Taniguchi Hironori, Busche Tobias, Patschkowski Thomas, Niehaus Karsten, Pátek Miroslav, Kalinowski Jörn, Wendisch Volker F
Genetics of Prokaryotes, Faculty of Biology, Bielefeld University, Bielefeld, Germany.
Center for Biotechnology, Bielefeld University, Bielefeld, Germany.
BMC Microbiol. 2017 Jul 12;17(1):158. doi: 10.1186/s12866-017-1067-6.
Sigma factors are one of the components of RNA polymerase holoenzymes, and an essential factor of transcription initiation in bacteria. Corynebacterium glutamicum possesses seven genes coding for sigma factors, most of which have been studied to some detail; however, the role of SigD in transcriptional regulation in C. glutamicum has been mostly unknown.
In this work, pleiotropic effects of sigD overexpression at the level of phenotype, transcripts, proteins and metabolites were investigated. Overexpression of sigD decreased the growth rate of C. glutamicum cultures, and induced several physiological effects such as reduced culture foaming, turbid supernatant and cell aggregation. Upon overexpression of sigD, the level of Cmt1 (corynomycolyl transferase) in the supernatant was notably enhanced, and carbohydrate-containing compounds were excreted to the supernatant. The real-time PCR analysis revealed that sigD overexpression increased the expression of genes related to corynomycolic acid synthesis (fadD2, pks), genes encoding corynomycolyl transferases (cop1, cmt1, cmt2, cmt3), L, D-transpeptidase (lppS), a subunit of the major cell wall channel (porH), and the envelope lipid regulation factor (elrF). Furthermore, overexpression of sigD resulted in trehalose dicorynomycolate accumulation in the cell envelope.
This study demonstrated that SigD regulates the synthesis of corynomycolate and related compounds, and expanded the knowledge of regulatory functions of sigma factors in C. glutamicum.
σ因子是RNA聚合酶全酶的组成成分之一，是细菌转录起始的必需因子。谷氨酸棒杆菌拥有7个编码σ因子的基因，其中大部分已得到一定程度的详细研究；然而，SigD在谷氨酸棒杆菌转录调控中的作用大多仍不清楚。
在本研究中，从表型、转录本、蛋白质和代谢物水平研究了sigD过表达的多效性。sigD过表达降低了谷氨酸棒杆菌培养物的生长速率，并诱导了多种生理效应，如培养物泡沫减少、上清液浑浊和细胞聚集。sigD过表达后，上清液中Cmt1（分枝菌酸转移酶）的水平显著提高，含碳水化合物的化合物被分泌到上清液中。实时PCR分析表明，sigD过表达增加了与分枝菌酸合成相关基因（fadD2、pks）、编码分枝菌酸转移酶的基因（cop1、cmt1、cmt2、cmt3）、L，D-转肽酶（lppS）、主要细胞壁通道亚基（porH）和包膜脂质调节因子（elrF）的表达。此外，sigD过表达导致海藻糖二分枝菌酸酯在细胞膜中积累。
本研究表明SigD调节分枝菌酸及相关化合物的合成，并扩展了对谷氨酸棒杆菌中σ因子调控功能的认识。
