Selenium in chemistry and biochemistry in comparison to sulfur

What makes selenoenzymes--seen from a chemist's view--so special that they cannot be substituted by just more analogous or adapted sulfur proteins? This review compiles and compares physicochemical properties of selenium and sulfur, synthetic routes to selenocysteine (Sec) and its peptides, and comparative studies of relevant thiols and selenols and their (mixed) dichalcogens, required to understand the special role of selenium in selenoproteins on the atomic molecular level. The biochemically most relevant differences are the higher polarizability of Se- and the lower pKa of SeH. The latter has a strikingly different pH-dependence than thiols, with selenols being active at much lower pH. Finally, selected typical enzymatic mechanisms which involve selenocysteine are critically discussed, also in view of the authors' own results.     

Bioconcentration of some macrominerals in soil,forage and buffalo hair continuum: A case study on pasture irrigated with sewage water

The present study aimed to evaluate the bioaccumulation of some macrominerals in grazing buffaloes fed forage irrigated with sewage water or canal water. In particular, the transfer of sodium (Na), magnesium (Mg), potassium (K) and calcium (Ca) from soil to plant and in turn to animals was evaluated under sub-tropical environmental conditions. Samples of soil, forage and buffalo hair were collected and digested by wet method. Sodium and K concentrations were significantly higher in the soil but lower in the forages; however, Mg and Ca concentrations in both soil and forages were higher. The correlation between soil, forage and hair showed an imbalanced flow of Na, Mg and K and a balanced flow of Ca from soil to forage and then to animals. Based on the findings, the highest rates of transfer of minerals were found for sewage water treatment, whereas lowest rates were found for canal water treatment, except for Na. As the transfer of minerals depends on their bioavailability, the highest values may be due to the high rates of mineral uptake by plants. Thus, the high transfer rate of some elements by plants could become toxic in future causing detrimental effect to grazing livestock.     

Post-exposure temperature influence on the toxicity of conventional and new chemistry insecticides to green lacewing Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae)

Chrysoperla carnea (Stephens) is an important biological control agent currently being used in many integrated pest management (IPM) programs to control insect pests. The effect of post-treatment temperature on insecticide toxicity of a spinosyn (spinosad), pyrethroid (lambda cyhalothrin), organophosphate (chlorpyrifos) and new chemistry (acetamiprid) to C. carnea larvae was investigated under laboratory conditions. Temperature coefficients of each insecticide tested were evaluated. From 20 to 40 °C, toxicity of lambda cyhalothrin and spinosad decreased by 2.15- and 1.87-fold while toxicity of acetamiprid and chlorpyrifos increased by 2.00 and 1.79-fold, respectively. The study demonstrates that pesticide effectiveness may vary according to environmental conditions. In cropping systems where multiple insecticide products are used, attention should be given to temperature variation as a key factor in making pest management strategies safer for biological control agents. Insecticides with a negative temperature coefficient may play a constructive role to conserve C. carnea populations.     

Antibiotic resistance and extended spectrum beta-lactamases: Types,epidemiology and treatment

Antibiotic resistance is a problem of deep scientific concern both in hospital and community settings. Rapid detection in clinical laboratories is essential for the judicious recognition of antimicrobial resistant organisms. Production of extended-spectrum β-lactamases (ESBLs) is a significant resistance-mechanism that impedes the antimicrobial treatment of infections caused by Enterobacteriaceae and is a serious threat to the currently available antibiotic armory. ESBLs are classified into several groups according to their amino acid sequence homology. Proper infection control practices and barriers are essential to prevent spread and outbreaks of ESBL producing bacteria. As bacteria have developed different strategies to counter the effects of antibiotics, the identification of the resistance mechanism may help in the discovery and design of new antimicrobial agents. The carbapenems are widely regarded as the drugs of choice for the treatment of severe infections caused by ESBL-producing Enterobacteriaceae, although comparative clinical trials are scarce. Hence, more expeditious diagnostic testing of ESBL-producing bacteria and the feasible modification of guidelines for community-onset bacteremia associated with different infections are prescribed.     

L-Tryptophan-dependent biosynthesis of indole-3-acetic acid (IAA) improves plant growth and colonization of maize by <Emphasis Type="BoldItalic">Burkholderia phytofirmans</Emphasis> PsJN

Burkholderia phytofirmans PsJN is a well-known plant growth-promoting bacterium that establishes rhizospheric and endophytic colonization in different plants. PsJN inoculation promotes growth of different horticultural crops. L-Tryptophan (L-TRP) application may further improve its effectiveness, due to substrate (L-TRP)-dependent inoculum (PsJN)-derived auxins in the rhizosphere. In the present study, the substrate (L-TRP)-dependent response of PsJN inoculation to maize growth and auxin biosynthesis was evaluated under pot conditions. In vitro auxin biosynthesis by PsJN was determined in the absence and presence of L-TRP, a physiological precursor of auxins. Surface-disinfected seeds were treated with peat-based inoculum and L-TRP solutions (10^?4 and 10^?5 M). Results revealed that L-TRP application and PsJN inoculation, when applied separately, significantly increased the growth parameters of maize compared to untreated control. However, PsJN inoculation supplemented with L-TRP (10^?5 M) gave the most promising results and significantly increased plant height, photosynthesis, chlorophyll content, root biomass and shoot biomass up to 18, 16, 45, 62 and 55 %, respectively, compared to the uninoculated control. Similarly, higher values of N, P and IAA content were observed with precursor (L-TRP)–inoculum (PsJN) interaction. The inoculant strain efficiently colonized maize seedlings and was recovered from the rhizosphere, root and shoot of plants. The results imply that substrate (L-TRP)-derived IAA biosynthesis in the rhizosphere by PsJN inoculation could be a useful approach for improving the growth, photosynthesis and nutrient content of maize plants.     

Culture‐dependent and culture‐independent characterization of potentially functional biphenyl‐degrading bacterial community in response to extracellular organic matter from Micrococcus luteus

Biphenyl (BP)‐degrading bacteria were identified to degrade various polychlorinated BP (PCB) congers in long‐term PCB‐contaminated sites. Exploring BP‐degrading capability of potentially useful bacteria was performed for enhancing PCB bioremediation. In the present study, the bacterial composition of the PCB‐contaminated sediment sample was first investigated. Then extracellular organic matter (EOM) from Micrococcus luteus was used to enhance BP biodegradation. The effect of the EOM on the composition of bacterial community was investigated by combining with culture‐dependent and culture‐independent methods. The obtained results indicate that Proteobacteria and Actinobacteria were predominant community in the PCB‐contaminated sediment. EOM from M. luteus could stimulate the activity of some potentially difficult‐to‐culture BP degraders, which contribute to significant enhancement of BP biodegradation. The potentially difficult‐to‐culture bacteria in response to EOM addition were mainly Rhodococcus and Pseudomonas belonging to Gammaproteobacteria and Actinobacteria respectively. This study provides new insights into exploration of functional difficult‐to‐culture bacteria with EOM addition and points out broader BP/PCB degrading, which could be employed for enhancing PCB‐bioremediation processes.     

Proteome-wide overexpression of host proteins for identification of factors affecting tombusvirus RNA replication: an inhibitory role of protein kinase C

To identify host genes affecting replication of Tomato bushy stunt virus (TBSV), a small model positive-stranded RNA virus, we overexpressed 5,500 yeast proteins individually in Saccharomyces cerevisiae, which supports TBSV replication. In total, we identified 141 host proteins, and overexpression of 40 of those increased and the remainder decreased the accumulation of a TBSV replicon RNA. Interestingly, 36 yeast proteins were identified previously by various screens, greatly strengthening the relevance of these host proteins in TBSV replication. To validate the results from the screen, we studied the effect of protein kinase C1 (Pkc1), a conserved host kinase involved in many cellular processes, which inhibited TBSV replication when overexpressed. Using a temperature-sensitive mutant of Pkc1p revealed a high level of TBSV replication at a semipermissive temperature, further supporting the idea that Pkc1p is an inhibitor of TBSV RNA replication. A direct inhibitory effect of Pkc1p was shown in a cell-free yeast extract-based TBSV replication assay, in which Pkc1p likely phosphorylates viral replication proteins, decreasing their abilities to bind to the viral RNA. We also show that cercosporamide, a specific inhibitor of Pkc-like kinases, leads to increased TBSV replication in yeast, in plant single cells, and in whole plants, suggesting that Pkc-related pathways are potent inhibitors of TBSV in several hosts.     

Acetylation regulates subcellular localization of eukaryotic translation initiation factor 5A (eIF5A)

Eukaryotic translation initiation factor 5A (eIF5A) is a protein subject to hypusination, which is essential for its function. eIF5A is also acetylated, but the role of that modification is unknown. Here, we report that acetylation regulates the subcellular localization of eIF5A. We identified PCAF as the major cellular acetyltransferase of eIF5A, and HDAC6 and SIRT2 as its major deacetylases. Inhibition of the deacetylases or impaired hypusination increased acetylation of eIF5A, leading to nuclear accumulation. As eIF5A is constitutively hypusinated under physiological conditions, we suggest that reversible acetylation plays a major role in controlling the subcellular localization of eIF5A.