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

Reductive tricarboxylic acid cycle enzymes and reductive amino acid synthesis pathways contribute to electron balance in a Rhodospirillum rubrum Calvin-cycle mutant.
Microbiology. 2019 Nov 27;:
Authors: McCully AL, Onyeziri MC, LaSarre B, Gliessman JR, McKinlay JB
Abstract
Purple non-sulfur bacteria (PNSB) use light for energy and organic substrates for carbon and electrons when growing photoheterotrophically. This lifestyle generates more reduced electron carriers than are required for biosynthesis, even during consumption of some of the most oxidized organic substrates like malate and fumarate. Reduced electron carriers not used in biosynthesis must still be oxidized for photoheterotrophic growth to occur. Diverse PNSB commonly rely on the CO2-fixing Calvin cycle to oxidize reduced electron carriers. Some PNSB also produce H2 or reduce terminal electron acceptors as alternatives to the Calvin cycle. Rhodospirillum rubrum Calvin-cycle mutants defy this trend by growing phototrophically on malate or fumarate without H2 production or access to terminal electron acceptors. We used 13C-tracer experiments to examine how a Rs. rubrum Calvin-cycle mutant maintains electron balance under such conditions. We detected the reversal of some tricarboxylic acid cycle enzymes, carrying reductive flux from malate or fumarate to αKG. This pathway and the reductive synthesis of αKG-derived amino acids are likely important for electron balance, as s...

Source: Microbiology - November 26, 2019 Category: Microbiology Authors: McCully AL, Onyeziri MC, LaSarre B, Gliessman JR, McKinlay JB Tags: Microbiology Source Type: research