Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
Meakins-Christie Laboratories and Translational Research in Respiratory Diseases Program, Research Institute of the McGill University Health Centre, Montréal, Québec, Canada.
J Bacteriol. 2019 May 22;201(12). doi: 10.1128/JB.00794-18. Print 2019 Jun 15.
frequently resides among ethanol-producing microbes, making its response to the microbially produced concentrations of ethanol relevant to understanding its biology. Our transcriptome analysis found that genes involved in trehalose metabolism were induced by low concentrations of ethanol, and biochemical assays showed that levels of intracellular trehalose increased significantly upon growth with ethanol. The increase in trehalose was dependent on the TreYZ pathway but not other trehalose-metabolic enzymes (TreS or TreA). The sigma factor AlgU (AlgT), a homolog of RpoE in other species, was required for increased expression of the gene and trehalose levels, but induction was not controlled by the well-characterized proteolysis of its anti-sigma factor, MucA. Growth with ethanol led to increased SpoT-dependent (p)ppGpp accumulation, which stimulates AlgU-dependent transcription of and other AlgU-regulated genes through DksA, a (p)ppGpp and RNA polymerase binding protein. Ethanol stimulation of trehalose also required acylhomoserine lactone (AHL)-mediated quorum sensing (QS), as induction was not observed in a Δ Δ strain. A network analysis using a model, eADAGE, built from publicly available transcriptome data sets (J. Tan, G. Doing, K. A. Lewis, C. E. Price, et al., Cell Syst 5:63-71, 2017, https://doi.org/10.1016/j.cels.2017.06.003) provided strong support for our model in which and coregulated genes are controlled by both AlgU- and AHL-mediated QS. Consistent with (p)ppGpp- and AHL-mediated quorum-sensing regulation, ethanol, even when added at the time of culture inoculation, stimulated transcript levels and trehalose production in cells from post-exponential-phase cultures but not in cells from exponential-phase cultures. These data highlight the integration of growth and cell density cues in the transcriptional response to ethanol. is often found with bacteria and fungi that produce fermentation products, including ethanol. At concentrations similar to those produced by environmental microbes, we found that ethanol stimulated expression of trehalose-biosynthetic genes and cellular levels of trehalose, a disaccharide that protects against environmental stresses. The induction of trehalose by ethanol required the alternative sigma factor AlgU through DksA- and SpoT-dependent (p)ppGpp. Trehalose accumulation also required AHL quorum sensing and occurred only in post-exponential-phase cultures. This work highlights how cells integrate cell density and growth cues in their responses to products made by other microbes and reveals a new role for (p)ppGpp in the regulation of AlgU activity.
常与产乙醇微生物共存，其对微生物产生的乙醇浓度的反应与理解其生物学特性相关。我们的转录组分析发现，参与海藻糖代谢的基因受到低浓度乙醇的诱导，生化分析表明，在乙醇生长过程中，细胞内海藻糖水平显著增加。海藻糖的增加依赖于 TreYZ 途径，但不依赖于其他海藻糖代谢酶（TreS 或 TreA）。sigma 因子 AlgU（AlgT）是其他物种中 RpoE 的同源物，是基因和海藻糖水平表达增加所必需的，但诱导不受其抗 sigma 因子 MucA 广泛特征性蛋白水解的控制。用乙醇培养会导致 SpoT 依赖性（p）ppGpp 积累增加，这通过 DksA 刺激 AlgU 依赖性转录和其他 AlgU 调节基因的转录，DksA 是（p）ppGpp 和 RNA 聚合酶结合蛋白。乙醇对海藻糖的刺激也需要酰基高丝氨酸内酯（AHL）介导的群体感应（QS），因为在 Δ Δ 菌株中没有观察到诱导。使用从公开可用的转录组数据集（J. Tan、G. Doing、K. A. Lewis、C. E. Price 等人，Cell Syst 5:63-71, 2017, https://doi.org/10.1016/j.cels.2017.06.003）构建的模型 eADAGE 进行的网络分析为我们的模型提供了强有力的支持，该模型表明，AlgU 和 AHL 介导的 QS 共同控制和其他核心调节基因。与（p）ppGpp 和 AHL 介导的群体感应调节一致，即使在培养接种时添加乙醇，也会刺激指数生长期培养物细胞中的转录水平和海藻糖的产生，但不会刺激指数生长期培养物细胞中的转录水平和海藻糖的产生。这些数据突出了在对乙醇的转录反应中，生长和细胞密度线索的整合。在与产生发酵产物（包括乙醇）的细菌和真菌一起发现。在与环境微生物产生的浓度相似的浓度下，我们发现乙醇刺激海藻糖生物合成基因的表达和细胞内海藻糖水平升高，海藻糖是一种防止环境应激的二糖。乙醇诱导海藻糖需要通过 DksA 和 SpoT 依赖性（p）ppGpp 依赖的替代 sigma 因子 AlgU。海藻糖的积累还需要 AHL 群体感应，并且仅在指数生长期后发生。这项工作强调了细胞如何在对其他微生物产生的产物的反应中整合细胞密度和生长线索，并揭示了（p）ppGpp 在调节 AlgU 活性中的新作用。
