Goto Toshitaka, Ogami Shinichi, Yoshimume Kazuaki, Yumoto Isao
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Sapporo, Japan.
Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
Front Microbiol. 2022 Mar 18;13:842785. doi: 10.3389/fmicb.2022.842785. eCollection 2022.
Alkaliphilic appear to produce ATP based on the H-based chemiosmotic theory. However, the bulk-based chemiosmotic theory cannot explain the ATP production in alkaliphilic bacteria because the H concentration required for driving ATP synthesis through the ATPase does not occur under the alkaline conditions. Alkaliphilic bacteria produce ATP in an H-diluted environment by retaining scarce H extruded by the respiratory chain on the outer surface of the membrane and increasing the potential of the H for ATP production on the outer surface of the membrane using specific mechanisms of ATP production. Under high-aeration conditions, the high ΔΨ (ca. -170 mV) of the obligate alkaliphilic retains H at the outer surface of the membrane and increases the intensity of the protonmotive force (Δp) per H across the membrane. One of the reasons for the production of high ΔΨ is the Donnan potential, which arises owing to the induction of impermeable negative charges in the cytoplasm. The intensity of the potential is further enhanced in the alkaliphiles compared with neutralophiles because of the higher intracellular pH (ca. pH 8.1). However, the high ΔΨ observed under high-aeration conditions decreased (∼ -140 mV) under low-aeration conditions. . produced 2.5-6.3-fold higher membrane bound cytochrome in the content of the cell extract under low-aeration conditions than under high-aeration conditions. The predominant membrane-bound cytochrome in the outer surface of the membrane possesses an extra Asn-rich segment between the membrane anchor and the main body of protein. This structure may influence the formation of an H-bond network that accumulates H on the outer surface of the membrane. Following accumulation of the H-bond network producing cytochrome , . constructs an H capacitor to overcome the energy limitation of low aeration at high pH conditions. . produces more ATP than other neutralophilic bacteria by enhancing the efficacy per H in ATP synthesis. In low H environments, . utilizes H efficiently by taking advantage of its high ΔΨ under high-aeration conditions, whereas under low-aeration conditions . uses cytochrome bound on its outer surface of the membrane as an H capacitor.
嗜碱菌似乎基于基于H的化学渗透理论产生ATP。然而，基于大量的化学渗透理论无法解释嗜碱菌中的ATP产生，因为在碱性条件下不会出现通过ATP酶驱动ATP合成所需的H浓度。嗜碱菌通过将呼吸链挤出的稀缺H保留在膜的外表面，并利用特定的ATP产生机制增加膜外表面用于ATP产生的H的电位，从而在H稀释的环境中产生ATP。在高通气条件下，专性嗜碱菌的高ΔΨ（约-170 mV）将H保留在膜的外表面，并增加每个H跨膜的质子动力（Δp）强度。产生高ΔΨ的原因之一是唐南电位，它是由于细胞质中不可渗透的负电荷的诱导而产生的。由于较高的细胞内pH（约pH 8.1），与嗜中性菌相比，嗜碱菌中电位的强度进一步增强。然而，在高通气条件下观察到的高ΔΨ在低通气条件下降低（约-140 mV）。在低通气条件下，细胞提取物中产生的膜结合细胞色素比高通气条件下高2.5至-6.3倍。膜外表面主要的膜结合细胞色素在膜锚定和蛋白质主体之间具有额外的富含Asn的片段。这种结构可能影响在膜外表面积累H的氢键网络的形成。在产生细胞色素的氢键网络积累之后，构建一个H电容器以克服高pH条件下低通气的能量限制。通过提高ATP合成中每个H的效率，产生的ATP比其他嗜中性细菌更多。在低H环境中，在高通气条件下利用其高ΔΨ有效利用H，而在低通气条件下，将结合在其膜外表面的细胞色素用作H电容器。
