蛇紋岩土壤鎳及鉻對微生物族群及根瘤線蟲的影響

Abstract

蛇紋岩土壤為一富含鎳、鉻的天然環境，低鈣鎂比為此土壤特性。目前台灣蛇紋岩土壤中微生物群相未知，本研究於2019年1月起調查蛇紋岩土壤中線蟲群相，採集我國宜花東共23個區域之蛇紋岩土壤與非蛇紋岩土壤，各分離出20與22科線蟲。比較相同樣本數下分離的線蟲總量，發現蛇紋岩土壤中的線蟲遠少於非蛇紋岩土壤，推論高濃度的鎳、鉻環境不利於線蟲生存。探究線蟲分群類別，Qudsianmenatidae科僅在蛇紋岩土壤中被發現，Anguinidae、Dolichodoridae、Rhabdolaimidae等科之線蟲則僅出現於非蛇紋岩土壤中。在非蛇紋岩土壤中出現頻率最高的Meloidogyne, Heterocephalobellus兩屬線蟲在蛇紋岩土壤中豐度明顯下降，推測該兩屬線蟲可能對於重金屬為較敏感，耐受性較低。因此，本研究首先探究高濃度鎳、鉻於根瘤線蟲體內所產生之生理影響。本研究挑選新興重要入侵病原象耳豆根瘤線蟲作為試驗材料，發現其在鎳、鉻環境中，繁殖、侵染、發育及代謝等生理能力皆受到影響，且高濃度下不利其生存；鎳濃度高於200 ppm時，象耳豆根瘤線蟲的死亡率會顯著上升，而高於50 ppm的鉻，則使象耳豆根瘤線蟲有100%死亡率。當環境中含有鎳時，象耳豆根瘤線蟲的卵孵化率、侵染能力及代謝速度皆下降，然而其卵及幼蟲發育速度皆加快。而環境中的鉻，則使象耳豆根瘤線蟲的卵孵化率、侵染植株及代謝等能力下降，並使幼蟲發育速度加快。於本研究調查中，發現蛇紋岩土壤中有一種對鎳、鉻具有高度耐受性之根瘤線蟲，推測該種類可能獲得環境中微生物之協助而產生較佳適應性。因此，本研究調查蛇紋岩土壤中的細菌群相，進行細菌功能性分析，結果發現，共有十七個屬 (Dongia, Pirellula, Anaerolinea , Haliangium, Sphinogomonas, Geobacter, Streptomyces Gaiella, Pseudolabrys, Rhodopseudomonas, Candidatus, Pedomicrobium, Pseudaminobacter, Steroidobacter, Reyrannella, Bacillus, Bradyrhizobium) 於蛇紋岩土壤中具有較高的相對豐度。其中，Sphinogomonas, Geobacter, Streptomyces, Pseudolabrys, Rhodopseudomonas, Candidatus_Solibacter, Steroidobacter, Reyrannella等八個屬，過去曾被報導於高濃度金屬環境中具耐受性，且有金屬吸附及螯合等能力。本研究發現，Bacillus nealsonii及Solitalea koreensis 與Acidobacteria bacterium等三菌株與土壤中鎳、鉻濃度具有高度正相關性。本研究中所篩選出之與重金屬相關菌群，可做為後續研究高鉻、鎳環境中線蟲-細菌交互作用的潛力菌株。

Serpentine soil is a rich nickel and chromium soil, and the low Mg/Ca ratio is its feature. Microbiome in serpentine soil is unknown. Since January 2019, the study investigated the soil microbiome in serpentine soil and compared them with non-serpentine soils in the same region. There were fewer nematodes in serpentine soil than non-serpentine soil, which suggested high concentration of environmental nickel and chromium are harmful to nematode. Among the 23 samples collected from the eastern Taiwan, a total of 20 families of nematodes were found in serpentine soils, while 22 families were found in non-serpentine soil. The family Qudsianmenatidae was only discovered in serpentine soil, while Anguinidae, Dolichodoridae, Rhabdolaimidae were only observed in non-serpentine soils. The top two abundant genera in non-serpentine soils, Meloidogyne spp. and Herterocephalobellus spp., only present significant low abundance in serpentine soil. Therefore, we assumed the two genera are sensitive and have lower tolerance level to heavy metals. We explored the physiological effects of Meloidogyne spp. in high concentration nickel and chromium environment. The emerging guava root-knot nematode, Meloidogyne enterolobii, was select as the experimental material in this study. This study revealed that the reproduction, development, invasion, and metabolism of the nematode were impacted by nickel and chromium, and that the high concentration of the two metals in the environment are toxic to nematodes and harm their survival. When the environmental nickel concentration is higher than 200 ppm, the mortality of M. enterolobii was significantly increased. Also, 100% M. enterolobii mortality would be reached when the environment contains higher than 50 ppm chromium. When the environment contains nickel, the egg hatching rate, invasion ability and metabolism of M. enterolobii were decreased, but the development rate of egg and juvenile were both increased. On the other hand, chromium decreased the egg hatching rate, invasion ability and metabolism of M. enterolobii, and increased development rate of juvenile. One Meloidogyne species, code species S, was discovered in serpentine soil, and had higher tolerance to nickel and chromium than other Meloidogyne species. We hypothesized Meloidogyne species S adapted to the environment with the help of microbes in the same environment. Therefore, this study investigated the bacteria communities in serpentine soil, and analyzed their potential gene functions. As results, seventeen genra were found to have higher relative abundance in serpentine soil: Dongia, Pirellula, Anaerolinea , Haliangium, Sphinogomonas, Geobacter, Streptomyces Gaiella, Pseudolabrys, Rhodopseudomonas, Candidatus , Pedomicrobium, Pseudaminobacter, Steroidobacter, Reyrannella, Bacillus and Bradyrhizobium. Among them, 8 genera (Sphinogomonas, Geobacter, Streptomyces, Pseudolabrys, Rhodopseudomonas, Candidatus_Solibacter, Steroidobacter, and Reyrannella) were previously reported to have higher tolerance to high metal concentrations, and were able to absorb metal and carry chelation. In our study, Bacillus nealsonii, Solitalea koreensis and Acidobacteria bacterium were found to have strong positive correlation to the concentration of nickel and chromium. The heavy-metal related bacteria revealed in this study can be use as candidate strains to study the interaction of nematode and bacteria in the high- nickel and chromium environments.