Mycobacterium smegmatis does not display functional redundancy in nitrate reductase enzymes

PLoS One. 2021 Jan 20;16(1):e0245745. doi: 10.1371/journal.pone.0245745. eCollection 2021.

Abstract

Reduction of nitrate to nitrite in bacteria is an essential step in the nitrogen cycle, catalysed by a variety of nitrate reductase (NR) enzymes. The soil dweller, Mycobacterium smegmatis is able to assimilate nitrate and herein we set out to confirm the genetic basis for this by probing NR activity in mutants defective for putative nitrate reductase (NR) encoding genes. In addition to the annotated narB and narGHJI, bioinformatics identified three other putative NR-encoding genes: MSMEG_4206, MSMEG_2237 and MSMEG_6816. To assess the relative contribution of each, the corresponding gene loci were deleted using two-step allelic replacement, individually and in combination. The resulting strains were tested for their ability to assimilate nitrate and reduce nitrate under aerobic and anaerobic conditions, using nitrate assimilation and modified Griess assays. We demonstrated that narB, narGHJI, MSMEG_2237 and MSMEG_6816 were individually dispensable for nitrate assimilation and for nitrate reductase activity under aerobic and anaerobic conditions. Only deletion of MSMEG_4206 resulted in significant reduction in nitrate assimilation under aerobic conditions. These data confirm that in M. smegmatis, narB, narGHJI, MSMEG_2237 and MSMEG_6816 are not required for nitrate reduction as MSMEG_4206 serves as the sole assimilatory NR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Gene Deletion
  • Mycobacterium smegmatis / enzymology*
  • Mycobacterium smegmatis / genetics
  • Nitrate Reductase / genetics*
  • Nitrate Reductase / metabolism
  • Nitrates / metabolism

Substances

  • Bacterial Proteins
  • Nitrates
  • Nitrate Reductase

Grants and funding

BK, NC, AOP DCOE015 South African National Research Foundation BK, NC, AOP South African Medical Research Council, with funds from the Department of Health The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.