附子是主要在中国西南地区特定环境中生长的毛茛科( Aconitum carmichaeli Debx.)块根植物,其块根具有良好的药用效果。附子连作障碍严重,随着连作次数增加,土传根系病害加重,产量显著降低。危害附子的常见土传病害为齐整小核菌( Sclerotium rolfsii )引起的附子白绢病和镰刀菌( Fusarium spp.)引起的根腐病。 我们团队研究发现,向附子根系分布区土壤中施入放线菌剂,附子根系土传病害病情指数显著降低 75.5%~77.0% 、经济器官块根产量显著提高 62.1%~74.1% 、根际土壤养分残留减少。该菌剂能显著增加根际土壤中有益菌数量,减少有害菌数量。该菌剂引起的根际土壤微生态效应可产生良好的后效,在两季均施用菌剂的处理中,下茬作物仍较对照病害显著减轻、产量显著增加。该菌剂中的放线菌发酵液可显著抑制附子土传病原菌齐整小核菌及腐皮镰刀菌菌丝生长,对腐皮镰刀菌菌丝有溶解及缢缩作用,且放线菌能在附子根表定殖(附图)。 该研究论文“ Biocontrol of root diseases and growth promotion of the tuberous plant Aconitum carmichaelii induced by actinomycetes are related to shifts in the rhizosphere microbiota ”发表于《 Microbial Ecology 》上( doi:10.1007/s10658-017-1177-x )。 博士研究生李玉龙为第一作者。 论文连接: https://link.springer.com/article/10.1007%2Fs10658-017-1177-x 放线菌对附子根系土传病害防治机理:
Journal club的第一次seminar,我负责四个杂志(Nature Biotechnology,Chemical Science,Molecular BioSystems,ACS Synthetic Biology),这次主要讲的是发表在《自然-生物技术》上的 Identifying producers of antibacterial compounds by screening for antibiotic resistance(通过筛选抗生素抗性鉴定抗生素产生菌)题目摘要全文链接见文后。 通过利用抗生素产生菌的自身保护机理,富集能够产生与该抗生素相关的化合物的细菌库。利用这种以抗性筛选为基础的分离方法,通过糖肽类(万古霉素)和安莎类抗生素(利福平)抗性筛选,发现抗生素产生菌的比率比传统的以活性为导向的筛选(表型筛选)和宏基因组文库筛选的方法增加了3-5个数量级。而且他们还介绍了一种以进化树为基础在筛选过程的初期能够预测或发现新骨架化合物的去重复(dereplication)方法。利用抗性筛选和进化树去重复,他们发现了一种新的万古霉素类化合物。 虽然利用抗生素抗性筛选分离抗生素产生菌在很早前就使用过,但是分离抗生素的目标不明显,比如用一些抗生素分离稀有放线菌,然后在利用 传统的以活性为导向的筛选(表型筛选)发现有活性菌株 ,导致重复筛选,很难发现新型 的活性物质。本文系统的利用抗性选择的方法富集抗生素产生菌,并且结合该已知抗生素的生物合成基因簇设计兼并PCR验证生物合成基因,而且创新性的利用PCR扩增出的产物构建进化树,可以将最后产生的化合物归类,避免重复发现,加快去重复过程。而且,利用这种方法筛选到的产生菌具有合成改该类抗生素的生物合成基因,但是在实验室的普遍培养条件下,该抗生素的产量很低或者没有,因此抗细菌活性就会很低或者没有,这些菌就很有可能在 经典的以活性为导向的筛选(表型筛选)中被忽略掉。 不足之处在于,利用这种方法富集产生菌只能得到一些跟改抗生素结构类似的化合物,很难发现新型新类的抗生素。同时也忽略掉了对改抗生素敏感的细菌,它们也有很大的产生活性化合物的潜力。 以前日本的一个学者Ochi利用选择抗生素抗性的方法,能够提高链霉菌中某些化合物的产量,甚至激活某些沉默基因簇产生新的化合物,他们将这种方法称为‘核糖体工程(Ribosome engineering)’。当年度硕士的时候,我的师姐们也用这种方法发现了一些活性物质,但是离开后一直没见文章发表。最近的关于核糖体工程的综述发表在Hopwood大牛的专刊J Ind Microbiol Biotechnol (2014) 41:403–414上(全文链接 http://link.springer.com/article/10.1007%2Fs10295-013-1349-4 )。 另外还有一个文章也是发表在 《自然-生物技术》上Antibacterial discovery in actinomycetes strains with mutations in RNA polymerase or ribosomal protein S12 Nature Biotechnology 27 , 462 - 464 (2009) Published online: 26 April 2009 | doi:10.1038/nbt.1538。(全文链接 http://www.nature.com/nbt/journal/v27/n5/abs/nbt.1538.html ) Identifying producers of antibacterial compounds by screening for antibiotic resistance Maulik N Thaker , Wenliang Wang , Peter Spanogiannopoulos , Nicholas Waglechner , Andrew M King , Ricardo Medina Gerard D Wright Nature Biotechnology 31,22–927(2013)doi:10.1038/nbt.2685 Received 18 March 2013, Accepted 07 August 2013, Published online 22 September 2013 Abstract Microbially derived natural products are major sources of antibiotics and other medicines, but discovering new antibiotic scaffolds and increasing the chemical diversity of existing ones are formidable challenges. We have designed a screen to exploit the self-protection mechanism of antibiotic producers to enrich microbial libraries for producers of selected antibiotic scaffolds. Using resistance as a discriminating criterion we increased the discovery rate of producers of both glycopeptide and ansamycin antibacterial compounds by several orders of magnitude in comparison with historical hit rates. Applying a phylogeny-based screening filter for biosynthetic genes enabled the binning of producers of distinct scaffolds and resulted in the discovery of a glycopeptide antibacterial compound, pekiskomycin, with an unusual peptide scaffold. This strategy provides a means to readily sample the chemical diversity available in microbes and offers an efficient strategy for rapid discovery of microbial natural products and their associated biosynthetic enzymes. 全文链接:http://www.nature.com/nbt/journal/v31/n10/full/nbt.2685.html
放线菌中的Frankia通常与桤木形成共生固氮的根瘤,不能与豆科植物形成根瘤。Trujillo等人的新近研究表明,放线菌中的另外一类菌小单胞菌属的细菌却能与豆科植物(如狭叶羽扇豆)形成根瘤,并且根瘤有固氮活性,扩增到的nifH基因与Frankia的相似性高达99%。原位杂交也表明,这些小单胞菌属的放线菌确实存在于根瘤内。其形成根瘤的机制还不清楚。另外由于Frankia没有根瘤菌所拥有的结瘤基因(nod),小单胞菌属是否拥有结瘤基因,也还未知。 相关论文如下: ISME J. 2010 May 6. The genus Micromonospora is widespread in legume root nodules: the example of Lupinus angustifolius. Trujillo ME , Alonso-Vega P , Rodrguez R , Carro L , Cerda E , Alonso P , Martnez-Molina E . Departamento de Microbiologa y Gentica, Edificio Departamental Lab. 205, Campus Miguel de Unamuno, Universidad de Salamanca, Salamanca, Spain. Abstract Our current knowledge of plant-microbe interactions indicate that populations inhabiting a host plant are not restricted to a single microbial species but comprise several genera and species. No one knows if communities inside plants interact, and it has been speculated that beneficial effects are the result of their combined activities. During an ecological study of nitrogen-fixing bacterial communities from Lupinus angustifolius collected in Spain, significant numbers of orange-pigmented actinomycete colonies were isolated from surface-sterilized root nodules. The isolates were analysed by BOX-PCR fingerprinting revealing an unexpectedly high genetic variation. Selected strains were chosen for 16S rRNA gene sequencing and phylogenetic analyses confirmed that all strains isolated belonged to the genus Micromonospora and that some of them may represent new species. To determine the possibility that the isolates fixed atmospheric nitrogen, chosen strains were grown in nitrogen-free media, obtaining in some cases, significant growth when compared with the controls. These strains were further screened for the presence of the nifH gene encoding dinitrogenase reductase, a key enzyme in nitrogen fixation. The partial nifH-like gene sequences obtained showed a 99% similarity with the sequence of the nifH gene from Frankia alni ACN14a, an actinobacterium that induces nodulation and fixes nitrogen in symbiosis with Alnus. In addition, in situ hybridization was performed to determine if these microorganisms inhabit the inside of the nodules. This study strongly suggests that Micromonospora populations are natural inhabitants of nitrogen-fixing root nodules.The ISME Journal advance online publication, 6 May 2010; doi:10.1038/ismej.2010.55. PMID: 20445637