The Ger Receptor Family from Sporulating Bacteria

Abstract

Bacterial spores are specialized cells that are exceptionally resistant to environmental stress. Spores convert back to actively growing cells, a process called germination, upon nutrient detection. The most common, initial step in the germination process is the recognition of small molecule germinants by germination (Ger) receptors. Ger receptors are inner-membrane heterocomplexes formed by three distinct protein products, the A-, B-, and C-subunits. In this review, we discuss and contrast published reports on representative Ger receptors from different Bacilli and Clostridia. We also present evidence for unrecognized germination pathways independent of Ger receptors. We further emphasize the function of L-alanine as a universal germinant. We also comment on biochemical aspects of germinant recognition and interaction between Ger receptor proteins. We propose that there are six general strategies used by Bacilli and Clostridia to integrate multiple germination signals. The use of different germinant recognition strategies results in germination response flexibility. Consequently, sporulating bacterial species that use the same biomolecules as germination signals can have different germination profiles. Finally, we discuss future directions for understanding the function of Ger receptors.

Multiple independent losses of sporulation and peptidoglycan in the Mycoplasmatales and related orders of the class Bacilli

“…CAG-631 and CAG-449 encode spo0A and many of the core set of sporulation genes present in the Erysipelotrichales so are predicted to form spores. However, most CAG-631 and CAG-449 lack gerQ and spoIID, which would reduce the number of environmental stimuli able to induce spore formation ( gerQ [61]). Most CAG-449 also lack cotJB , gpr , spoIIE and spoVAD but have an additional non-essential germination protein yaaH [62], and many of the sporulation genes that were present were not present in all species.…”

Catabolism of germinant amino acids is required to prevent premature spore germination inBacillus subtilis

“…It is well understood that endospore-forming bacteria carry distinct germinant receptors that respond to specific germinants or sets of germinants (32). Not nearly as well understood are the selective forces that determine which molecules function as germinants.…”

“…Many germinant receptors respond to combinations of molecules, rather than to single molecules (32). For example, the B. subtilis GerB and GerK receptors require D-glucose, D-fructose, L-asparagine, and K + for activation (20, 33).…”

“…2). The inner membrane of B. subtilis spores contains three receptors, GerA, GerB and GerK, that mediate the initiation of germination in response to particular molecules in the environment (32). Either alanine or valine can on its own trigger germination via GerA (20), but no single germinant has been found to trigger germination via GerB or GerK.…”

Mechanism of germination inhibition ofClostridioides difficilespores by an aniline substituted cholate derivative (CaPA)

“…Spores do not cause disease but germinate into toxin-producing cells [7][8][9][10][11][12]. Despite the germination requirement to complete its lifecycle and to initiate disease, all sequenced strains of C. difficile lack homologs to the classical Ger receptor proteins found in other Bacilli and Clostridia species [13][14][15][16].…”