微生物生物被膜的形成在病原微生物持續(xù)性感染中起著非常重要的作用，也是微生物在自然界的普遍存在方式之一,。微生物生物被膜依賴于胞外多聚物質(zhì)（EPS）維持其群體結(jié)構(gòu),。多糖是生物被膜胞外多聚物質(zhì)的重要組分之一,，研究生物被膜胞外多糖有助于理解生物被膜的形成機(jī)制，從而有針對(duì)性地開發(fā)治療手段,，解決生物被膜相關(guān)的問題,。
中國科學(xué)院微生物研究所微生物資源前期開發(fā)國家重點(diǎn)實(shí)驗(yàn)室馬旅雁課題組以條件致病菌銅綠假單胞菌為模式菌來研究生物被膜。銅綠假單胞菌極易形成生物被膜的原因之一是它可以產(chǎn)生多種胞外多糖,，包括脂多糖（LPS）,，名為Psl、Pel和Alginate的多糖,，它們都與生物被膜的形成相關(guān),。Alginate的化學(xué)組份與褐藻中分離的多糖相似，被譯為褐藻多糖,。銅綠假單胞菌一旦在囊性纖維化（cystic fibrosis,， CF）病人肺部定植后，常會(huì)突變成為黏液型菌株（Mucoid）,，即大量產(chǎn)生alginate多糖的菌,。Alginate的大量合成一直以來被認(rèn)為是銅綠假單胞菌難以從CF患者清除的原因之一。
近期，馬旅雁課題組的研究表明,，在非黏液型菌的生物被膜形成中起關(guān)鍵作用的Psl多糖也是黏液型銅綠假單胞菌形成生物被膜的關(guān)鍵多糖(FEMS Immunol. Med. Microbiol. DOI：10.1111/j.1574 -695X.2012. 00934.x),。這為治療CF患者的銅綠假單胞菌感染提供了靶標(biāo)。
此外,，該課題組近期的研究還揭示了銅綠假單胞菌調(diào)控上述四種胞外多糖的一種機(jī)制,。研究發(fā)現(xiàn)，同時(shí)具有磷酸甘露糖變位酶和磷酸葡萄糖變位酶活性的雙功能酶AlgC是生物被膜形成相關(guān)的四種多糖LPS,、Psl,、Pel和Alginate的合成所必需的。進(jìn)一步研究發(fā)現(xiàn),，AlgC是這些多糖合成途徑中的關(guān)鍵節(jié)點(diǎn)酶,，它通過控制這幾種多糖前體物質(zhì)的代謝流來控制這些多糖的合成。類似AlgC的酶在許多原核甚至真核生物的糖代謝中均有發(fā)現(xiàn),。該研究所揭示的調(diào)控機(jī)制很可能有普遍性,。研究論文發(fā)表在Environ. Microbiol.( doi:10.1111/j.1462-2920.2012.02753.x)上。
相關(guān)工作得到了俄亥俄州立大學(xué),、華盛頓大學(xué)和圭爾夫大學(xué)部分合作者的支持,。(生物谷：Bioon.com)
doi: 10.1111/j.1574-695X.2012.00934.x
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The roles of biofilm matrix polysaccharide Psl in mucoid Pseudomonas aeruginosa biofilms
Ma, Luyan; Wang, Shiwei; Wang, Di; Parsek, Matthew R.; Wozniak, Daniel J.
The opportunistic pathogen Pseudomonas aeruginosa causes life-threatening, persistent infections in patients with cystic fibrosis (CF). Persistence is attributed to the ability of these bacteria to form structured communities (biofilms). Biofilms rely on an extracellular polymeric substances matrix to maintain structure. Psl exopolysaccharide is a key matrix component of nonmucoid biofilms, yet the role of Psl in mucoid biofilms is unknown. In this report, using a variety of mutants in a mucoid P. aeruginosa background, we found that deletion of Psl-encoding genes dramatically decreased their biofilm formation ability, indicating that Psl is also a critical matrix component of mucoid biofilms. Our data also suggest that the overproduction of alginate leads to mucoid biofilms, which occupy more space, whereas Psl-dependent biofilms are densely packed. These data suggest that Psl polysaccharide may have significant contributions in biofilm persistence in patients with CF and may be helpful for designing therapies for P. aeruginosa CF infection.
doi: 10.1111/j.1462-2920.2012.02753.x
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PMID:
Synthesis of multiple Pseudomonas aeruginosa biofilm matrix exopolysaccharides is post-transcriptionally regulated
Luyan Ma, Juan Wang, Shiwei Wang, Erin M. Anderson, Joseph S. Lam, Matthew R. Parsek, Daniel J. Wozniak
Exopolysaccharide is a critical biofilm matrix component, yet little is known about how the synthesis of multiple exopolysaccharides is regulated. Pseudomonas aeruginosa can produce several biofilm matrix exopolysaccharides that include alginate, Psl and Pel. Here we demonstrated that AlgC, a key enzyme that provides sugar precursors for the synthesis of alginate and lipopolysaccharides (LPS) is also required for both Psl and Pel production. We showed that forced-synthesis of Psl in alginate-producing mucoid bacteria reduced alginate production but this was not due to transcription of the alginate biosynthesis-operon. Likewise, when either alginate or Psl were overproduced, levels of B-band LPS decreased. Induction of Pel resulted in a reduction of Psl levels. Because the effects of reduced exopolysaccharide synthesis when another is overproduced didn't appear to be regulated at the transcriptional level, this suggests that the biosynthesis pathways of Psl, Pel, alginate, and LPS compete for common sugar precursors. As AlgC is the only enzyme that provides precursors for each of these exopolysaccharides, we propose that AlgC is a key checkpoint enzyme that coordinates the total amount of exopolysaccharide biosynthesis by controlling sugar precursor pool. Our data also provide a plausible strategy that P. aeruginosa utilizes to modulate its biofilm matrix exopolysaccharides.
