The ability of four plant growth-promoting rhizobacteria, isolated in a previous study, to induce systemic resistance on Arabidopsis thaliana Col 0 against biotic and abiotic stress was evaluated. All the bacteria enhanced protection against the foliar pathogen Pseudomonas syringae DC3000 and increased plant tolerance to salt stress (NaCl 60 mM). Bacillus sp. strain L81 and Arthrobacter oxidans strain BB1 performed best with a decrease in the disease index of 61.2 and 52.3%, respectively, and a reduction in the mortality due to salt stress of 72.4 and 57.8%, respectively. Additionally, significant differences were found in growth and photosynthesis, again, L81 and BB1 performed best either in normal or under stress conditions. In order to elucidate the pathway elicited by these two strains to induce systemic resistance, experiments with the transgenic line of Arabidopsis thaliana NahG (defective in salicylic acid [SA]) and with the jar1 mutant (defective in jasmonic acid) were carried out. Results showed that the SA-dependent pathway was involved in the defense response induced by strains L81 and BB1. Results from quantitative reverse transcription-polymerase chain reaction analysis of the PR1 gene, related to the SA-dependent pathway and the PDF1.2 gene related to the SA-independent pathway, showed an increased expression of PR1 in BB1-treated plants, confirming involvement of the SA-dependent pathway in the defensive response.

Microbial cells do not live in isolation in their environment, but rather they communicate with each other using chemical signals. This sophisticated mode of cell-to-cell signalling, known as quorum sensing, was first discovered in bacteria, and coordinates the behaviour of microbial population behaviour in a cell-density-dependent manner. More recently, these mechanisms have been described in eukaryotes, particularly in fungi, where they regulate processes such as pathogenesis, morphological differentiation, secondary metabolite production and biofilm formation. In this manuscript, we review the information available to date on these processes in yeast, dimorphic fungi and filamentous fungi. We analyse the diverse chemical 'languages' used by different groups of fungi, their possible cross-talk and interkingdom interactions with other organisms. We discuss the existence of these mechanisms in multicellular organisms, the ecophysiological role of QS in fungal colonisation and the potential applications of these mechanisms in biotechnology and pathogenesis.

A study of plant defensive systemic responses induced by three plant growth promoting rhizobacteria (PGPR) on Arabidopsis thaliana Col 0 against Pseudomonas syringae pv. tomato DC3000 at the biochemical and transcriptional levels is reported in this paper. All three strains decreased disease severity when applied to A. thaliana prior to pathogen inoculation. At the biochemical level, each of the three strains induced ethylene (ET) when incubated with 1-amino-cyclopropane-1-carboxylic acid, and salicylic acid (SA) production in the plant. Plants treated with each of the three strains were also reduced in salicylic acid production after pathogen challenge compared to untreated controls. This effect was more marked in plants treated with Chryseobacterium balustinum AUR9, the strain most effective in decreasing disease severity. The expression level of PR1, a transcriptional marker of the SA-dependent pathway in C. balustinum AUR9-treated plants, is fourfold that of controls while the expression of PDF1.2, a transcriptional marker for the SA-independent pathway, is not induced. C. balustinum cell wall lipopolysaccharides, being putative bacterial elicitor molecules, are able to reproduce this systemic induction effect at low doses. From these observations, we hypothesize that certain PGPR strains are capable of stimulating different systemic responses in host plants. With C. balustinum AUR9, the SA-dependent pathway is stimulated first, as indicated by increases in SA levels and PR1 expression, followed by induction of the SA-independent pathway, as indicated by the increases in ET concentrations. The effects of both pathways combined with respect to disease suppression appear to be additive.

Summary: Two Gram‐negative, plant growth‐promoting rhizobacteria (PGPRs), denominated as M12 and M14, were classified by 16S rDNA sequencing as Burkholderia graminis species. Both strains were shown to produce a variety of N‐acyl‐homoserine lactone (AHL) quorum sensing (QS) signalling molecules. The involvement of these molecules in plant growth promotion and the induction of protection against salt stress was examined. AHL production was evaluated in vitro by thin‐layer chromatography using AHL biosensors, and the identity of the AHLs produced was determined by liquid chromatography‐tandem mass spectrometry. The in situ production of AHLs by M12 and M14 in the rhizosphere of Arabidopsis thaliana plants was detected by co‐inoculation with green fluorescent protein‐based biosensor strains and confocal laser scanning microscopy. To determine whether plant growth promotion and protection against salt stress were mediated by QS, these PGPRs were assayed on wild‐type tomato plants, as well as their corresponding transgenics expressing YenI (short‐chain AHL producers) and LasI (long‐chain AHL producers). In wild‐type tomato plants, only M12 promoted plant growth, and this effect disappeared in both transgenic lines. In contrast, M14 did not promote growth in wild‐type tomatoes, but did so in the LasI transgenic line. Resistance to salt stress was induced by M14 in wild‐type tomato, but this effect disappeared in both transgenic lines. The strain M12, however, did not induce salt resistance in wild‐type tomato, but did so in LasI tomato plants. These results reveal that AHL QS signalling molecules mediate the ability of both PGPR strains M12 and M14 to promote plant growth and to induce protection against salt stress.

Lipases and sterol esterases are enzymes with broad biotechnological applications, which catalyze the hydrolysis or synthesis of long-chain acylglycerols and sterol esters, respectively. In this paper, we review the current knowledge on the so-called Candida rugosa-like family of enzymes, whose members display in most cases affinity against the two substrates mentioned above. The family includes proteins with the α/β-hydrolase folding, sharing conserved motifs in their sequences, and common structural features. We will go through their production and purification, relate their described structures and catalytic activity, and discuss the influence of the hydrophobic character of these lipases on their aggregation state and activity. On the basis of the few crystal structures available, the role of each of the functional areas in catalysis will be analyzed. Considering the particular characteristics of this group, we propose their classification as "Versatile Lipases" (EC 3.1.1.x).