Nitrosomonas europaea is a chemolithotroph that obtains energy through the oxidation of ammonia to hydroxylamine while assimilates atmospheric CO₂ to cover the cell carbon demands for growth. This microorganism plays a relevant role in the nitrogen biogeochemical cycle on Earth but its carbon metabolism remains poorly characterized. Based on sequence homology, we identified two genes (cbbG and gabD) coding for redox enzymes in N. europaea. Cloning and expression of the genes in Escherichia coli, allowed the production of recombinant enzymes purified to determine their biochemical properties. The protein CbbG is a glyceraldehyde-3-phosphate (Ga3P) dehydrogenase (Ga3PDHase) catalyzing the reversible oxidation of Ga3P to 1,3-bis-phospho-glycerate (1,3bisPGA), using specifically NAD⁺/NADH as cofactor. CbbG showed ∼6-fold higher K_m value for 1,3bisPGA but ∼5-fold higher k_cat for the oxidation of Ga3P. The protein GabD irreversibly oxidizes Ga3P to 3Pglycerate using NAD⁺ or NADP⁺, thus resembling a non-phosphorylating Ga3PDHase. However, the enzyme showed ∼6-fold higher K_m value and three orders of magnitude higher catalytic efficiency with succinate semialdehyde (SSA) and NADP⁺. Indeed, the GabD protein identity corresponds to an SSA dehydrogenase (SSADHase). CbbG seems to be the only Ga3PDHase present in N. europaea; which would be involved in reducing triose-P during autotrophic carbon fixation. Otherwise, in cells grown under conditions deprived of ammonia and oxygen, the enzyme could catalyze the glycolytic step of Ga3P oxidation producing NADH. As an SSADHase, GabD would physiologically act producing succinate and preferentially NADPH over NADH; thus being part of an alternative pathway of the tricarboxylic acid cycle converting α-ketoglutarate to succinate. The properties determined for these enzymes contribute to better identify metabolic steps in CO₂ assimilation, glycolysis and the tricarboxylic acid cycle in N. europaea. Results are discussed in the framework of metabolic pathways that launch biosynthetic intermediates relevant in the microorganism to develop and fulfill its role in nature.

欧洲亚硝化单胞菌是一种化学营养型生物，它通过将氨氧化为羟胺而吸收能量，同时吸收大气中的CO ₂来满足细胞对生长所需的碳的需求。这种微生物在地球上的氮生物地球化学循环中起着重要的作用，但是其碳代谢的特征仍然很差。基于序列同源性，我们确定了两个基因（CBBG和gabD）编码为氧化还原酶N.油橄榄。大肠杆菌中基因的克隆和表达允许生产纯化的重组酶，以确定其生化特性。CbbG蛋白是一种3-磷酸甘油醛（Ga3P）脱氢酶（Ga3PDHase），使用NAD ⁺ / NADH作为辅助因子，催化将Ga3P可逆氧化为1,3-双磷酸甘油酯（1,3bisPGA）。CBBG表明〜6倍高的ķ_米为1,3bisPGA值但〜5倍高ķ_猫为Ga3P的氧化。GabD蛋白使用NAD ⁺或NADP ⁺不可逆地将Ga3P氧化为3P甘油酸酯，因此类似于非磷酸化的Ga3PDHase。但是，该酶显示出高出约6倍的K _m琥珀酸半醛（SSA）和NADP ^+的催化效率提高了3个数量级。实际上，GabD蛋白质身份对应于SSA脱氢酶（SSADHase）。CbbG似乎是欧洲猪笼草中唯一的Ga3PDHase; 在自养碳固定过程中可能与降低triose-P有关。否则，在缺乏氨和氧的条件下生长的细胞中，该酶可以催化Ga3P氧化产生NADH的糖酵解步骤。作为SSADHase，GabD会在生理上发挥作用，产生琥珀酸，而相对于NADH优先产生NADPH；因此，它是三羧酸循环将α-酮戊二酸转化为琥珀酸的另一种途径的一部分。为这些酶确定的特性有助于更好地识别欧洲猪笼草中CO ₂同化，糖酵解和三羧酸循环的代谢步骤。在代谢途径的框架中讨论了结果，这些途径会启动与微生物相关的生物合成中间体，从而发展并发挥其在自然界中的作用。