The purple nonsulfur phototrophic bacterium Rhodopseudomonas palustris strain CGA009 uses the three-carbon dicarboxylic acid malonate as a sole carbon source under phototrophic conditions. However, this bacterium grows extremely slowly on this compound and does not have operons for the two pathways for malonate degradation that have been described in other bacteria. Many bacteria grow on a spectrum of carbon sources, some of which are classified as "poor" growth substrates because they support slow growth rates. This trait is rarely addressed in the literature, but slow growth is potentially useful in biotechnological applications where it is imperative for bacteria to divert cellular resources to value-added products rather than to growth. This prompted us to explore the genetic and physiological basis for the slow growth of R. palustris with malonate as a carbon source. There are two unlinked genes annotated as encoding a malonyl-CoA synthetase (MatB) and a malonyl-CoA decarboxylase (MatA) in the genome of R. palustris, which we verified as having the predicted functions. Additionally, two tripartite ATP-independent periplasmic transporters (TRAP systems) encoded by rpa2047-2049 and rpa2541-2543 were needed for optimal growth on malonate. Most of these genes were expressed constitutively during growth on several carbon sources, including malonate. Our data indicate that R. palustris uses a piecemeal approach to growing on malonate. The data also raise the possibility that this bacterium will evolve to use malonate efficiently if confronted with an appropriate selection pressure.

Importance There is interest in understanding how bacteria metabolize malonate because this three-carbon dicarboxylic acid can serve as a building block in bioengineering applications to generate useful compounds that have an odd number of carbons. We found that the phototrophic bacterium Rhodopseudomonas palustris grows extremely slowly on malonate. We identified two enzymes and two TRAP transporters involved in the uptake and metabolism of malonate, but some of these elements are apparently not very efficient. R. palustris cells growing with malonate have the potential to be excellent biocatalysts because cells would be able to divert cellular resources to the production of value-added compounds instead of to support rapid growth. In addition, our results suggest that R. palustris is a candidate for directed evolution studies to improve growth on malonate and to observe the kinds of genetic adaptations that occur to make a metabolic pathway operate more efficiently.

紫色非硫光养细菌帕氏红假单胞菌CGA009菌株在光养条件下使用三碳二羧酸丙二酸酯作为唯一碳源。但是，该细菌在该化合物上生长极其缓慢，并且没有其他细菌中描述的丙二酸降解两条途径的操纵子。许多细菌在一系列碳源上生长，其中一些被归类为“不良”生长底物，因为它们支持缓慢的生长速率。该特性在文献中很少涉及，但是缓慢生长在生物技术应用中很有用，因为细菌必须将细胞资源转移到增值产品而不是生长上。这促使我们探索慢石楠生长的遗传和生理基础。以丙二酸酯为碳源。在palustris的基因组中，有两个未链接的基因被注释为编码丙二酰辅酶A合成酶（MatB）和丙二酰辅酶A脱羧酶（MatA），我们证实其具有预测的功能。另外，需要两个由rpa2047-2049和rpa2541-2543编码的不依赖三重ATP的周质转运蛋白（TRAP系统），以在丙二酸上实现最佳生长。这些基因中的大多数在包括丙二酸在内的几种碳源生长过程中组成性表达。我们的数据表明，R。palustris使用零星的方法在丙二酸上生长。数据还提出，如果面临适当的选择压力，这种细菌将进化为有效利用丙二酸的可能性。

重要性有兴趣了解细菌如何代谢丙二酸，因为这种三碳二羧酸可以作为生物工程应用中的基础材料，生成具有奇数个碳的有用化合物。我们发现光养细菌Phodopseudomonas palustris在丙二酸上生长极其缓慢。我们发现了丙二酸的吸收和代谢中涉及的两种酶和两种TRAP转运蛋白，但其中某些元素显然效率不高。用丙二酸酯生长的帕氏疟原虫细胞具有成为极好的生物催化剂的潜力，因为细胞能够将细胞资源转移到增值化合物的生产中，而不是支持其快速生长。此外，我们的结果表明R. palustris是定向进化研究的候选者，以改善丙二酸的生长并观察发生的遗传适应类型，从而使代谢途径更有效地运转。