Carles Louis, Rossi Florent, Besse-Hoggan Pascale, Blavignac Christelle, Leremboure Martin, Artigas Joan, Batisson Isabelle
Laboratoire Microorganismes: Génome et Environnement, CNRS, Université Clermont Auvergne, Clermont-Ferrand, France.
Institut de Chimie de Clermont-Ferrand, CNRS, Sigma Clermont, Université Clermont Auvergne, Clermont-Ferrand, France.
Front Microbiol. 2018 Dec 19;9:3167. doi: 10.3389/fmicb.2018.03167. eCollection 2018.
Nicosulfuron is a selective herbicide belonging to the sulfonylurea family, commonly applied on maize crops. Its worldwide use results in widespread presence as a contaminant in surface streams and ground-waters. In this study, we isolated, for the first time, the AR1 nicosulfuron-degrading fungal strain, a new record from leaf litter submerged in freshwater. The degradation of nicosulfuron by AR1 was achieved by a co-metabolism process and followed a first-order model dissipation. Biodegradation kinetics analysis indicated that, in planktonic lifestyle, nicosulfuron degradation by this strain was glucose concentration dependent, with a maximum specific degradation rate of 1 g/L in glucose. When grown on natural substrata (leaf or wood) as the sole carbon sources, the AR1 developed as a well-established biofilm in 10 days. After addition of nicosulfuron in the medium, the biofilms became thicker, with rising mycelium, after 10 days for leaves and 21 days for wood. Similar biofilm development was observed in the absence of herbicide. These fungal biofilms still conserve the nicosulfuron degradation capacity, using the same pathway as that observed with planktonic lifestyle as evidenced by LC-MS analyses. This pathway involved first the hydrolysis of the nicosulfuron sulfonylurea bridge, leading to the production of two major metabolites: 2-amino-4,6-dimethoxypyrimidine (ADMP) and 2-(aminosulfonyl)-,-dimethyl-3-pyridinecarboxamide (ASDM). One minor metabolite, identified as 2-(1-(4,6-dimethoxy-pyrimidin-2-yl)-ureido)--dimethyl-nicotinamide (N3), derived from the cleavage of the C-S bond of the sulfonylurea bridge and contraction by elimination of sulfur dioxide. A last metabolite (N4), detected in trace amount, was assigned to 2-(4,6-dimethoxy-pyrimidin-2-yl)--dimethyl-nicotinamide (N4), resulting from the hydrolysis of the N3 urea function. Although fungal growth was unaffected by nicosulfuron, its laccase activity was significantly impaired regardless of lifestyle. Leaf and wood surfaces being good substrata for biofilm development in rivers, AR1 strain could thus have potential as an efficient candidate for the development of methods aiming to reduce contamination by nicosulfuron in aquatic environments.
烟嘧磺隆是一种属于磺酰脲类的选择性除草剂，常用于玉米作物。它在全球范围内的使用导致其作为污染物广泛存在于地表溪流和地下水中。在本研究中，我们首次从淹没在淡水中的落叶中分离出AR1烟嘧磺隆降解真菌菌株，这是一个新记录。AR1对烟嘧磺隆的降解是通过共代谢过程实现的，并遵循一级模型消散。生物降解动力学分析表明，在浮游生活方式下，该菌株对烟嘧磺隆的降解依赖于葡萄糖浓度，在葡萄糖浓度为1 g/L时具有最大比降解率。当以天然基质（树叶或木材）作为唯一碳源生长时，AR1在10天内形成了成熟的生物膜。在培养基中添加烟嘧磺隆后，树叶生物膜在10天后、木材生物膜在21天后变得更厚，菌丝体增多。在没有除草剂的情况下也观察到了类似的生物膜发育。这些真菌生物膜仍然保留着烟嘧磺隆降解能力，使用与浮游生活方式相同的途径，液相色谱-质谱分析证明了这一点。该途径首先涉及烟嘧磺隆磺酰脲桥的水解，产生两种主要代谢物：2-氨基-4,6-二甲氧基嘧啶（ADMP）和2-（氨基磺酰基）-N,N-二甲基-3-吡啶甲酰胺（ASDM）。一种次要代谢物，被鉴定为2-（1-（4,6-二甲氧基嘧啶-2-基）脲基）-N,N-二甲基烟酰胺（N3），源自磺酰脲桥的C-S键断裂并通过消除二氧化硫而收缩。最后一种代谢物（N4），以痕量检测到，则是由N3脲官能团的水解产生的2-（4,6-二甲氧基嘧啶-2-基）-N,N-二甲基烟酰胺（N4）。尽管真菌生长不受烟嘧磺隆影响，但其漆酶活性无论生活方式如何均受到显著损害。树叶和木材表面是河流中生物膜发育的良好基质，因此AR1菌株有可能成为开发旨在减少水环境中烟嘧磺隆污染方法的有效候选菌株。
