| Calcium (Ca) functions as a universal signal messenger in eukaryotes and regulates many
intracellular processes such as cell division and gene expression. However, in bacteria, the
physiological roles of Ca remain limited. Previous published work investigating the mgtA
Mn/Ca-sensing riboswitch indicated that Ca may be interconnected with manganese (Mn)
physiology in Streptococcus pneumoniae. In this study, we examined a role for Ca in Mn
homeostasis. We demonstrate that mntE-null mutants, lacking the Mn efflux transporter, exhibit
impaired growth due to accumulation of Mn when exposed to elevated exogenous Mn. This Mn-
sensitive growth defect is rescued by exogenous Ca, in a Ca-dependent manner. Despite
restoring ΔmntE growth to wildtype levels, we find that Mn remains elevated in ΔmntE.
Additional analysis shows ΔmntE expresses thicker capsular polysaccharide and decreased
capacity to adhere to surfaces which is consistent with ΔmntE experiencing Mn intoxication
despite growth rescue by Ca. We also show that Mn intoxication inhibits biofilm formation, and
that Ca has no significant impact on bacterial capsule production or biofilm formation. To our
surprise, differential RNA-sequence analysis revealed no significant changes in gene expression
levels in the presence of Ca, suggesting to us that Ca may be functioning as signal messenger at
the post-transcriptional level. Together, these data describe the first possible role of Ca in S.
pneumoniae that has potential implication in virulence since it affects cell growth and likely
impacts Mn cellular processes.
Keywords: Streptococcus pneumoniae, capsular polysaccharide, manganese |