**膠藻菌**（Gloeobacteria）又稱**膠藍菌**、**無類囊體藍藻**，在演化樹上位於藍菌演化支的基部，為藍菌的基群、所有其他藍菌的姊妹群。膠藻菌是所有可行有氧光合作用的生物細胞中唯一不具有類囊體者，其光系統也與其他藍菌有相當差異，可能是最早可行有氧光合作用的生物。**膠藻菌屬**（學名：*Gloeobacter*）僅包含三個物種，另外近年發表的*Aurora vandensis*與*Anthocerotibacter panamensis*兩新種也屬於廣義的膠藻菌，皆不具類囊體與其他藍菌都有的一些光系統蛋白。分子鐘分析顯示膠藻菌的演化支約於距今20億年前與其他藍菌（冠群藍菌）分家，可能保有較多原始藍菌的祖徵（英语：）。

物種
--

膠藻菌屬於1974年被描述發表，包含紫膠藻菌（*Gloeobacter violaceus*）、基拉韋厄膠藻菌（*Gloeobacter kilaueensis*）與莫雷洛斯膠藻菌（*Gloeobacter morelensis*）等三個物種，多分布於光照不強的潮濕岩壁上，在世界各地均有發現。模式種紫膠藻菌採自瑞士上瓦爾登州的一塊石灰岩上，外型呈桿狀，胞外有黏液鞘將數個細胞包覆在一起，後來也在歐洲與墨西哥被發現，應為分布廣泛的陸生藍菌；基拉韋厄膠藻菌採自夏威夷大島基拉韋厄火山口（英语：）熔岩洞內的生物薄膜上，於2013年發表；莫雷洛斯膠藻菌則採自墨西哥莫雷洛斯州一座瀑布洞穴中的生物薄膜上，於2021年發表，與紫膠藻菌的關係較為接近，為其姊妹群。此外2020年還有總體基因體學研究發表了另一膠藻菌的不完整基因組序列，暫稱為*G.* SpSt-379；2021年又有5個完整的膠藻菌基因組序列被定序發表，分別採自格陵蘭島、加拿大不列颠哥伦比亚、阿拉斯加北部與夏威夷考艾島的馬尼尼霍洛洞穴（Maniniholo Cave）等地，應分別代表一種新種的膠藻菌。

膠藻菌與基拉韋厄膠藻菌演化支分家的時間估計約為2.8億年前，基因組長約470萬bp，莫雷洛斯膠藻菌則約有490萬bp，三者基因組都已被完整定序，其中許多光系統蛋白的基因皆闕如。紫膠藻菌可合成葉綠素a（英语：）、β-胡蘿蔔素、海膽烯酮（英语：）、别藻藍蛋白（英语：）、藻藍蛋白（英语：）與藻紅蛋白（英语：）等色素，其外觀呈紫色可能是葉綠素含量較低造成；基拉韋厄膠藻菌可合成葉綠素a與β-胡蘿蔔素，外觀也是紫色。

紫膠藻菌的學名可能不符合《國際植物命名法規》，因其發表時缺少了拉丁文的物種鑑定描述，雖然2011年法規修改後已不要求物種發表者提供拉丁文描述，紫膠藻菌的學名仍可能因當初發表的模式標本為活體菌株、非乾燥標本而不被法規接受；紫膠藻菌發表時，發表者即認為其與1927年發表、所知甚少的藍菌*Gloeothece coerulea*關係密切；1880年發表的藍菌*Aphanothece caldariorum*與紫膠藻菌的形態與分子序列均非常接近，應屬同屬物種，並可能為同物異名，若這些學名確為紫膠藻菌的異名，根據命名法規，種小名*coerulea*與*caldariorum*的優先級均高於紫膠藻菌的種小名*violaceus*

### 相關類群

2020年，有一自南極麥克默多乾燥谷萬達湖的微生物席採得的新種藍菌DNA序列發表，被歸入新屬*Aurora*，學名為*Aurora vandensis*，此藍菌在演化樹上也位於藍菌演化支的基部，應不具類囊體；2021年又有一不具類囊體的新種藍菌發表，採自巴拿馬雨林中的平孢角苔（英语：）植株上，屬於新屬*Anthocerotibacter*，學名為*Anthocerotibacter panamensis*，可能為*Aurora vandensis*的姊妹群，兩者的演化支則為膠藻菌屬的姊妹群，在約14億年前與其分家。*Aurora*與*Anthocerotibacter*也被視為廣義的膠藻菌，兩者比膠藻菌屬缺少了更多光系統蛋白的基因（如PsbM、PsbU、PetM與PetN），*Anthocerotibacter*行光合作用的效率相當有限。下為膠藻菌與相關類群的演化樹：

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| 藍菌 | 

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|   | 

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|   | 

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|   | 

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| **膠藻菌** | 

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|   | *Aurora vandensis* |
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|   | *Anthocerotibacter panamensis* |
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| **膠藻菌屬** | 

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|   | *G.* SpSt-379 |
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|   | 

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|   | 紫膠藻菌（*G. violaceus*） |
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|   | 莫雷洛斯膠藻菌（*G. morelensis*） |
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|   | 基拉韋厄膠藻菌（*G. kilaueensis*） |
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|   | 其他藍菌（冠群） |
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特色
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膠藻菌不具類囊體，其光系統中的光能捕獲複合體（英语：）（藻膽體（英语：））位於細胞膜上，且結構較其他藍菌的原始，呈束狀而非典型的半圓盤狀。相較於其他行有氧光合作用的生物在類囊體膜上形成光反應（英语：）所需的質子梯度，此類藍菌的質子梯度是在細胞膜上產生。膠藻菌雖有一與形成類囊體所需的Vipp1蛋白同源的蛋白，但比其他藍菌與植物的Vipp1蛋白少了一段序列，冠群藍菌的Vipp1蛋白可能是後來才獲得了促進類囊體形成的新功能。

膠藻菌用於行光合作用的的蛋白皆集中在細胞膜上的特定區域，佔細胞膜表面積尚不及三分之一，可行光合作用的膜表面積比具類囊體的細胞（其他藍菌與葉綠體）低很多，每個細胞僅約1μm²，相較之下具類囊體的藍菌行光合作用的膜表面積超過10μm²，類囊體較多者可達50至70μm²，光合作用效率大大提升。膠藻菌的細胞膜是由負曲率的脂類（HexII型）與零曲率的脂類（Lm）以一定比例組成，HexII型的脂類包括單葡萄糖基二脂酰甘油（monoglucosyldiacylglycerol，MGlcDG）與單半乳糖基二脂酰甘油（monogalactosyldiacylglycerol，MGDG），Lm型的則有與磷酸醯甘油（英语：）（PtdGro）與二半乳糖基二脂酰甘油（digalactosyldiacylglycerol，DGDG），相較之下其他藍菌多了一種Lm脂類磺基-6-脫氧葡糖基二脂醯甘油（sulfoquinovosyldiacylglycerol，SQDG），類囊體的起源可能即為膜受到擾動（如提高膜中PtdGro與DGDG等Lm脂質的比例，加入新的Lm脂質SQDG，以及Vipp1等蛋白的協助）後發生HexII → Lm相變，進而形成高度捲曲、多層的膜結構。

膠藻菌合成β-胡蘿蔔素的反應途徑與非藍菌的其他細菌和真菌較為相似，由八氢番茄红素（英语：）合成全反式番茄紅素的步驟僅使用CrtI一種去飽和酶，不像其他藍菌與植物使用CrtP與CrtQb兩種同源的去飽和酶將八氫番茄紅素加上雙鍵，以及異構酶CrtH將其轉為反式，不過*Aurora vandensis*與*Anthocerotibacter panamensis*合成β-胡蘿蔔素的途徑皆是「植物型」而非「細菌型」，顯示含膠藻菌在內所有藍菌的共同祖先應該具有CrtP、CrtQb與CrtH等酵素，而膠藻菌屬演化的過程中丟失了這些酵素，改使用細菌型途徑合成β-胡蘿蔔素。

另外，多數藍菌有生物鐘系統，由KaiA、KaiB與KaiC等三個蛋白負責達成，膠藻菌基因組中沒有發現這三個基因，因此應不具生物鐘。

參見
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* 光合作用的演化

註腳
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1. ↑  包括藍菌與植物等真核生物細胞中的葉綠體。
2. ↑  膠藻菌缺少的光系統蛋白包括PsbY、PsbZ與Psb27等光系統 II的蛋白，以及PsaI、PsaJ、PsaK與PsaX等光系統 I的蛋白。
3. ↑  因其與膠藻菌屬物種一樣不具形成類囊體所需的VIPP1基因。
4. ↑  指極性頭端的體積比非極性尾的體積小的脂類。
5. ↑  SQDG可在缺磷的環境下取代PtdGro，使細胞得以在缺磷的環境下生長。
6. ↑  指可行無氧光合作用的細菌，如紫硫菌、綠硫菌等。

參考文獻
----

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2. ↑ . 國立臺灣大學. 2021-06-02  [2021-12-08]. （原始内容存档于2021-12-09）.
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6. 1 2  R. Rippka, J. Waterbury, G. Cohen-Bazire.. Archives of Microbiology. 1974, **100**: 419–436  [2021-12-08]. （原始内容存档于2021-12-08）.
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8. ↑  Montejano, G. Becerra-Absalón, I. Gold-Morgan, M.; et al.. Plant Syst Evol. 2018, **304**: 1221–1229. doi:10.1007/s00606-018-1542-z.  引文格式1维护：显式使用等标签 (link)
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11. ↑  Grettenberger CL.. mSphere. 2021, **6** (4): e0006121  [2021-12-10]. PMC 8386580 可免费查阅. PMID 34287010. doi:10.1128/mSphere.00061-21. （原始内容存档于2021-12-10）.
12. 1 2 3 4  Grettenberger CL, Sumner DY, Wall K, Brown CT, Eisen JA, Mackey TJ; et al.. ISME J. 2020, **14** (8): 2142–2152. PMC 7368068 可免费查阅. PMID 32424249. doi:10.1038/s41396-020-0668-5.
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14. ↑  Boyce Thompson Institute（英语：）.. ScienceDaily. 2021-05-15  [2021-12-08]. （原始内容存档于2021-12-08）.
15. 1 2 3 4 5  Guéguen N, Maréchal E.. J Exp Bot. 2021  [2021-12-10]. PMID 34537843. doi:10.1093/jxb/erab429. （原始内容存档于2021-12-10）.
16. ↑  Rexroth S, Mullineaux CW, Ellinger D, Sendtko E, Rögner M, Koenig F.. Plant Cell. 2011, **23** (6): 2379–90  [2021-12-10]. PMC 3160022 可免费查阅. PMID 21642550. doi:10.1105/tpc.111.085779. （原始内容存档于2021-12-10）.
17. ↑  George DM, Vincent AS, Mackey HR.. Biotechnol Rep (Amst). 2020, **28**: e00563. PMC 7714679 可免费查阅. PMID 33304839. doi:10.1016/j.btre.2020.e00563.
18. ↑  Steiger S, Jackisch Y, Sandmann G.. Arch Microbiol. 2005, **184** (4): 207–14  [2021-12-09]. PMID 16235086. doi:10.1007/s00203-005-0004-5. （原始内容存档于2021-12-09）.
19. ↑  Dvornyk V, Mei Q.. Sci Rep. 2021, **11** (1): 9995. PMC 8113500 可免费查阅. PMID 33976298. doi:10.1038/s41598-021-89345-7.

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| 分類單元識別碼 | 
* 维基数据: Q5571156
* 維基物種: Gloeobacter
* AlgaeBase: 44849
* EoL: 90918
* EPPO: 1GLBCG
* GBIF: 3216318
* IRMNG: 1073523
* LPSN: gloeobacter
* NCBI: 33071
* WoRMS: 601242

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