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Ainala, S.K.,Seol, E.,Park, S. Elsevier Science Publishers 2015 Journal of biotechnology Vol.211 No.-
We report here the complete genome sequence of Citrobacter amalonaticus Y19 isolated from an anaerobic digester. PacBio single-molecule real-time (SMRT) sequencing was employed, resulting in a single scaffold of 5.58Mb. The sequence of a mega plasmid of 291Kb size is also presented.
Ainala, S.K.,Seol, E.,Sekar, B.S.,Park, S. Pergamon Press ; Elsevier Science Ltd 2014 International journal of hydrogen energy Vol.39 No.20
Citrobacter amalonaticus Y19 (Y19) can produce hydrogen (H<SUB>2</SUB>) from oxidation of carbon monoxide (CO) via the water-gas shift reaction. The reaction is catalyzed by two enzymes, carbon monoxide dehydrogenase (CODH) and carbon monoxide-dependent hydrogenase (CO-Hyd). The contig genome sequencing of Y19 exhibited the presence of unique CO oxidizing gene clusters encoding CODH (cooFS), CO-Hyd (cooMKLXUH) and a putative CO-responsive transcriptional activator (cooA). To improve CO-dependent H<SUB>2</SUB> production activity, we developed recombinant Y19 by homologously over-expressing cooA. The over-expression of cooA improved the whole-cell CO-dependent H<SUB>2</SUB> production activity (3.4-fold), and enzyme activities of CODH (5.3-fold) and CO-Hyd (1.2-fold). Furthermore, quantitative PCR analysis revealed a significant increase in the transcription of the genes located in CODH and CO-Hyd operons of recombinant Y19. The high CO-dependent H<SUB>2</SUB> production activity of the recombinant C. amalonaticus was stably maintained during repeated exposure to CO.
Ainala, S.K.,Seol, E.,Kim, J.R.,Park, S. Pergamon Press ; Elsevier Science Ltd 2016 International journal of hydrogen energy Vol.41 No.16
<P>Citrobacter amalonaticus Y19 is a unique chemoheterotrophic microorganism capable of carbon monoxide (CO)-dependent hydrogen (H-2) production. To improve its biocatalytic potential, the effects of medium composition on cell growth and H-2 production were investigated. Among several carbon sources tested, maltose resulted in the best CO consumption and H-2 production. Meanwhile, L-cysteine supplementation improved cell growth and H-2 production, suggesting that this amino acid stimulates synthesis of Fe-S clusters. When molybdenum and selenium, which are essential cofactors of formate hydrogen lyase (FHL), were added, formate accumulation was reduced. Optimized medium composition improved the activities of CO-dependent H-2 production (6.3-fold), CODH (22.3-fold) and hydrogenase (2.9-fold). The optimized medium composition also enhanced H-2 production in recombinant C. amalonaticus Y19-cooA, which homologously over expresses CooA, the transcriptional activator of the coo operons. Cells grown under this condition exhibited improved stability in the course of repeated-batch CO-dependent H-2 production under non-growing conditions. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.</P>
Glycerol assimilation and production of 1,3-propanediol by Citrobacter amalonaticus Y19
Ainala, Satish Kumar,Ashok, Somasundar,Ko, Yeounjoo,Park, Sunghoon Springer-Verlag 2013 Applied microbiology and biotechnology Vol.97 No.11
<P>Citrobacter amalonaticus Y19 (Y19) was isolated because of its ability for carbon monoxide-dependent hydrogen production (water-gas shift reaction). This paper reports the assimilation of glycerol and the production of 1,3-propanediol (1,3-PDO) by Y19. Genome sequencing revealed that Y19 contained the genes for the utilization of glycerol and 1,2-propanediol (pdu operon) along with those for the synthesis of coenzyme B12 (cob operon). On the other hand, it did not possess the genes for the fermentative metabolism of glycerol of Klebsiella pneumoniae, which consists of both the oxidative (dhaD and dhaK) and reductive (dhaB and dhaT) pathways. In shake-flask cultivation under aerobic conditions, Y19 could grow well with glycerol as the sole carbon source and produced 1,3-PDO. The level of 1,3-PDO production was improved when vitamin B12 was added to the culture medium under aerobic conditions. Under anaerobic conditions, cell growth and 1,3-PDO production on glycerol was also possible, but only when an exogenous electron acceptor, such as nitrate or fumarate, was added. This is the first report of the glycerol metabolism and 1,3-PDO production by C. amalonaticus Y19.</P>
Seol, E.,Ainala, S.K.,Sekar, B.S.,Park, S. Pergamon Press 2014 International journal of hydrogen energy Vol.39 No.33
The co-production of H<SUB>2</SUB> and ethanol from glucose was studied to address the low H<SUB>2</SUB> production yield in dark fermentation. Several mutant strains devoid of ackA-pta, pfkA or pgi were developed using Escherichia coli BW25113 ΔhycA ΔhyaAB ΔhybBC ΔldhA ΔfrdAB as base strain. Disruption of ackA-pta eliminated acetate production during glucose fermentation but resulted in the secretion of a significant amount of pyruvate (0.73 mol mol<SUP>-1</SUP> glucose) without improving the co-production of H<SUB>2</SUB> and ethanol. When pfkA or pgi was further disrupted to enhance NAD(P)H supply by diverting the carbon flux from Embden-Meyerhof-Parnas (EMP) pathway to the pentose phosphate pathway (PPP), the cell growth of both strains was severely impaired under anaerobic conditions, and only the ΔpfkA mutant could recover its growth after adaptive evolution. The production yields of the ΔpfkA strain (H<SUB>2,</SUB> 1.03 mol mol<SUP>-1</SUP> glucose and ethanol, 1.04 mol mol<SUP>-1</SUP> glucose) were higher than those of the pfkA<SUP>+</SUP> strain (H<SUB>2</SUB>, 0.69 mol mol<SUP>-1</SUP> glucose and ethanol, 0.95 mol mol<SUP>-1</SUP> glucose), but pyruvate excretion was not reduced. The excessive excretion of pyruvate in the ΔpfkA mutant was attributed to an insufficient NAD(P)H supply caused by the diversion of carbon flux from the EMP pathway to the Entner-Doudoroff pathway (EDP), rather than the PPP as intended. This study suggests that co-production of H<SUB>2</SUB> and ethanol from glucose is possible, but further metabolic pathway engineering is required to fully activate PPP under anaerobic conditions.