Spermidine promotes Bacillus subtilis biofilm formation by activating expression of the matrix regulator slrR

Abstract

Ubiquitous polyamine spermidine is not required for normal planktonic growth of Bacillus subtilis but is essential for robust biofilm formation. However, the structural features of spermidine required for B. subtilis biofilm formation are unknown and so are the molecular mechanisms of spermidine-stimulated biofilm development. We report here that in a spermidine-deficient B. subtilis mutant, the structural analogue norspermidine, but not homospermidine, restored biofilm formation. Intracellular biosynthesis of another spermidine analogue, aminopropylcadaverine, from exogenously supplied homoagmatine also restored biofilm formation. The differential ability of C-methylated spermidine analogues to functionally replace spermidine in biofilm formation indicated that the aminopropyl moiety of spermidine is more sensitive to C-methylation, which it is essential for biofilm formation, but that the length and symmetry of the molecule is not critical. Transcriptomic analysis of a spermidine-depleted B. subtilis speD mutant uncovered a nitrogen-, methionine-, and S-adenosylmethionine-sufficiency response, resulting in repression of gene expression related to purine catabolism, methionine and S-adenosylmethionine biosynthesis and methionine salvage, and signs of altered membrane status. Consistent with the spermidine requirement in biofilm formation, single-cell analysis of this mutant indicated reduced expression of the operons for production of the exopolysaccharide and TasA protein biofilm matrix components and SinR antagonist slrR. Deletion of sinR or ectopic expression of slrR in the spermidine-deficient ΔspeD background restored biofilm formation, indicating that spermidine is required for expression of the biofilm regulator slrR. Our results indicate that spermidine functions in biofilm development by activating transcription of the biofilm matrix exopolysaccharide and TasA operons through the regulator slrR.

Homospermidine biosynthesis in the cyanobacterium Anabaena requires a deoxyhypusine synthase homologue and is essential for normal diazotrophic growth

“…These dried samples were used for LC-MS analysis as described previously (Lowe-Power et al, 2018). Alternatively, polyamine derivatization by Accufluor reagent and subsequent analysis by HPLC was performed as described previously (Hobley et al, 2017).…”

Polyamine‐independent growth and biofilm formation, and functional spermidine/spermine N‐acetyltransferases in Staphylococcus aureus and Enterococcus faecalis

“…The spirochaete and agent of Lyme Disease Borrelia burgdorferi does not synthesize polyamines but it is absolutely dependent on the spermidine uptake transporter potABCD for growth (Bontemps-Gallo et al, 2018). Polyamines are also essential for robust biofilm formation in Y. pestis (Patel et al, 2006), Vibrio cholerae (Karatan et al, 2005;Lee et al, 2009) and Bacillus subtilis (Burrell et al, 2010;Hobley et al, 2014;Hobley et al, 2017), whereas endogenous polyamines inhibit biofilm formation in Shewanella oneidensis (Ding et al, 2014), A. tumefaciens and Synechocystis (Kera et al, 2018). It has been known for more than 50 years that many Gram-positive species do not contain spermidine or tetraamine spermine ( Fig.…”

Bacillus velezensis Wall Teichoic Acids Are Required for Biofilm Formation and Root Colonization

“…Zwick et al (37) demonstrated that AhpC is highly expressed in both stationary-phase planktonic cells and biofilms and that strains lacking ahpC do not form a biofilm. In addition, SpeE is a spermidine synthase, and Hobley et al (38) found that spermidine promotes B. subtilis biofilm formation by activating the expression of the matrix regulator slrR. Overall, it is likely that the lower expression of these proteins affects the biofilm development of the sfp mutant.…”