Paoli G C, Tabita F R
The Department of Microbiology and Plant Molecular Biology/Biotechnology Program, The Ohio State University, 484 West 12th Avenue, Columbus, Ohio 43210-1292, USA.
Arch Microbiol. 1998 Jul;170(1):8-17. doi: 10.1007/s002030050609.
Photosynthetic prokaryotes that assimilate CO2 under anoxic conditions may also grow chemolithoautotrophically with O2 as the electron acceptor. Among the nonsulfur purple bacteria, two species (Rhodobacter capsulatus and Rhodopseudomonas acidophilus), exhibit aerobic chemolithoautotrophic growth with hydrogen as the electron donor. Although wild-type strains of Rhodobacter sphaeroides grow poorly, if at all, with hydrogen plus oxygen in the dark, we report here the isolation of a spontaneous mutant (strain HR-CAC) of Rba. sphaeroides strain HR that is fully capable of this mode of growth. Rba. sphaeroides and Rba. capsulatus fix CO2 via the reductive pentose phosphate pathway and synthesize two forms of ribulose 1, 5-bisphosphate carboxylase/oxygenase (RubisCO). RubisCO levels in the aerobic-chemolithoautotrophic-positive strain of Rba. sphaeroides were similar to those in wild-type strains of Rba. sphaeroides and Rba. capsulatus during photoheterotrophic and photolithoautotrophic growth. Moreover, RubisCO levels of Rba. sphaeroides strain HR-CAC approximated levels obtained in Rba. capsulatus when the organisms were grown as aerobic chemolithoautotrophs. Either form I or form II RubisCO was able to support aerobic chemolithoautotrophic growth of Rba. capsulatus strain SB 1003 and Rba. sphaeroides strain HR-CAC at a variety of CO2 concentrations, although form II RubisCO began to lose the capacity to support aerobic CO2 fixation at high O2 to CO2 ratios. The latter property and other facets of the physiology of this system suggest that Rba. sphaeroides and Rba. capsulatus strains may be effectively employed for the biological selection of RubisCO molecules of altered substrate specificity.
在缺氧条件下同化二氧化碳的光合原核生物也可以以氧气作为电子受体进行化能无机自养生长。在非硫紫色细菌中，有两个物种（荚膜红细菌和嗜酸红假单胞菌）以氢气作为电子供体表现出好氧化能无机自养生长。尽管球形红细菌的野生型菌株在黑暗中利用氢气加氧气生长很差甚至根本不生长，但我们在此报告了球形红细菌菌株HR的一个自发突变体（菌株HR-CAC）的分离，该突变体完全能够进行这种生长模式。球形红细菌和荚膜红细菌通过还原性戊糖磷酸途径固定二氧化碳，并合成两种形式的1,5-二磷酸核酮糖羧化酶/加氧酶（RubisCO）。在光合异养和光合自养生长过程中，球形红细菌的好氧化能无机自养阳性菌株中的RubisCO水平与球形红细菌和荚膜红细菌的野生型菌株中的水平相似。此外，当生物体作为好氧化能无机自养生物生长时，球形红细菌菌株HR-CAC的RubisCO水平接近荚膜红细菌中的水平。在各种二氧化碳浓度下，I型或II型RubisCO都能够支持荚膜红细菌菌株SB 1003和球形红细菌菌株HR-CAC的好氧化能无机自养生长，尽管在高氧气与二氧化碳比例下，II型RubisCO开始失去支持好氧二氧化碳固定的能力。该系统生理学的后一个特性和其他方面表明，球形红细菌和荚膜红细菌菌株可有效地用于对底物特异性改变的RubisCO分子进行生物学筛选。
