TCA Cycle Replenishing Pathways in Photosynthetic Purple Non-Sulfur Bacteria Growing with Acetate

Abstract

Purple non-sulfur bacteria (PNSB) are anoxygenic photosynthetic bacteria harnessing simple organic acids as electron donors. PNSB produce a-aminolevulinic acid, polyhydroxyalcanoates, bacteriochlorophylls a and b, ubiquinones, and other valuable compounds. They are highly promising producers of molecular hydrogen. PNSB can be cultivated in organic waste waters, such as wastes after fermentation. In most cases, wastes mainly contain acetic acid. Therefore, understanding the anaplerotic pathways in PNSB is crucial for their potential application as producers of biofuels. The present review addresses the recent data on presence and diversity of anaplerotic pathways in PNSB and describes different classifications of these pathways.

Ambient temperature CO2 fixation to pyruvate and subsequently to citramalate over iron and nickel nanoparticles

“…Citramalate seems to be unstable during the catalytic reaction; it is further decomposed to acetate, formate and CO 2 . In modern metabolism, citramalate is a key intermediate in various anaplerotic routes that feed carbon backbones into the TCA cycle 54 , and it can be easily formed over native metals without enzymes. Overall, the solid Ni-Fe catalyst functions not only in a manner similar to the acetyl-CoA pathway 25 but also similar to citramalate synthase 54 .…”

“…However, there are a number of microorganisms that can still grow in the absence of the essential TCA enzyme isocitrate lyase 53 . One of the alternative pathways for these microorganisms to synthesize TCA intermediates is the citramalic acid cycle 54 . This has been well-characterized in the purple bacterium Rhodosprillum rubrum, which can grow on acetate via the citramalate (CMA) pathway when CO 2 is present in the environment [55][56][57] .…”

With a pinch of salt: metagenomic insights into Namib Desert salt pan microbial mats and halites reveal functionally adapted and competitive communities

“…The archaeal methylaspartate cycle, which has been described as an adaptation to halophilic conditions and carbon starvation (Borjian et al, 2016) was detected in the archaeal-dominated halite metagenomes, concurrent with the high presence of gene phaC , coding for the polyhydroxyalkanoate (PHA) synthase, in the Halobacteraceae and Haloferacaceae , as well as the Alphaproteobacteria (Supplementary Table 7). PHAs are major storage compounds in prokaryotes, and as the ethylmalonyl pathway is interrelated with the synthesis of PHAs, this cycle together with the methylaspartate pathway is linked to the capacity to adapt to environmental stresses (Petushkova et al, 2021).…”

Metabolism of Photosynthetic Organisms

“…Comprehensive reviews presented in our Special Issue summarize the recent research advances on the carbon metabolism of purple non-sulfur bacteria, oxidative stress-Life 2021, 11, 946 specific alteration of pant metabolism, and the role of microRNAs in the regulation of plant metabolism and stress tolerance [5][6][7].…”

“…Petushkova et al [5] present a very detailed and comprehensive review summarizing the recent data on the presence and diversity of anaplerotic pathways in purple non-sulfur bacteria. Purple non-sulfur bacteria produce a broad selection of valuable compounds, including molecular hydrogen.…”