固氮酶极端怕氧，根瘤却是好氧代谢旺盛的组织，这个矛盾如何解决？
Nitrogenase is extremely oxygen-sensitive, yet nodules are metabolically active aerobic tissue; how is this conflict resolved?
固氮酶的铁硫簇和铁钼辅因子会被氧不可逆破坏，但把氮气还原为铵每分子需要十六个 ATP，必须靠类菌体的氧化磷酸化供能，因此需要极低但不为零的氧浓度。根瘤通过皮层的氧扩散屏障把内部游离氧压降到纳摩尔量级，并用高丰度的豆血红蛋白结合氧、以极高的通量把氧输送给类菌体的高亲和力末端氧化酶。此外根瘤菌自身还通过 FixL-FixJ 等氧感应系统在低氧下才诱导固氮基因表达，从而在时空上把耗氧与固氮分开。
The iron-sulfur clusters and iron-molybdenum cofactor of nitrogenase are irreversibly damaged by oxygen, yet reducing one molecule of dinitrogen to ammonium consumes about sixteen ATP that must come from bacteroid oxidative phosphorylation, so the enzyme needs an oxygen level that is very low but not zero. Nodules impose a cortical oxygen diffusion barrier that holds free oxygen in the infected zone at nanomolar levels, while abundant leghemoglobin binds oxygen and delivers it at high flux to high-affinity terminal oxidases of the bacteroid. Rhizobia additionally use oxygen sensors such as FixL-FixJ so that nitrogen fixation genes are induced only under microaerobic conditions, separating respiration from fixation in space and time.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Ott T 等,《Symbiotic Leghemoglobins Are Crucial for Nitrogen Fixation in Legume Root Nodules but Not for General Plant Growth and Development》,Current Biology,2005 (DOI: 10.1016/j.cub.2005.01.042)
T. Ott et al., 'Symbiotic Leghemoglobins Are Crucial for Nitrogen Fixation in Legume Root Nodules but Not for General Plant Growth and Development', Current Biology, 2005, DOI: 10.1016/j.cub.2005.01.042
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1016/j.cub.2005.01.042
#固氮酶 #豆血红蛋白 #氧扩散屏障 #微氧调控
有些寄生物能改变宿主行为，这类操纵是通过什么途径实现的？
Some parasites alter host behaviour; through what routes is such manipulation achieved?
研究较清楚的途径有三类：分泌神经活性物质或调控宿主神经递质系统，如寄生蜂向猎物特定神经节注射毒素造成选择性瘫痪；改变宿主的免疫与内分泌状态间接影响脑功能，如弓形虫在脑内形成包囊并伴随多巴胺代谢改变，与啮齿类对猫尿气味的回避减弱相关；直接侵入并重塑运动相关组织，如虫草真菌在蚂蚁体内诱导定型的攀高与咬紧行为以利孢子扩散。判断是否为适应性操纵需要证明该行为提高了寄生物的传播成功率，而非仅是宿主生病的副产物。
Three routes are reasonably well documented: secreting neuroactive compounds or hijacking host neurotransmitter systems, as when a parasitoid wasp injects venom into specific ganglia to cause selective paralysis; altering immune and endocrine state to affect brain function indirectly, as with Toxoplasma cysts in the brain accompanied by changes in dopamine metabolism and reduced rodent aversion to cat odour; and directly invading and remodelling locomotor tissue, as when Ophiocordyceps fungi drive infected ants into stereotyped climbing and biting that favours spore dispersal. Calling such changes adaptive manipulation requires showing that the behaviour raises parasite transmission success rather than being a by-product of illness.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Adamo,《Parasites: evolution’s neurobiologists》,Journal of Experimental Biology,2013 (DOI: 10.1242/jeb.073601)
Adamo, 'Parasites: evolution’s neurobiologists', Journal of Experimental Biology, 2013, DOI: 10.1242/jeb.073601
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1242/jeb.073601
#宿主操纵 #神经寄生学 #弓形虫 #虫草真菌
互利共生与寄生之间可以互相演化转变吗，什么条件决定方向？
Can mutualism and parasitism evolve into each other, and what conditions set the direction?
两者是同一连续谱上的位置，系统发育重建显示细菌共生体在不同谱系中多次在互利与寄生间转换。关键条件是伙伴利益的对齐程度：垂直传播使共生体的繁殖成功与宿主适合度绑定，倾向演化出互利并常伴随基因组缩减；水平传播和多株共感染则加剧共生体之间的竞争，容易走向剥削。宿主一方的制裁机制，如豆科植物对固氮低效根瘤减少碳供应，也能稳定合作。环境营养条件改变时，原本必需的伙伴可能变成负担，关系随之重新调整。
The two are positions on one continuum, and phylogenetic reconstruction shows bacterial symbionts have shifted repeatedly between mutualism and parasitism across lineages. The decisive condition is how well partner interests align: vertical transmission ties symbiont reproductive success to host fitness and favours mutualism, often with genome reduction, whereas horizontal transmission and mixed infection intensify competition among symbionts and push toward exploitation. Host sanctions also stabilize cooperation, as when legumes cut carbon supply to nodules that fix little nitrogen. When nutrient conditions change, a once-essential partner can become a burden and the relationship is renegotiated.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Sachs JL, Skophammer RG, Regus JU. Evolutionary transitions in bacterial symbiosis. PNAS (2011) 108:10800-10807
Sachs JL, Skophammer RG, Regus JU. Evolutionary transitions in bacterial symbiosis. PNAS (2011) 108:10800-10807
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1073/pnas.1100304108
#互利共生 #寄生 #垂直传播 #宿主制裁
菌根真菌怎样帮助植物获取养分，自己又得到什么？
How do mycorrhizal fungi help plants acquire nutrients, and what do the fungi get in return?
丛枝菌根真菌的菌丝从根系向外延伸数厘米到数十厘米，极大扩展了吸收面积，尤其能获取扩散慢、易被根际耗尽的磷酸盐，也参与氮、锌等元素的转运。真菌在根皮层细胞内形成丛枝结构，与植物之间通过特化的周丛枝膜进行物质交换。作为回报，植物把光合固定碳的百分之十到二十以己糖和脂质形式交给真菌，后者自身缺乏合成脂肪酸的能力，因此严格依赖宿主。这种互作还能提高植物抗旱性并改善土壤团聚结构。
Hyphae of arbuscular mycorrhizal fungi extend centimetres to tens of centimetres beyond the root, greatly enlarging the absorbing surface and especially capturing phosphate, which diffuses slowly and is quickly depleted near roots, while also carrying nitrogen and zinc. Inside cortical cells the fungus builds arbuscules, and exchange occurs across a specialized periarbuscular membrane. In return the plant delivers ten to twenty percent of its photosynthetically fixed carbon as hexoses and lipids, and because these fungi cannot synthesize fatty acids themselves they depend obligately on the host. The partnership also improves drought tolerance and soil aggregate structure.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Bonfante P, Genre A. Mechanisms underlying beneficial plant-fungus interactions in mycorrhizal symbiosis. Nature Communications (2010) 1:48
Bonfante P, Genre A. Mechanisms underlying beneficial plant-fungus interactions in mycorrhizal symbiosis. Nature Communications (2010) 1:48
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1038/ncomms1046
#菌根真菌 #丛枝菌根 #磷吸收 #碳交换
支持线粒体和叶绿体起源于内共生的证据有哪些？
What evidence supports an endosymbiotic origin for mitochondria and chloroplasts?
两类细胞器都保留自己的环状 DNA、细菌型核糖体和 fMet 起始的翻译系统，对氯霉素等抗细菌药物敏感；它们由双层膜包裹，内膜的脂质组成与细菌相似，且只能通过自身分裂而非从头合成产生。系统发育分析把线粒体基因归入 α 变形菌，把叶绿体基因归入蓝细菌，同时大量原共生体基因已转移到宿主核基因组，其产物再被运回细胞器。这些互相独立的证据共同支持真核细胞由古菌宿主吞入细菌后长期整合而来。
Both organelles retain their own circular DNA, bacterial-type ribosomes and formylmethionine-initiated translation, and are sensitive to antibacterial drugs such as chloramphenicol; each is bounded by a double membrane whose inner layer resembles bacterial lipid composition, and each arises only by division of a pre-existing organelle rather than de novo. Phylogenetic analysis places mitochondrial genes among alphaproteobacteria and chloroplast genes among cyanobacteria, while many former endosymbiont genes have moved to the host nuclear genome with their products imported back. These independent lines converge on eukaryotes arising from long-term integration of bacteria engulfed by an archaeal host.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Martin WF, Garg S, Zimorski V. Endosymbiotic theories for eukaryote origin. Philosophical Transactions of the Royal Society B (2015) 370:20140330
Martin WF, Garg S, Zimorski V. Endosymbiotic theories for eukaryote origin. Philosophical Transactions of the Royal Society B (2015) 370:20140330
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1098/rstb.2014.0330
#内共生学说 #线粒体 #叶绿体 #基因转移
豆科植物与根瘤菌建立共生固氮关系需要经过哪些步骤？
What steps establish the nitrogen-fixing symbiosis between legumes and rhizobia?
植物根系在缺氮时分泌类黄酮，诱导根瘤菌合成并释放脂质壳寡糖类的结瘤因子；宿主根毛表面的 LysM 类受体激酶识别该信号，引发钙振荡并激活共生信号通路的转录程序。根毛随后卷曲形成侵染线，细菌沿侵染线进入皮层，同时皮层细胞重新启动分裂形成根瘤原基。细菌在根瘤细胞内被侵染体膜包裹并分化为类菌体，开始把氮气还原为铵供植物使用，植物则提供二羧酸类碳源。
Nitrogen-starved legume roots secrete flavonoids that induce rhizobia to make and release lipochitooligosaccharide nodulation factors; LysM-type receptor kinases on the root hair perceive the signal, triggering calcium spiking and the transcriptional programme of the common symbiosis pathway. The root hair then curls to form an infection thread through which bacteria travel into the cortex, while cortical cells resume division to build a nodule primordium. Inside nodule cells the bacteria are enclosed in symbiosome membranes and differentiate into bacteroids that reduce dinitrogen to ammonium for the plant, which supplies dicarboxylic acid carbon in return.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Ed Yong,《I Contain Multitudes》Ecco/HarperCollins,2016;中译《我包罗万象》(郑李译),后浪丨北京联合出版公司,2019
Ed Yong, I Contain Multitudes, Ecco/HarperCollins, 2016; Chinese ed. (Zheng Li tr.), Beijing United Publishing (Houlang), 2019
#共生固氮 #根瘤菌 #结瘤因子 #类菌体
疟原虫的生活周期为什么需要蚊和人两个宿主？
Why does the malaria parasite require both a mosquito and a human host in its life cycle?
疟原虫在按蚊体内完成有性生殖：配子体在蚊胃内结合形成合子并发育为动合子，穿过中肠壁形成卵囊，释放的子孢子迁移到唾液腺。叮咬时子孢子进入人体，先在肝细胞内大量增殖，再进入红细胞进行周期性的无性裂殖，导致周期性发热和贫血，部分虫体分化为配子体等待被蚊再次吸入。因此蚊是有性阶段和传播媒介，人是无性扩增阶段，缺少任一环节循环即中断，这也是控蚊、抗疟药与疫苗分别针对不同阶段的原因。
Sexual reproduction occurs in the Anopheles mosquito: gametocytes fuse in the midgut to form a zygote that becomes a motile ookinete, crosses the gut wall as an oocyst, and releases sporozoites that migrate to the salivary glands. A bite delivers sporozoites into a human, where they first multiply in hepatocytes and then invade red cells for cyclical asexual replication that causes periodic fever and anaemia, with some parasites differentiating into gametocytes awaiting the next mosquito. The mosquito thus hosts the sexual stage and transmission while the human hosts asexual amplification, so breaking either link stops the cycle, which is why vector control, antimalarial drugs and vaccines each target different stages.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Cowman AF, Healer J, Marapana D, Marsh K. Malaria: biology and disease. Cell (2016) 167:610-624
Cowman AF, Healer J, Marapana D, Marsh K. Malaria: biology and disease. Cell (2016) 167:610-624
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1016/j.cell.2016.07.055
#疟原虫 #生活周期 #按蚊 #传播阻断
猫粪里的弓形虫真的会影响人的性格吗?它是怎么进入人体的?
Does Toxoplasma from cat feces really influence human personality, and how does it get into our bodies?
刚地弓形虫的有性生殖只在猫科肠道内完成,随猫粪排出的卵囊在土壤中经数天发育才具感染力,人主要通过食用未煮熟的含包囊肉类或误食污染的蔬菜感染。多数健康人只有轻微流感样症状或无症状,但免疫低下者和孕妇风险显著。一些研究报道慢性感染者风险偏好等行为指标存在统计学差异,机制仍在争论中。
Toxoplasma gondii completes sexual reproduction only in feline intestines; oocysts shed in cat feces need days in soil to become infectious, while humans are infected mainly by eating undercooked meat containing tissue cysts or contaminated vegetables. Healthy people usually show mild flu-like symptoms or none at all, but immunocompromised patients and pregnant women face serious risk. Some studies report statistical differences in risk-related behavior among chronically infected people, though mechanisms remain debated.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Dubey J.P.,《Toxoplasmosis of Animals and Humans》,CRC Press;Flegr J.,刊于《Schizophrenia Bulletin》2007 年的综述 Effects of Toxoplasma on human behavior
J. P. Dubey, Toxoplasmosis of Animals and Humans, CRC Press; Flegr J., 'Effects of Toxoplasma on human behavior', Schizophrenia Bulletin, 2007
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL16940268W：Toxoplasmosis of anima
#弓形虫生活史 #机会性感染
恶性疟原虫靠什么机制在人红细胞内长期躲避抗体的清除?
What mechanism lets Plasmodium falciparum evade antibody clearance inside human red blood cells for months?
它的基因组带有约60个var基因,各自编码受染红细胞表面的黏附蛋白PfEMP1,但同一时刻只表达其中一个。虫体以表观遗传方式定期切换活跃的var基因,使红细胞的抗原面貌持续翻新。抗体对新表型必须重新应答,病原体便借此维持长期感染并推高重症风险。
Its genome carries about sixty var genes, each encoding the red-cell surface adhesion protein PfEMP1, yet only one is active at a time. The parasite switches which var gene is expressed in an epigenetic, periodic manner, constantly renewing the antigenic appearance of infected cells. Antibodies must respond anew to every phenotype, so the pathogen sustains chronic infection and raises the risk of severe disease.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
《Annual Review of Microbiology》2007年第61卷综述《Antigenic Variation in Plasmodium falciparum》(doi:10.1146/annurev.micro.61.080706.093134)
'Antigenic Variation in Plasmodium falciparum', Annual Review of Microbiology 61 (2007), doi:10.1146/annurev.micro.61.080706.093134
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1146/annurev.micro.61.080706.093134：Antig
#寄生虫学 #抗原变异