Search

ABSTRACT Spo0A is a master regulator that governs the metabolic shift of solventogenic Clostridium species such as Clostridium beijerinckii. Its disruption can thus potentially cause a significant alteration of cellular physiology as well as metabolic patterns. To investigate the specific effect of spo0A disruption in C. beijerinckii, a spo0A mutant of C. beijerinckii was characterized in this study. In a batch fermentation with pH control at 6.5, the spo0A mutant accumulated butyrate and butanol up to 8.96 g/L and 3.32 g/L, respectively from 60 g/L glucose. Noticing the unique phenotype of the spo0A mutant accumulating both butyrate and butanol at significant concentrations, we decided to use the spo0A mutant for the production of butyl butyrate that can be formed by the condensation of butyrate and butanol during the ABE fermentation in the presence of the enzyme lipase. Butyl butyrate is a value-added chemical that has numerous uses in the food and fragrance industry. Moreover, butyl butyrate as a biofuel is compatible with Jet A-1 aviation kerosene and used for biodiesel enrichment. In an initial trial of small-scale extractive batch fermentation using hexadecane as the extractant with supplementation of lipase CalB, the spo0A mutant was subjected to acid crash due to the butyrate accumulation, and thus produced only 98 mg/L butyl butyrate. To alleviate the butyrate toxicity, the biphasic medium was supplemented with 10 g/L CaCO3 and 5 g/L butanol. The butyl butyrate production was then increased up to 2.73 g/L in the hexadecane layer. When continuous agitation was performed to enhance the esterification and extraction of butyl butyrate, 3.32 g/L butyl butyrate was obtained in the hexadecane layer. In this study, we successfully demonstrated the use of the C. beijerinckii spo0A mutant for the butyl butyrate production through the simultaneous ABE fermentation, condensation, and extraction. Biotechnol. Bioeng. 2017;114: 106-112. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT CRISPR-Cas9 has been explored as a powerful tool for genome engineering for many organisms. Meanwhile, dCas9 which lacks endonuclease activity but can still bind to target loci has been engineered for efficient gene transcription repression. Clostridium beijerinckii, an industrially significant species capable of biosolvent production, is generally difficult to metabolically engineer. Recently, we reported our work in developing customized CRISPR-Cas9 system for genome engineering in C. beijerinckii. However, in many cases, gene expression repression (rather than actual DNA mutation) is more desirable for various biotechnological applications. Here, we further demonstrated gene transcription repression in C. beijerinckii using CRISPR-dCas9. A small RNA promoter was employed to drive the expression of the single chimeric guide RNA targeting on the promoter region of amylase gene, while a constitutive thiolase promoter was used to drive Streptococcus pyogenes dCas9 expression. The growth assay on starch agar plates showed qualitatively significant repression of amylase activity in C. beijerinckii transformant with CRISPR-dCas9 compared to the control strain. Further amylase activity quantification demonstrated consistent repression (65-97% through the fermentation process) on the activity in the transformant with CRISPR-dCas9 versus in the control. Our results provided essential references for engineering CRISPR-dCas9 as an effective tool for tunable gene transcription repression in diverse microorganisms. Biotechnol. Bioeng. 2016;113: 2739-2743. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]