APPLIED MICROBIAL AND CELL PHYSIOLOGY Sequence and transcriptional analysis of the genes responsible for curdlan biosynthesis in Agrobacterium sp. ATCC 31749 under simulated dissolved oxygen gradients conditions Hong-Tao Zhang & Xiao-Bei Zhan & Zhi-Yong Zheng & Jian-Rong Wu & Xiao-Bin Yu & Yun Jiang & Chi-Chung Lin Received: 22 January 2011 /Revised: 6 March 2011 /Accepted: 6 March 2011 /Published online: 7 April 2011 # Springer-Verlag 2011 Abstract Expression at the mRNA level of ten selected genes in Agrobacterium sp. ATCC 31749 under various dissolved oxygen (DO) levels during curdlan fermentation related to electron transfer chain (ETC), tricarboxylic acid (TCA) cycle, peptidoglycan/lipopolysaccharide biosynthe- sis, and uridine diphosphate (UDP)-glucose biosynthesis were determined by qRT-PCR. Experiments were per- formed at DO levels of 30%, 50%, and 75%, as well as under low-oxygen conditions. The effect of high cell density on transcriptional response of the above genes under low oxygen was also studied. Besides cytochrome d (cyd A), the transcription levels of all the other genes were increased at higher DO and reached maximum at 50% DO. Under 75% DO, the transcriptional levels of all the genes were repressed. In addition, transcription levels of icd, sdh, cyo A, and fix N genes did not exhibit significant fluctuation with high cell density culture under low oxygen. These results suggested a mechanism for DO regulation of curdlan synthesis through regulation of transcriptional levels of ETCs, TCA, and UDP-glucose synthesis genes during curdlan fermentation. To our knowledge, this is the first report that DO concentration apparently regulates curdlan biosynthesis in Agrobacterium sp. ATCC 31749 providing essential lead for the optimization of the fermentation at the industrial scale. Keywords Agrobacterium sp. . Curdlan productivity . Dissolve oxygen . TCA cycle . Aerobic and anaerobic metabolism . Transcriptomics Introduction Dissolved oxygen (DO) concentration is an important environmental factor in the growth, metabolism, and target product synthesis in a microbial fermentation process (Trujillo-Roldan et al. 2004; Duan et al. 2009). Conse- quently, accurate estimation of the effect of DO on gene translation and metabolic activity of cell at the scale-down level will help us in predicting the metabolic flux for both growth and production of any target metabolite in the fermentation production process. It is an essential parameter for the improvement and scale-up of the microbial fermentation process. Agrobacterium sp. ATCC 31749 (formerly known as Alcaligenes faecalis var. myxogenes) is a non-pathogenic aerobic soil bacterium widely used for the industrial production of curdlan, a water-insoluble polysaccharide (Phillips et al. 1983). We have previously evaluated the effect of metabolic structures and energy requirements of Agrobacterium sp. ATCC 31749 on curdlan production and shown that energy efficiency as the major constrain for the improvement of curdlan production (Zheng et al. 2007). Similar to the production of many other bacterial exopoly- Electronic supplementary material The online version of this article (doi:10.1007/s00253-011-3243-1) contains supplementary material, which is available to authorized users. H.-T. Zhang : X.-B. Zhan (*) : Z.-Y. Zheng : J.-R. Wu : X.-B. Yu : Y. Jiang : C.-C. Lin Key Laboratory of Industrial Biotechnology of Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China e-mail: xbzhan@yahoo.com Appl Microbiol Biotechnol (2011) 91:163–175 DOI 10.1007/s00253-011-3243-1