Bernard M. Simon

Bacterial Reduction of Ferric Iron in a Stratified Eutrophic Lake

SUMMARY: The rate of release of Fe(II) from anoxic lake sediments was lower in the presence than in the absence of nitrate. The reduction of Fe(III) by the sediments had a temperature optimum of 30 °C and was inhibited by HgCl2, suggesting that the process was largely biological in nature. Of the iron sources tested with cultures of anaerobic iron-reducing bacteria, FeCl3 was the most readily reduced and goethite the least. Reduction was faster in the presence of a chelating agent and was suppressed by the addition of NO- 3, ClO- 3, MnO2, Mn2O3 and O2. An iron-reducing chemoorganotroph, tentatively identified as a member of the genus Vibrio, was isolated. Physical contact between the bacterium and iron particles was essential to ensure maximum rates of Fe(III) reduction but > 30% of the activity appeared to be associated with extracellular components. Although Fe(III) reduction by whole cells and cell-free extracts was decreased in the presence of electron transport inhibitors, the molar growth yield of the organism was unaffected by the presence of Fe(III). It is assumed that the organism used the Fe(III) as a hydrogen sink. A second organism, an anaerobic facultative chemolithotroph, appeared to conserve energy by the reduction of Fe(III). Biomass yield (measured as ATP) was greater in the presence of Fe(III), and the organism was able to use H2 as a source of reducing power.

Differences in Microbial Decomposition Processes in Profundal and Littoral Lake Sediments, with Particular Reference to the Nitrogen Cycle

An investigation of sediments from the littoral (shallow water) and profundal (deep water) zones of Blelham Tarn, a shallow eutrophic lake, showed marked differences in the microbial decomposition processes. These differences were due largely to differences in the degree of oxygenation, supply of electron acceptors, and mean summer temperature at the two sites. The changes in the hypolimnion (the deep water zone formed on thermal stratification, which may be treated essentially as a closed system) could be used to calculate profundal rates of aerobic respiration, NO- 3 and SO2- 4 reduction, and methanogenesis, relative to the accumulation of CO2. Laboratory measurements demonstrated that NH+ 4 accumulation, SO2- 4 reduction and methanogenesis were more intense in the profundal than in the littoral zone. Anaerobic processes that occurred in the littoral sediments did so at greater depths than in the profundal sediments. The release of CH4 and N2 bubbles also provided estimates of the importance of these processes at the two sites. At both sites aerobic respiration was the most important component (about 50%) of carbon mineralization; SO2- 4 reduction was the least important, accounting for only a small percentage of carbon turnover. Pathways of NO- 3 reduction and methanogenesis accounted for approximately equal proportions (varying between 15 and 25%) of the carbon mineralized. When the results were adjusted to account for the relative areas of the profundal and littoral zones, the former was the more important site of methanogenesis and SO2- 4 reduction, whereas aerobic respiration and NO- 3 reduction were greater in the littoral zone. The major end-product of NO- 3 reduction was NH+ 4 in the profundal and N2 in the littoral zone. The higher and continued levels of nitrification, which recycled the NH+ 4 in the littoral sediments, were thought to contribute to this.

Factors Affecting Methanogenesis and Associated Anaerobic Processes in the Sediments of a Stratified Eutrophic Lake

SUMMARY: Factors affecting methanogenesis in the sediments of a eutrophic lake were studied during late summer, a period during which CH4 gas production slowed down dramatically or stopped completely. The most active methanogenesis occurred in the surface sediments and the temperature optimum for the process in these deeper sediments was 30 °C. Addition of H2 or formic acid to sediment slurries stimulated CH4 production to a greater extent than did acetic or pyruvic acid. Analysis of the kinetics of the conversion of H2 to CH4 suggested that the sediments were severely limited in H2, the concentration being considerably less than 2·5 μmol 1-1, the Km for the process. Methanogenesis was not stimulated by the addition of trace quantities of Ni2+, Co2+, MoO4 2- or Fe2+ ions but was inhibited by 0·5 mmol SO4 2- 1-1. Under natural conditions the sediments were also limited in SO4 2- and sulphate reducers acted as net H2 donors to the methanogens; addition of SO4 2- allowed the sulphate reducers to compete effectively for H2. The addition of 20 mmol Na2MoO4 1-1 to sediments inhibited methanogenesis but this was not due entirely to its effect in the H2 transfer from sulphate reducers; it also inhibited CO2 uptake by sediments and the production of CH4 from CH3COOH and CO2 by cultures of methanogens. It is therefore inadvisable to use MoO4 2- at this concentration as a specific inhibitor of sulphate reducers in such freshwater sediments. Experiments with other inhibitors of methanogens suggested that they may interact with sulphate reducers, acetogens or anaerobic bacteria involved in fatty acid decomposition. Small, sealed sediment cores, which were used to reproduce natural conditions, particularly of available H2 concentration, were injected with trace quantities of H14CO3 - and 14CH3COOH. The results suggested that more than 75% of the CH4 was derived from CO2 and the remainder from CH3COOH. The overall rates of methanogenesis in the small cores agreed well with results from the field.

A Microbiological Study of Sediments from the Cumbrian Lakes

Summary: The microbiology of the benthos of 16 lakes in Cumbria was studied. The lakes formed a series ranging from oligotrophic to eutrophic, and the results were compared with other surveys of their chemistry and biology. The sediments of the more productive lakes contained more organic matter, E h measurements indicated that they were more reduced, and the overlying water was deoxygenated to a greater degree. These results correlated with greater microbial activity, biomass and numbers in the sediments of the richer lakes, as measured by electron transport system activity, ATP and direct counts. The data obtained from the sediments were, however, more variable, and showed poorer agreement with the assumed ranking of the lakes than the results obtained from the water column in this and past surveys. The microbiology of the benthos suggested that the more productive lakes might be considered as a distinct group, but more detailed sampling and careful choice of indicator micro-organisms would be required to provide statistically significant evidence for this.

Microbiological Sources of Ammonia in Freshwater Lake Sediments

SUMMARY: During summer stratification ammonia is released from the profundal sediments of Blelham Tarn (English Lake District). The quantity of ammonia released exceeds the consumption of nitrate in the hypolimnion. Nitrate dissimilation may be a component in the generation of ammonia, but only during early summer when nitrate is still available. The remainder of the ammonia arises largely from the deamination of proteins, amino acids and urea. Population estimates of bacteria which produced ammonia from nitrate, amino acids and urea were of the same order of magnitude. Numbers of bacteria which produced ammonia from nitrate increased with sediment depth, and urea decomposers were more numerous in the profundal (deep water) sediments. While nitrate was available in the water column, surface sediments converted nitrate almost exclusively to nitrogen gas. After depletion of the nitrate, the release of ammonia from washed sediment particles was largely microbiological, whereas there was a significant chemical component to the release from intact sediment cores. Chemical binding of ammonia by the sediments was demonstrated and this hindered calculations of inorganic nitrogen metabolism based on changes in water chemistry. Trace additions of 14C-labelled protein, amino acids and urea to sediments showed that urea was turned over the most rapidly, but more reliable estimates of available protein in the sediments are required before decomposition rates can be treated with confidence.

Measure of microbial turnover of carbon in anoxic freshwater sediments: cautionary comments

Abstract Small sediment cores were used to determine the turnover of a range of carbon substrates, particularly volatile fatty acids, by bentic bacteria. Volatile fatty acids were determined using an HPLC sytem in cojunction with a conductivity detector. At the low eluent strength used 1 μM acetate was detected with ease. Small cores were used in an attempt to maintain the natural partial pressure of hydrogen, an important factor in the control of anerobic metabolism of fatty acids. Although this is preferable to the disturbance of the sediment which occurs if it is resuspended a a slurry, problems are encountered at low substrate concentrations. The time taken for the added substrate to equilibrate in both radial and vertical planes may result in turnover times which vary with the incubation time used. Reduction of the qunatity of added substrate and increased replication may improve the accuracy of the estimates obtained, but more serious consideration must be given to the availability of the substrates to the benthic bacteria.

Microbiological Sources of Sulphide in Freshwater Lake Sediments

SUMMARY: The sources of sulphide which appeared in the profundal zone of Blelham Tarn (English Lake District) were investigated. In experimental sediment cores, the absence of sulphate in the overlying water resulted in a drastic decrease in the release of sulphide, which suggested that sulphate reduction was a major contributor to the process. The quantity of suphide produced was much less than that of sulphate removed. This, and the inability to detect free sulphide in sediment interstitial water, was attributed to its rapid precipitation as FeS. In the absence of sulphate, production of sulphide would be from organic sources such as protein. Most probable number estimates indicated that the population of bacteria capable of producing sulphide from cysteine was much larger than that of sulphate reducers. Trace additions of 35S-labelled sulphate, cysteine and methionine were used to determine their turnover time to sulphide. Sulphate was turned over the fastest and methionine the slowest, and the turnover time was always shorter in profundal sediment. Poor recoveries of added label from littoral sediments were thought to be due to adsorption and higher rates of assimilation. Estimates of flux based on concentrations of sulphate and organic sulphur suggested that putrefaction was a more important source of sulphide in the littoral zone but contributed less than sulphate reduction in the profundal sediments.

Nutritional strategy of a benthic filamentous bacterium

Filibacter limicola is a filamentous gliding bacterium isolated from the profundal sediment of a eutrophic lake. It is an obligate amino acid utilizer. The kinetic parameters for the metabolism of four amino acids byF. limicola, Vitreoscilla spp. and the bacterial populations of water and sediment samples were compared.F. limicola exhibited low half-saturation constants (K) which were of the same order as those obtained with water samples. The K values for theVitreoscilla spp. and the sediment were an order of magnitude higher. It would appear that the bacterium is a specialist, inhabiting a niche which is sufficiently nutrient rich to support an organism with a limited substrate range. It also possesses a high affinity uptake system for some amino acids which may permit it to compete effectively during periods of nutrient depletion.

Gas chromatographic determination of total amino acids and protein in sediments using the ninhydrin-CO2 reaction

A sensitive modification of the ninhydrin-CO2 method involving the gas chromatographic determination of the total protein and amino acid content of sediment is described. The method gives a linear response over the amino acid concentration range 10−5 M to 4 × 10−2 M. It can be used for whole sediment, hydrolysates and interstitial water. The performance of the method is compared with the fluorescamine method for primary amines.