The Effect of Iron Limitation on the Transcriptome and Proteome of Pseudomonas fluorescens Pf-5

One of the most important micronutrients for bacterial growth is iron, whose bioavailability in soil is limited. Consequently, rhizospheric bacteria such as Pseudomonas fluorescens employ a range of mechanisms to acquire or compete for iron. We investigated the transcriptomic and proteomic effects of iron limitation on P. fluorescens Pf-5 by employing microarray and iTRAQ techniques, respectively. Analysis of this data revealed that genes encoding functions related to iron homeostasis, including pyoverdine and enantio-pyochelin biosynthesis, a number of TonB-dependent receptor systems, as well as some inner-membrane transporters, were significantly up-regulated in response to iron limitation. Transcription of a ribosomal protein L36-encoding gene was also highly up-regulated during iron limitation. Certain genes or proteins involved in biosynthesis of secondary metabolites such as 2,4-diacetylphloroglucinol (DAPG), orfamide A and pyrrolnitrin, as well as a chitinase, were over-expressed under iron-limited conditions. In contrast, we observed that expression of genes involved in hydrogen cyanide production and flagellar biosynthesis were down-regulated in an iron-depleted culture medium. Phenotypic tests revealed that Pf-5 had reduced swarming motility on semi-solid agar in response to iron limitation. Comparison of the transcriptomic data with the proteomic data suggested that iron acquisition is regulated at both the transcriptional and post-transcriptional levels

Micropropagation of Eucalyptus nitens maiden (Shining gum)

Summary Eucalyptus nitens Maiden (shining gum) is a frost-tolerant species of Eucalyptus that can be used as an alternative species to Eucalyptus globulus in some regions of Portugal where winter temperatures are too low. Seedlings and 1-yr-old shoot tips and nodes were used for micropropagation of E. nitens. The best multiplication rate (2.25) was obtained when seedling shoots (<15 mm) were cultured on a medium containing the major nutrients (at half-strength) and minor elements of Murashige and Skoog (1962) medium, the organics of De Fossard medium (De Fossard et al., 1974) and a combination of benzyladenine (0.9 µM) and 1-naphthaleneacetic acid (0.05 µM). Seedling cuttings (4-,8-, and 10-wk-old) rooted well on media containing several concentrations of 3-indolebutyric acid (4.9, 9.8, and 14.8 µM) or 3-indoleacetic acid (5.7, 11.4, and 17.1 µM), giving frequencies of root induction above 80%. With this type of explant, root formation was also found on basal medium without growth regulators. Rooting of in vitro-propagated shoots obtained from seedlings (8-wk-old) after four subcultures (every 3 wk) was more difficult, with the best results obtained on a medium containing 14.7 µM 3-indolebutyric acid (60.0% root induction). No root formation was achieved when shoots from 1-yr-old explants were used. After a period of 4 mo., 96.3% of the plants transferred to the greenhouse survived acclimatization