Increased Uptake of Putrescine in the Rhizosphere Inhibits Competitive Root Colonization by Pseudomonas fluorescens Strain WCS365

Abstract

Sequence analysis of the chromosomal Tn5lacZ flanking regions of the Pseudomonas fluorescens WCS365 competitive root colonization mutant PCL1206 showed that the Tn5lacZ is inserted between genes homologous to bioA and potF. The latter gene is the first gene of the potF1F2GHI operon, which codes for a putrescine transport system in Escherichia coli. The position of the Tn5lacZ suggests an effect on the expression of the pot operon. A mutation in the potF1 gene as constructed in PCL1270, however, had no effect on competitive root colonization. The rate of uptake of [1,4-14C]putrescine by cells of mutant PCL1206 appeared to be increased, whereas cells of strain PCL1270 were strongly impaired in the uptake of putrescine. Dansylation of tomato root exudate and subsequent thin-layer chromatography showed the presence of a component with the same Rf value as dansyl-putrescine, which was identified as dansyl-putrescine by mass spectrometric analyses. Other polyamines such as spermine and spermidine were not detected in the root exudate. Growth of mutant strains, either alone or in competition with the wild type, was tested in media containing putrescine, spermine, or spermidine as the sole nitrogen source. The results show that mutant PCL1206 is strongly impaired in growth on putrescine and slightly impaired on spermine and spermidine. The presence of the polyamines had a similar effect on the growth rate of strain PCL1270 in the presence of putrescine but a less severe effect in the presence of spermine and spermidine. We conclude that an increased rate of putrescine uptake has a bacteriostatic effect on Pseudomonas spp. cells. We have shown that putrescine is an important tomato root exudate component and that root-colonizing pseudomonads must carefully regulate their rate of uptake because increased uptake causes a decreased growth rate and, therefore, a decreased competitive colonization ability.

Unraveling the Secret Lives of Bacteria: Use of In Vivo Expression Technology and Differential Fluorescence Induction Promoter Traps as Tools for Exploring Niche-Specific Gene Expression

“…During plant root colonization, Pseudomonas fluorescens upregulates a gene involved in putrescine uptake (potF2) (218). This observation is consistent with the ability of Pseudomonas fluorescens to utilize putrescine as sole nitrogen source (132). Degradation of putrescine during infection of tomato plants by Ralstonia solanacearum is suggested by the upregulation of a gabD1 homologue, encoding a putative succinate semialdehyde dehydrogenase (26).…”

Wheat roots efflux a diverse array of organic N compounds and are highly proficient at their recapture

“…Nevertheless most of the compound classes and many of the individual compounds have been previously reported from root exudates. For example, compounds and classes that were present in root exudates of wheat and have been reported previously from wheat and other species include the polyamine putrescine (Kuiper et al 2001), quaternary ammonium compounds such as betaine and choline (Ikegami et al 1982;de Rudder et al 1999;Fan Fig. 5 The relationship between concentration of 45 organic N exudate compounds and the rate of uptake divided by the rate of efflux (uptake/efflux).…”

Comparative Whole-Genome Hybridization Reveals Genomic Islands inBrucellaSpecies

“…GI-5 has 19 ORFs encoding peptide ABC-type transporters such as Dpp, Opp, and Pot systems. Homologs of these transporters in other bacteria are important for root colonization, intracellular survival, attachment to host cell, and virulence (4,27,32). B. ovis is highly sensitive to cationic antimicrobial peptides in contrast to other Brucella species, including the rough mutants of B. abortus (14).…”