Sulphate reduction in oxic and sub-oxic North-East Atlantic sediments

Abstract Oxic and sub-oxic N.-E. Atlantic sediments were examined for sulphate-reducing activity. Oxygen and/or nitrate reduction are probably the dominant mineralisation processes in the abyssal plain sediment studied. A low rate of sulphate reduction (0.1 nmol SO²⁻₄/ml/day) was recorded in the surface 5 cm of the continental slope sediment, together with the presence of a range of sulphate-reducing bacteria (SRB). A higher activity of sulphate reduction (2.2 nmol SO²⁻₄/ml/day) occurred in the continental shelf sediment which led to a small decrease in pore water sulphate and an increase in titration alkalinity. This sediment contained approx. 10²–10³ acetate, lactate and propionate oxidising SRB/ml. No low- M _r organic acids were detected in these sediments. However, amendment with 75 μM acetate stimulated sulphate-reducing activity in the shelf sediment.     

Purification and properties of 1-phosphofructokinase from Escherichia coli

Abstract The thermophilic facultatively phototrophic green bacterium Chloroflexus aurantiacus strain Ok-70-fl was shown to possess sulfide-repressed hydrogenase activity. Biosynthesis of the enzyme was severely repressed by S²⁻ (5.7 mM) and stimulated specifically by Ni²⁺ and by molecular hydrogen. The hydrogenase was shown to be localized in the cytoplasmic membrane and could be solubilized from the latter by the detergent Triton X-100 in a state forming one enzymatically active band ( M _r 170 × 10³) in polyacrylamide gels. In the membraneous state, the hydrogenase had its maximal activity at 73°C and was active with methyl viologen, methylene blue, menadione and flavins, but not with NAD or NADP as electron acceptors. Solubilization of the enzyme with Triton X-100 resulted in a drastic increase in the FAD/FMN-linked activity.     

Heterologous hybridization of Azospirillum DNA to Rhizobium nod and fix genes

Abstract Probes containing the nod and hsn regions of Rhizobium meliloti and the fixABC genes of Rhizobium japonicum were used to perform hybridization experiments with endonuclease-restricted DNA from Azospirillum brasilense strains and 2 Azospirillum lipoferum strains. Homology to nod, hsn and fixA was found in the 4 Azospirillum strains.     

Evidence for adenylylation/deadenylylation control of the glutamine synthetases of Rhodospirillum tenue and Rhodocyclus purpureus

The phylogenetically related phototrophic bacteria Rhodospirillum tenue and Rhodocyclus purpureus modulate activity of their glutamine synthetases by adenylylation/deadenylylation. Evidence for covalent modification includes the inhibitory effect of Mg²⁺ on the activity of glutamine synthetase extracted from cells of either species grown on excess ammonia, and the lack of Mg²⁺ inhibition of activity of the enzyme isolated from N₂-(R. tenue) or glutamine (R. purpureus)-grown cells. In addition, snake venom phosphodiesterase treatment of glutamine synthetase from either species grown on excess ammonia relieved Mg²⁺ inhibition of the enzyme (as measured via the -glutamyl transferase assay), and changed the cation specificity from Mn²⁺ to Mg²⁺ (in the biosynthetic assay).     

Whole-cell antigens of members of the sulfate-reducing genus Desulfovibrio

Antisera have been developed against the wholecell antigens of Desulfovibrio africanus Benghazi and Walvis Bay, D. vulgaris Hildenborough, D. salexigens British Guiana, D. gigas, and D. desulfuricans Essex 6. An enzymelinked immunoadsorption assay (ELISA) was developed to measure the reaction of these antisera with the homologous and heterologous antigens. The ELISA method demonstrated a reaction between pre-immune sera and cells of D. africanus, D. gigas and D. desulfuricans, suggesting the presence of a lectin-like substance on these cell surfaces. Extensive cross-reactions were seen between the antisera and heterologous cells, suggesting the sharing of a number of surface antigens amongst the Desulfovibrio. However, the pattern of these cross-reactions was different from that observed for an ELISA reaction developed for the cytochrome c₃ from various Desulfovibrio.Abbreviation ELISA enzyme-linked immunoadsorption assay     

Energy conservation in whole cells of the methylotrophic bacterium Methylophilus methylotrophus

Respiratory chain phosphorylation has been investigated in the methylotrophic bacterium Methylophilus methylotrophus following the addition of oxidisable substrates to aerobic, whole cell suspensions. Initial-rate experiments showed that ATP synthesis occurred at the overall expense of AMP and inorganic phosphate via the sequential action of the ATP phosphohydrolase and adenylate kinase; some of the nascent ATP was rapidly used to synthesis nonadenine nucleoside triphosphates. After being corrected for ATP turnover, Pi/O quotients of 0.46 to 0.54, 0.77 and 1.37 nmol/ng-atom O were obtained for the oxidation of methanol dehydrogenase-linked substrates (methanol, ethanol and acetaldehyde), duroquinol and formate (NAD⁺-linked) respectively. These values were proportional to the H⁺/O and/or K⁺/O quotients exhibited by these substrates, and yielded an average H⁺/ATP (H⁺/Pi) quotient of 4.2 ng-ion H⁺/nmol. Steady-state experiments showed that the extent of cellular energisation varied with the respiration rate but was always in the order methanol > duroquinol > acetaldehyde, thus indicating that under these longer-term conditions methanol was completely oxidised to yield PQQH₂ and 2NAD(P)H. These results are discussed in terms of the various reactions which lead to the generation or utilisation of the protonmotive force in this organism.Abbreviations FCCP carbonylcyanide p-trifluoromethyxyphenyl-hydrazone - bulk phase, transmembrane electrochemical potential difference of protons ( ) - pH bulk phase, transmembrane pH difference (pH_in–pH_out) - bulk phase, transmembrane electrical potential difference (_in - _out) - [P] concentration of anhydride phosphate bonds in adenine nucleotides (2[ATP]+[ADP]) - FPLC fast protein liquid chromatography - PQQ pyrroloquinoline quinone - Gp phosphorylation potential     

Persistence of Bacillus thuringiensis parasporal crystal insecticidal activity in soil

Spores and parasporal crystals of a Bacillus thuringiensis var. aizawai (H-serotype 7), strain HD137, streptomycin-resistant mutant were added to acidic (pH 5.0) natural and autoclaved soil and incubated at ?0.10 MPa, 25°C. Populations of B. thuringiensis in both soil treatments showed exponential rates of mortality which were represented by linear regression, the loss of viability being greater in natural than autoclaved soil. In natural soil, parasporal crystal insecticidal activity was lost at a complex, nonexponential rate. The initial, rapid decrease of activity gradually slowed, and the level of activity stabilized at 10% of the original inoculum level after 250 days incubation, until the cessation of sampling at >2 years. In autoclaved soil no significant (P > 0.2) loss of parasporal crystal insecticidal activity was detected over the same period, which suggested that soil microorganisms were responsible for the loss of crystal insecticidal activity in the natural, nonsterilized soil. The rate of loss of crystal activity in natural soil correlated well with assay data reported in the literature using Galleria mellonella, which measures the combined activity of spore and crystal. In autoclaved soil correlation was poor, probably due to variability in the bioassay data.     

The relationship between hydrogen metabolism,sulfate reduction and nitrogen fixation in sulfate reducers

Summary Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D₂–H⁺ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism.