Putrescine Transport in a Cyanobacterium Synechocystis sp. PCC 6803

Abstract

The transport of putrescine into a moderately salt tolerant cyanobacterium Synechocystis sp. PCC 6803 was characterized by measuring the uptake of radioactively-labeled putrescine. Putrescine transport showed saturation kinetics with an apparent K(m) of 92 +/- 10 microM and V(max) of 0.33 +/- 0.05 nmol/min/mg protein. The transport of putrescine was pH-dependent with highest activity at pH 7.0. Strong inhibition of putrescine transport was caused by spermine and spermidine whereas only slight inhibition was observed by the addition of various amino acids. These results suggest that the transport system in Synechocystis sp. PCC 6803 is highly specific for polyamines. Putrescine transport is energy-dependent as evidenced by the inhibition by various metabolic inhibitors and ionophores. Slow growth was observed in cells grown under salt stress. Addition of low concentration of putrescine could restore growth almost to the level observed in the absence of salt stress. Upshift of the external osmolality generated by either NaCl or sorbitol caused an increased putrescine transport with an optimum 2-fold increase at 20 mosmol/kg. The stimulation of putrescine transport mediated by osmotic upshift was abolished in chloramphenicol-treated cells, suggesting possible involvement of an inducible transport system.

Na+-stimulated nitrate uptake with increased activity under osmotic upshift in Synechocystis sp. strain PCC 6803

“…Similar studies in Synechocystis sp. strain PCC 6803 on the uptake of putrescine, a polycationic compound, have shown that the stimulation of the uptake of putrescine by NaCl or sorbitol was a result of an osmotic effect rather than an ionic effect (Raksajit et al 2006). The transport of nitrate in Synechocystis is mediated by an ABC-type transporter.…”

Computational prediction of the osmoregulation network in Synechococcus sp. WH8102

“…• E. coli has 31 genes known to be involved in the osmoregulation process, namely a two-component system for regulating two major porin-encoding genes [12], two Na + antiporters [4] and three active K + transport systems whose activation is determined by the environmental condition [3,13,14], and a number of transporters and synthetases for betaine [3], trehalose [15,16], putrescine and spermidine [17], respectively. σ 38 , one of the seven types of σ subunits of RNA polymerase, is a master regulator in a complex regulatory network that governs the expression of many stationary-phase-inducible genes, and was recently proposed as a global regulator in the osmoregulation network [18,19];…”

Role of Spermidine in Overwintering of Cyanobacteria

“…We tested spermine (tetramine), homospermidine (triamine), cadaverine (diamine), and putrescine (diamine). Of these polyamines, at least putrescine has been shown to be taken up by Synechocystis 6803 (30), and the uptake of spermine has been shown in another cyanobacterium (29). The addition of 0.0l or 0.1 mM spermine/homospermidine restored the RACLT of CASDC mutant to the wildtype level, while cadaverine and putrescine only slightly increased the RACLT (Fig.…”

“…Homospermidine synthase is not found, but deoxyhypusine synthase may transform putrescine into homospermidine, in certain groups of cyanobacteria (28). Like other bacteria, cyanobacteria can take up polyamines from the environment (29)(30)(31)(32) and may secrete polyamines (32).…”