Journal ArticleDOI
Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism
TLDR
The GS-15 organism as mentioned in this paper is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation.Abstract:
The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2–4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits.read more
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Dissimilatory Fe(III) and Mn(IV) reduction.
TL;DR: The physiological characteristics of Geobacter species appear to explain why they have consistently been found to be the predominant Fe(III)- and Mn(IV)-reducing microorganisms in a variety of sedimentary environments.
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Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth.
TL;DR: The rates of reduction of the metal ions by Neem leaf extract are much faster than those observed by us in earlier studies using microorganisms such as fungi, highlighting the possibility that nanoparticle biological synthesis methodologies will achieve rates of synthesis comparable to those of chemical methods.
Journal ArticleDOI
Novel mode of microbial energy metabolism: organic carbon oxidation coupled to dissimilatory reduction of iron or manganese.
TL;DR: This is the first demonstration that microorganisms can completely oxidize organic compounds with Fe(III) or Mn(IV) as the sole electron acceptor and that oxidation of organic matter coupled to dissimilatory Fe( III), Mn( IV), or Mn (IV) reduction can yield energy for microbial growth.
Journal ArticleDOI
Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium oxysporum
Absar Ahmad,Priyabrata Mukherjee,Satyajyoti Senapati,Deendayal Mandal,M. Islam Khan,Rajiv Kumar,Murali Sastry +6 more
TL;DR: It is observed that aqueous silver ions when exposed to the fungus Fusarium oxysporum are reduced in solution, thereby leading to the formation of an extremely stable silver hydrosol, creating the possibility of developing a rational, fungal-based method for the synthesis of nanomaterials over a range of chemical compositions, which is currently not possible by other microbe-based methods.
Journal ArticleDOI
Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001.
David S. McKay,Everett K. Gibson,Kathie L. Thomas-Keprta,Hojatollah Vali,Christopher S. Romanek,Simon J. Clemett,Xavier D. F. Chillier,C. R. Maechling,Richard N. Zare +8 more
TL;DR: High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and iron sulfides.