Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan.
Instrumental Research Support Office, Research Institute of Green Science and Technology, Shizuoka University, Shizuoka, Japan.
J Bacteriol. 2021 May 20;203(12):e0065520. doi: 10.1128/JB.00655-20. Epub 2021 Apr 5.
Haloferax volcanii is a facultative anaerobic haloarchaeon that can grow using nitrate or dimethyl sulfoxide (DMSO) as a respiratory substrate under anaerobic conditions. Comparative transcriptome analysis of denitrifying and aerobic cells of H. volcanii indicated extensive changes in gene expression involving the activation of denitrification, suppression of DMSO respiration, and conversion of the heme biosynthetic pathway under denitrifying conditions. The anaerobic growth of H. volcanii by DMSO respiration was inhibited at nitrate concentrations of <1 mM, whereas nitrate-responsive growth inhibition was not observed in the Δ mutant. A reporter assay demonstrated that the transcription of the operon was suppressed by nitrate. In contrast, the anaerobic growth of the Δ mutant by denitrification was little affected by the addition of DMSO. NarO has been identified as an activator of denitrification-related genes in response to anaerobic conditions, and here, we found that NarO is also involved in nitrate-responsive suppression of the operon. Nitrate-responsive suppression of DMSO respiration is known in several bacteria such as Escherichia coli and photosynthetic species. This is the first report to show that a regulatory mechanism that suppresses DMSO respiration in response to nitrate exists not only in bacteria but also in haloarchaea. Haloferax volcanii can grow anaerobically by denitrification (nitrate respiration) or DMSO respiration. In facultative anaerobic bacteria that can grow by both nitrate respiration and DMSO respiration, nitrate respiration is preferentially induced when both nitrate and DMSO are available as the respiratory substrates. The results of transcriptome analysis, growth phenotyping, and reporter assays indicated that DMSO respiration is suppressed in response to nitrate in H. volcanii. The haloarchaeon-specific regulator NarO, which activates denitrification under anaerobic conditions, is suggested to be involved in the nitrate-responsive suppression of DMSO respiration.
火球菌是一种兼性厌氧的嗜盐古菌，在无氧条件下可以利用硝酸盐或二甲基亚砜（DMSO）作为呼吸底物进行生长。对 H. volcanii 的反硝化和需氧细胞的比较转录组分析表明，基因表达发生了广泛变化，涉及反硝化的激活、DMSO 呼吸的抑制以及反硝化条件下血红素生物合成途径的转换。在硝酸盐浓度<1 mM 的情况下，火球菌通过 DMSO 呼吸进行的无氧生长受到抑制，而在Δ突变体中没有观察到硝酸盐响应的生长抑制。报告基因测定表明， 操纵子的转录受到硝酸盐的抑制。相比之下，Δ突变体通过反硝化进行的无氧生长受 DMSO 添加的影响较小。NarO 已被鉴定为响应无氧条件下与反硝化相关的基因的激活因子，在这里，我们发现 NarO 还参与硝酸盐响应抑制 操纵子。在几种细菌中，如大肠杆菌和光合 物种，已经知道硝酸盐响应抑制 DMSO 呼吸的现象。这是第一个表明不仅在细菌中，而且在嗜盐古菌中也存在响应硝酸盐抑制 DMSO 呼吸的调节机制的报告。火球菌可以通过反硝化（硝酸盐呼吸）或 DMSO 呼吸进行无氧生长。在可以通过硝酸盐呼吸和 DMSO 呼吸进行生长的兼性厌氧细菌中，当硝酸盐和 DMSO 都可作为呼吸底物时，硝酸盐呼吸优先被诱导。转录组分析、生长表型和报告基因测定的结果表明，在 H. volcanii 中，DMSO 呼吸受到硝酸盐的抑制。在无氧条件下激活反硝化的 haloarchaeon 特异性调节剂 NarO 被认为参与了硝酸盐响应抑制 DMSO 呼吸的过程。
