Meinelt Thomas, Paul Andrea, Phan Thuy My, Zwirnmann Elke, Krüger Angela, Wienke Andreas, Steinberg Christian E W
Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
Aquat Toxicol. 2007 Jun 15;83(2):93-103. doi: 10.1016/j.aquatox.2007.03.013. Epub 2007 Mar 24.
Humic substances (HS) account for 50-80% of the dissolved organic matter in non-eutrophicated freshwater ecosystems. HS are not inert, but are taken up by and may interact with aquatic organisms. However, at present no information is available on the interaction of HS with fungi, for instance, the fish-pathogenous species Saprolegnia parasitica. To fill this gap, we tested effects of HS on S. parasitica growth in-vitro using 25-500mgL(-1) carbon of HS on GY-agar. We investigated 20 HS including natural organic matter (NOM) samples, two lignite derived HS, and one synthetic HS. The aim was (1) to find out, if there are inhibiting effects and (2) if potential effects can be explained by humic matter properties by structure activity relationships. The growth of S. parasitica was related to the growth on HS-free agar controls. Characterization of HS and NOMs included elemental analysis, high-pressure size exclusion chromatography (HPSEC), UV/VIS, FTIR-, and EPR-spectroscopy in order to obtain information on elemental and structural composition including various metals, molecular weights of the HS fraction, aromaticity, free organic radicals, and functional groups. NOMs with high moieties of high-molecular carbohydrates supported the growth of S. parasitica, all other HS and NOMs reduced it. However, no inhibition of the development of the sporangia and primary zoospores was found. Therefore, the impact of the HS on S. parasitica has to be classified as fungistatic, rather than fungicidal. Synthetic and lignite-derived HS were among the most efficient HS sources. Growth inhibition was correlated (p<0.05) with the molecular weights of the HS-fraction, sUVa, COOH groups, C and H. Our results suggest that especially HS with higher molecular weights and aromaticity which contain a high number of organic radicals are the most efficient in reducing fungal growth. Furthermore, highly functionalized HS seem to be important for the observed effect. The development of internal oxidative stress could be a mechanism explaining the observed growth inhibition of S. parasitica.
腐殖质（HS）在未富营养化的淡水生态系统中占溶解有机物的50 - 80%。HS并非惰性物质，而是会被水生生物摄取并可能与其相互作用。然而，目前尚无关于HS与真菌（如鱼病原性物种寄生水霉）相互作用的信息。为填补这一空白，我们在GY - 琼脂上使用25 - 500mgL(-1)碳含量的HS测试了HS对寄生水霉体外生长的影响。我们研究了20种HS，包括天然有机物（NOM）样品、两种褐煤衍生的HS和一种合成HS。目的是（1）确定是否存在抑制作用，以及（2）潜在影响是否可通过结构 - 活性关系由腐殖质特性来解释。寄生水霉的生长与无HS琼脂对照上的生长情况相关。对HS和NOMs的表征包括元素分析、高压尺寸排阻色谱（HPSEC）、紫外/可见光谱、傅里叶变换红外光谱（FTIR）和电子顺磁共振光谱（EPR），以便获取有关元素和结构组成的信息，包括各种金属、HS组分的分子量、芳香性、游离有机自由基和官能团。含有高分子碳水化合物高比例部分的NOMs促进了寄生水霉的生长，所有其他HS和NOMs则抑制了其生长。然而，未发现对孢子囊和初级游动孢子发育的抑制作用。因此，HS对寄生水霉的影响必须归类为抑菌作用，而非杀菌作用。合成HS和褐煤衍生的HS是最有效的HS来源之一。生长抑制与HS组分的分子量、sUVa、COOH基团、C和H相关（p < 0.05）。我们的结果表明，尤其是分子量较高且具有芳香性、含有大量有机自由基的HS在抑制真菌生长方面最为有效。此外，高度官能化的HS似乎对观察到的效果很重要。内部氧化应激的发展可能是解释观察到的寄生水霉生长抑制现象的一种机制。
