Genetic and Biochemical Aspects of Ectoine Biosynthesis in Moderately Halophilic and Halotolerant Methylotrophic Bacteria | Science Publications

American Journal of Agricultural and Biological Sciences

Alexander S. Reshetnikov¹  Valentina N. Khmelenina¹  Marina G. Kalyuzhnaya¹  Yuri A. Trotsenko¹  Ildar I. Mustakhimov¹ 

关键词: Halophilic bacteria;    osmoadaptation;    ectoine;    enzymes;    transcriptional regulation;   

DOI  :  10.3844/ajabssp.2010.446.458

学科分类：农业科学（综合）

来源: Science Publications

【 摘 要 】

Problem statement: The cyclic imino acid ectoine is a widely distributed compatiblesolute synthesizing by halophilic and halotolerant bacteria to prevent osmotic stress at high externalsalinity. This water-keeping compound is used in a variety of commercial cosmetics and therapeuticproducts. Approach: Development of integrated, predictive functional model of the metabolic andregulatory netwoks of ectoine-producing microbes is an active area of research. In this article wepresent a brief overview of the current knowledge on genetic and biochemical aspects of ectoinebiosynthesis in aerobic halophilic and halotolerant bacteria utilizing C₁ compounds (methylotrophs).Although enzymology and genetics of the ectoine biosynthesis in methylotrophs are similar to otherhalophilic bacteria, the regulatory patterns are different. In all methylotrophic bacteria studied, thegenes coding for specific enzymes of ectoine biosynthesis: Diaminobutyric Acid (DABA)aminotransferase (EctB), DABA acetyltransferase (EctA) and ectoine synthase (EctC) are organizedinto ectABC or ectABC-ask, whith is linked to gene encoding Aspartokinase isozyme (Ask).Results: Remarkably, the methylotrophic bacteria possessing a four-gene cluster showed higherhalotolerance and accumulated more ectoine than bacteria with a cluster composed of three genes. TheDABA acetyltransferases from three methylotrophic species have been comparatively characterized.The properties of the enzymes correlate with eco-physiological and metabolic particularities of thehost. Some elements of the regulatory system governing the ectoine pathway operation have beenrevealed in both methane and methanol utilizing bacteria. In Methylomicrobium alcaliphilumtranscription of the ectABC-ask operon is initiated from two σ⁷⁰-like promoters and controlled by theEctR, a MarR-type negative regulator. EctR orthologs were identified in genomes of severalheterotrophic halophilic bacteria. Here we present genomic data indicating that similar regulatorysystem may occur in diverse halophilic and halotolerant bacteria. Conclusion: Currently available datasuggest that in methylotrophic bacteria the ectoine biosynthesis pathways are evolutionary wellconserved, particularly with respect to the genes and enzymes involved. However, some differences inthe ect-gene cluster organization and regulation could be observed.

【 授权许可】

Unknown