The Essential Role of Spermidine in Growth of Agrobacterium tumefaciens Is Determined by the 1,3-Diaminopropane Moiety

Abstract

The ubiquitous polyamine spermidine is indispensable for eukaryotic growth and cell proliferation. A conserved vital function of spermidine across eukaryotes is conferred by its aminobutyl group that is transferred to a single lysine in translation factor eIF5A to form the essential hypusine post-translational modification required for cellular translation. In direct contrast, although spermidine is absolutely essential for growth of alpha-proteobacterial plant pathogen Agrobacterium tumefaciens, we have found, by employing a suite of natural polyamines and synthetic methylated spermidine analogues together with spermidine biosynthetic mutants, that it is solely the 1,3-diaminopropane moiety of spermidine that is required for growth. Indeed, any polyamine containing an intact terminal 1,3-diaminopropane moiety can replace spermidine for growth, including the simple diamine 1,3-diaminopropane itself, a paradigm shift in understanding polyamine function in bacteria. We have identified for the first time a spermidine retroconversion activity in bacteria, producing diamine putrescine from triamine spermidine, however, exogenously-supplied tetraamine spermine is resistant to retroconversion. When spermidine levels are pharmacologically decreased, synthesis of spermine from spermidine is induced via the same biosynthetic enzymes, carboxyspermidine dehydrogenase and carboxyspermidine decarboxylase that produce spermidine from putrescine, the first identification of a spermine biosynthetic pathway in bacteria. This also suggests that spermidine represses spermine biosynthesis, but when spermidine levels decrease, it is then converted by carboxyspermidine dehydrogenase and decarboxylase enzymes to spermine, which is resistant to retroconversion and constitutes a sequestered pool of protected 1,3-diaminopropane modules required for growth. We also identify an efficient N-acetylspermidine deacetylase activity, indicative of a sophisticated bacterial polyamine homeostasis system.

Spermidine Inversely Influences Surface Interactions and Planktonic Growth in Agrobacterium tumefaciens

“…Our recent studies have revealed that the polyamine spermidine is essential for growth in Agrobacterium tumefaciens and that this is due to a requirement for its 1,3-diaminopropane moiety (11). In the current study, we isolated Agrobacterium tumefaciens transposon mutants that led to the elevated production of cellulose and increased biofilm formation and found that they were disrupted for the polyamine biosynthetic pathway.…”

“…WT, wild type. and accumulates ornithine (11). The mutant does produce low levels of spermidine (see Fig.…”

“…A. tumefaciens can transport various polyamines, and the weak growth of this mutant can be rescued with the addition of exogenous polyamines that, like spermidine, possess a terminal 1,3-diaminopropane moiety (Fig. 1), including norspermidine, a symmetrical polyamine one methylene group shorter than spermidine (11). Most organisms have dedicated systems for the uptake of polyamines from the environment, and there are several presumptive polyamine transporters in the A. tumefaciens C58 genome (24,25).…”

Polyamines in Eukaryotes, Bacteria, and Archaea

“…The CASDC/CASDH pathway was shown to produce Nspd from Dap and Spd from Put in V. cholerae (64); and Spd from Put, and aminopropylcadaverine and bis(aminopropylcadaverine) from Cad in the ␣-proteobacterium Agrobacterium tumefaciens (75). Triamine Hspd can be produced either by HSS, an enzyme related to CASDH, or from the DHS homologue DHSlike HSS (39).…”

“…No specific bacterial SpmSyn has been identified, and it is likely that in some species the Spd biosynthetic machinery can recognize Spd as a substrate to synthesize Spm (75). It has also been claimed that homologues of the plant A. thaliana acl5-encoded aminopropyltransferase TspmSyn found in bacteria are also specific for Tspm synthesis (77); however, it is more likely that those homologues encode agmatine aminopropyltransferase (70), because there are no reports of Tspm in the bacteria that pos-sess Acl5 homologues.…”