Greer-Phillips Suzanne E, Stephens Bonnie B, Alexandre Gladys
Department of Microbiology and Molecular Genetics, School of Medicine, Loma Linda University, California, USA.
J Bacteriol. 2004 Oct;186(19):6595-604. doi: 10.1128/JB.186.19.6595-6604.2004.
Motility responses triggered by changes in the electron transport system are collectively known as energy taxis. In Azospirillum brasilense, energy taxis was shown to be the principal form of locomotor control. In the present study, we have identified a novel chemoreceptor-like protein, named Tlp1, which serves as an energy taxis transducer. The Tlp1 protein is predicted to have an N-terminal periplasmic region and a cytoplasmic C-terminal signaling module homologous to those of other chemoreceptors. The predicted periplasmic region of Tlp1 comprises a conserved domain that is found in two types of microbial sensory receptors: chemotaxis transducers and histidine kinases. However, the function of this domain is currently unknown. We characterized the behavior of a tlp1 mutant by a series of spatial and temporal gradient assays. The tlp1 mutant is deficient in (i) chemotaxis to several rapidly oxidizable substrates, (ii) taxis to terminal electron acceptors (oxygen and nitrate), and (iii) redox taxis. Taken together, the data strongly suggest that Tlp1 mediates energy taxis in A. brasilense. Using qualitative and quantitative assays, we have also demonstrated that the tlp1 mutant is impaired in colonization of plant roots. This finding supports the hypothesis that energy taxis and therefore bacterial metabolism might be key factors in determining host specificity in Azospirillum-grass associations.
由电子传递系统变化引发的运动反应统称为能量趋化性。在巴西固氮螺菌中，能量趋化性被证明是运动控制的主要形式。在本研究中，我们鉴定出一种新型的类化学感受器蛋白，命名为Tlp1，它作为能量趋化性的转导器。预测Tlp1蛋白具有一个N端周质区域和一个与其他化学感受器同源的胞质C端信号模块。预测的Tlp1周质区域包含一个保守结构域，该结构域存在于两种类型的微生物感官受体中：趋化性转导器和组氨酸激酶。然而，该结构域的功能目前尚不清楚。我们通过一系列空间和时间梯度试验对tlp1突变体的行为进行了表征。tlp1突变体在以下方面存在缺陷：（i）对几种可快速氧化底物的趋化性，（ii）对末端电子受体（氧气和硝酸盐）的趋化性，以及（iii）氧化还原趋化性。综合来看，这些数据强烈表明Tlp1介导了巴西固氮螺菌中的能量趋化性。通过定性和定量试验，我们还证明了tlp1突变体在植物根定殖方面存在缺陷。这一发现支持了以下假设：能量趋化性以及细菌代谢可能是决定固氮螺菌与草类共生关系中宿主特异性的关键因素。
