Investigation of the polyamine biosynthetic and transport capability of Streptococcus agalactiae: the non-essential PotABCD transporter

Abstract

Polyamines constitute a group of organic polycations positively charged at physiological pH. They are involved in a large variety of biological processes, including the protection against physiological stress. In this study, we show that the genome of Streptococcus agalactiae , a commensal bacterium of the intestine and the vagina and one of the most common agents responsible of neonate infections, does not encode proteins homologous to the specific enzymes involved in the known polyamine synthetic pathways. This lack of biosynthetic capability was verified experimentally by TLC analysis of the intracellular content of S. agalactiae grown in the absence of polyamines. However, similar analyses showed that the polyamines spermidine, spermine and putrescine can be imported from the growth media into the bacteria. We found that all strains of S. agalactiae possess the genes encoding the polyamine ABC transporter PotABCD. We demonstrated that these genes form an operon with folK, a gene involved in folate biosynthesis, murB, a gene involved in peptidoglycan biosynthesis, and with clc, a gene encoding a Cl−/H+ antiporter involved in resistance to acid stress in Escherichia coli . Transcription of the potABCD operon is induced by peroxide-induced oxidative stress but not by acidic stress. Spermidine and spermine were found to be inducers of potABCD transcription at pH 7.4 whereas putrescine induces this expression only during peroxide-induced oxidative stress. Using a deletion mutant of potABCD, we were nevertheless unable to associate phenotypic traits to the PotABCD transporter, probably due to the existence of one or more as yet identified transporters with a redundant action.

Streptococcus agalactiae imports spermidine by a member of the amino acid/polyamine antiporter family to endure citric acid stress at the vaginal pH

“…S2). We previously showed that the wild-type strain and the Δ potABCD mutant transport spermine, spermidine and putrescine similarly [14]. TLC analysis of the intracellular content of the Δ sak_1604 and Δ sak_1604 Δ potABCD mutants show that both mutants are also not affected in the transport of these polyamines during growth at pH 7.4 or pH 5.5 (Fig.…”

“…We previously reported that S. agalactiae lacks polyamine biosynthesis capability [14]. However, we found that S.…”

“…Intracellular polyamine content of S. agalactiae strains was visualized as described elsewhere [14, 27]. In brief, aliquots from bacterial cultures were pelleted.…”

“…S1, available with the online version of this article.). We then compared the growth of the two deletion mutants, the Δsak_1604 complemented strain and the wild-type strain at pH 5.5 (pH of the intestine), in the absence or in the presence of 1 mM spermine, 1 mM spermidine or 1 mM putrescine (a previously found non-inhibitory concentration of polyamine for S. agalactiae) [14]. The addition of each of these polyamines slightly improved the growth of all strains similarly, indicating that the SAK_1604 and the PotABCD transporters are not involved in this effect (Fig.…”

“…However, we were unable to show that the PotABCD transporter has an influence on the growth of S. agalactiae at pH 7.4 and pH 5.5 or on the survival capacity of this bacteria at pH 4.0 or during peroxide-induced oxidative stress, probably due to the existence of one or more transporters with a redundant action [14].…”