Three novel strains of methylotrophic methanogens were isolated from Skan Bay, Alaska, by using anaerobic cultivation techniques. The water was 65 m deep at the sampling site. Strains AK-4 (=OCM 774), AK-5 T (=OCM 775 T =DSM 17273 T ) and AK-9 (=OCM 793) were isolated from the sulfate-reducing zone of the sediments. Each of the strains was a non-motile coccus and occurred singly. Cells grew with trimethylamine as a catabolic substrate and strain AK-4 could also catabolize methanol. Yeast extract and trypticase peptones were not required for growth, but their addition to the culture medium slightly stimulated growth. Each of the strains grew at temperatures of 5-28 6C; they were slight halophiles and grew fastest in the neutral pH range. Analysis of the 16S rRNA gene sequences indicated that strain AK-4 was most closely related to Methanosarcina baltica. DNA-DNA hybridization studies showed 88 % relatedness, suggesting that strain AK-4 represents a novel strain within this species. Strains AK-5 T and AK-9 had identical 16S rRNA gene sequences that were most closely related to the sequence of Methanococcoides burtonii (99?8 % sequence similarity). DNA-DNA hybridization studies showed that strains AK-5 T and AK-9 are members of the same species (88 % relatedness value), but strain AK-5 T had a DNA-DNA relatedness value of only 55 % to Methanococcoides burtonii. This indicates that strains AK-5 T and AK-9 should be considered as members of a novel species in the genus Methanococcoides. We propose the name Methanococcoides alaskense sp. nov., with strain AK-5 T (=OCM 775 T =DSM 17273 T ) as the type strain.In the marine environment, sulfate reduction is the dominant microbial process in the upper sediment layers. Generally, when sulfate is present, sulfate reduction is the major catabolic process and methanogenesis is limited. Because of their higher affinity for hydrogen and acetate, sulfate-reducing bacteria out-compete methanogens for these important substrates (King et al., 1983;King, 1984;Oremland & Taylor, 1978). As a result, methanogenesis becomes a dominant process only in deeper sediments in which the sulfate ions have been exhausted. The limited methane production that occurs together with sulfate reduction is due to the activity of methylotrophic methanogens (King, 1984;Oremland & Taylor, 1978;Oremland & Polcin, 1982).Methanogens that belong to the family Methanosarcinaceae are characterized as having the broadest substrate range of methanogens; many can grow by reducing CO 2 with H 2 or by the splitting of acetate and all can grow by dismutating methyl compounds (Kendall & Boone, 2004). The family Methanosarcinaceae includes eight genera: Methanosarcina, Methanolobus, Methanococcoides, Methanohalobium, Methanohalophilus, Methanosalsum, Methanomethylovorans and Methanimicrococcus. The only described species of Methanimicrococcus, Methanimicrococcus blatticola, is unique among the Methanosarcinaceae because it reduces methylated compounds only in the presence of H 2 (Sprenger et al., 2000). The GenBank/EMB...

Nitric oxide (NO) acts in a concentration and redox-dependent manner to counteract oxidative stress either by directly acting as an antioxidant through scavenging reactive oxygen species (ROS), such as superoxide anions (O(2)(-)*), to form peroxynitrite (ONOO(-)) or by acting as a signaling molecule, thereby altering gene expression. NO can interact with different metal centres in proteins, such as heme-iron, zinc-sulfur clusters, iron-sulfur clusters, and copper, resulting in the formation of a stable metal-nitrosyl complex or production of varied biochemical signals, which ultimately leads to modification of protein structure/function. The thiols (ferrous iron-thiol complex and nitrosothiols) are also involved in the metabolism and mobilization of NO. Thiols bind to NO and transport it to the site of action whereas nitrosothiols release NO after intercellular diffusion and uptake into the target cells. S-nitrosoglutathione (GSNO) also has the ability to transnitrosylate proteins. It is an NO˙ reservoir and a long-distance signaling molecule. Tyrosine nitration of proteins has been suggested as a biomarker of nitrosative stress as it can lead to either activation or inhibition of target proteins. The exact molecular mechanism(s) by which exogenous and endogenously generated NO (or reactive nitrogen species) modulate the induction of various genes affecting redox homeostasis, are being extensively investigated currently by various research groups. Present review provides an in-depth analysis of the mechanisms by which NO interacts with and modulates the activity of various ROS scavenging enzymes, particularly accompanying ROS generation in plants in response to varied abiotic stress.

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Nitric oxide (NO) is established as a modulator of various developmental processes in plants through its interaction with multiple enzymatic and non-enzymatic biomolecules. Lateral root (LR) induction and extension in sunflower (Helianthus annuus L.) has been observed to be governed by a probable crosstalk between NO and ethylene biosynthesizing enzyme-ACC oxidase. NaCl (120 mM) stress not only lowers LR induction but also reduces their extension growth. Quenching of endogenous NO by raising seedlings in presence of 40 µM hemoglobin in the growth medium does not affect LR induction but lowers their extension growth. NaCl stress and NO depletion have additive effects on the enhancement of ACC oxidase activity, leading to enhanced ethylene biosynthesis. Role of NO has been further confirmed by raising sunflower seedlings in the presence of 20-60 µM of two NO donors, sodium nitroprusside (SNP) and diethylenetriamine NONOate (DETA). LR extension growth was higher with DETA than SNP as NO donor at 40 µM. Iron-deficiency also promoted LR proliferation. It also significantly lowered ACC oxidase activity in the seedling roots in response to salt stress. Based on the present findings it is proposed that salt stress-mediated LR proliferation is regulated by NO through its binding with ACC oxidase (an iron-containing enzyme). This results in the formation of a stable ternary complex (ACC-ACC oxidase-NO) which leads to the reduction in ethylene biosynthesis. Lesser availability of ethylene consequently brings about enhanced LR formation.

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