Sohrab Abeer, Kaiser Shadman, Bhattarai Bishav, Stancheva Rosalina, Goel Ramesh
Department of Civil & Environmental Engineering, University of Utah, 110 S Central Campus, Salt Lake City, UT 84112, United States of America.
Department of Environmental Science and Policy, George Mason University, Fairfax, VA 22030, United States of America.
Sci Total Environ. 2025 Aug 7;997:180194. doi: 10.1016/j.scitotenv.2025.180194.
Nitrogen (N) and Phosphorus (P) are essential nutrients which support cyanobacterial growth in lakes (as suspended cells or flocs) and flowing waters (as benthic mats). However, some toxic cyanobacteria can thrive even under depleted nutrient conditions. In this study, we investigated benthic toxic cyanobacterial mats in the Virgin River, Zion National Park, at two sites where visible benthic mats were observed at three different times. Our study focused on phosphorus and nitrogen cycling within these mats. The reactive P was below detection limits (<0.05 mg/L as P). Likewise, the dissolved inorganic N varied from below the detection limit to 0.06 mg/L as N. The relative abundance (based on total sequenced reads) of cyanobacteria ranged from 16.87 % to 50.02 % for samples from the Visitor's Center site and 10.34 % to 32.68 % for samples from the North Creek site with the presence of genera Microcoleus, Pseudoanabaena, Oscillatoria, Microcystis, and Cyanobium. The Visitors Center and North Creek sites shared several key heterotrophic bacteria, with Sandarakinorhabdus, Planctomyces, Brevundimonas, Thiomonas, and Pseudomonas being the most prominent ones. Notably, a toxic Microcoleus strain was identified in the nutrient-limited conditions of the Virgin River. This strain harbored an anatoxin-a biosynthesis gene cluster but lacked the anaK gene, suggesting limited toxin variability. We investigated the role of heterotrophic bacteria in nutrient cycling and their interactions with cyanobacterial populations within benthic mats of the Virgin River. Microcoleus and other cyanobacteria employed the Pho regulon, expressing genes such as pstS and alkaline phosphatase, to efficiently acquire organic phosphorus in low-nutrient environments. Nitrogen cycling also played a crucial role, with coexisting heterotrophic bacteria contributing to nitrogen fixation (nif gene) and assimilation, as well as denitrification (nosZ, nir, and nar genes). This research signifies the importance of integrated molecular approaches in unraveling nutrient cycling dynamics and toxin production mechanisms in benthic cyanobacterial mats. These insights are critical for understanding harmful cyanobacterial benthic blooms in freshwater ecosystems.
氮（N）和磷（P）是湖泊中（作为悬浮细胞或絮体）以及流动水体中（作为底栖生物垫）支持蓝藻生长的必需营养物质。然而，一些有毒蓝藻即使在营养物质匮乏的条件下也能茁壮成长。在本研究中，我们调查了锡安国家公园维珍河两个地点的底栖有毒蓝藻垫，这两个地点在三个不同时间观察到了明显的底栖生物垫。我们的研究重点是这些生物垫内的磷和氮循环。活性磷低于检测限（以磷计<0.05毫克/升）。同样，溶解无机氮的含量从低于检测限到以氮计0.06毫克/升不等。来自游客中心地点样本的蓝藻相对丰度（基于总测序读数）在16.87%至50.02%之间，来自北溪地点样本的蓝藻相对丰度在10.34%至32.68%之间，存在微鞘藻属、伪鱼腥藻属、颤藻属、微囊藻属和蓝菌属。游客中心和北溪地点共有几种关键的异养细菌，其中最突出的是桑德拉基诺杆菌属、浮霉菌属、短波单胞菌属、硫单胞菌属和假单胞菌属。值得注意的是，在维珍河营养受限的条件下鉴定出了一种有毒的微鞘藻菌株。该菌株含有anatoxin-a生物合成基因簇，但缺少anaK基因，这表明毒素变异性有限。我们研究了异养细菌在维珍河底栖生物垫营养循环中的作用及其与蓝藻种群的相互作用。微鞘藻和其他蓝藻利用Pho调控子，表达诸如pstS和碱性磷酸酶等基因，以便在低营养环境中有效获取有机磷。氮循环也起着关键作用，共存的异养细菌有助于固氮（nif基因）和同化，以及反硝化作用（nosZ、nir和nar基因）。这项研究表明了综合分子方法在揭示底栖蓝藻垫营养循环动态和毒素产生机制方面的重要性。这些见解对于理解淡水生态系统中有害蓝藻底栖水华至关重要。
