SAR11 Cells Rely on Enzyme Multifunctionality to Transport and Metabolize a Range of Polyamine Compounds

In the ocean surface layer and cell culture, the polyamine transport protein PotD of SAR11 bacteria is often one of the most abundant proteins detected. Polyamines are organic cations produced by all living organisms and are thought to be an important component of dissolved organic matter (DOM) produced in planktonic ecosystems. We hypothesized that SAR11 cells transport and metabolize multiple polyamines and use them as sources of carbon and nitrogen. Metabolic footprinting and fingerprinting were used to measure the uptake of five polyamine compounds (putrescine, cadaverine, agmatine, norspermidine, and spermidine) in two SAR11 strains that represent the majority of SAR11 cells in the surface ocean environment, Ca. Pelagibacter st. HTCC7211 and C. P. ubique st. HTCC1062. Both strains transported all five polyamines and concentrated them to micromolar or millimolar intracellular concentrations. Both strains could use most of the polyamines to meet their nitrogen requirements, but we did not find evidence of use as carbon sources. We propose potABCD transports cadaverine, agmatine, and norspermidine, in addition to its usual substrates of spermidine and putrescine, and that spermidine synthase, speE, is reversible, catalyzing the breakdown of spermidine and norspermidine, in addition to its usual biosynthetic role. These findings provide support for the hypothesis that enzyme multifunctionality enables streamlined cells in planktonic ecosystems to increase the range of DOM compounds they oxidize.

The Role of Spermidine Synthase (SpdS) and Spermine Synthase (Sms) in Regulating Triglyceride Storage in Drosophila

Polyamines are small organic cations that are important for several biological processes such as cell proliferation, cell cycle progression, and apoptosis. The dysregulation of intracellular polyamines is often associated with diseases such as cancer, diabetes, and developmental disorders. Although polyamine metabolism has been well studied, the effects of key enzymes in the polyamine pathway on lipid metabolism are not well understood. Here, we determined metabolic effects resulting from the absence of spermidine synthase (SpdS) and spermine synthase (Sms) in Drosophila. While SpdS mutants developed normally and accumulated triglycerides, Sms mutants had reduced viability and stored less triglyceride than the controls. Interestingly, when decreasing SpdS and Sms, specifically in the fat body, triglyceride storage increased. While there was no difference in triglycerides stored in heads, thoraxes and abdomen fat bodies, abdomen fat body DNA content increased, and protein/DNA decreased in both SpdS- and Sms-RNAi flies, suggesting that fat body-specific knockdown of SpdS and Sms causes the production of smaller fat body cells and triglycerides to accumulate in non-fat body tissues of the abdomen. Together, these data provide support for the role that polyamines play in the regulation of metabolism and can help enhance our understanding of polyamine function in metabolic diseases.

Effect of Spermidine on Biofilm Formation in Escherichia coli K-12

ABSTRACT Polyamines are essential for biofilm formation in Escherichia coli, but it is still unclear which polyamines are primarily responsible for this phenomenon. To address this issue, we constructed a series of E. coli K-12 strains with mutations in genes required for the synthesis and metabolism of polyamines. Disruption of the spermidine synthase gene (speE) caused a severe defect in biofilm formation. This defect was rescued by the addition of spermidine to the medium but not by putrescine or cadaverine. A multidrug/spermidine efflux pump membrane subunit (MdtJ)-deficient strain was anticipated to accumulate more spermidine and result in enhanced biofilm formation compared to the MdtJ+ strain. However, the mdtJ mutation did not affect intracellular spermidine or biofilm concentrations. E. coli has the spermidine acetyltransferase (SpeG) and glutathionylspermidine synthetase/amidase (Gss) to metabolize intracellular spermidine. Under biofilm-forming conditions, not Gss but SpeG plays a major role in decreasing the too-high intracellular spermidine concentrations. Additionally, PotFGHI can function as a compensatory importer of spermidine when PotABCD is absent under biofilm-forming conditions. Last, we report here that, in addition to intracellular spermidine, the periplasmic binding protein (PotD) of the spermidine preferential ABC transporter is essential for stimulating biofilm formation. IMPORTANCE Previous reports have speculated on the effect of polyamines on bacterial biofilm formation. However, the regulation of biofilm formation by polyamines in Escherichia coli has not yet been assessed. The identification of polyamines that stimulate biofilm formation is important for developing novel therapies for biofilm-forming pathogens. This study sheds light on biofilm regulation in E. coli. Our findings provide conclusive evidence that only spermidine can stimulate biofilm formation in E. coli cells, not putrescine or cadaverine. Last, ΔpotD inhibits biofilm formation even though the spermidine is synthesized inside the cells from putrescine. Since PotD is significant for biofilm formation and there is no ortholog of the PotABCD transporter in humans, PotD could be a target for the development of biofilm inhibitors.

The eggplant transcription factor MYB44 enhances resistance to bacterial wilt by activating the expression of spermidine synthase

SmMYB44 directly binds to the promoter of a spermidine synthase (SPDS) gene and activates its expression, governing spermidine biosynthesis and resistance to bacterial wilt in eggplant.

Fruit Architecture in Polyamine-Rich Tomato Germplasm Is Determined via a Medley of Cell Cycle, Cell Expansion, and Fruit Shape Genes

Shape and size are important features of fruits. Studies using tomatoes expressing yeast Spermidine Synthase under either a constitutive or a fruit-ripening promoter showed obovoid fruit phenotype compared to spherical fruit in controls, suggesting that polyamines (PAs) have a role in fruit shape. The obovoid fruit pericarp exhibited decreased cell layers and pericarp thickness compared to wild-type fruit. Transgenic floral buds and ovaries accumulated higher levels of free PAs, with the bound form of PAs being predominant. Transcripts of the fruit shape genes, SUN1 and OVATE, and those of CDKB2, CYCB2, KRP1 and WEE1 genes increased significantly in the transgenic ovaries 2 and 5 days after pollination (DAP). The levels of cell expansion genes CCS52A/B increased at 10 and 20 DAP in the transgenic fruits and exhibited negative correlation with free or bound forms of PAs. In addition, the cell layers and pericarp thickness of the transgenic fruits were inversely associated with free or bound PAs in 10 and 20 DAP transgenic ovaries. Collectively, these results provide evidence for a linkage between PA homeostasis and expression patterns of fruit shape, cell division, and cell expansion genes during early fruit development, and suggest role(s) of PAs in tomato fruit architecture.