Assessment of the Requirements for Magnesium Transporters in Bacillus subtilis

Abstract

Magnesium is the most abundant divalent metal in cells and is required for many structural and enzymatic functions. For bacteria, at least three families of proteins function as magnesium transporters. In recent years, it has been shown that a subset of these transport proteins is regulated by magnesium-responsive genetic control elements. In this study, we investigated the cellular requirements for magnesium homeostasis in the model microorganism Bacillus subtilis. Putative magnesium transporter genes were mutationally disrupted, singly and in combination, in order to assess their general importance. Mutation of only one of these genes resulted in strong dependency on supplemental extracellular magnesium. Notably, this transporter gene, mgtE, is known to be under magnesium-responsive genetic regulatory control. This suggests that the identification of magnesium-responsive genetic mechanisms may generally denote primary transport proteins for bacteria. To investigate whether B. subtilis encodes yet additional classes of transport mechanisms, suppressor strains that permitted the growth of a transporter-defective mutant were identified. Several of these strains were sequenced to determine the genetic basis of the suppressor phenotypes. None of these mutations occurred in transport protein homologues; instead, they affected housekeeping functions, such as signal recognition particle components and ATP synthase machinery. From these aggregate data, we speculate that the mgtE protein provides the primary route of magnesium import in B. subtilis and that the other putative transport proteins are likely to be utilized for more-specialized growth conditions.

Rhomboid intramembrane protease YqgP licenses bacterial membrane protein quality control as adaptor of FtsH AAA protease

“…Intriguingly, ectopic expression of a proteolytically inactive S288A mutant of YqgP also rescued the phenotype of the parent strain, which was initially surprising and suggested that YqgP may have a role independent of its protease activity. Together, these results reveal that a physiological function of YqgP is the protection from manganese stress by contributing to the degradation of the main magnesium transporter MgtE in B. subtilis (Wakeman et al , ).…”

“…The only high‐confidence overlap between the two proteomic datasets was the high‐affinity magnesium transporter MgtE (Fig C and E), promoting it to the highest likelihood candidate substrate. MgtE is the main magnesium transporter in B. subtilis , it is essential for magnesium homeostasis (Wakeman et al , ), and we thus examined the possible functional relationship between YqgP and MgtE.…”

Defect in the Formation of 70S Ribosomes Caused by Lack of Ribosomal Protein L34 Can Be Suppressed by Magnesium

“…Detailed studies on MgtE, including crystal structure analyses in Thermus thermophilus, have demonstrated that MgtE is an Mg 2ϩ transporter that plays a central role in Mg 2ϩ homeostasis (52)(53)(54). Recently, it has also been reported that MgtE in B. subtilis, which shows 33% sequence identity with MgtE of T. thermophilus, provides the primary route of magnesium import, although YfjQ, a homologue of the magnesium/cobalt transporter CorA, is also able to import Mg 2ϩ (74). Disruption of yhdP and overexpression of mgtE restored the reduction in the cellular Mg 2؉ content caused by lack of L34.…”

When Too Much ATP Is Bad for Protein Synthesis

“…In support of this notion, the MgtC protein inhibits the F 1 F o ATP synthase thereby reducing ATP levels [5]. Moreover, spontaneous mutations that restored growth to a mutant B. subtilis requiring unusually high Mg 2+ concentrations for growth due to mutations in multiple Mg 2+ transporters mapped to the genes specifying subunits of the F 1 F o ATP synthase [95]. …”