Physiological and genetic description of dissimilatory perchlorate reduction by the novel marine bacterium Arcobacter sp. strain CAB.

A novel dissimilatory perchlorate-reducing bacterium (DPRB), Arcobacter sp. strain CAB, was isolated from a marina in Berkeley, CA. Phylogenetically, this halophile was most closely related to Arcobacter defluvii strain SW30-2 and Arcobacter ellisii. With acetate as the electron donor, strain CAB completely reduced perchlorate (ClO4(-)) or chlorate (ClO3(-)) [collectively designated (per)chlorate] to innocuous chloride (Cl(-)), likely using the perchlorate reductase (Pcr) and chlorite dismutase (Cld) enzymes. When grown with perchlorate, optimum growth was observed at 25 to 30°C, pH 7, and 3% NaCl. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) preparations were dominated by free-swimming straight rods with 1 to 2 polar flagella per cell. Strain CAB utilized a variety of organic acids, fructose, and hydrogen as electron donors coupled to (per)chlorate reduction. Further, under anoxic growth conditions strain CAB utilized the biogenic oxygen produced as a result of chlorite dismutation to oxidize catechol via the meta-cleavage pathway of aerobic catechol degradation and the catechol 2,3-dioxygenase enzyme. In addition to (per)chlorate, oxygen and nitrate were alternatively used as electron acceptors. The 3.48-Mb draft genome encoded a distinct perchlorate reduction island (PRI) containing several transposases. The genome lacks the pcrC gene, which was previously thought to be essential for (per)chlorate reduction, and appears to use an unrelated Arcobacter c-type cytochrome to perform the same function. IMPORTANCE The study of dissimilatory perchlorate-reducing bacteria (DPRB) has largely focused on freshwater, mesophilic, neutral-pH environments. This study identifies a novel marine DPRB in the genus Arcobacter that represents the first description of a DPRB associated with the Campylobacteraceae. Strain CAB is currently the only epsilonproteobacterial DPRB in pure culture. The genome of strain CAB lacks the pcrC gene found in all other DPRB tested, demonstrating a new variation on the (per)chlorate reduction pathway. The ability of strain CAB to oxidize catechol via the oxygenase-dependent meta-cleavage pathway in the absence of external oxygen by using the biogenic oxygen produced from the dismutation of chlorite provides a valuable model for understanding the anaerobic degradation of a broad diversity of xenobiotics which are recalcitrant to anaerobic metabolism but labile to oxygenase-dependent mechanisms

Isolation and Characterization of Glycerol-3-Phosphate Dehydrogenase-Defective Mutants of \u3cem\u3eNeurospora crassa\u3c/em\u3e

Three glycerol-nonutilizing mutants deficient in the mitochondrial glycerol-3-phosphate (G3P) dehydrogenase (EC 1.1.99.5) were isolated from inlts derivatives of Neurospora crassa following inositolless death at elevated temperatures on minimal glycerol medium. These mutants failed to grow on glycerol as a sole carbon source, but could grow on acetate, glucose, or mannitol media and were female fertile in genetic crosses, thereby distinguishing them from the previously reported polyol-protoperithecial defective Neurospora mutants. In addition, these glp mutants exhibited a distinct morphological alteration during vegetative growth on sucrose slants and colonial growth on sorbose-containing semicomplete medium. The glp-2 locus was assigned a location between arg-5 and nuc-2 on chromosome IIR on the basis of two-factor crosses and by duplication coverage by insertional translocation ALS176, but not NM177. All mutations were allelic as judged from the absence of both complementation in forced heterokaryons and genetic recombination among glp-2 mutations. The reversion frequency of all three mutations was less than 1010, indicating probable deletions in these strains. No G3P dehydrogenase activity could be detected in either cytosolic or mitochondrial extracts from mutant strains grown on glycerol, glucose, or galactose media. These results suggest that the glp-2 locus may be the structural gene for both the cytosolic and mitochondrial forms of G3P dehydrogenase or for a cytosolic precursor of the mitochondrial G3P dehydrogenase. The defect is specific for the G3P dehydrogenase since normal activities of the mitochondrial cytochrome oxidase and succinate dehydrogenase and the cytosolic glycerol dehydrogenase and dihydroxyacetone phosphate reductase are detected in mutant extracts. During attempted growth of glp-2 mutants on glycerol media, there was an accumulation of G3P in culture filtrates, a reduction in the mycelial growth rate, and a decreased level of glycerokinase induction

Distinct roles in autophagy and importance in infectivity of the two ATG4 cysteine peptidases of leishmania major

Macroautophagy in Leishmania, which is important for the cellular remodeling required during differentiation, relies upon the hydrolytic activity of two ATG4 cysteine peptidases (ATG4.1 and ATG4.2). We have investigated the individual contributions of each ATG4 to Leishmania major by generating individual gene deletion mutants (Δatg4.1 and Δatg4.2); double mutants could not be generated, indicating that ATG4 activity is required for parasite viability. Both mutants were viable as promastigotes and infected macrophages in vitro and mice, but Δatg4.2 survived poorly irrespective of infection with promastigotes or amastigotes, whereas this was the case only when promastigotes of Δatg4.1 were used. Promastigotes of Δatg4.2 but not Δatg4.1 were more susceptible than wild type promastigotes to starvation and oxidative stresses, which correlated with increased reactive oxygen species levels and oxidatively damaged proteins in the cells as well as impaired mitochondrial function. The antioxidant N-acetylcysteine reversed this phenotype, reducing both basal and induced autophagy and restoring mitochondrial function, indicating a relationship between reactive oxygen species levels and autophagy. Deletion of ATG4.2 had a more dramatic effect upon autophagy than did deletion of ATG4.1. This phenotype is consistent with a reduced efficiency in the autophagic process in Δatg4.2, possibly due to ATG4.2 having a key role in removal of ATG8 from mature autophagosomes and thus facilitating delivery to the lysosomal network. These findings show that there is a level of functional redundancy between the two ATG4s, and that ATG4.2 appears to be the more important. Moreover, the low infectivity of Δatg4.2 demonstrates that autophagy is important for the virulence of the parasite

The evolutionary rewiring of ubiquitination targets has reprogrammed the regulation of carbon assimilation in the pathogenic yeast Candida albicans

Date of Acceptance: 13/11/2012 This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-ShareAlike 3.0 Unported license, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Correction for Sandai et al., The Evolutionary Rewiring of Ubiquitination Targets Has Reprogrammed the Regulation of Carbon Assimilation in the Pathogenic Yeast Candida albicans published 20-01-2015 DOI: 10.1128/mBio.02489-14Peer reviewedPublisher PD

Safe design of cooled tubular reactors for exothermic multiple reactions: Multiple-reaction networks

The model of the pseudo-homogeneous, one-dimensional cooled tubular reactor is applied to a multiple-reaction network. It is demonstrated for a network which consists of two parallel and two consecutive reactions. Three criteria are developed to obtain an integral yield which does not deviate more than a chosen fraction from the maximum yield that can be obtained in an isothermal reactor. The criteria enable us to choose relevant design and operating conditions for the safe execution of a reaction network in a tubular reactor. The method is illustrated for the production of maleic anhydride by air oxidation of benzene