Microbial biomass and productivity in seagrass beds.

Different methods for measuring the rates of processes mediated by bacteria in sediments and the rates of bacterial cell production have been compared. In addition, net production of the seagrass Zostera capricorni and bacterial production have been compared and some interrelationships with the nitrogen cycle discussed. Seagrass productivity was estimated by measuring the plastochrone interval using a leaf stapling technique. The average productivity over four seasons was 1.28 +/- 0.28 g C m-2 day-1 (mean +/- standard deviation, n = 4). Bacterial productivity was measured five times throughout a year using the rate of tritiated thymidine incorporated into DNA. Average values were 33 +/- 12 mg C m-2 day-1 for sediment and 23 +/- 4 for water column (n = 5). Spatial variability between samples was greater than seasonal variation for both seagrass productivity and bacterial productivity. On one occasion, bacterial productivity was measured using the rate of 32P incorporated into phospholipid. The values were comparable to those obtained with tritiated thymidine. The rate of sulfate reduction was 10 mmol SO4(-2) m-2 day-1. The rate of methanogenesis was low, being 5.6 mg CH4 produced m-2 day-1. A comparison of C flux measured using rates of sulfate reduction and DNA synthesis indicated that anaerobic processes were predominant in these sediments. An analysis of microbial biomass and community structure, using techniques of phospholipid analysis, showed that bacteria were predominant members of the microbial biomass and that of these, strictly anaerobic bacteria were the main components. Ammonia concentration in interstitial water varied from 23 to 71 micromoles. Estimates of the amount of ammonia required by seagrass showed that the ammonia would turn over about once per day. Rapid recycling of nitrogen by bacteria and bacterial grazers is probably important.

The taxonomy of some new isolates of dissimilatory sulfate-reducing bacteria.

The interrelationships between 92 isolates of sporing and non-sporing sulfate-reducing bacteria were determined. Of the 116 biochemical and physiological characteristics examined, only 25 were useful for discrimination of groups. Responses to most of the test were negative. A similarity coefficient and a principal component factor analysis of these data were made. The deoxyribonucleic acids buoyant densities (DNA) from all strains and the electrophoretic properties of adenylylsulfotransferase (ATP-sulfurylase), adenylphosphosulfate (APS)-reductase, and sulfite reductase of selected isolated were determined. On the basis of these various data eight groups were recognized. Isolated of seven of these groups appeared to be similar to one or more named strains. Isolates of group E(DNA buoyant density, 1.708) were different from previously named strains. Sporins strains were not isolated from the Papua New Guinea location. Halophilic and non-halotolerant strains were isolated from highly saline locations in Australia. Results pertinent to the taxonomy and ecology of the sulfate-reducing bacteria are discussed.

Dithionite reduction in the presence of a tetrapyrrole-containing fraction from the desulfoviridin of Desulfovibrio gigas.

Low-molecular-weight fractions obtained from the desulfoviridin of D. gigas and from the growth medium of Desulfovibrio sp. 10455 promoted the reduction of sodium dithionite to sulphide in the presence of reduced methylviologen. These fractions contained a tetrapyrrole of the isobacteriochlorin type which was not complexed with iron, nor was it complexed with protein. The observations are discussed in relation to the function of sulphite reductases in the sulphate-reducing bacteria.

Variations in the spectrum of desulfoviridin from Desulfovibrio gigas.

Desulfoviridin preparations from D. gigas showed variations in the position of the absorption maximum the beta-peak) in the 580-nm region of the specturm. On treatment with Na2S2O4 a preparation with a beta-peak at 585 nm was affected rapidly, the 585-nm peak shifting to the 596-nm region; this was partially reversed by K3Fe(CN)6. Treatment of the original preparation with K3Fe(CN)6 resulted in a shift of the beta-peak to 582-583 nm. Desulfoviridins with beta-peaks from 580 to 583 nm were not rapidly affected by Na2S2O4. The spectrum of the chromophore of desulfoviridin way also affected by Na2S2O4 with the peak at 587 nm shifting to 597 nm; this effect was completely reversed by oxygen. There was no evidence to show that spectral variations in desulfoviridin preparations were due to the loss or acquisition of metal ions during growth or to the selection of mutants containing spectrally different desulfoviridins. It is suggested that during biosynethesis oal detachment of the chromophore, thus causing a change towards the spectral properites of the detached chromophore.

Effect of enzymic assay conditions on sulfite reduction catalysed by desulfoviridin from Desulfovibrio gigas.

The type and the amount of end products resulting from sulfite reduction catalysed by a single partially purified desulfoviridin preparation from Desulfovibrio gigas were shown to depend upon the enzymic assay conditions employed. Both manometric and spectrophotometric assays were used, with reduced methyl viologen serving as the electron donor in each system. Trithionate, thiosulfate, tetrathionate and sulfide were identified as possible end products. In the manometric assays, sulfide production was favoured by high reduced methyl viologen concentrations, low sulfite concentrations and a pH value of 7.0 as opposed to 6.0. In the spectrophotometric assays, results approaching the stoichiometric conversion of sulfite to sulfide were obtained only at high initial reduced methyl viologen concentrations.

Guanine plus cytosine contents of the deoxyribonucleic acids of some sulfate-reducing bacteria: a reassessment.

Guanine plus cytosine (GC) contents of the deoxyribonucleic acids of Desulfovibrio and Desulfotomaculum have been used as a basis for classification. Some of these data have been incorrectly calculated, resulting in errors of as much as 5% GC. This situation has been corrected by a reanalysis of existing data and by the contribution of new data.