Electron-paramagnetic-resonance studies on the molybdenum of nitrate reductase from Escherichia coli K12.

Studies on the respiratory nitrate reductase (EC 1.7.99.4) from Escherichia coli K12 by electron-paramagnetic-resonance spectroscopy indicate that its molybdenum centre is comparable with that in other molybdenum-containing enzymes. Two Mo(V) signals may be observed; one shows interaction of Mo(V) with a proton exchangeable with the solvent and has: A (1H) 0.9-1.2mT; g1 = 1.999; g2=1.985; g3 = 1.964; gav. = 1.983. Molybdenum of both signal-giving species may be reduced with dithionite and reoxidized with nitrate.     

COMPARATIVE ULTRASTRUCTURE OF THE VALVES OF SOME CYCLOTELLA SPECIES (BACILLARIOPHYCEAE)1

Cyclotella atomus Hust., C. meneghiniana Kütz., C. comta (Ehr.) Kütz., C. antiqua W. Sm., C. michiganiana Skv., C. ocellata Pant., C. glomerata Bachmann, C. pseudostelligera Hust., and C. stelligera (Cleve et Grun.) V. H., were selected for ultrastructure investigations on the basis of their ready availability. Specimens were examined employing both transmission and scanning electron microscopy. Strutted processes, labiate processes, spines and other special features were surveyed in all species. On the basis of these observations the species of Cyclotella observed seem to be in one of 3 morphological groups, the meneghiniana group, the comta group, and the stelligera group.     

Catalytic facilitation by diffusion of adsorbed substrate on membrane surface

Membrane-alkaline phosphatase shows greater velocity of reaction than solubilized enzyme at low substrate concentration, whereas at saturation-concentration the opposite is true. The catalytic rate enhancement with the membrane-enzyme, when substrate availability is limiting, is attributed to non-specific adsorption of substrate to the membrane followed by its surface-diffusion to the active site resulting in an enhanced collision rate for the substrate with the enzyme. Experimental evidence for the adsorption-diffusion is provided by the dynamic quenching of 1-anilino-naphthalene-8-sulphonate, a membrane-bound probe's fluorescence by the substrate, 4-nitrophenyl-phosphate.     

Membrane lipid composition and susceptibility to bile salt damage

Erythrocyte membranes with low sphingomyelin: choline-containing phospholipid ratios haemolyse at low concentrations of the bile salt, glycocholate. Erythrocytes with higher sphingomyelin: choline-containing phospholipid ratios require progessively greater concentrations of the bile salt for lysis.Sublytic concentrations of glycocholate remove phospholipid and acetylcholinesterase from the membranes. Membranes with low sphingomyelin: choline-containing phospholipid ratios lose both particulate (microvesicles of distinct composition) and ‘solubilized’ material, the particulate form predominating. The proportion of particulate material falls with increase of the membrane sphingomyelin: choline-containing phospholipid ratio and those membranes of highest sphingomyelin: choline-containing phospholipid ratio lose material predominantly in ‘solubilized’ form.Sheep erythrocytes treated to increase their content of phosphatidylcholine (and thereby reduce their membrane sphingomyelin: choline-containing phospholipid ratio) become more susceptible to lysis by glycocholate.These observations indicate a correlation between membrane lipid composition and the perturbation of membranes with bile salt; they also point to possible features of membranes capable of surviving exposure to the high bile salt concentrations of the biliary tract.     

Location of receptor-binding region of protective antigen from Bacillus anthracis

The pag gene, which codes for protective antigen (PA), a common component of the lethal and edema toxins of Bacillus anthracis, was cloned and expressed in Escherichia coli. Nested deletions of pag were generated into the C-terminus coding region. Recombinant proteins were analyzed by Western blot with either an anti-PA polyclonal antisera or two monoclonal antibodies that neutralized lethal toxin and edema toxin activities by inhibiting the binding of PA to cell receptors. Localization of the receptor binding domain within the C-terminal region of PA was suggested by the inability of the monoclonal antibodies 3B6 and 14B7 to recognize the recombinant proteins expressed by C-terminal deletions of the pag gene.     

A soil archaeal community responds to a decade of ecological restoration

Large‐scale restoration efforts are underway globally to mitigate the impact of decades of land degradation by returning functional and biodiverse ecosystems. Revegetation is a heavily relied upon restoration intervention, and one that is expected to result in associated biodiversity returns. However, the outcome of such restoration interventions rarely considers recovery to the soil microbiome, a mega‐diverse and functionally important ecosystem component. Here we examine the archaeal component of the soil microbiome and track community change after a decade of eucalypt woodland restoration in southern Australia. We employed DNA metabarcoding to show that archaeal community composition, richness, and diversity shifted significantly, and towards a restored state 10 years after the restoration intervention. Changes in soil pH and nitrate associated with changes to the archaeal community, potentially relating to the pH responsive properties and close relationship with the nitrogen cycle of some archaea. Our study helps shed light on archaeal community dynamics, as no other study has used DNA metabarcoding to study archaeal responses across a restoration chronosequence. Our results provide great promise for the development of molecular monitoring of the soil microbiome as a future restoration monitoring tool.     

Kulikovskiyia gen. nov. (Bacillariophyceae) from the lateritic rock pools of the Western Ghats,India and from Hainan Province,China

A new triundulate naviculoid diatom genus is described from the Western Ghats of Peninsular India and Hainan Province, China. The new taxon, Kulikovskiyia gen. nov. has robust conical spines along its margin and at the apices and the external valve face has longitudinally‐oriented siliceous slat system extending the length of the valve. The external distal raphe ends bifurcate and terminates on the valve face. There appear to be superficial similarities between this Asian genus and species and Playaensis, a genus comprised of two species found only in the western USA. The systematic position of Kulikovskiyia is discussed, and other than noting its similarities to other biraphid naviculoid diatoms due to symmetry features and the position of the raphe, we are uncertain about its systematic placement at finer levels of classification.     

First record of a potential neonate tiger shark (Galeocerdo cuvier) at a remote oceanic island in the Eastern Tropical Pacific

Tiger sharks (Galeocerdo cuvier) play an important ecological role as top predators, yet knowledge of their reproductive ecology is scarce. Here, the authors report the first observation of a potential neonate G. cuvier at Cocos Island, a predator-dominated oceanic island in the Eastern Tropical Pacific (ETP). The individual was detected using baited remote underwater video stations (BRUVS). The cameras also detected female individuals potentially pregnant, suggesting that parturition may take place at or near the island. Nonetheless, it is still unclear if the presence of a single neonate is an isolated event or evidence that the species is using the island for reproduction.