Enzymatic reduction of chromate: comparative studies using sulfate-reducing bacteria

Various sulfate-reducing bacteria of the genera Desulfovibrio and Desulfomicrobium were tested and compared for enzymatic reduction of chromate. Our study demonstrated that the ability to reduce chromate is widespread among sulfate-reducing bacteria. Among them, Desulfomicrobium norvegicum reduced Cr(VI) with the highest reaction rate. This strain grew in the presence of up to 500 μM chromate, but Cr(VI) reduction in the absence of sulfate was not associated with growth. The presence of chromate induced morphological changes and leakage of periplasmic proteins into the medium. The ability of isolated polyheme cytochromes c from sulfate- and sulfur-reducing bacteria to reduce chromate was also analyzed. Tetraheme cytochrome c ₃(M _r. 13,000) from Desulfomicrobium norvegicum showed twice as much activity as either tetraheme cytochrome c ₃ from Desulfovibrio vulgaris strain Hildenborough or triheme cytochrome c ₇ from Desulfuromonas acetoxidans. Results with cytochromes c ₃ and other c-type cytochromes altered by site-directed mutagenesis indicated that negative redox potential hemes are crucial for metal reductase activity. The present study also demonstrated that the (Fe) hydrogenase from sulfate-reducing bacteria could reduce chromate. Received: 14 April 2000 / Received revision: 6 July 2000 / Accepted: 9 July 2000     

Mapping, characterization, and expression analysis of the SM-20 human homologue, c1orf12, and identification of a novel related gene, SCAND2

Major psychosis was shown to segregate with a balanced translocation (1q42.1; 11q14.3) in a multigenerational family. This study describes the identification of a human SM-20 homologue gene that lies at about 400 kb on the centromeric side of the 1q42.1 breakpoint. The full-length cDNA sequence and gene structure were determined. Expression analysis was performed, showing high expression levels in skeletal and cardiac muscles; in the central nervous system, expression was restricted to dopaminergic neurons and spinal motoneurons. A second gene displaying high sequence similarity with SM-20 was also identified by BLAST. This gene, located on chromosome 15, is likely to have evolved by retroposition of SM-20 mRNA and an exon-shuffling mechanism. It encodes a 306-amino-acid protein harboring strong homology with an N-terminal motif found in some zinc-finger proteins. This gene was named SCAND2 (SCAN domain-containing 2).     

An interlaboratory comparison of physiological and genetic properties of four Saccharomyces cerevisiae strains

To select a Saccharomyces cerevisiae reference strain amenable to experimental techniques used in (molecular) genetic, physiological and biochemical engineering research, a variety of properties were studied in four diploid, prototrophic laboratory strains. The following parameters were investigated: 1) maximum specific growth rate in shake-flask cultures; 2) biomass yields on glucose during growth on defined media in batch cultures and steady-state chemostat cultures under controlled conditions with respect to pH and dissolved oxygen concentration; 3) the critical specific growth rate above which aerobic fermentation becomes apparent in glucose-limited accelerostat cultures; 4) sporulation and mating efficiency; and 5) transformation efficiency via the lithium-acetate, bicine, and electroporation methods. On the basis of physiological as well as genetic properties, strains from the CEN.PK family were selected as a platform for cell-factory research on the stoichiometry and kinetics of growth and product formation.     

Analysis of TwoStaphylococcus epidermidisPlasmids Coding for Resistance to Streptogramin A

The twoStaphylococcus epidermidisplasmids pIP1629 (7.5 kb) and pIP1630 (14.4 kb) contain thevgagene conferring resistance to streptogramin A. All the sequences of pIP1629, except two of the four 22-nt iterons preceding the replication gene, were found in pIP1630. The additional 6.9-kb fragment of pIP1630 is similar to the mobilizableS. epidermidisplasmid pSK639, carrying thedfrA-thyE-orf140operon and thought to replicate by an iteron controlled theta-type replication mechanism. The replication-mobilization elements of pIP1629 and pSK639 are very similar despite having been isolated in France and in Australia, respectively, showing that they are geographically widely dispersed inS. epidermidis.The genethyEencoding thymidylate synthetase carried by pSK639 is not present in pIP1630. pIP1630 probably arose by the recombination of two homologous plasmids carrying distinct resistance determinants.     

New evidence for a 67,000-year-old human presence at Callao Cave, Luzon, Philippines

Documentation of early human migrations through Island Southeast Asia and Wallacea en route to Australia has always been problematic due to a lack of well-dated human skeletal remains. The best known modern humans are from Niah Cave in Borneo (40-42 ka), and from Tabon Cave on the island of Palawan, southwest Philippines (47 ± 11 ka). The discovery of Homo floresiensis on the island of Flores in eastern Indonesia has also highlighted the possibilities of identifying new hominin species on islands in the region. Here, we report the discovery of a human third metatarsal from Callao Cave in northern Luzon. Direct dating of the specimen using U-series ablation has provided a minimum age estimate of 66.7 ± 1 ka, making it the oldest known human fossil in the Philippines. Its morphological features, as well as size and shape characteristics, indicate that the Callao metatarsal definitely belongs to the genus Homo. Morphometric analysis of the Callao metatarsal indicates that it has a gracile structure, close to that observed in other small-bodied Homo sapiens. Interestingly, the Callao metatarsal also falls within the morphological and size ranges of Homo habilis and H. floresiensis. Identifying whether the metatarsal represents the earliest record of H. sapiens so far recorded anywhere east of Wallace’s Line requires further archaeological research, but its presence on the isolated island of Luzon over 65,000 years ago further demonstrates the abilities of humans to make open ocean crossings in the Late Pleistocene.     

Metabolic processes sustaining the reviviscence of lichen <Emphasis Type="Italic">Xanthoria elegans</Emphasis> (Link) in high mountain environments

To survive in high mountain environments lichens must adapt themselves to alternating periods of desiccation and hydration. Respiration and photosynthesis of the foliaceous lichen, Xanthoria elegans, in the dehydrated state were below the threshold of CO₂-detection by infrared gas analysis. Following hydration, respiration totally recovered within seconds and photosynthesis within minutes. In order to identify metabolic processes that may contribute to the quick and efficient reactivation of lichen physiological processes, we analysed the metabolite profile of lichen thalli step by step during hydration/dehydration cycles, using ³¹P- and ¹³C-NMR. It appeared that the recovery of respiration was prepared during dehydration by the accumulation of a reserve of gluconate 6-P (glcn-6-P) and by the preservation of nucleotide pools, whereas glycolytic and photosynthetic intermediates like glucose 6-P and ribulose 1,5-diphosphate were absent. The large pools of polyols present in both X. elegans photo- and mycobiont are likely to contribute to the protection of cell constituents like nucleotides, proteins, and membrane lipids, and to preserve the integrity of intracellular structures during desiccation. Our data indicate that glcn-6-P accumulated due to activation of the oxidative pentose phosphate pathway, in response to a need for reducing power (NADPH) during the dehydration-triggered down-regulation of cell metabolism. On the contrary, glcn-6-P was metabolised immediately after hydration, supplying respiration with substrates during the replenishment of pools of glycolytic and photosynthetic intermediates. Finally, the high net photosynthetic activity of wet X. elegans thalli at low temperature may help this alpine lichen to take advantage of brief hydration opportunities such as ice melting, thus favouring its growth in harsh high mountain climates.     

Reduced secretion and expression of gelatinase profile in Toxoplasma gondii-infected human monocytic cells

The apicomplexan Toxoplasma gondii, an obligate intracellular parasite, can infect humans and a wide range of vertebrates. Following oral infection, the parasite invades tissues by crossing non-permissive biological barriers such as the placenta or the blood-brain barrier. But the molecular mechanisms underlying migration of T. gondii remain poorly characterized. The crossing of various basal membranes and infiltration into the extracellular matrix by T. gondii could involve matrix metalloproteinases (MMPs). We demonstrated a decrease in proMMP-2 and proMMP-9 secretion by THP-1 cells at 24 and 48h post invasion with regulation at the mRNA level throughout infection. This down regulation was associated with a decrease in TIMP-2 secretion and an inhibition of its expression. Moreover, results showed an activation of MT1-MMP; its expression was regulated after 6, 24, and 48h.     

Adaptation of acidogenic sludge to increasing glycerol concentrations for biohydrogen production

Hydrogen is a promising alternative as an energetic carrier and its production by dark fermentation from wastewater has been recently proposed, with special attention to crude glycerol as potential substrate. In this study, two different feeding strategies were evaluated for replacing the glucose substrate by glycerol substrate: a one-step strategy (glucose was replaced abruptly by glycerol) and a step-by-step strategy (progressive decrease of glucose concentration and increase of glycerol concentration from 0 to 5 g L^?1), in a continuous stirred tank reactor (12 h of hydraulic retention time (HRT), pH 5.5, 35 °C). While the one-step strategy led to biomass washout and unsuccessful H₂ production, the step-by-step strategy was efficient for biomass adaptation, reaching acceptable hydrogen yields (0.4?±?0.1 mol_H2?mol^?1 _{glycerol consumed}) around 33 % of the theoretical yield independently of the glycerol concentration. Microbial community structure was investigated by single-strand conformation polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE) fingerprinting techniques, targeting either the total community (16S ribosomal RNA (rRNA) gene) or the functional Clostridium population involved in H₂ production (hydA gene), as well as by 454 pyrosequencing of the total community. Multivariate analysis of fingerprinting and pyrosequencing results revealed the influence of the feeding strategy on the bacterial community structure and suggested the progressive structural adaptation of the community to increasing glycerol concentrations, through the emergence and selection of specific species, highly correlated to environmental parameters. Particularly, this work highlighted an interesting shift of dominant community members (putatively responsible of hydrogen production in the continuous stirred tank reactor (CSTR)) according to the gradient of glycerol proportion in the feed, from the family Veillonellaceae to the genera Prevotella and Clostridium sp., putatively responsible of hydrogen production in the CSTR.