The genus Xanthomonas is a diverse and economically important group of bacterial phytopathogens, belonging to the gamma-subdivision of the Proteobacteria. Xanthomonas axonopodis pv. citri (Xac) causes citrus canker, which affects most commercial citrus cultivars, resulting in significant losses worldwide. Symptoms include canker lesions, leading to abscission of fruit and leaves and general tree decline. Xanthomonas campestris pv. campestris (Xcc) causes black rot, which affects crucifers such as Brassica and Arabidopsis. Symptoms include marginal leaf chlorosis and darkening of vascular tissue, accompanied by extensive wilting and necrosis. Xanthomonas campestris pv. campestris is grown commercially to produce the exopolysaccharide xanthan gum, which is used as a viscosifying and stabilizing agent in many industries. Here we report and compare the complete genome sequences of Xac and Xcc. Their distinct disease phenotypes and host ranges belie a high degree of similarity at the genomic level. More than 80% of genes are shared, and gene order is conserved along most of their respective chromosomes. We identified several groups of strain-specific genes, and on the basis of these groups we propose mechanisms that may explain the differing host specificities and pathogenic processes.

Despite the intense interest in the metabolic regulation and evolution of the ATP-producing pathways, the long standing question of why most multicellular microorganisms metabolize glucose by respiration rather than fermentation remains unanswered. One such microorganism is the cellulolytic fungus Trichoderma reesei (Hypocrea jecorina). Using EST analysis and cDNA microarrays, we find that in T. reesei expression of the genes encoding the enzymes of the tricarboxylic acid cycle and the proteins of the electron transport chain is programmed in a way that favors the oxidation of pyruvate via the tricarboxylic acid cycle rather than its reduction to ethanol by fermentation. Moreover, the results indicate that acetaldehyde may be channeled into acetate rather than ethanol, thus preventing the regeneration of NAD ؉ , a pivotal product required for anaerobic metabolism. The studies also point out that the regulatory machinery controlled by glucose was most probably the target of evolutionary pressure that directed the flow of metabolites into respiratory metabolism rather than fermentation. This finding has significant implications for the development of metabolically engineered cellulolytic microorganisms for fuel production from cellulose biomass.Evolution has produced a diverse array of metabolic pathways and regulatory mechanisms that reflect the adaptation of an immense variety of microorganisms to different environments and nutritional requirements. A prominent example is the metabolism of glucose, the primary and preferred fuel for eukaryotic microorganisms. Although glucose is metabolized by a highly conserved series of connected enzymatic reactions, the mechanisms that regulate its fate and the properties of the ATP-producing pathways have been subjected to selection pressure during evolution. Aerobic (respiration) and anaerobic (fermentation) pathways are used by microorganisms to obtain energy from glucose, in the form of ATP. These pathways allow organisms to produce ATP at different rates and with different efficiencies; respiration proceeds at a lower rate and with a high yield, whereas fermentation operates at higher rates but with lower yield. Selection pressure imposed by energy limitation and the high ATP yield of respiration has been implicated in facilitating the evolutionary transition from unicellular to undifferentiated multicellular organisms (1).Unicellular microorganisms, such as the yeast Saccharomyces cerevisiae, use both pathways depending on the metabolic state of the cell, whereas multicellular microorganisms, such as filamentous fungi, preferentially use respiration (2). Mucor racemosus, a dimorphic fungus that can grow either in a unicellular (yeast-like) or a multicellular (mycelial) form, also uses both; the unicellular form exploits fermentation, whereas the multicellular form is capable of respiration (3-5).S. cerevisiae preferentially ferments glucose, even in the presence of oxygen, producing ethanol and CO 2 by anaerobic metabolism. Only after exhaustion of the available glucose...

Background: Molecular features underlying enzyme function in extreme environments are poorly understood. Results: Identification of the basis for thermostability, halophilicity, and detoxification activity in a mercuric reductase from hot deep-sea brine. Conclusion: A small number of structural modifications accounts for the enzyme's robustness. Significance: This work defines novel adaptations that enable enzymes to cope with multiple abiotic stressors simultaneously.

Fungal habitats include soil, water, and extreme environments. With around 100,000 fungus species already described, it is estimated that 5.1 million fungus species exist on our planet, making fungi one of the largest and most diverse kingdoms of eukaryotes. Fungi show remarkable metabolic features due to a sophisticated genomic network and are important for the production of biotechnological compounds that greatly impact our society in many ways. In this review, we present the current state of knowledge on fungal biodiversity, with special emphasis on filamentous fungi and the most recent discoveries in the field of identification and production of biotechnological compounds. More than 250 fungus species have been studied to produce these biotechnological compounds. This review focuses on three of the branches generally accepted in biotechnological applications, which have been identified by a color code: red, green, and white for pharmaceutical, agricultural, and industrial biotechnology, respectively. We also discuss future prospects for the use of filamentous fungi in biotechnology application.

Oxygen is essential for the survival of obligatorily aerobic eukaryotic microorganisms, such as the multicellular fungus Trichoderma reesei. However, the molecular basis for the inability of such cells to survive for extended periods under anoxic conditions is not fully understood. Using cDNA microarray analysis, we show that changes in oxygen availability have a drastic effect on gene expression in T. reesei. The expression levels of 392 (19.6%) out of 2000 genes examined changed significantly in response to hypoxia, transient anoxia, and reoxygenation. In addition to modulating many genes with no previously assigned function, cells respond to hypoxia by readjusting the balance of expression between genes required for energy production and consumption, and altering the expression of genes involved in protective mechanisms and signaling pathways. Moreover, we show that transient anoxia strongly represses genes for enzymes that are critical for glycolysis, and are essential for energy production under anaerobic conditions. Our study thus reveals crucial differences between the facultative anaerobe Saccharomyces cerevisiae and T. reesei with regard to the oxygen-dependent transcriptional control of the glycolytic pathway, which can account for the differential survival of the two species in the absence of oxygen.