was extracted with methanol, and purified by column chromatography and semi-preparative HPLC. Based on micrOTOF-Q and NMR analyses, the pigment was chemically characterized as 2,2 '-((((1E,3E,5E,7E,9E,11E,13E,15E,17E,19E)-3,7,14,18-tetramethylicosa-1,3,5,7,9,11,13,15,17,19-decaene-1,20-diyl)bis(2,2,4-trimethylcyclohex-3-ene-3,1-diyl)) bis(ethan-2-yl-1-ylidene))bi(propane-1,3-diol), and named arthroxanthin. The biological activities of arthroxanthin were evaluated with DPPH, ABTS and MTT assays. Arthroxanthin exhibited excellent radical scavenging properties, as shown for 2, 20-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-n-(3,2-ethyl-benzothiazole-6-sulfonic acid) ammonium salt (ABTS), respectively, with IC50s of 69.8 and 21.5 mu g/mL. It also showed moderate anticancer activities against HepG2, Hela, MDAB-231, SW480, and MKN-45 with IC50 values of 107.6, 150.4, 143.4, 195.9, and 145.5 mu g/mL, respectively. Therefore, arthroxanthin derived from Arthrobacter sp. QL17 may be a potent antioxidant and anticancer agent for food and pharmaceutical use.

对青海省祁连山永久冻土区天然气水合物DK-2钻孔的11件样品进行分析,通过微生物群落分析来探寻水合物层样品与非水合物层样品的差别。在11件样品中均发现了细菌16S rDNA,未检测到海洋天然气水合物地区常见的古菌16S rDNA、mcrA(Ⅰ,Ⅱ)、pmoA、mmoX和mxaF。分析得到的细菌16S rDNA分属5个门,包括变形杆菌门、放线菌门、拟杆菌门、厚壁菌门和异常球菌-栖热菌门,随着样品深度的增加,细菌多样性有降低的趋势。对非水合物层样品DK2-19和水合物层样品DK2-25进行细菌系统发育树分析,发现这2个样品群落结构相差较大。水合物层样品与非水合物层样品细菌群落对比后发现,水合物层样品中γ-变形杆菌的比例低于非水合物层样品中γ-变形杆菌的比例,而Arthrobacter属多发现于非水合物层的样品中。