Hese facts, it is clear that XoxF functions in the regulation of methanol metabolism, but its catalytic function as an MDH has not been clear. In our previous work, we showed that lanthanum (La), cerium (Ce), and praseodymium (Pr), all of which are belong to the rare earth elements (REE), increased MDH activity in cell extracts of M. radiotolerans and the non-methylotrophic bacteria Bradyrhizobium sp. [23,24]. Moreover, the MDHs purified from the cells grown in media containing these metal ions corresponded to XoxF1, while the MDH purified from Ca2+-grown cells corresponded to MxaFIXoxF1 Is La3+-Dependent MDH[23,24]. These results indicate that the MDHs dependent on La3+, Ce3+ or Pr3+ are products of xoxF and that these ions may have important physiological roles in C1 metabolism. The REEs are a group of 17 elements, specifically, 15 lantanoids plus Sc and Y, and are widely dispersed among many primary and Acid Yellow 23 web secondary minerals, such as phosphates, carbonates, fluorides, and silicates, especially pegmatites, granites, and related metamorphic and igneous rocks [25]. They are regarded as “the vitamins of modern industry”, since many of them are utilized in a wide range of industrial products such as glass, catalysts, alloys, ceramics, and magnets. As for their effects on life forms, the REEs have not been characterized as either essential or strongly toxic elements in the environment [26], although some have negative effects as inhibitors of several enzymes and proteins [27?0], and some exert positive effects as growth promoters for various crops [27]. In this study, using M. extorquens strain AM1 as a model organism to investigate REEs-dependent methylotrophy, we set out (i) to see whether La3+ is involved in methylotrophic growth of the strain, (ii) to assess whether the strain has REE-dependent MDH activity, (iii) to identify the gene encoding REE-dependent MDH, and (iv) to validate the role of XoxF1 and La3+ in methanol metabolism. Our results suggest that XoxF1 is a La3+-dependent functional MDH that may participate in methanol metabolism.Results M. extorquens strain AM1 has a methanol-oxidation system independent of Ca2+Although MDH activity in Methylobacterium species has been shown to depend on Ca2+ [14], the growth of these strains on methanol without Ca2+ has never been examined. In our previous work, we showed that some REEs increased MDH activity in M. radiotolerans and the non-methylotrophic Bradyrhizobium sp. [23,24]. These facts suggest that REEs may have some roles as activators or Methionine enkephalin inducers of MDH. Thus, we examined whether M. extorquens strain AM1 could grow on methanol in the presence of La3+ instead of Ca2+. As shown in Fig. 1, strain AM1 could grow normally in methanol/Ca2+ medium. In methanol medium without Ca2+ and La3+, the strain showed very slow growth, because the medium contained a small amount of Ca2+ (0.867 mM). In methanol media containing La3+ and not Ca2+, the strain grew as well as it did in methanol/Ca2+ medium, and the addition of La3+ to methanol/ Ca2+ medium had no effect on the growth of strain AM1 (Fig. 1). On the other hand, strain AM1 did not show any growth defect in succinate media even without Ca2+ and La3+. Ca3+ and La3+ have an important role in methanol metabolism but not in succinate metabolism, and strain AM1 has a novel methanol-metabolic pathway that depends on La3+ and not Ca2+.XoxF1 is a functional 26001275 La3+-dependent MDHThe growth defect of strain AM1 in the methanol medium without Ca2+ was.Hese facts, it is clear that XoxF functions in the regulation of methanol metabolism, but its catalytic function as an MDH has not been clear. In our previous work, we showed that lanthanum (La), cerium (Ce), and praseodymium (Pr), all of which are belong to the rare earth elements (REE), increased MDH activity in cell extracts of M. radiotolerans and the non-methylotrophic bacteria Bradyrhizobium sp. [23,24]. Moreover, the MDHs purified from the cells grown in media containing these metal ions corresponded to XoxF1, while the MDH purified from Ca2+-grown cells corresponded to MxaFIXoxF1 Is La3+-Dependent MDH[23,24]. These results indicate that the MDHs dependent on La3+, Ce3+ or Pr3+ are products of xoxF and that these ions may have important physiological roles in C1 metabolism. The REEs are a group of 17 elements, specifically, 15 lantanoids plus Sc and Y, and are widely dispersed among many primary and secondary minerals, such as phosphates, carbonates, fluorides, and silicates, especially pegmatites, granites, and related metamorphic and igneous rocks [25]. They are regarded as “the vitamins of modern industry”, since many of them are utilized in a wide range of industrial products such as glass, catalysts, alloys, ceramics, and magnets. As for their effects on life forms, the REEs have not been characterized as either essential or strongly toxic elements in the environment [26], although some have negative effects as inhibitors of several enzymes and proteins [27?0], and some exert positive effects as growth promoters for various crops [27]. In this study, using M. extorquens strain AM1 as a model organism to investigate REEs-dependent methylotrophy, we set out (i) to see whether La3+ is involved in methylotrophic growth of the strain, (ii) to assess whether the strain has REE-dependent MDH activity, (iii) to identify the gene encoding REE-dependent MDH, and (iv) to validate the role of XoxF1 and La3+ in methanol metabolism. Our results suggest that XoxF1 is a La3+-dependent functional MDH that may participate in methanol metabolism.Results M. extorquens strain AM1 has a methanol-oxidation system independent of Ca2+Although MDH activity in Methylobacterium species has been shown to depend on Ca2+ [14], the growth of these strains on methanol without Ca2+ has never been examined. In our previous work, we showed that some REEs increased MDH activity in M. radiotolerans and the non-methylotrophic Bradyrhizobium sp. [23,24]. These facts suggest that REEs may have some roles as activators or inducers of MDH. Thus, we examined whether M. extorquens strain AM1 could grow on methanol in the presence of La3+ instead of Ca2+. As shown in Fig. 1, strain AM1 could grow normally in methanol/Ca2+ medium. In methanol medium without Ca2+ and La3+, the strain showed very slow growth, because the medium contained a small amount of Ca2+ (0.867 mM). In methanol media containing La3+ and not Ca2+, the strain grew as well as it did in methanol/Ca2+ medium, and the addition of La3+ to methanol/ Ca2+ medium had no effect on the growth of strain AM1 (Fig. 1). On the other hand, strain AM1 did not show any growth defect in succinate media even without Ca2+ and La3+. Ca3+ and La3+ have an important role in methanol metabolism but not in succinate metabolism, and strain AM1 has a novel methanol-metabolic pathway that depends on La3+ and not Ca2+.XoxF1 is a functional 26001275 La3+-dependent MDHThe growth defect of strain AM1 in the methanol medium without Ca2+ was.
