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Front. Microbiol. | doi: 10.3389/fmicb.2019.00301

Porphyrin excretion resulting from mutation of a gene encoding a class I fructose 1,6-bisphosphate aldolase in Rhodobacter capsulatus

 Hao Ding1, Rafael G. Saer2 and  J Thomas Beatty1*
  • 1University of British Columbia, Canada
  • 2Washington University in St. Louis, United States

This paper describes a mutant (called SB1707) of the Rhodobacter capsulatus wild type strain SB1003 in which a transposon-disrupted rcc01707 gene resulted in a ~25-fold increase in the accumulation of coproporphyrin III in the medium of phototrophic (anaerobic) cultures grown in a yeast extract/peptone medium. There was little or no stimulation of pigment accumulation in aerobic cultures. Therefore, this effect of rcc01707 mutation appears to be specific for the anaerobic coproporphyrinogen III oxidase HemN as opposed to the aerobic enzyme HemF. The protein encoded by rcc01707 is homologous to Class I fructose 1,6-bisphosphate aldolases, which catalyze a glycolytic reaction that converts fructose 1, 6-bisphosphate to dihydroxyacetone phosphate and glyceraldehyde 3-phosphate, precursors of pyruvate. There were significant differences in coproporphyrin III accumulation using defined media with individual organic acids and sugars as the sole carbon source: pyruvate, succinate and glutamate stimulated accumulation the most, whereas glucose suppressed coproporphyrin III accumulation to 10% of that of succinate. However, although quantitatively lesser, similar effects of carbon source on the amount of accumulated pigment in the culture medium were seen in a wild type control. Therefore, this mutation appears to exaggerate effects also seen in the wild type strain. It is possible that mutation of rcc01707 causes a metabolic bottleneck or imbalance that was not rectified during growth on the several carbon sources tested. However, we speculate that, analogous to other fructose 1,6-bisphosphate aldolases, the rcc01707 gene product has a "moonlighting" activity that in this case is needed for the maximal expression of the hemN gene. Indeed, it was found that the rcc01707 gene is needed for maximal expression of a hemN promoter-lacZ reporter. With the decrease in hemN expression due to the absence of the rcc01707 gene product, coproporphyrinogen III accumulates and is released from the cell, yielding the spontaneous oxidation product coproporphyrin III.

Keywords: Coproporphyrinogen III, HemN, Fructose 1,6-bisphosphate aldolase, Class I FBA, Moonlight activity, porphyrin excretion

Received: 28 Oct 2018; Accepted: 04 Feb 2019.

Edited by:

Thomas E. Hanson, University of Delaware, United States

Reviewed by:

Ulrike Kappler, University of Queensland, Australia
Jill Zeilstra-Ryalls, Bowling Green State University, United States
Carsten Sanders, Kutztown University of Pennsylvania, United States  

Copyright: © 2019 Ding, Saer and Beatty. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. J Thomas Beatty, University of British Columbia, Vancouver, V6T 1Z2, British Columbia, Canada,