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Investigation of yeast flora in the sea surface microlayer at Keelung on the north-east coast of Taiwan and their resistance to UV radiation
|Authors: ||Chin-Feng Chang|
|Contributors: ||NTOU:Institute of Marine Biology|
sea surface microlayer;yeast;mycosporines;carotenoids
|Issue Date: ||2011-07-04
|Abstract: ||海洋表面微層是位於海水與大氣交界面間的一層液態薄膜，厚度約在1-1000 μm左右，其重要性主要與海洋及大氣之間物質的交換有關。海洋表面微層有著嚴苛的環境條件，通常伴隨著高劑量的太陽可見光與紫外光及高濃度的污染物質。因此表面微層對微生物而言經常被認為是屬於極端的環境，可能包含了不尋常的物種與微生物相，這些生存在其中的微生物可能也具備了特殊存活的機制。 本論文係利用培養的方式調查棲息於台灣基隆沿岸表面微層中酵母菌族群並與次表層海水(50 cm深)中的酵母菌族群作比較。進行為期一年共四次的採樣總共分離出420株酵母菌菌株。利用多相的分子研究方法包括分析26S rDNA D1/D2 domains與5.8S-ITS region的序列可將這些菌株分成43個酵母菌種。海洋表面微層分離出12個屬39種菌種，其中包括7個新種：Cryptococcus sp. (1)、Candida spp. (4)與Rhodotorula spp. (2)。次表層海水分離出10個屬21種菌種，其中包括1個新種：Rhodotorula sp. (1)。Rhodotorula mucilaginosa被發現是在海洋表面微層(37.6%)與次表層海水(29.3%)樣品中佔主要的出現頻率。被分離的新種也進一步的針對其形態學、生理學與分子生物學的特性研究。 這些菌株經由序列分析及形態生理特徵結果已確認所屬菌種，並且針對菌株暴露在模擬的太陽紫外線光源下的生長情形進行研究，將這些菌株對紫外線抗性程度做分級。此外，也分析這些酵母菌株產生光保護物質(類胡蘿蔔素與類菌胞素)的能力。海洋表面微層與次表層海水中酵母菌分離株利用擬太陽輻射的紫外光照射4種不同時間由1小時到6小時之間，照射後依照菌株生長的情形將菌株作抗性程度的分級。表面微層酵母菌分離株對紫外線的抗性主要分布在抗性程度的第三級(49%)，而次表層海水中酵母菌分離株對紫外線的抗性主要分布在抗性程度的第二級(43%)。這些結果顯示海洋表面微層酵母菌與次表層海水中酵母菌對抗紫外線的能力並不相同，表面微層菌株顯示比次表層海水菌株有較佳的紫外線抗性。 經紫外線照射後表面微層分離出的菌種有9株、由次表層海水分離出的菌種有8株會誘導出菌孢素的產生。此菌孢素在310 nm有最大吸收波長並且鑑定為mycosporine-glutaminol-glucoside (myc–glu–glu)與mycosporine-glutamicol-glucoside (myc–glc–glu)。具有菌孢素產生能力的菌株主要分布在紫外線抗性程度的第二級(59%)而不具有菌孢素產生能力的菌株主要分布在紫外線抗性程度的第三級(54%)。總類胡蘿蔔素在照射紫外光後合成的模式有兩種，一種顯示細胞在類胡蘿蔔素組成份原先較高者在紫外線誘導後呈現降低的趨勢，而細胞在類胡蘿蔔素組成份原先較低者在紫外線誘導後成呈現增加的趨勢。 很明顯的具有色素與類菌孢素的酵母菌細胞相較於不具有色素與類菌孢素的酵母菌細胞並沒有較強的紫外線抗性。類胡蘿蔔素與具遮擋陽光能力的化合物在酵母菌抵抗太陽輻射上可能只是附加的因子，在本研究中具有高度抗紫外線能力的酵母菌種需要進一步研究這些酵母菌種能存活在高劑量紫外線壓力下的機制。|
The sea surface microlayer (SSML), a thin film (about 0-1000 μm thick) of liquid at the interface of sea and atmosphere, is of considerable importance in exchanges between the sea and the atmosphere. The conditions at the sea surface microlayer are harsh with high level of visible and ultraviolet radiation (UVR) and high concentration of pollutants. Therefore, the SSML has often considered as an extreme environment for microorganisms and that may contain unusual species and taxa. In order to survive, microorganisms inhabiting surface microlayer would have to develop mechanisms to aid their life under such harsh conditions. Yeast populations inhabiting the SSML in the Northeast coast of Taiwan were examined with cultivation method and were compared with those inhabiting underlying water (UW) (50 cm depth). Culturable yeasts were recovered from the sea water samples collected from the SSML and the UW in the morning during 4 field campaigns and 420 strains were isolated. The 420 isolates were grouped into 43 species by a polyphasic molecular approach including sequence analysis of 26S rDNA D1/D2 domains and 5.8S-ITS region. The SSML contains 12 genus and 39 yeast species, including 7 new species of the genera Cryptococcus sp. (1), Candida spp. (4), and Rhodotorula spp. (2). The UW contains 10 genus and 21 species, including 1 new yeast species of the genera Rhodotorula sp. (1). Rhodotorula mucilaginosa was the majority of the yeast community in sea water samples from the SSML (37.6%) and the UW (29.3%). Detailed studies on morphological, physiological and molecular characteristics had been done for these new species. UVR resistance of these yeast strains were determined by monitoring the growth pattern following UV exposure. Different levels of resistance were found among them and the ability of these strains to produce photoprotective compounds, e.g. carotenoids and mycosporines were different too. The SSML and UW yeast isolates were subjected to four different exposure times, ranging from 1 to 6 h of simulated solar radiation. Following exposure, the growth of each isolate was monitored, and different levels of resistance were determined according to the growth pattern. Majority of the SSML yeasts isolates were found in the resistant (R) level (49%), while majority of the UW yeast isolates were found in the weak resistant (wR) level (43%). These results showed that resistance to solar radiation was different between SSML and UW yeast isolates. There were 9 strains isolated from SSML, 8 strains isolated from UW produced mycosporines after exposure to UV radiation. These compounds showed an absorption maximum at 310 nm and were identified as mycosporine-glutaminol-glucoside (myc–glu–glu) and mycosporine-glutamicol-glucoside (myc–glc–glu). Most mycosporines positive cells were in the wR level (59%) while mycosporines negative cells were in the R level (54%). There were two types of carotenoid compounds synthesis pattern after exposure to UV radiation, carotenoids concentration in cells with higher constitutive levels of carotenoids were decreased after exposure to UVR, and carotenoids concentration in cells with lower constitutive levels of carotenoids were increased after exposure to UVR. Pigmented yeasts or mycosporines positive yeasts are not more resistant to solar radiation than non-pigmented and mycosporines negative yeasts. Compounds such as carotenoids and sunscreen molecules could be additional factors used by yeasts to resist solar radiation. Discoveries of the high resistance from UV stress of several yeast species, as determined in the present study, should encourage further investigations to characterize the mechanisms involved in the resistance to solar radiation.
|Appears in Collections:||[海洋生物研究所] 博碩士論文|
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