Important Role Player Research Articles

The impact of social transformation on the non‐government welfare sector and the social work profession

This article examines changes to non‐government social welfare, their impact on service delivery and on the social work profession. To redress the legacy of the past and the consequent inequalities in social welfare, in the first decade of democracy the government allocated the bulk of its welfare resources to transforming the social security system at the expense of social service delivery. As a result, South Africa has a costly social security budget with social services on the brink of collapse, leaving social workers and other social service professionals with low morale in the face of the huge challenge of providing welfare services with scarce resources, especially in the non‐government sector. Nevertheless, social work remains an important role player in social development. From its marginalised position in the first decade of democracy, in the second decade it is repositioning itself as a recognised contributor to reconstruction and development in South Africa.

Multiple sets of arsenic resistance genes are present within highly arsenic-resistant industrial strains of the biomining bacterium, Acidithiobacillus caldus

The moderately thermophilic, sulfur-oxidizing bacterium Acidithiobacillus caldusis an important role player in continuous-flow biooxidation processes associated with the biooxidation of arsenopyrite concentrates. Certain isolates of these bacteria have been exposed to high concentrations of arsenic for many years and have become highly arsenic-resistant. We investigated the arsenic resistance genes of the highly resistant strains of At. caldus and compared these with those of less arsenic-resistant isolates. Up to three sets of arsenic resistance genes were found in the most resistant strains. One set of genes was located on a 12-kb Tn 21-like transposon flanked by Tn 21-like 40-bp inverted repeats (IR) and the transposon was active in the bacterium, Escherichia coli. This transposon was present only in highly arsenic-resistant strains and contained an unusual ars operon with arsR, arsC, two arsD-like, two arsA-like and arsB genes. Situated between the arsA and arsB genes are two open reading frames encoding for NADH oxidase-like enzyme and a protein with a CBS domain that is also present in IMP dehydrogenases. Deletion of one copy of the arsDA genes occurred readily but there were no marked differences in arsenic resistance in the deleted clones. The second set of arsenic resistance genes appeared to be related to the first set although some of the genes were missing. The third set was distantly related and appeared to be present on the chromosomes of all At. caldus strains irrespective of whether they had been exposed to elevated levels of arsenic.

A transposon-located arsenic resistance mechanism from a strain of Acidithiobacillus caldus isolated from commercial, arsenopyrite biooxidation tanks

The moderately thermophilic, sulfur-oxidizing bacterium Acidithiobacillus caldus is an important role player in continuous-flow biooxidation processes associated with biomining. Biooxidation of arsenopyrite concentrates by a combination of Leptospirillum and At. caldus results in the release of soluble arsenic into the surrounding environment. Arsenate and arsenite are toxic to most organisms, yet At. caldus is able to thrive in this harsh environment. The purpose of this study was to identify and investigate arsenic resistance genes in At. caldus and compare its ars operon with those previously studied in other bacteria. A gene bank of a South African At. caldus strain #6 was constructed and transformed into an Escherichia coli arsenic-sensitive mutant strain to identify clones containing At. caldus arsenic resistance genes. A clone with an insert of 6.4 kb was selected and after two cycles of chromosome-walking a further 5.6 kb of DNA upstream of the original clone was isolated. This region was sequenced and found to have an unusual ars operon with a functional arsB gene, two arsD-like and two arsA-like genes. The arsenic resistance mechanism appears to be located on a Tn 21-like transposon and includes transposase and resolvase-like genes with the entire assemblage being flanked by Tn 21-like 38 bp inverted repeats (IR). Southern hybridization experiments using the arsB gene as a probe against total DNA from six different At. caldus strains indicated that the three South African strains which had been previously exposed to arsenic gave a positive hybridization signal, while three other At. caldus strains (KU, BC13 and C-SH12) did not. Southern hybridization of pulse field gels indicated that the arsB gene was chromosomally encoded. Genes encoding for NADH oxidase-like and IMP dehydrogenase-like enzymes were situated between the arsA and arsB genes. PCR and Southern hybridization experiments revealed that this unusual arrangement was not an artefact of cloning but that the 2.1 kb NADH oxidase-like and IMP dehydrogenase-like gene containing region was present between the arsA and arsB genes in all three South African strains. When transformed into the E. coli arsenic-sensitive mutant, the transposon-located system conferred increased resistance to arsenite, but not to arsenate. This indicated that the NADH oxidase-like gene did not function as an arsenate reductase in E. coli. It is possible that increased exposure to arsenic placed selection pressure on the three South African strains to acquire a Tn 21-like transposon containing an ars operon to enhance their arsenic resistance.

IGF-I isoforms and ageing skeletal muscle: an 'unresponsive' hypertrophy agent?

IGF-I isoforms and ageing skeletal muscle: an 'unresponsive' hypertrophy agent?