Evaluation of the efficiency of measures for sulphidic mine waste mitigation

To control the environmentally detrimental impact of acid rock drainage, two different countermeasures, layers of acid-buffering materials and sodium dodecyl sulphate addition, were tested for their efficiency in laboratory percolation experiments. In the experiment with a layer of calcium bentonite, only the iron output was reduced. The experiments with layers of concrete grains demonstrated a decrease of the microbial activity as well as a precipitation of heavy-metal ions, whereas the cell numbers did not decrease. Furthermore, finely grained concrete (1–5 mm) formed a water-tight hardpan (self-sealing layer). In the experiment with 1 mM sodium dodecyl sulphate, all the microorganisms were killed and hence metal sulphide dissolution was stopped. With 0.1 mM sodium dodecyl sulphate only a short, transient inhibition of leaching was achieved. The bacteria remained alive. Received: 16 February 1998 / Accepted: 23 February 1998     

Non‐pollinating cheater wasps benefit from seasonally poor performance of the mutualistic pollinating wasps at the northern limit of the range of Ficus microcarpa

1. Species interactions in tightly bound ecological mutualisms often feature highly specialised species' roles in which competitive exclusion may preclude multi‐species coexistence. Among the 800 fig (Ficus) species, it was originally considered that each was pollinated by their own wasp (Agaonidae). However, recent investigations show that this ‘one‐to‐one’ rule often breaks down, as fig species regularly host multiple agaonids but in ways suggesting that competitive processes still mediate biodiversity outcomes. 2. A phenological survey was conducted of the fig–fig wasp pair, Ficus microcarpa and its associated pollinating wasp, alongside its sister species, the cheating wasp, in Xishuangbanna, China. 3. Reproductive output underwent extreme seasonal variation. Seed and pollinator production fell markedly during cooler, drier months, although high levels of fig production continued. However, this resource was predominantly utilised by the cheater species, which offers no pollination services. Pollinators and cheaters rarely co‐occur, suggesting that temporal coexistence is constrained by competition for access to figs. 4. The overall findings indicate periodic rearrangements of mutualism dynamics, probably resulting from a strongly seasonal environment. Sympatric co‐occurrence may result from a window of opportunity for a functionally divergent agaonid, potentially due to constraints on the main pollinator in adapting to variable year‐round conditions that prevent competitive exclusion.     

Involvement of the galactosyl-1-phosphate transferase encoded by the Salmonella enterica rfbP gene in O-antigen subunit processing.

rfbT of Salmonella enterica LT2 was previously thought, together with rfaL, to be involved in the ligation of polymerized O antigen to core-lipid A, and three mutants were known. We report the mapping of the mutations to rfbP, the galactosyl-1-phosphate transferase gene, which is now shown to encode a bifunctional protein. The mutations which have the former rfbT phenotype are referred to as rfbP(T). We also show that rfbP(T) mutants are not blocked in the ligation step as previously believed but in an earlier step, possibly in flipping the O-antigen subunit on undecaprenyl pyrophosphate from the cytoplasmic to periplasmic face of the cytoplasmic membrane.     

Increased Expression of Apolipoprotein D Following Experimental Traumatic Brain Injury

Increasing evidence suggests that apolipoprotein D (apoD) could play a major role in mediating neuronal degeneration and regeneration in the CNS and the PNS. To investigate further the temporal pattern of apoD expression after experimental traumatic brain injury in the rat, male Sprague-Dawley rats were subjected to unilateral cortical impact injury. The animals were killed and examined for apoD mRNA and protein expression and for immunohistological analysis at intervals from 15 min to 14 days after injury. Increased apoD mRNA and protein levels were seen in the cortex and hippocampus ipsilateral to the injury site from 48 h to 14 days after the trauma. Immunohistological investigation demonstrated a differential pattern of apoD expression in the cortex and hippocampus, respectively: Increased apoD immunoreactivity in glial cells was detected from 2 to 3 days after the injury in cortex and hippocampus. In contrast, increased expression of apoD was seen in cortical and hippocampal neurons at later time points following impact injury. Concurrent histopathological examination using hematoxylin and eosin demonstrated dark, shrunken neurons in the cortex ipsilateral to the injury site. In contrast, no evidence of cell death was observed in the hippocampus ipsilateral to the injury site up to 14 days after the trauma. No evidence of increased apoD mRNA or protein expression or neuronal pathology by hematoxylin and eosin staining was detected in the contralateral cortex and hippocampus. Our results reveal induction of apoD expression in the cortex and hippocampus following traumatic brain injury in the rat. Our data also suggest that increased apoD expression may play an important role in cortical neuronal degeneration after brain injury in vivo. However, increased expression of apoD in the hippocampus may not necessarily be indicative of neuronal death.     

Enhanced activation of a T cell line specific for acetylcholine receptor (AChR) by using anti-AChR monoclonal antibodies plus receptors

Immune complex-mediated regulation of the immune response has been studied by using T cell lines and monoclonal antibodies (MAb), both specific for the acetylcholine receptor (AChR). Rat T lymphocytes bearing the W3/25 phenotype and specific for AChR from Torpedo californica have been propagated in vitro for nearly 1 yr. These T cells proliferate in response to optimal concentrations of AChR presented by irradiated syngeneic thymus cells. At suboptimal concentrations of antigen there is little activation of the T cell line. We report here that the addition of small amounts of anti-AChR MAb produces dramatic stimulation of the T cell lines at suboptimal doses of AChR. Enhanced activation depends on the isotype and not the fine specificity of the MAb that are used. The observed phenomenon is antigen specific, and in fact, the immune complexes may actually suppress the proliferative response of irrelevant T cells to some extent. The MAb plus antigen are rapidly bound to the surface of the antigen-presenting cell, which we have shown is the dendritic cell.     

Expression of ultraviolet-induced restriction alleviation in Escherichia coli K-12. Detection of a lambda phage fraction with a retarded mode of DNA injection

Ultraviolet-induced restriction alleviation is an SOS function which partially relieves the K-12-specific DNA restriction in Escherichia coli. Restriction alleviation is determined by observing elevated survival of unmodified phage lambda in cells irradiated with ultraviolet prior to infection. We demonstrate that restriction of lambda is also relieved when log-phase cells are irradiated as late as 50 min after adsorption of lambda. At this time more than 60% of the lambda DNA is already released as acid-soluble material from the cells. Experiments involving reextraction of lambda DNA from infected cells and a mild detergent treatment removing absorbed phages from the cellular surface showed that only a small specific fraction of all lambda infections is destined to escape restriction due to restriction alleviation. This fraction (10-20%) has a retarded mode of DNA injection (60 min or longer) after adsorption which allows the expression of the restriction alleviation function before the phage DNA is exposed to restriction endonucleases. This behaviour of a fraction of lambda phages explains why the SOS function restriction alleviation could initially be discovered. We show that the retarded mode of DNA injection is not required for another SOS function acting on lambda DNA, the increased repair of ultraviolet-irradiated DNA (Weigle reactivation).     

Escherichia coli RecBC pseudorevertants lacking chi recombinational hotspot activity

Pseudorevertants of an Escherichia coli exonuclease V (RecBC enzyme)-negative mutant have been isolated after ethyl methane sulfonate mutagenesis of a recC73 (presumed missense) mutant. The remedial mutations in each of the four pseudorevertants studied in detail map and complement as recC mutations. By several criteria, such as recombination proficiency, support of phage growth, RecBC nuclease activity, and cell viability, the pseudorevertants appear to have regained partially or completely various aspects of RecBC activity. However, chi recombinational hotspots, which stimulate exclusively the RecBC pathway of recombination, have no detectable activity in lambda vegetative crosses in the pseudorevertants. The properties of these mutants, in which the RecBC pathway of recombination is active yet in which chi is not active, are consistent with the hypothesis that wild-type RecBC enzyme directly interacts with chi sites; alternatively, the mutants may block or bypass the productive interaction of another recombinational enzyme with chi.     

A statistical method for correlating tRNA sequence with amino acid specificity.

A statistical method for finding the nucleotide positions in tRNA sequences that correlate with amino acid specificity has been developed. The procedure involves finding the subset of nucleotide positions and groups of positions where the marginal density of one amino acid tRNA class does not overlap that of any other amino acid class. The procedure is an application of a statistical method known as the Expectation Maximization algorithm.