Reductive tricarboxylic acid cycle enzymes and reductive amino acid synthesis pathways contribute to electron balance in a Rhodospirillum rubrum Calvin-cycle mutant

McCully, Alexandra L.; Onyeziri, Maureen C.; LaSarre, Breah; Gliessman, Jennifer R; McKinlay, James B.

doi:10.1099/mic.0.000877

Cited by 21 publications

(33 citation statements)

References 55 publications

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“…Proteins related to branched‐chain amino acid metabolism, whose synthesis can re‐oxidize cellular electron carriers for R . palustris during photoheterotrophic growth on succinate but not on acetate (McCully et al ., ), are more abundant in this treatment (Fig. S8).…”

Section: Resultsmentioning

confidence: 83%

“…oxidative TCA cycle, which is associated with greater CO 2 loss (McKinlay and Harwood, 2011) and reduced electron flow through the energy acquiring electron transport chain (Alsiyabi et al, 2019). Proteins related to branched-chain amino acid metabolism, whose synthesis can re-oxidize cellular electron carriers for R. palustris during photoheterotrophic growth on succinate but not on acetate (McCully et al, 2019), are more abundant in this treatment (Fig. S8).…”

Section: Mo-nase Strain Grows Slowly Compared With the Wild Type Strainmentioning

confidence: 94%

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Carbon substrate re‐orders relative growth of a bacterium using Mo‐, V‐, or Fe‐nitrogenase for nitrogen fixation

Luxem

Kraepiel

Zhang

et al. 2020

Environmental Microbiology

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Summary Biological nitrogen fixation is catalyzed by the molybdenum (Mo), vanadium (V) and iron (Fe)‐only nitrogenase metalloenzymes. Studies with purified enzymes have found that the ‘alternative’ V‐ and Fe‐nitrogenases generally reduce N2 more slowly and produce more byproduct H2 than the Mo‐nitrogenase, leading to an assumption that their usage results in slower growth. Here we show that, in the metabolically versatile photoheterotroph Rhodopseudomonas palustris, the type of carbon substrate influences the relative rates of diazotrophic growth based on different nitrogenase isoforms. The V‐nitrogenase supports growth as fast as the Mo‐nitrogenase on acetate but not on the more oxidized substrate succinate. Our data suggest that this is due to insufficient electron flux to the V‐nitrogenase isoform on succinate compared with acetate. Despite slightly faster growth based on the V‐nitrogenase on acetate, the wild‐type strain uses exclusively the Mo‐nitrogenase on both carbon substrates. Notably, the differences in H2:N2 stoichiometry by alternative nitrogenases (~1.5 for V‐nitrogenase, ~4–7 for Fe‐nitrogenase) and Mo‐nitrogenase (~1) measured here are lower than prior in vitro estimates. These results indicate that the metabolic costs of V‐based nitrogen fixation could be less significant for growth than previously assumed, helping explain why alternative nitrogenase genes persist in diverse diazotroph lineages and are broadly distributed in the environment.

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Section: Resultsmentioning

confidence: 83%

Section: Mo-nase Strain Grows Slowly Compared With the Wild Type Strainmentioning

confidence: 94%

Carbon substrate re‐orders relative growth of a bacterium using Mo‐, V‐, or Fe‐nitrogenase for nitrogen fixation

Luxem

Kraepiel

Zhang

et al. 2020

Environmental Microbiology

View full text Add to dashboard Cite

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“…The poor annotation of these enzymes and the lack of information regarding their specificity make interpretation of these results complicated. Interestingly, a recent study by McCully et al [30] concluded that reductive amino acid synthesis and, in particular, isoleucine synthesis could be used by Rs. rubrum as an electron balancing mechanism during malate and fumarate assimilation.…”

Section: The Branched Chain Amino Acids Biosynthesis Pathway Is Upregmentioning

confidence: 99%

New perspectives on butyrate assimilation in Rhodospirillum rubrum S1H under photoheterotrophic conditions

et al. 2020

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Background: The great metabolic versatility of the purple non-sulfur bacteria is of particular interest in green technology. Rhodospirillum rubrum S1H is an α-proteobacterium that is capable of photoheterotrophic assimilation of volatile fatty acids (VFAs). Butyrate is one of the most abundant VFAs produced during fermentative biodegradation of crude organic wastes in various applications. While there is a growing understanding of the photoassimilation of acetate, another abundantly produced VFA, the mechanisms involved in the photoheterotrophic metabolism of butyrate remain poorly studied. Results: In this work, we used proteomic and functional genomic analyses to determine potential metabolic pathways involved in the photoassimilation of butyrate. We propose that a fraction of butyrate is converted to acetyl-CoA, a reaction shared with polyhydroxybutyrate metabolism, while the other fraction supplies the ethylmalonyl-CoA (EMC) pathway used as an anaplerotic pathway to replenish the TCA cycle. Surprisingly, we also highlighted a potential assimilation pathway, through isoleucine synthesis and degradation, allowing the conversion of acetyl-CoA to propionyl-CoA. We tentatively named this pathway the methylbutanoyl-CoA pathway (MBC). An increase in isoleucine abundance was observed during the early growth phase under butyrate condition. Nevertheless, while the EMC and MBC pathways appeared to be concomitantly used, a genome-wide mutant fitness assay highlighted the EMC pathway as the only pathway strictly required for the assimilation of butyrate. Conclusion: Photoheterotrophic growth of Rs. rubrum with butyrate as sole carbon source requires a functional EMC pathway. In addition, a new assimilation pathway involving isoleucine synthesis and degradation, named the methylbutanoyl-CoA (MBC) pathway, could also be involved in the assimilation of this volatile fatty acid by Rs. rubrum.

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“…Photosynthesis causes a surplus of energy and reducing equivalents and thus an imbalance in the redox homeostasis. In anaerobic organisms, it has been shown that reductive metabolic pathways like the CBB cycle or some rTCA cycle enzymes are important to maintain redox homeostasis during photosynthesis (McCully et al 2020). Despite the obligately aerobic lifestyle of AAP bacteria, several studies have reported a reduced respiration rate in light, which suggests that reductive metabolic pathways in these In the rTCA cycle the ATP-dependent citrate lyase (Acl) generates acetyl-CoA, a reaction that could also be catalyzed by the citrate synthase (Cs) in the roTCA cycle, as recently shown.…”

Section: Functional Degeneracy and Multifunctionality: The 3-hydroxypmentioning

confidence: 99%

Biochemical unity revisited: microbial central carbon metabolism holds new discoveries, multi-tasking pathways, and redundancies with a reason

Borzyskowski

Bernhardsgrütter

Erb

2020

Biological Chemistry

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For a long time, our understanding of metabolism has been dominated by the idea of biochemical unity, i.e., that the central reaction sequences in metabolism are universally conserved between all forms of life. However, biochemical research in the last decades has revealed a surprising diversity in the central carbon metabolism of different microorganisms. Here, we will embrace this biochemical diversity and explain how genetic redundancy and functional degeneracy cause the diversity observed in central metabolic pathways, such as glycolysis, autotrophic CO2 fixation, and acetyl-CoA assimilation. We conclude that this diversity is not the exception, but rather the standard in microbiology.

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Reductive tricarboxylic acid cycle enzymes and reductive amino acid synthesis pathways contribute to electron balance in a Rhodospirillum rubrum Calvin-cycle mutant

Cited by 21 publications

References 55 publications

Carbon substrate re‐orders relative growth of a bacterium using Mo‐, V‐, or Fe‐nitrogenase for nitrogen fixation

Carbon substrate re‐orders relative growth of a bacterium using Mo‐, V‐, or Fe‐nitrogenase for nitrogen fixation

New perspectives on butyrate assimilation in Rhodospirillum rubrum S1H under photoheterotrophic conditions

Biochemical unity revisited: microbial central carbon metabolism holds new discoveries, multi-tasking pathways, and redundancies with a reason

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