A bacterial phylogenetic survey of three environmentally distinct Antarctic Dry Valley soil biotopes showed a high proportion of so-called "uncultured" phylotypes, with a relatively low diversity of identifiable phylotypes. Cyanobacterial phylotypic signals were restricted to the high-altitude sample, whereas many of the identifiable phylotypes, such as the members of the Actinobacteria, were found at all sample sites. Although the presence of Cyanobacteria and Actinobacteria is consistent with previous culture-dependent studies of microbial diversity in Antarctic Dry Valley mineral soils, many phylotypes identified by 16S rDNA analysis were of groups that have not hitherto been cultured from Antarctic soils. The general belief that such "extreme" environments harbor a relatively low species diversity was supported by the calculation of diversity indices. The detection of a substantial number of uncultured bacterial phylotypes showing low BLAST identities (< 95%) suggests that Antarctic Dry Valley mineral soils harbor a pool of novel psychrotrophic taxa.

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In the vertebrate host, the malaria parasite invades and replicates asexually within circulating erythrocytes. Parasite proteolytic enzymes play an essential but poorly understood role in erythrocyte invasion. We have identified a Plasmodium falciparum gene, denoted pfsub-1, encoding a member of the subtilisin-like serine protease family (subtilases). The pfsub-1 gene is expressed in asexual blood stages of P. falciparum, and the primary gene product (PfSUB-1) undergoes post-translational processing during secretory transport in a manner consistent with its being converted to a mature, enzymatically active form, as documented for other subtilases. In the invasive merozoite, the putative mature protease (p47) is concentrated in dense granules, which are secretory organelles located toward the apical end of the merozoite. At some point following merozoite release and completion of erythrocyte invasion, p47 is secreted from the parasite in a truncated, soluble form. The subcellular location and timing of secretion of p47 suggest that it is likely to play a role in erythrocyte invasion. PfSUB-1 is a new potential target for antimalarial drug development.Plasmodium falciparum, the causative agent of the most severe form of human malaria, is an obligate intracellular apicomplexan parasite. The life cycle of the organism includes a number of specialized invasive (zoite) stages. In the vertebrate host, replication of the parasite in circulating erythrocytes is initiated when the cells are invaded by merozoites. The parasite replicates asexually within the infected erythrocyte to produce a number of progeny merozoites. Upon rupture of the host cell, these are released to invade fresh erythrocytes and perpetuate the blood stage cycle. Erythrocyte invasion by the malaria merozoite has been the subject of intensive study, since intervention strategies that prevent invasion would effectively block both replication of the parasite and the associated clinical disease.Electron microscopic studies have shown that erythrocyte invasion by the malaria merozoite takes place in a number of discrete stages. Initial reversible attachment of the parasite to the red cell surface is rapidly followed by reorientation, the formation of an irreversible junction between the apical prominence of the merozoite and the host cell surface, and finally entry of the parasite into the cell by a mechanism resembling a form of induced endocytosis (1-4). The process is facilitated by the controlled release of the contents of three types of secretory organelles, called rhoptries, micronemes, and dense granules, situated at or toward the apical domain of the merozoite (2, 5, 6). There is extensive evidence indicating an essential role for parasite-derived proteases in invasion. Invasion by P. falciparum merozoites is blocked in the presence of the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) 1 (7), and invasion by merozoites of a number of Plasmodium species is prevented by chymostatin (8 -13). The inhibitory effect of chymostatin on inv...

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The Cape Floral Kingdom is an area of unique plant biodiversity in South Africa with exceptional concentrations of rare and endemic species and experiencing drastic habitat loss. Here we present the first molecular study of the microbial diversity associated with the rhizosphere soil of endemic plants of the Proteaceae family (Leucospermum truncatulum and Leucadendron xanthoconus). Genomic DNA was extracted from L. truncatulum rhizosphere soil, L. xanthoconus rhizosphere and non-rhizosphere soil and used as a template for the polymerase chain reaction (PCR) amplification of the 16S ribosomal RNA gene (rDNA). Construction and sequencing of 16S rDNA libraries revealed a high level of biodiversity and led to the identification of several novel bacterial phylotypes. The bacterial community profiles were compared by 16S rDNA denaturing gradient gel electrophoresis (DGGE). Cluster analysis and biodiversity indices revealed that the rhizosphere soil samples were more similar to each other than to non-rhizosphere soil and the rhizosphere soil contained a bacterial diversity that was richer and more equitable compared with non-rhizosphere soil. A Chloroflexus and an Azospirillum genospecies were restricted to the L. xanthoconus rhizosphere soil and Stenotrophomonas genospecies was identified in all rhizosphere soil samples but was not present in the non-rhizosphere soil. Taxon-specific nested PCR and DGGE-identified differences between the Proteaceae plant rhizosphere soil with a Frankia genospecies restricted the L. truncatulum rhizosphere. Archaea-specific rDNA PCR, DGGE and DNA sequencing revealed that Crenarcheote genospecies were excluded from the plant rhizosphere soil and only present in non-rhizosphere soil.

The hydrolysis of vitamin BIZ under a wide variety of experimental conditions has been studied. Electrophoresis on paper has proved most useful for analysing the complex mixtures of basic, neutral, and acidic products so formed. Vitamin BIZ contains three primary amide groups, which can be hydrolysed stepwise, under comparatively mild conditions, to the corresponding acids. The acids so obtained, three mono-, three di-, and one tri-basic, have all been reconverted into the parent vitamin. Conditions for the hydrolytic removal of the 5 : 6-dimethylbenziminazole nucleotide, both before and after hydrolysis of the amide groups, have been defined and the crystalline free nucleotide has been isolated. 1-Aminopropan-2-01 is believed to be attached by ester linkage to the nucleotide and by amide linkage to the rest of the molecule. The moderately stable cobalt-containing end products from vigorous acid hydrolysis contain five, six, and seven acidic groupings and, from alkaline hydrolysis, five and six acidic groupings.THE combined results of the degradative work so f a r reported on vitamin B,, the antipernicious anaemia factor, have led to the partial formula ( I ) for the vitamin. Its precise molecular formula is not known with certainty, but C,,_,H84-92013-14NlpPCo covers the * A feature of the structure ( I ) is the 5 : 6-dimethyl-l-(a-D-ribofuranosyl)benzhinazoIe-2'(or 3') phosphate residue, which must be fully esterified as the vitamin itself contains no free acidic groups. The benziminazole nucleotide has been isolated from the products of acid hydrolysis of vitamin B,,, both as the barium salt (Buchanan, Johnson, Mills, and Todd, J., 1950, 2845) and as the free acid (Kaczka, Heyl, Jones, and Folkers, J . Amer. Chem. SOC., 1952, 74, 5549; see also Experimental section), and a synthesis has been reported (Kaczka et al., Zoc. cit.), although the point of attachment of the phosphate to the sugar side-chain (i.e,, whether 2' or 3') is still uncertain. The corresponding nucleoside has also been isolated from acid hydrolysates (Brink and Folkers, J . Amer. Chem. SOC., 1952, 74, 2856) and its structure, 5 : 6-dimethyl-l-(~~-~-~bofuranosyl)benz~~nazole, has been confirmed by synthesis (Holly, Shunk, Peel, Cahill, Lavigne, and Folkers, ibid., p. 4521) ; 5 : 6-dimethylbenzirninazole itself has been isolated from the products of vigorous acid hydrolysis of the vitamin (Brink and Folkers, ibid., 1950, 72, 4442; Beaven, Holiday, Johnson, Ellis, Mamalis, Petrow, and Sturgeon, J . Pharm. Pharmacol., 1949, 1, 957).Ammonia and D,-1-aminopropan-2-01 (Wolf, Jones, Valiant, and Folkers, J . Amer. Chem. SOC., 1950, 72, 2820) are also produced on acid hydrolysis, and it has been claimed by Chargaff, Levine, Green, and Kream (Exferientia, 1950, 6, 229) that two moles of the alkanolamine and four-five moles of ammonia are formed from each mole of the vitamin after hydrolysis with G~-hydrochloric acid for 6 hr. at 100" in a sealed tube. On the other hand Cooley, Davies, Ellis, Petrow, and Sturgeon ( J . Pharm. Pharmacol., 1953, 5, ...