BackgroundGluconacetobacter diazotrophicus Pal5 is an endophytic diazotrophic bacterium that lives in association with sugarcane plants. It has important biotechnological features such as nitrogen fixation, plant growth promotion, sugar metabolism pathways, secretion of organic acids, synthesis of auxin and the occurrence of bacteriocins.ResultsGluconacetobacter diazotrophicus Pal5 is the third diazotrophic endophytic bacterium to be completely sequenced. Its genome is composed of a 3.9 Mb chromosome and 2 plasmids of 16.6 and 38.8 kb, respectively. We annotated 3,938 coding sequences which reveal several characteristics related to the endophytic lifestyle such as nitrogen fixation, plant growth promotion, sugar metabolism, transport systems, synthesis of auxin and the occurrence of bacteriocins. Genomic analysis identified a core component of 894 genes shared with phylogenetically related bacteria. Gene clusters for gum-like polysaccharide biosynthesis, tad pilus, quorum sensing, for modulation of plant growth by indole acetic acid and mechanisms involved in tolerance to acidic conditions were identified and may be related to the sugarcane endophytic and plant-growth promoting traits of G. diazotrophicus. An accessory component of at least 851 genes distributed in genome islands was identified, and was most likely acquired by horizontal gene transfer. This portion of the genome has likely contributed to adaptation to the plant habitat.ConclusionThe genome data offer an important resource of information that can be used to manipulate plant/bacterium interactions with the aim of improving sugarcane crop production and other biotechnological applications.

Nitrogen-fixing bacteria have been isolated from sugarcane in an endophytic and beneficial interaction that promotes plant growth. In this work, for the first time, the involvement of ethylene signalling in this interaction was investigated by molecular characterizing members of this pathway in sugarcane. The expression pattern of a putative ethylene receptor (SCER1) and two putative ERF transcription factors (SCERF1 and SCERF2) show exclusive modulation in plants inoculated with the diazotrophic endophytes. The gene expression profile of SCER1, SCERF1, and SCERF2 is differentially regulated in sugarcane genotypes that can establish efficient or inefficient associations with diazotrophic micro-organisms, exhibiting high or low biological nitrogen fixation (BNF) rates, respectively. In addition, SCER1, SCERF1, and SCERF2 expression is different in response to interactions with pathogenic and beneficial micro-organisms. Taken together, that data suggest that SCER1, SCERF1, and SCERF2 might participate in specific ethylene signalling cascade(s) that can identify a beneficial endophytic association, modulating sugarcane responses toward the diazotrophic endophytes.

Endophytic nitrogen-fixing bacteria have been isolated from graminaceous plants such as maize, rice, and sugarcane. They are thought to promote plant growth, not only by fixing nitrogen, but also by the production of plant hormones. The molecular mechanisms involved in this interaction are not yet clear. In this work, the identification of a receptor-like kinase (RLK), named SHR5, which may participate in signal transduction involved in the establishment of plant-endophytic bacteria interaction is described for the first time. SHR5 seems to be part of a novel subclass of RLKs present in a wide range of plant species. The expression of this gene is down-regulated in sugarcane plants associated exclusively with beneficial endophytic bacteria and is not a general response caused by micro-organisms or abiotic stress. In addition, more successful sugarcane-endophytic bacteria associations have a more pronounced decrease in SHR5 expression, suggesting that SHR5 mRNA levels in plant cells are inversely related to the efficiency of the association.

Gluconacetobacter diazotrophicus is a plant-growth-promoting bacterium that colonizes sugarcane. In order to investigate molecular aspects of the G. diazotrophicus-sugarcane interaction, we performed a quantitative mass spectrometry-based proteomic analysis by (15)N metabolic labeling of bacteria, root samples, and co-cultures. Overall, more than 400 proteins were analyzed and 78 were differentially expressed between the plant-bacterium interaction model and control cultures. A comparative analysis of the G. diazotrophicus in interaction with two distinct genotypes of sugarcane, SP70-1143 and Chunee, revealed proteins with fundamental roles in cellular recognition. G. diazotrophicus presented proteins involved in adaptation to atypical conditions and signaling systems during the interaction with both genotypes. However, SP70-1143 and Chunee, sugarcane genotypes with high and low contribution of biological nitrogen fixation, showed divergent responses in contact with G. diazotrophicus. The SP70-1143 genotype overexpressed proteins from signaling cascades and one from a lipid metabolism pathway, whereas Chunee differentially synthesized proteins involved in chromatin remodeling and protein degradation pathways. In addition, we have identified 30 bacterial proteins in the roots of the plant samples; from those, nine were specifically induced by plant signals. This is the first quantitative proteomic analysis of a bacterium-plant interaction, which generated insights into early signaling of the G. diazotrophicus-sugarcane interaction.

Gluconacetobacter diazotrophicus, an endophyte isolated from sugarcane, is a strict aerobe that fixates N2. This process is catalyzed by nitrogenase and requires copious amounts of ATP. Nitrogenase activity is extremely sensitive to inhibition by oxygen and reactive oxygen species (ROS). However, the elevated oxidative metabolic rates required to sustain biological nitrogen fixation (BNF) may favor an increased production of ROS. Here, we explored this paradox and observed that ROS levels are, in fact, decreased in nitrogen-fixing cells due to the up-regulation of transcript levels of six ROS-detoxifying genes. A cluster analyses based on common expression patterns revealed the existence of a stable cluster with 99.8% similarity made up of the genes encoding the α-subunit of nitrogenase Mo–Fe protein (nifD), superoxide dismutase (sodA) and catalase type E (katE). Finally, nitrogenase activity was inhibited in a dose-dependent manner by paraquat, a redox cycler that increases cellular ROS levels. Our data revealed that ROS can strongly inhibit nitrogenase activity, and G. diazotrophicus alters its redox metabolism during BNF by increasing antioxidant transcript levels resulting in a lower ROS generation. We suggest that careful controlled ROS production during this critical phase is an adaptive mechanism to allow nitrogen fixation.

Background and Objectives: Staphylococcus aureus is an important pathogen and a frequent cause of infections associated with biofilm production in implantable medical devices. Biofilm production can be induced by sub-inhibitory concentrations (sub-MICs) of certain antibiotics, but few studies have researched this occurrence in S. aureus. In this study, we investigated the effect of sub-MICs of rifampicin and minocycline on biofilm production by five clinical and five non-clinical S. aureus isolates.Methods:Microtiter Plate assay and Congo Red Agar Test were used to analyze the biofilm production. The biofilm composition was evaluated by the detachment assay with sodium metaperiodate and proteinase K.Results:Rifampicin sub-MICs induced very high biofilm formation in seven isolates that were non-producers in Tryptic Soy Broth. In one producer isolate, the biofilm formation level was not affected by sub-MICs of this drug. Sub-MICs of minocycline did not induce biofilm production in all isolates tested and in two producer isolates, instead, MIC/2 and MIC/4 inhibited biofilm production. The results of the drugs in combination were similar to those with rifampicin alone. The biofilm matrix was identified as polysaccharide, except for one producer isolate, classified as proteinaceous. Polysaccharide biofilm producer isolates, when grown on Congo Red Agar without sucrose, but with sub-MICs of rifampicin, showed results in agreement with those obtained in Microtiter Plate Test.Conclusion:The high biofilm production induced by sub-MICs of rifampicin has potential clinical relevance, because this is one of the drugs commonly used in the impregnation of catheters. In addition, it is used adjunctively to treat certain S. aureus infections.

Breast cancer is one of the most prevalent cancers in the world and is also the leading cause of cancer death in women. The use of bioactive compounds of functional foods contributes to reduce the risk of chronic diseases, such as cancer and vascular disorders. In this study, we evaluated the antioxidant potential and the influence of pitaya extract (PE) on cell viability, colony formation, cell cycle, apoptosis, and expression of BRCA1, BRCA2, PRAB, and Erα in breast cancer cell lines (MCF-7 and MDA-MB-435). PE showed high antioxidant activity and high values of anthocyanins (74.65 ± 2.18). We observed a selective decrease in cell proliferation caused by PE in MCF-7 (ER+) cell line. Cell cycle analysis revealed that PE induced an increase in G0/G1 phase followed by a decrease in G2/M phase. Also, PE induced apoptosis in MCF-7 (ER+) cell line and suppressed BRCA1, BRCA2, PRAB, and Erα gene expression. Finally, we also demonstrate that no effect was observed with MDA-MB-435 cells (ER−) after PE treatment. Taken together, the present study suggests that pitaya may have a protective effect against breast cancer.

W i i r m eu n d S t o f f i i b e r t r a g u n g© Springer- Verlag 1990 Heat transfer solutions in laminar co-current flow E. Nogueira a n d R. M. Cotta, Rio de Janeiro, Brasil of immiscible liquids Abstract. Thermal entry region solutions are analytically determined for horizontal, co-current laminar flow of immiscible liquids in direct contact, inside circular tubes and parallel plate channels, km The related eigenvalue problem for such a composite media is read-£ _ kt ily solved by extending the ideas in the recently advanced sign-count -k~ method. It is assumed a core-annular flow configuration for circular g-= dp tubes and sheat-core flow for the parallel plates channel, without -d--~ consideration of interface instabilities and stratified flow. First, the rh velocity problem is solved for fully developed flow and pumping rh,~ power expressions established for different operating conditions. L Then, the temperature problem is analytically handled to yield exr~ pressions for quantities of practical interest such as total heat exr 2 change rates, along the duct length and, again, for different flow To," rates and pressure drop requirements. The analysis is illustrated T,~ through consideration of an application dealing with pumping of a ti very viscous oil with the addition of an external thin layer of a less u re(r) viscous fluid (water). Pumping power and total heat exchange are zi,, then evaluated for both geometries and critically compared to the single fluid flow problem. L6sungen fiir die W~irmeiibertragung von unvermischbaren Fliissigkeiten in einer laminaren Gleichstr6mungZusammenfassung. Hier sind L6sungen ffir die thermische Eintrittsstrecke yon horizontalen, laminaren Gleichstr6mungen in unvermischbaren FRissigkeiten, die in direktem Kontakt untereinander sind, analytisch bestimmt worden. Die L6sungen gelten ffir Gleichstr6mungen in R6hren und in parallelen flachen Kan/ilen. Das betreffende Eigenwertproblem ffir solch ein zusammengesetztes Medium ist vollkommen mit dem Gedanken des kfirzlich weiterentwickelten Zeichenzfihlverfahrens ge16st worden. Ffir die Rohre sind kreisring-und kernf6rmige Str6mungen und ffir die paralMen Plattenkanfile Sehichtkernstr6mungen angenommen worden. Hierbei ist die Grenzfl/icheninstabilitfit nicht in Betracht gezogen worden. Als erstes ist das Geschwindigkeitsproblem ffir eine vollkommen entwickelte Str6mung ge16st undes sind Ausdr/icke ffir die Pumpleistung ffir verschiedene Betriebsbedingungen ermittelt worden. Dann ist das Temperaturproblem analytisch behandelt worden, um Ausdrficke fiir die Gr6Ben yon praktischem Interesse zu erzielen, wie die gesamte W~irmeaustauschrate fiber die Kanalt~nge ffir verschiedene Str6mungsgeschwindigkeiten und Druckverlustanforderungen. Die Berechnung ist durch die Betrachtung eines Anwendungsbeispiels veranschaulicht worden, bei dem sehr z/ihflfissiges O1 mit einer zus/itzlichen/iugeren, dfinnen Schicht, die weniger z/ihflfissig ist, gepumpt wurde. Die Pumpleistung und der gesamte Wfirmeaustausch sind ffir beide Geometrien ausgew...