Metal(loid) speciation and transformation by aerobic methanotrophs

Abstract: Manufacturing and resource industries are the key drivers for economic growth with a huge environmental cost (e.g. discharge of industrial effluents and post-mining substrates). Pollutants from waste streams, either organic or inorganic (e.g. heavy metals), are prone to interact with their physical environment that not only affects the ecosystem health but also the livelihood of local communities. Unlike organic pollutants, heavy metals or trace metals (e.g. chromium, mercury) are non-biodegradable, bioaccumulate through food-web interactions and are likely to have a long-term impact on ecosystem health. Microorganisms provide varied ecosystem services including climate regulation, purification of groundwater, rehabilitation of contaminated sites by detoxifying pollutants. Recent studies have highlighted the potential of methanotrophs, a group of bacteria that can use methane as a sole carbon and energy source, to transform toxic metal (loids) such as chromium, mercury and selenium. In this review, we synthesise recent advances in the role of essential metals (e.g. copper) for methanotroph activity, uptake mechanisms alongside their potential to transform toxic heavy metal (loids). Case studies are presented on chromium, selenium and mercury pollution from the tanneries, coal burning and artisanal gold mining, respectively, which are particular problems in the developing economy that we propose may be suitable for remediation by methanotrophs. 6g_ZKsLH11vt1AExshJzH4Video Abstrac

Expression, purification and crystallization of a novel metagenome-derived salicylaldehyde dehydrogenase from Alpine soil

Salicylaldehyde dehydrogenase (SALD) catalyses the last reaction in the upper pathway of naphthalene degradation: the oxidation of salicylaldehyde to salicylate. This enzyme has been isolated and studied from a few organisms that belong to the betaproteobacteria and gammaproteobacteria, predominantly Pseudomonas putida. Furthermore, there is only one crystal structure of this enzyme, which was obtained from P. putida G7. Here, crystallographic studies and analysis of the crystal structure of an Alpine soil metagenome-derived SALD (SALD(AP)) from an alphaproteobacterium are presented. The SALD(AP) gene was discovered using gene-targeted sequence assembly and it was cloned into a pLATE51 vector. The recombinant protein was overexpressed in Escherichia coli BL21 (DE3) cells and the soluble protein was purified to homogeneity. The protein crystallized at 20°C and diffraction data from the crystals were collected at a resolution of 1.9 Å. The crystal belonged to the orthorhombic space group C222(1), with unit-cell parameters a = 116.8, b = 121.7, c = 318.0 Å. Analysis of the crystal structure revealed its conformation to be similar to the organization of the aldehyde dehydrogenase superfamily with three domains: the catalytic, NAD(+)-binding and bridging domains. The crystal structure of NahF from P. putida G7 was found to be the best structural homologue of SALD(AP), even though the enzymes share only 48% amino-acid identity. Interestingly, a carboxylic acid (protocatechuic acid) was found to be a putative ligand of the enzyme and differential scanning fluorimetry was employed to confirm ligand binding. These findings open up the possibility of studying the mechanism(s) of product inhibition and biocatalysis of carboxylic acids using this enzyme and other related aldehyde dehydrogenases

Coadministration of L‐alanine and L‐glutamine ameliorate blood glucose levels, biochemical indices and histological features in alloxan‐induced diabetic rats

We evaluated the effects of supplementation of L-alanine and L-glutamine on blood glucose levels and biochemical parameters in alloxan-induced diabetic rat. Forty-nine animals were distributed into seven equal groups. Except for the non-diabetic control, diabetes was induced in all groups by intravenous alloxan injection followed by daily supplementation with amino acids for 14 days. Weight and blood glucose were monitored during supplementation, while biochemical parameters such as liver and renal functions, lipid profile, and antioxidant markers were evaluated post-intervention. A significant increase (p < .05) in weight and decrease in blood glucose were observed in the amino acid(s) treated groups. The supplementation with both amino acids restored important tissue antioxidants, liver and kidney functions and rescued islets cells degeneration. Histopathological examinations of important tissues showed the restoration of alloxan-induced physiopathological changes by the amino acids. Thus, these amino acids might serve as nutraceuticals for the management and treatment of diabetes. Practical Applications The discovery and production of antidiabetic bioactive compounds are often challenging, and the existing antidiabetic drugs are expensive. Amino acids are key regulators of glucose metabolism, insulin secretion, and insulin sensitivity; thus, they can play a crucial role in alleviating diabetes. Here, we present findings that strongly suggest the potential of pure amino acids (L-alanine and L-glutamine) for the management and treatment of diabetes. We show that these amino acids, when supplemented singly or coadministered can lower blood glucose levels and restore several other biochemical parameters implicated in diabetes. Hence, these cheap amino acids may be consumed as nutraceuticals or food supplements by diabetics for the treatment/management of diabetes. Foods rich in these amino acids may also be consumed as part of the diet of diabetic patients