Importance of Individual Germination Receptor Subunits in the Cooperative Function between GerA and Ynd

Abstract

Germination of Bacillus spores is triggered by the binding of specific nutrients to germinant receptors (GRs) located in the spore’s inner membrane. The GRs typically consist of A, B, and C subunits, encoded by tricistronic ger operons. The Bacillus licheniformis genome contains the gerA family operons gerA, ynd, and gerK. In contrast to the ABC(D) organization that characterizes gerA operons of many Bacillus species, B. licheniformis genomes contain a pentacistronic ynd operon comprising the yndD, yndE3, yndE2, yndF1, and yndE1 genes encoding A, B, B, C, and B GR subunits, respectively (subscripts indicate paralogs). Here we show that B. licheniformis spores can germinate in the absence of the Ynd and GerK GRs, although cooperation between all three GRs is required for optimal germination with amino acids. Spores carrying an incomplete set of Ynd B subunits demonstrated reduced germination efficiencies, while depletion of all three Ynd B subunits restored germination of the spore population to levels only slightly lower than those of wild-type spores at high germinant concentrations. This suggests that the presence of an incomplete set of Ynd B subunits exhibits a dominant negative effect on germination and that the A and C subunits of the Ynd GR are sufficient for the cooperative functionality between Ynd and GerA. In contrast to the B subunits of Ynd, the B subunit of GerA was essential for amino acid-induced germination. This study provides novel insights into the role of individual GR subunits in the cooperative interaction between GRs in triggering spore germination. IMPORTANCE Spore-forming bacteria are problematic for the food industry, as spores can survive decontamination procedures and subsequently revive in food products, with the risk of food spoilage and foodborne disease. The Ynd and GerA germination receptors (GRs) cooperate in triggering efficient germination of Bacillus licheniformis spores when nutrients are present in the surrounding environment. This study shows that the single B subunit of GerA is essential for the cooperative function between Ynd and GerA, while the three B subunits of the Ynd GR are dispensable. The ability of GRs lacking individual subunits to stimulate germination together with other GRs could explain why ger operons lacking GR subunit genes are maintained in genomes of spore-forming species.

Sporulation, Structure Assembly, and Germination in the Soil Bacterium Bacillus thuringiensis: Survival and Success in the Environment and the Insect Host

“…Moreover, to awaken the dormant endospore is to favor inner membrane (IM) structure permeability through the expression of the proteins (SpoVA) that form the channels (seven in B.subtilis spores) [203,213] for the movement, passage, and release of monovalent cations, including H + , K + , and Na + CaDPA (sodium calcium dipicolinic acid) [203,210,[214][215][216][217][218]. These are proteins that take part in the release of DPA through channels encoded in one or more operons in all spore-forming bacilli [203,[214][215][216]219,220]. In the particular case of B. subtilis, it is a heptacistronic operon.…”

“…Indeed, B. licheniformis genomes contain a pentacistronic ynd operon, the yndD, yndE3, yndE2, yndF1, and yndE1 genes, encoding A, B, B, C, and B GR subunits, respectively (subscripts indicate paralogs). In contrast to the B subunits of Ynd, the B subunit of GerA was essential for amino-acid-induced germination [220,235,239,240]. Therefore, in addition to the operon organization of the GR receptors, dynamic structural studies have provided novel insights into the role of individual GR subunits involved in the cooperative interaction among GR, in triggering spore germination [220,235,239,240] (Figure 3).…”

“…In contrast to the B subunits of Ynd, the B subunit of GerA was essential for amino-acid-induced germination [220,235,239,240]. Therefore, in addition to the operon organization of the GR receptors, dynamic structural studies have provided novel insights into the role of individual GR subunits involved in the cooperative interaction among GR, in triggering spore germination [220,235,239,240] (Figure 3). As outlined in Figure 1A,B, dormant spores can awake in several ways: (1) by external stimuli, external environmental signals; (2) in the host by nutrients; (3) by germinants receptors (GR) present in the inner membrane or in the outer membrane; (4) by other components such as CwLJ, or directly signal through SPoVA (independently of GR).…”

Dormant spores sense amino acids through the B subunits of their germination receptors

“…Germination does not require the active transport of these molecules into the spore and it is therefore thought that the Ger receptors function as nutrient sensors 2 . Over the last four decades Ger-type receptors have been studied in Bacillus subtilis 1 , Bacillus megaterium 3,4 , Bacillus cereus 5,6 , Bacillus anthracis 7,8 , Bacillus licheniformis 9,10 , Clostridium botulinum, Clostridium sporogenes 11 , and Clostridium perfringens 12,13 . In some cases, a receptor is required for spores to respond to a single germinant.…”