Biotransformation of mercury by bacteria isolated from a river collecting cinnabar mine waters

One hundred six strains of aerobic bacteria were isolated from the Fiora River which drains an area of cinnabar deposits in southern Tuscany, Italy. Thirty-seven of the strains grew on an agar medium containing 10g/ml Hg (as HgCl₂) with all of these strains producing elemental mercury. Seven of the 37 strains also degraded methylmercury. None of 106 sensitive and resistant strains produced detectable monomethylmercury although 15 strains produced a benzene-soluble mercury species. Two strains of alkylmercury (methyl-, ethyl- and phenylmercury) degrading bacteria were tested for the ability to degrade several other analogous organometals and organic compounds, but no activity was detected toward these compounds. Mercury methylation is not a mechanism of Hg resistance in aerobic bacteria from this environment. Growth of bacteria on the agar medium containing 10g/ml HgCl₂ was diagnostic for Hg detoxification based on reduction.     

Site selection by the tRNA splicing endonuclease of Xenopus laevis

To investigate the mechanism by which the purified Xenopus tRNA splicing endonuclease recognizes its splice sites, we utilized yeast pre-tRNA(3Leu) and pre-tRNA(Phe) variants constructed by in vitro mutagenesis. We found that the endonuclease interacts with conserved features of the mature tRNA domain. In particular, U8 and C56 may be examples of contact points between protein and RNA. Given that there are no conserved sequences at the splice junctions, the specificity of cutting at both splice sites is determined by the length of the anticodon stem. Although in general, the sequence of the intron is unimportant for splicing, there are some structural requirements.     

Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state

The genes for cellobiose utilization are normally cryptic in Escherichia coli. The cellobiose system was used as a model to understand the process by which silent genes are maintained in microbial populations. Previously reported was (1) the isolation of a mutant strain that expresses the cellobiose-utilization (Cel) genes and (2) that expression of those genes allows utilization of three beta- glucoside sugars: cellobiose, arbutin, and salicin. The Cel gene cluster has now been cloned from that mutant strain. In the course of locating the Cel genes within the cloned DNA segment, it was discovered that inactivation of the Cel-encoded hydrolase rendered the host strain sensitive to all three beta-glucosides as potent inhibitors. This sensitivity arises from the accumulation of the phosphorylated beta- glucosides. Because even the fully active genes conferred some degree of beta-glucoside sensitivity, the effects of cellobiose on a series of five Cel+ mutants of independent origin were investigated. Although each of those strains utilizes cellobiose as a sole carbon and energy source, cellobiose also acts as a potent inhibitor that reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand, wild-type strains that cannot utilize cellobiose are not inhibited. The observation that the same compound can serve either as a nutrient or as an inhibitor suggests that, under most conditions in which cellobiose will be present together with other resources, there is a strong selective advantage to having the cryptic (Cel0) allele. In those environments in which cellobiose is the sole, or the best, resource, mutants that express the genes (Cel+) will have a strong selective advantage. It is suggested that temporal alternation between these two conditions is a major factor in the maintenance of these genes in E. coli populations. This alternation of environments and fitnesses was predicted by the model for cryptic-gene maintenance that was previously published.      

Lipid-bound sugars in malignant human breast tumors

Microsomal preparations from malignant human breast tumors catalyzed the transfer of mannose and glucose from GDP-[14C]-Man and UDP-[14C]-Glc into lipid-linked sugars and glycoprotein-like substances. As judged by several criteria the obtained lipid-linked monosaccharides behaved as dolichyl phosphate mannose and dolichyl phosphate glucose whereas lipid-linked oligosaccharides behaved as polyprenyl diphosphate derivatives. The optimum conditions for mannosyl- and glucosyl-transfer reactions and the effect of dolichyl phosphate, detergent and EDTA on incubation mixture were described.     

On alternatives to selection-induced mutation in the Bgl operon of Escherichia coli

Selection-induced mutations are nonrandom mutations that occur as specific and direct responses to environmental challenge. Examples of selection-induced mutations have been reported both in bacteria and in yeast. I previously showed (Hall 1988) that excisions of the mobile genetic element IS150 from within bglF are selection induced and argued that they occurred because they were potentially advantageous under the selective conditions employed. Mittler and Lenski (Mittler and Lenski 1992) have argued that such excisions are not selection induced but that they occur randomly in nondividing cells. Here I provide further evidence that IS150 excisions are induced by selection and that the excisions are immediately, rather than only potentially, advantageous to the cell. I also provide evidence that excisions, which Mittler and Lenski claim occur randomly in saturated broth cultures, actually occur after samples from those cultures are plated onto selective medium.      

Reduction of vanadate to vanadyl by a strain of Saccharomyces cerevisiae

Three strains of Saccharomyces cerevisiae, SC-1, DBVPG 6173 and DBVPG 6037, were studied for vanadate resistance in complex Sabouraud medium since they did not thrive in different minimal media (yeast nitrogen base with and without amino acids). The strain SC-1 was resistant up to 16 mm of vanadate, whereas the strains DBVPG 6173 and DBVPG 6037 were inhibited by 8 mm and 4 mm vanadate, respectively. The vanadate resistance in strain SC-1 was constitutive and due to the reduction of this oxyanion to vanadyl, which was detected by EPR spectroscopy and visible spectroscopy. The transformation of vanadate to vanadyl took place during the exponential growth phase; 10 mm of vanadate was reduced to vanadyl outside the cells since the oxyanion was not detected in the cell biomass and only a negligible concentration of vanadyl (25 nmoles mg cells dry weight) was found in the biomass. The other two vanadate-sensitive yeast strains only accumulated vanadate and did not reduce the oxyanion to vanadyl.     

Effect of CMV-immunoglobulins (cytotect biotest) prophylaxis on CMV pneumonia after lung transplantation

Lung transplant (LT) recipients among solid organ transplant recipients are at high risk for cytomegalovirus (CMV) infections. We evaluated the effect of CMV-Immunoglobulins (CMV-IG) (Cytotect Biotest) on CMV pneumonia diagnosed in 303 follow-up transbronchial biopsies (TBB) of lung transplant recipients. 24 patients (control group, 155 TBB from 1999 to 2002) received acyclovir for 24 months and 33 recipients (study group, 148 TBB from 2003 to 2008) received a combined CMV prophylaxis consisting of CMV-IG (Cytotect Biotest) for 12 months and a short Ganciclovir or Valganciclovir therapy from 21th to 42th postoperative day followed by acyclovir up to 24 months. In our study the percentage of pneumonia at first month TBB was similar in the study group vs the control group, 9.1% (3/33) vs 8.3% (2/24), p=0.9 ns, but after the first month the percentage was significantly lower in the study group in the first year at follow-up TBB, 1% (1/99) vs 6.4% (5/78), p=0.048, and in first two years follow-up TBB, 0.8% (1/122) vs 6.5% 8/124), p=0.018 (Statistical analysis: Chi-square test for proportion differences). Our data suggest a strong efficacy of CMV-IG prophylaxis in reducing CMV pneumonia after first month in lung transplant recipients.     

Lysine acetylome profiling uncovers novel histone deacetylase substrate proteins in Arabidopsis

Histone deacetylases have central functions in regulating stress defenses and development in plants. However, the knowledge about the deacetylase functions is largely limited to histones, although these enzymes were found in diverse subcellular compartments. In this study, we determined the proteome‐wide signatures of the RPD3/HDA1 class of histone deacetylases in Arabidopsis. Relative quantification of the changes in the lysine acetylation levels was determined on a proteome‐wide scale after treatment of Arabidopsis leaves with deacetylase inhibitors apicidin and trichostatin A. We identified 91 new acetylated candidate proteins other than histones, which are potential substrates of the RPD3/HDA1‐like histone deacetylases in Arabidopsis, of which at least 30 of these proteins function in nucleic acid binding. Furthermore, our analysis revealed that histone deacetylase 14 (HDA14) is the first organellar‐localized RPD3/HDA1 class protein found to reside in the chloroplasts and that the majority of its protein targets have functions in photosynthesis. Finally, the analysis of HDA14 loss‐of‐function mutants revealed that the activation state of RuBisCO is controlled by lysine acetylation of RuBisCO activase under low‐light conditions.     

The RB-related gene Rb2/p130 in neuroblastoma differentiation and in B-myb promoter down-regulation

The retinoblastoma family of nuclear factors is composed of RB, the prototype of the tumour suppressor genes and of the strictly related genes p107 and Rb2/p130. The three genes code for proteins, namely pRb, p107 and pRb2/p130, that share similar structures and functions. These proteins are expressed, often simultaneously, in many cell types and are involved in the regulation of proliferation and differentiation. We determined the expression and the phosphorylation of the RB family gene products during the DMSO-induced differentiation of the N1E-115 murine neuroblastoma cells. In this system, pRb2/p130 was strongly up-regulated during mid-late differentiation stages, while, on the contrary, pRb and p107 resulted markedly decreased at late stages. Differentiating N1E-115 cells also showed a progressive decrease in B-myb levels, a proliferation-related protein whose constitutive expression inhibits neuronal differentiation. Transfection of each of the RB family genes in these cells was able, at different degrees, to induce neuronal differentiation, to inhibit [3H]thymidine incorporation and to down-regulate the activity of the B-myb promoter.