Biologically active compounds of semi-metals

Formation, Occurrence, Significance, and Analysis of Organoselenium and Organotellurium Compounds in the Environment

Among all environmentally-relevant trace elements, selenium has one of the most diverse organic chemistries. It is also one of the few trace elements that may biomagnify in food chains under certain conditions. Yet, the exact chemical forms of selenium involved in the uptake into organisms and transfer to higher trophic levels, as well as the biochemical mechanisms that lead to their subsequent metabolism in organisms, are still not well understood. This is in part due to the analytical challenges associated with measuring the myriad of discrete Se species occurring in organisms. While there are generalized concepts of selenium metabolism, there is a lack of conclusive analytical evidence supporting the existence of many postulated intermediates. Likewise, there is a disconnect between the major selenium species encountered in abiotic compartments (waters, soils, and sediment), and those found in organisms, which renders the qualitative and quantitative description of the bioaccumulation process uncertain. Here, we summarize the knowledge on important selenium and tellurium species in all environmental compartments, and identify gaps and uncertainties in the existing body of knowledge, with emphasis on problems associated with past and current analytical methodology.

Microbial diversity of boron-rich volcanic hot springs of St. Lucia, Lesser Antilles

The volcanic Sulphur Springs, St. Lucia, present an extreme environment due to high temperatures, low pH values, and high concentrations of sulfate and boron. St. Lucia offers some unique geochemical characteristics that may shape the microbial communities within the Sulphur Springs area. We chose six pools representing a range of geochemical characteristics for detailed microbial community analyses. Chemical concentrations varied greatly between sites. Microbial diversity was analyzed using 16S rRNA gene clone library analyses. With the exception of one pool with relatively low concentrations of dissolved ions, microbial diversity was very low, with Aquificales sequences dominating bacterial communities at most pools. The archaeal component of all pools was almost exclusively Acidianus spp. and did not vary between sites with different chemical characteristics. In the pool with the highest boron and sulfate concentrations, only archaeal sequences were detected. Compared with other sulfur springs such as those at Yellowstone, the microbial diversity at St. Lucia is very different, but it is similar to that at the nearby Lesser Antilles island of Montserrat. While high elemental concentrations seem to be related to differences in bacterial diversity here, similarities with other Lesser Antilles sites suggest that there may be a biogeographical component as well.

Enhanced enzymatic saccharification of rice straw by microwave pretreatment

In this study, Box-Behnken design and response surface methodology were employed to plan experiments and optimize the microwave pretreatment of rice straw. Experimental results show that microwave intensity (MI), irradiation time (IT) and substrate concentration (SC) were main factors governing the enzymatic saccharification of rice straw. The maximal efficiencies of cellulose, hemicellulose and total saccharification were respectively increased by 30.6%, 43.3% and 30.3% under the optimal conditions of MI 680 W, IT 24 min and SC 75 g/L. The chemical composition analysis of straw further confirmed that microwave pretreatment could disrupt the silicified waxy surface, break down the lignin-hemicellulose complex and partially remove silicon and lignin.

Fungal volatilization of trivalent and pentavalent arsenic under laboratory conditions

Production of volatile derivatives of arsenic was studied using pure cultures of different fungal strains under laboratory conditions. Arsenic was used in its trivalent and pentavalent forms to evaluate the effect of arsenic valency on its biovolatilization. The average amount of volatilized arsenic for all fungal strains ranged from 0.026 mg to 0.257 mg and 0.024 mg to 0.191 mg of trivalent and pentavalent arsenic, respectively. These results show that approximately 23% of arsenic was volatilized from all culture media originally enriched with approximately 4 and 17 mg L(-1) of arsenic in trivalent form. The average amount of biovolatilized arsenic from culture media originally enriched with 4 and 17 mg L(-1) of arsenic in pentavalent form was 24% and 16%, respectively. The order of ability of arsenic biovolatilization is Neosartorya fischeri > Aspergillus clavatus > Aspergillus niger. Toxicity and fungal resistance to trivalent and pentavalent arsenic were also evaluated based on radial growth and biomass weight.