Isolation of methanogens from Arabian sea sediments and their salt tolerance

Abstract Sea sediments in tropical regions have been less studied for methanogenesis and methanogens present therein. Three species of methanogens viz. Methanobacterium bryantii, Methanococcus voltae and Methanosarcina barkeri were isolated from Arabian sea sediments collected near the west coast of India. Maximum methane was formed by M. voltae at 3.0% (w/v) NaCl and other two methanogens at 0.06% (w/v) NaCl. M. bryantii and M. barkeri tolerated 2.5 and 3.0% (w/v) NaCl respectively due to which these methanogens must have survived in salt conditions of the sea sediments.     

A new method of measurement of permeability of lipid membranes

A new method, based on potential measurements to obtain permeabilities and mobilities of ionic species passing through membranes, under the influence of concentration gradients is proposed. This method is applied to three different lipid membranes in aqueous KCl solutions. The values of permeabilities and mobilities obtained by this simple method is in good agreement with those reported in literature     

Mechanism to combat cobalt toxicity in cobalt resistant mutants of <Emphasis Type="Italic">Aspergillus nidulans</Emphasis>

Characteristics of fungal species tolerant to high levels of metals in natural environment can be amplified by isolation and selection of resistant mutants. Step-by-step culturing led to identification of highly stable Co-resistant (Co^R) mutants of A. nidulans. Based on two distinct morphological features, Co-resistant mutants were categorized as Co^RI and Co^RII. The two mutants varied in their growth behavior and colony morphology that were reflected in supplemented as well as unsupplemented growth media over the generations. As compared to the Co^RI, Co^RII mutant exhibited sparse mycelia and conidiation but secreted higher amount of melanin. Co^R mutants could tolerate up to 2.5mM Co in the medium, however, required a threshold concentration of 0.25mM Co for optimal growth and germination. Absence of Co in the medium caused a stressful situation for the Co^R mutants and led to the secretion of a white extracellular precipitate found to be a glycoprotein. In response to interactions with Co-ions, Co^R mutants produced oxalic acid and bioprecipitated Co as Co-oxalate providing scope for metal reclamation as well as oxalic acid extraction. The mutants could help to recover the insoluble Co-oxalate salt from aqueous solutions by entrapping it in their growing mycelial meshwork.     

Iron complexes of chiral phenol-oxazoline ligands: Structural studies and oxidation catalysis

Iron complexes of two ligands, HphoxCOOH and HphoxiPr, have been synthesized and characterized by crystal structure analyses. The complexes (HNEt₃)₂[Fe(phoxCOO)₂](ClO₄) and [Fe(phoxiPr)₃] are reported. Reactions of the ligands rac-HphoxCOOH and rac-HphoxiPr with iron(II) or iron(III) perchlorate result in the formation of iron(III) complexes with pseudo-octahedral geometry around the metal center. The iron complex obtained from rac-HphoxCOOH crystallized in the centrosymmetric space group Cmca. The two ligands are bound in a tridentate manner generating a meridional coordination with both dianionic ligands on a metal center having the same chirality; due to the center of symmetry the complex with opposite chirality is also present. The complex (HNEt₃)₂[Fe(phoxCOO)₂](ClO₄) is the first accurate structural model of the iron complex of a siderophore analog commonly observed in mycobactins. The three didentate ligands in the complex [Fe(phoxiPr)₃] are bound with like atoms in a meridional manner to the metal center. The metal ion is surrounded by two ligands of the same chirality and one ligand of opposite chirality (ie. RRS or SSR); due to the presence of a center of symmetry both isomers are present in the crystal structure. The complex (HNEt₃)₂[Fe(phoxCOO)₂](ClO₄) shows promising activity in the oxidation of alkanes, such as toluene, ethylbenzene and cumene, while the complex [Fe(phoxiPr)₃] does not show any catalytic activity in alkane oxidations under the conditions tested. The complex (HNEt₃)₂[Fe(phoxCOO)₂](ClO₄) is reasonably efficient in the conversion of H₂O₂ to oxidation products.