Brooks Chequita N, Field Erin K
Department of Biology, East Carolina University, Greenville, NC, United States.
Louisiana Universities Marine Consortium, Chauvin, LA, United States.
Front Microbiol. 2024 May 10;15:1388973. doi: 10.3389/fmicb.2024.1388973. eCollection 2024.
Hydrocarbon pollution is a widespread issue in both groundwater and surface-water systems; however, research on remediation at the interface of these two systems is limited. This interface is the oxic-anoxic boundary, where hydrocarbon pollutant from contaminated groundwaters flows into surface waters and iron mats are formed by microaerophilic iron-oxidizing bacteria. Iron mats are highly chemically adsorptive and host a diverse community of microbes. To elucidate the effect of hydrocarbon exposure on iron mat geochemistry and microbial community structure and function, we sampled iron mats both upstream and downstream from a leaking underground storage tank. Hydrocarbon-exposed iron mats had significantly higher concentrations of oxidized iron and significantly lower dissolved organic carbon and total dissolved phosphate than unexposed iron mats. A strong negative correlation between dissolved phosphate and benzene was observed in the hydrocarbon-exposed iron mats and water samples. There were positive correlations between iron and other hydrocarbons with benzene in the hydrocarbon-exposed iron mats, which was unique from water samples. The hydrocarbon-exposed iron mats represented two types, flocculent and seep, which had significantly different concentrations of iron, hydrocarbons, and phosphate, indicating that iron mat is also an important context in studies of freshwater mats. Using constrained ordination, we found the best predictors for community structure to be dissolved oxygen, pH, and benzene. Alpha diversity and evenness were significantly lower in hydrocarbon-exposed iron mats than unexposed mats. Using 16S rDNA amplicon sequences, we found evidence of three putative nitrate-reducing iron-oxidizing taxa in microaerophile-dominated iron mats (, and ). 16S rDNA amplicons also indicated the presence of taxa that are associated with hydrocarbon degradation. Benzene remediation-associated genes were found using metagenomic analysis both in exposed and unexposed iron mats. Furthermore, the results indicated that season (summer vs. spring) exacerbates the negative effect of hydrocarbon exposure on community diversity and evenness and led to the increased abundance of numerous OTUs. This study represents the first of its kind to attempt to understand how contaminant exposure, specifically hydrocarbons, influences the geochemistry and microbial community of freshwater iron mats and further develops our understanding of hydrocarbon remediation at the land-water interface.
烃类污染在地下水和地表水系统中都是一个普遍存在的问题；然而，关于这两个系统界面处修复的研究却很有限。这个界面是有氧-缺氧边界，受污染的地下水中的烃类污染物流入地表水，微需氧的铁氧化细菌形成铁垫。铁垫具有很强的化学吸附性，并且拥有多样的微生物群落。为了阐明烃类暴露对铁垫地球化学以及微生物群落结构和功能的影响，我们从一个泄漏的地下储油罐的上下游采集了铁垫样本。与未暴露的铁垫相比，受烃类暴露的铁垫具有显著更高的氧化铁浓度，以及显著更低的溶解有机碳和总溶解磷酸盐含量。在受烃类暴露的铁垫和水样中，观察到溶解磷酸盐与苯之间存在很强的负相关。在受烃类暴露的铁垫中，铁和其他烃类与苯之间存在正相关，这与水样不同。受烃类暴露的铁垫有絮凝状和渗流状两种类型，它们的铁、烃类和磷酸盐浓度存在显著差异，这表明铁垫也是淡水垫研究中的一个重要背景。通过受限排序，我们发现群落结构的最佳预测因子是溶解氧、pH值和苯。受烃类暴露的铁垫中的α多样性和均匀度显著低于未暴露的铁垫。利用16S rDNA扩增子序列，我们在以微需氧菌为主的铁垫中发现了三种假定的硝酸盐还原铁氧化分类群（、和）的证据。16S rDNA扩增子还表明存在与烃类降解相关的分类群。通过宏基因组分析，在暴露和未暴露的铁垫中都发现了与苯修复相关的基因。此外，结果表明季节（夏季与春季）加剧了烃类暴露对群落多样性和均匀度的负面影响，并导致大量操作分类单元（OTU）的丰度增加。这项研究是首次尝试了解污染物暴露，特别是烃类，如何影响淡水铁垫的地球化学和微生物群落，并进一步加深了我们对陆地-水界面烃类修复的理解。
