Insight Into the Molecular Mechanisms for Microcystin Biodegradation in Lake Erie and Lake Taihu
Insight Into the Molecular Mechanisms for Microcystin Biodegradation in Lake Erie and Lake Taihu
复制标题
DOI：
10.3389/fmicb.2019.02741
复制
发表时间：
2019-12-10
影响因子：
5.2
通讯作者：
Wilhelm, Steven W.
中科院分区：
文献类型：
--
作者：
Krausfeldt, Lauren E.;Steffen, Morgan M.;Wilhelm, Steven W.
微囊藻毒素是一种有效的肝毒素，经常在受有毒蓝藻困扰的淡水湖中检测到。微生物生物降解已被认为是去除水生环境中微囊藻毒素的最重要途径。与微囊藻毒素降解最常见的生化途径是由mlrABCD （mlr）盒式编码的。这一途径的生态意义尚不清楚，因为没有研究检查这些基因在自然环境中的表达。从产生微囊藻毒素的微囊藻华中产生了6个亚转录组，并对其进行了分析，以评估该途径在环境样品中的活性。从美国/加拿大伊利湖和中国太湖收集了78份样本，筛选了mlr基因转录本的存在。mlr盒的reads图谱表明这些基因的转录本缺失，在37亿个reads中只有77个与mlr盒的任何部分对应。对组装的亚转录组的分析支持了这一点，只有远亲序列被鉴定为mlrabc样。这些观察结果是在微囊藻毒素存在的情况下进行的，并且超过500,000次读取映射到微囊藻毒素生产的mcy磁带。谷胱甘肽s -转移酶和碱性蛋白酶先前被假设为微囊藻毒素生物降解的替代途径，并且在两个湖泊中检测到这些基因的跨空间和时间表达。虽然这些替代途径的活性需要实验证实，但它们可能单独或集体比自然环境中的mlr基因更重要。重要的是，缺乏mlr表达可能表明在所分析的样品中没有发生微囊藻毒素的生物降解。本研究对微囊藻毒素生物降解的普遍性、特异性和局地性提出了有趣的问题，并强调了对自然群落中微囊藻毒素的相关机制进行表征的必要性，以了解微囊藻毒素在环境中的命运和对公众健康的风险。
Microcystins are potent hepatotoxins that are frequently detected in fresh water lakes plagued by toxic cyanobacteria. Microbial biodegradation has been referred to as the most important avenue for removal of microcystin from aquatic environments. The biochemical pathway most commonly associated with the degradation of microcystin is encoded by the mlrABCD (mlr) cassette. The ecological significance of this pathway remains unclear as no studies have examined the expression of these genes in natural environments. Six metatranscriptomes were generated from microcystin-producing Microcystis blooms and analyzed to assess the activity of this pathway in environmental samples. Seventy-eight samples were collected from Lake Erie, United States/Canada and Lake Tai (Taihu), China, and screened for the presence of mlr gene transcripts. Read mapping to the mlr cassette indicated transcripts for these genes were absent, with only 77 of the collective 3.7 billion reads mapping to any part of the mlr cassette. Analysis of the assembled metatranscriptomes supported this, with only distantly related sequences identified as mlrABC-like. These observations were made despite the presence of microcystin and over 500,000 reads mapping to the mcy cassette for microcystin production. Glutathione S-transferases and alkaline proteases have been previously hypothesized to be alternative pathways for microcystin biodegradation, and expression of these genes was detected across space and time in both lakes. While the activity of these alternative pathways needs to be experimentally confirmed, they may be individually or collectively more important than mlr genes in the natural environment. Importantly, the lack of mlr expression could indicate microcystin biodegradation was not occurring in the analyzed samples. This study raises interesting questions about the ubiquity, specificity and locality of microcystin biodegradation, and highlights the need for the characterization of relevant mechanisms in natural communities to understand the fate of microcystin in the environment and risk to public health.