Ositadinma Ona

Transcriptional Analysis of the Azospirillum brasilense Indole-3-Pyruvate Decarboxylase Gene and Identification of a cis-Acting Sequence Involved in Auxin Responsive Expression

Expression of the Azospirillum brasilense ipdC gene, encoding an indole-3-pyruvate decarboxylase, a key enzyme in the production of indole-3-acetic acid (IAA) in this bacterium, is upregulated by IAA. Here, we demonstrate that the ipdC gene is the promoter proximal gene in a bicistronic operon. Database searches revealed that the second gene of this operon, named iaaC, is well conserved evolutionarily and that the encoded protein is homologous to the Escherichia coli protein SCRP-27A, the zebrafish protein ES1, and the human protein KNP-I/GT335 (HES1), all of unknown function and belonging to the DJ-1/PfpI superfamily. In addition to this operon structure, iaaC is also transcribed monocistronically. Mutation analysis of the latter gene indicated that the encoded protein is involved in controlling IAA biosynthesis but not ipdC expression. Besides being upregulated by IAA, expression of the ipdC-iaaC operon is pH dependent and maximal at acidic pH. The ipdC promoter was studied using a combination of deletion analyses and site-directed mutagenesis. A dyadic sequence (ATTGTTTC(GAAT)GAAACAAT), centered at -48 was demonstrated to be responsible for the IAA inducibility. This bacterial auxin-responsive element does not control the pH-dependent expression of ipdC-iaaC.

Optimal fed batch experiment design for estimation of monod kinetics of Azospirillum brasilense: from theory to practice.

In this paper the problem of reliable and accurate parameter estimation for unstructured models is considered. It is illustrated how a theoretically optimal design can be successfully translated into a practically feasible, robust, and informative experiment. The well‐known parameter estimation problem of Monod kinetic parameters is used as a vehicle to illustrate our approach. As known for a long time, noisy batch measurements do not allow for unique and accurate estimation of the kinetic parameters of the Monod model. Techniques of optimal experiment design are, therefore, exploited to design informative experiments and to improve the parameter estimation accuracy. During the design process, practical feasibility has to be kept in mind. The designed experiments are easy to implement in practice and do not require additional monitoring equipment. Both design and experimental validation of informative fed batch experiments are illustrated with a case study, namely, the growth of the nitrogen‐fixing bacteria Azospirillum brasilense.

A Prototype Model for Indole-3-Acetic Acid (IAA) Production by Azospirillum brasilense SP245

Abstract Given the vital role of nitrogen for plant growth on the one hand, versus the severe impact on the environment of extensive use of inorganic nitrogen fertilizers on the other hand, the need for alternative fertilization becomes apparent. In this respect, the nitrogen fixing bacteria of the genus Azospirillum offer interesting perspectives since inoculation of the plant roots with these bacteria positively affects plant growth. Studies have shown that the growth promoting power of the bacteria can probably be attributed more to the production of the auxin indole-3-acetic acid (IAA) than to the nitrogen fixation qualities of the genus. The aim of this study is therefore to characterize and quantify the IAA production of Azospirillum brasilense Sp245 on a macroscopic level as to exploit the resulting model in optimal experiment design studies. The data obtained from these optimal experiments should be rich enough to aid in further unravelling the studied IAA production mechanism.

OPTIMAL EXPERIMENT DESIGN IN BIOPROCESS MODELING: FROM THEORY TO PRACTICE

Abstract In this paper the problem of parameter identification for the Monod model is considered. As known for a long time, noisy batch measurements do not allow unique and accurate estimation of the kinetic parameters of the Monod model. Techniques of optimal experiment design are, therefore, addressed to design informative experiments and improve the parameter estimation accuracy. During the design process, practical feasibility has to be kept in mind. In this paper it is demonstrated how a theoretical optimal design can successfully be translated to a feasible optimal design. Both design and validation of informative fed batch experiments are illustrated with a case study that models the growth of the nitrogen fixing bacteria Azospirillum brasilense.