Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation
Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation
复制标题
DOI：
10.1128/aem.02782-15
复制
发表时间：
2015-12-01
影响因子：
4.4
通讯作者：
Alexandre, Gladys
中科院分区：
文献类型：
--
作者：
Bible, Amber N.;Khalsa-Moyers, Gurusahai K.;Alexandre, Gladys
细菌监测其新陈代谢并相应调整其行为的能力对于保持在环境中的竞争力至关重要。能运动的微需氧细菌巴西固氮螺菌通过趋气性引导氧气梯度，以找到可以支持新陈代谢的低氧气浓度。当细胞暴露在周围环境中氧气水平升高时，能动的巴西曲霉细胞会对趋气性产生另一种反应，并通过细胞与细胞之间的相互作用形成短暂的团块。结块被认为代表了一种保护运动细胞免受通气水平短暂升高的影响的行为。利用野生型和突变株的蛋白质组学对其聚集能力的影响程度，我们发现细胞间的聚集代表了一种代谢清除策略，可能使细胞为进一步的代谢应激做好准备。对碳或氮代谢影响的突变体的分析证实了这一假设。随着结块过程的进行，代谢变化促使细胞发生絮凝，这是在通气条件提高和氮限制条件下引发的细胞形态和代谢变化。对结块和絮凝过程中各种突变体的分析表征了伴随代谢变化的细胞包膜特性的一组有序变化。这些数据还表明，尽管通气条件提高，但结块和早期絮凝的行为与固氮基因的表达相一致。因此，细胞间的聚集可能会在高氧条件下允许微需氧的巴西曲霉细胞进行固氮，并在代谢应激持续存在的情况下通过絮凝为它们的长期生存做好准备。
The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacterium Azospirillum brasilense navigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motile A. brasilense cells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Cell-to-cell clumping may thus license diazotrophy to microaerophilic A. brasilense cells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.