Biomedical subjects

D B Nedwell

Publications and source records attributed to D B Nedwell.

6 recordsLinked to original sources

PubMed1994

Influence of temperature on growth rate and competition between two psychrotolerant Antarctic bacteria: low temperature diminishes affinity for substrate uptake.

The growth kinetics of two psychrotolerant Antarctic bacteria, Hydrogenophaga pseudoflava CR3/2/10 (2/10) and Brevibacterium sp. strain CR3/1/15 (1/15), were examined over a range of temperatures in both batch culture and glycerol-limited chemostat cultures. The maximum specific growth rate (mu max) and Ks values for both bacteria were functions of temperature, although the cell yields were relatively constant with respect to temperature. The mu max values of both strains increased up to an optimum temperature, 24 degrees C for 2/10 and 20 degrees C for 1/15. Strain 1/15 might therefore be considered to be more psychrophilic than strain 2/10. For both bacteria, the specific affinity (mu max/Ks) for glycerol uptake was lower at 2 than at 16 degrees C, indicating a greater tendency to substrate limitation at low temperature. As the temperature increased from 2 to 16 degrees C, the specific affinity of 1/15 for glycerol increased more rapidly than it did for 2/10. Thus 1/15, on the basis of this criterion, was less psychrophilic than was 2/10. The steady-state growth kinetics of the two strains at 2 and 16 degrees C imply that 1/15 would be able to outgrow 2/10 only at relatively low substrate concentrations (< 0.32 g of glycerol.liter-1) and high temperatures (> 12 degrees C), which suggests that 1/15 has a less psychrotolerant survival strategy than does 2/10. Our data were compared with other data in the literature for bacteria growing at low temperatures. They also showed an increase of substrate-specific affinity with increasing temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Antarctic Regions↗

PubMed1994

Influence of changing temperature on growth rate and competition between two psychrotolerant Antarctic bacteria: competition and survival in non-steady-state temperature environments.

Competition between two psychrotolerant bacteria was examined in glycerol-limited chemostat experiments subjected to non-steady-state conditions of temperature. One bacterium, a Brevibacterium sp. strain designated CR3/1/15, responded rapidly to temperature change, while a second, Hydrogenophaga pseudoflava, designated CR3/2/10, exhibited a lag in growth after a shift-down during a square-wave temperature cycle but not after a shift-up. The effects on competition and survival by these bacteria of both sine-wave and square-wave temperature changes between 2 and 16 degrees C over a 24-h cycle time were examined, as well as square-wave cycles over 12 and 96 h. The changing proportion of each bacterium in the chemostat was determined by plate counting at regular intervals. Under a sine-wave temperature cycle H. psedoflava outcompeted the Brevibacterium sp., but under square-wave temperature cycles the two bacteria coexisted because the lag by H. pseudoflava after the temperature shift-down favored the faster-responding Brevibacterium sp. The two bacteria thus exhibited different survival strategies, with H. pseudoflava adapted to effective competition under steady-state conditions and the Brevibacterium sp. adapted to rapid adaptation and survival in a changing environment. The degree of perturbation of the bacteria, expressed as a temperature challenge index (delta temp/delta time), was greater under a square-wave temperature cycle than under a sine-wave cycle of equivalent amplitude and frequency, and higher-temperature challenge favored the Brevibacterium sp. A computer model was developed to examine competition between the bacteria in transient environments. The frequency of the temperature cycle influenced competition, as with a longer cycle (96 h) the significance of the lag by H. pseudoflava decreased compared with that of a 24-h cycle, and H. pseudoflava predominated in a mixed culture with a 96-h cycle. The shift-down lag by H. pseudoflava, during which it adapted to low temperature, disadvantaged it in a changing temperature environment, but at a short cycle time (12 h) this disadvantage was countered by the incomplete loss of low-temperature adaptation between cycles and thus the carryover of some low-temperature adaptation. Also, it was demonstrated that, as well as consideration of the effect of temperature changes on inducing lags in growth, the loss of adaptation to low temperature between cycles had to be taken into account in the computer model if it was to reproduce the trends in the experimental data.

Antarctic Regions↗

PubMed1984

A note on 'plotless' methods for estimating bacterial cell densities.

' Plotless ' techniques for determining population densities have been developed for, and applied to, higher plant populations. They can often be carried out more rapidly than techniques involving total counts of individuals in plots, or quadrants, but such plotless techniques have not been generally applied to the estimation of densities of bacterial cells. Direct microscopical counting of cell numbers in a field of view, an example of a plot-related method, has been traditionally used for microbial cell counts. In this study 'plot' and ' plotless ' methods on a variety of bacterial samples are compared. Estimates of bacterial cell density were obtained by measuring the distance of cells from a fixed point in a field of view. The values, which were more rapidly obtained, were directly correlated with total cell counts. Although there was some apparent deviation from a perfect 1:1 relationship with total counts, as indicated by a correlation coefficient less than 1.0, there were no significant differences between the replicated counts of bacteria on samples of tissue from the surface of Hypholoma basidiocarps (P less than 0.05). This indicated that the methods of enumeration were comparable. The distance-related estimates could readily be obtained from fields of view with cell densities varying over several orders of magnitude. It was more rapidly applied, particularly at high density, and the method was applicable not only to random cell distributions but also to the non-random distributions encountered when microbial cells aggregated into microcolonies. The method appears to be particularly well-suited for automated, digitized, direct counting procedures, as well as to estimating bacterial numbers on membrane filters and natural substrates.

Bacteria↗

PubMed1980

Serological characteristics within the genus Desulfovibrio.

Antisera were prepared against one strain each of Desulfovibrio desulfuricans, D. vulgaris and D. salexigens. The antisera were tested for cross reactivity against 36 heterologous Desulfovibrio strains by both agglutination titration and by double immunodiffusion percipitin plates. Generally no cross-reaction was demonstrated by agglutination even between heterologous strains of the same species, suggesting that the surface antigens of Desulfovibrio are highly specific. In immunodiffusion plates a single apparently genus-specific surface antigen could be shown to be present in all but two of the strains tested. Although other common precipitin bands showed the presence of some antigens common between heterologous strains these appeared to be randomly distributed among the strains tested, with the exception of one band shown to be generally specific to strains of D. salexigens. With this exception no other precipitin band could be shown to be consistently specific to any other species, nor consistently common to more than one species.

Agglutination Tests↗

PubMed1978

Inhibition of methanogenesis by sulphate reducing bacteria competing for transferred hydrogen.

A methanogenic bacterial consortium was obtained after inoculation of benzoate medium under N2/CO2 atmosphere with intertidal sediment. A hydrogen donating organotroph and Methanococcus mazei were isolated from this enrichment. H2-utilising sulphate reducing bacteria were isolated under H2/CO2 in the absence of organic electron donors. The Methanococcus was able to produce methane in yeast extract medium under N2/CO2 if the H2 donating organism was present, and sulphate reduction occurred if the hydrogen utilising sulphate reducing bacteria were grown with the H2 donating organism. The ability of the H2 utilising sulphate reducing bacteria to inhibit Methanococcus competitively was shown in clutures containing both of these H2 utilising bacteria.

Bacteria↗

PubMed1978

Hydrogen as a substrate for methanogenesis and sulphate reduction in anaerobic saltmarsh sediment.

Hydrogen gas stimulated sulphate reduction in a saltmarsh sediment and the importance of H2 transferred from organotrophic bacteria to the sulphate-reducers is discussed. beta-fluorolactate inhibited sulphate reduction whether lactate, ethanol or hydrogen was being used as growth substrate. When added to sediment beta-fluorolactate inhibited sulphate reduction with a consequent increase in methane production. Addition of H2 stimulated methanogenesis in sediment and this stimulation was greater if CO2 was also present. Hydrogen availability was the primary limitation of methanogenesis but the low concentration of dissolved CO2 in seawater may limit methane production even if H2 is available. The removal of inhibition of methanogenesis by the use of fluorolactate to suppress sulphate reduction or by the provision of hydrogen indicates competitive inhibition of methanogens by sulphate reducers utilizing transferred hydrogen.

Desulfovibrio↗