No abstract

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 (ILmax) and K, values for both bacteria were functions of temperature, although the cell yields were relatively constant with respect to temperature. The pUmax values of both strains increased up to an optimum temperature, 24°C for 2/10 and 20°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 (Fm1ax/Ks) for glycerol uptake was lower at 2 than at 16°C, indicating a greater tendency to substrate limitation at low temperature. As the temperature increased from 2 to 16WC, 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°C imply that 1/15 would be able to outgrow 2/10 only at relatively low substrate concentrations (<0.32 g of glycerolliter-') and high temperatures (>12°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. Our results explain recent reports of decreased affinity for substrates by heterotrophic bacteria in polar seas, with consequently increased difficulty of substrate uptake at low temperature, and may also be significant in explaining the limitation of primary production in the Southern Ocean.

Liver and skin tumor prevalences in brown bullheads Ameiurus nebulosus have been used in the North American Great Lakes to designate highly contaminated areas of concern and monitor their recovery. Here we interpret the results of six surveys conducted in the Chesapeake Bay watershed between 1992 and 2006, with data for 647 fish. The objective has been to develop an adequate database to critically evaluate the use of tumor prevalence as a habitat quality indicator within the watershed. Surveys featured randomized fish collection; recording of sex, length, weight, and age; and histopathology of all livers and all raised skin lesions. The Bayes information criterion was used to analyze all possible combinations of age, gender, length, and weight as covariates for logistic regression. Length and gender were the covariates that best described liver tumor prevalence. There were no covariates in the model for skin tumor prevalence. In some surveys, biomarkers, such as biliary polynuclear aromatic hydrocarbon (PAH)-like metabolites, hepatic cytochrome P450 activity, and hepatic DNA adducts, were used with sediment and tissue chemistry data to evaluate classes of chemicals as likely contributors to tumor prevalence. We highlight two surveys of the Anacostia River, Washington, D.C. (average = 55% liver tumors, 23% skin tumors), where sediment PAHs, biliary PAH-like metabolites, and hepatic DNA adducts were high, suggesting that PAHs play a major role. We show that logistic regression is an appropriate procedure for comparing "contaminated" versus "reference" locations, and we evaluate the utility of tumor surveys as an environmental indicator for the Chesapeake Bay watershed.

Nitrate‐metabolising bacteria were isolated from estuarine sediment in carbon‐limited anaerobic chemostats with nitrate as the only electron acceptor, at constant low temperature (5°C), constant high temperature (20°C), or square wave temperature cycle (5–20°C over 24 h). The steady‐state communities isolated were sampled randomly, and isolates identified. At constant 20°C and under cycling temperature the communities were dominated by bacteria with obligately fermentative metabolism; Klebsiella spp. at 20°C and Enterobacter spp. in cycling temperature, which were nitrate‐ammonifiers. The dominant isolates at 5°C were bacteria with the capacity for oxidative, respiratory metabolism, which were able to denitrify. The physiologies of representative isolates of these two distinct high and low temperature communities were examined further. An Arrhenius plot for growth of the 20°C isolate A1 (Klebsiella oxytoca) increased linearly from 10°C up to the optimum at 28°C, but decreased above the optimum and at temperatures <10°C. A1 was unable to grow at 5°C. The unidentifiable 5°C isolate (E3) was capable of both fermentative and oxidative metabolism, but when respiring nitrate the Arrhenius plot for growth was linear between 3–18°C with an optimum at 19°C. A cross‐over in μmax of these two isolates occurred at about 23°C. The ability of each bacterium to scavenge nitrate was examined in anaerobic nitrate‐limited chemostats, measuring the specific affinity (aA) of each bacterium for nitrate at different temperatures. Specific affinity for nitrate increased with temperature in both bacteria, indicating an improved ability to sequester nitrate at higher temperatures. Isolate A1 had a higher aA for nitrate than E3 at 20°C, but E3 had a higher aA at low temperature. A crossover in the specific affinities of these two bacteria occurred between 5 and 20°C, so that A1 was better able to sequester nitrate at high temperature while E3 was more effective in sequestering nitrate at lower temperature. We propose that at low temperature denitrifying bacteria predominate in estuarine sediments as they are selected by their improved ability to scavenge limited concentrations of nitrate at low temperature, whereas fermentative nitrate‐ammonifiers are better competitors for nitrate at the higher summer temperatures. Seasonal changes in environmental temperature therefore result in seasonal selection of different nitrate‐utilising communities.

No abstract

No abstract

No abstract

No abstract