Factors controlling bacterial production in marine and freshwater sediments

We collected benthic bacterial production data measured by ³H thymidine incorporation (TTI) (25 studies), frequency of dividing cells (FDC) (3 studies), dark-C0₂ assimilation (1 study) and ³H-adenine uptake (2 studies) from the literature, which included 18 marine, 6 river, and 2 lake studies. In all of the studies that used the TTI method, ³H-DNA was isolated and incubations were carried out at in situ temperatures. Most of the researchers also determined ³H-DNA extraction efficiencies and isotope dilution, thus interpretable estimates of bacterial production were used in the analysis. In marine sediments, bacterial production rates were linked to bacterial biomass, bacterial abundance, sediment organic matter, temperature, and sediment chlorophyll a, with these variables explaining between 40% and 68% of the variation in production rates. Simple relationships between production and bacterial biomass or bacterial abundance, or between production and sediment organic matter, were improved by also including temperature in the analysis of marine sediments. Sediment organic matter explained an appreciable fraction (58%) of the observed production in freshwater sediments. Temperature was the most powerful predictor of the observed variability in specific growth rates (r ² = 0.48 and r ² = 0.58) in marine and freshwater sediments, respectively. Thus, bacterial production and specific growth rates are most closely linked to substrate supply and temperature in marine and freshwater sediments. Offprint requests to: B. C. Sander.     

The effect of temperature and effluent recycle rate on hydrogen production by undefined bacterial granules

Biohydrogen production in an anaerobic fluidized granular bed bioreactor was strongly dependent on temperature and effluent recycle rates. At 45 °C as the effluent recycle rate was increased from 1.3 to 3.5 L/min, the total H? output for the bioreactor increased from 10.6 to 43.2 L/h. Volumetric H(2) productivity also increased from 2.1 to 8.7 L H?/L/h. At 70°C as the effluent recycle was increased from 1.3 to 3.5 L/min, the total H? output for the bioreactor increased from 13.8 to 73.8L/h. At 70 °C volumetric H(2) productivities increased from 2.8 to 14.8L H?/L/h as the effluent recycle rate was increased from 1.3 to 3.5 L/min. At 45 °C % H? was 45% and reached 67% at 70 °C. Maximum hydrogen yields at 45 °C were 1.24 and 2.2 mol H?/mol glucose at 70 °C.     

The effect of growth temperature on the bioenergetics of photosynthetic algal cultures

Two photosynthetic algal cultures, one Chlorella vulgaris, and the other a Chlorogonium sp., were cultured under light limitations in chemostats. The effects of growth temperature on their energy yield and maintenance energy requirement were studied. It was observed that a lowering in temperature resulted in a lower maximum growth yield from the light energy, Y(G). This was attributed to two reasons. First, at low temperatures there was a change in the algal cell composition with more energy being expended to synthesize a higher biomass protein content. Secondly, at low temperatures, a cyanide-resistant respiratory pathway became operative which led to a decrease in the number of ATP being generated. The maintenance energy coefficient was a function of temperature increasing with decreasing temperature. This might reflect energy wastage by the cell at low temperatures. The maximum specific growth rate dropped with decreasing temperature, and can be described by an Arrhenius type rate-temperature model up to the optimal temperature for growth; i.e., activation energy remained constant.     

The effect of temperature on growth and lipid and fatty acid composition on marine microalgae used for biodiesel production

Cultivation temperature is one of the major factors affecting the growth and lipid accumulation of microalgae. In this study, the effects of temperature on the growth, lipid content, fatty acid composition and biodiesel properties of the marine microalgae Chaetoceros sp. FIKU035, Tetraselmis suecica FIKU032 and Nannochloropsis sp. FIKU036 were investigated. These species were cultured at different temperatures (25, 30, 35 and 40 °C). The results showed that the specific growth rate, biomass and lipid content of all microalgae decreased with increasing temperature. With regards to fatty acids, the presence of saturated fatty acids (SFAs) in T. suecica FIKU032 and Nannochloropsis sp. FIKU036 decreased with increasing temperature, in contrast with polyunsaturated fatty acids (PUFAs). Moreover, Chaetoceros sp. FIKU035 was the only species that could grow at 40 °C. The highest lipid productivity was observed in Chaetoceros sp. FIKU035 when cultivated at 25 °C (66.73 ± 1.34 mg L^?1 day^?1) and 30 °C (61.35 ± 2.89 mg L^?1 day^?1). Moreover, the biodiesel properties (cetane number, cold filter plugging point, kinematic viscosity and density) of the lipids obtained from this species were in accordance with biodiesel standards. This study indicated that Chaetoceros sp. FIKU035 can be considered as a suitable species for biodiesel production in outdoor cultivation.     

Modeling the temperature effect on the specific growth rate of phytoplankton: a review

Phytoplankton are key components of ecosystems. Their growth is deeply influenced by temperature. In a context of global change, it is important to precisely estimate the impact of temperature on these organisms at different spatial and temporal scales. Here, we review the existing deterministic models used to represent the effect of temperature on microbial growth that can be applied to phytoplankton. We first describe and provide a brief mathematical analysis of the models used in constant conditions to reproduce the thermal growth curve. We present the mechanistic assumptions concerning the effect of temperature on the cell growth and mortality, and discuss their limits. The coupling effect of temperature and other environmental factors such as light are then shown. Finally, we introduce the models taking into account the acclimation needed to thrive with temperature variations. The need for new thermal models, coupled with experimental validation, is argued.     

The effects of chlorhexidine on the maximum specific growth rate, biomass and hydrolytic enzyme production of Bacteroides gingivalis grown in continuous culture

Bacteroides gingivalis was grown in continuous culture in the presence of chlorhexidine. Maximum specific growth rates and biomass levels initially increased but then decreased as the chlorhexidine level increased from 0 to 30 micrograms/ml. Total inhibition of growth occurred when the chlorhexidine concentration reached 60 micrograms/ml. The steady-state levels of cell-bound, extracellular vesicle and extracellular soluble enzymes, trypsin-like protease, alkaline phosphatase and N-acetyl-beta-glucosaminidase were measured. With increasing sub-lethal concentrations of chlorhexidine, levels of alkaline phosphatase increased noticeably in all three fractions of culture, whilst cell-bound and extracellular vesicle levels of N-acetyl-beta-glucosaminidase remained approximately constant. Extracellular soluble levels of alkaline phosphatase and N-acetyl-beta-glucosaminidase increased with increasing levels of chlorhexidine. The levels of trypsin-like protease decreased significantly in all fractions of the culture when cells were grown in the presence of chlorhexidine. Thus, chlorhexidine has a differential effect on the production of B. gingivalis hydrolytic enzymes.     

The effects of chlorhexidine on the maximum specific growth rate, biomass and hydrolytic enzyme production of Bacteroides gingivalis grown in continuous culture

Bacteroides gingivalis was grown in continuous culture in the presence of chlorhexidine. Maximum specific growth rates and biomass levels initially increased but then decreased as the chlorhexidine level increased from 0 to 30 μg/ml. Total inhibition of growth occurred when the chlorhexidine concentration reached 60 μg/ml. The steady-state levels of cell-bound, extracellular vesicle and extracellular soluble enzymes, trypsin-like protease, alkaline phosphatase and N -acetyl-β-glucosaminidase were measured. With increasing sub-lethal concentrations of chlorhexidine, levels of alkaline phosphatase increased noticeably in all three fractions of culture, whilst cell-bound and extracellular vesicle levels of N -acetyl-β-glucosaminidase remained approximately constant. Extracellular soluble levels of alkaline phosphatase and N -acetyl-β-glucosaminidase increased with increasing levels of chlorhexidine. The levels of trypsin-like protease decreased significantly in all fractions of the culture when cells were grown in the presence of chlorhexidine. Thus, chlorhexidine has a differential effect on the production of B. gingivalis hydrolytic enzymes.     

Problems in developing the biotechnology of algal biomass production

Summary The effects of environmental conditions (solar irradiance and temperature) and population density on the production of Spirulina biomass with brackish water are reported for cultures grown in outdoor ponds. Higher specific growth rates were observed at lower population densities. Lower growth rates were associated with limitation by light in dense cultures under optimum conditions in the summer. Seasonal variation in productivity was observed. In summer, light was the limiting factor, whereas in winter the low daytime temperature appeared to constitute the major limitation. The oxygen concentration in the culture can serve as a useful indicator of limiting factors and can also be used to estimate the extent of such limitations.     

Real-time estimation of biomass and specific growth rate in physiologically variable recombinant fed-batch processes

The real-time measurement of biomass has been addressed since many years. The quantification of biomass in the induction phase of a recombinant bioprocess is not straight forward, since biological burden, caused by protein expression, can have a significant impact on the cell morphology and physiology. This variability potentially leads to poor generalization of the biomass estimation, hence is a very important issue in the dynamic field of process development with frequently changing processes and producer lines. We want to present a method to quantify “biomass” in real-time which avoids off-line sampling and the need for representative training data sets. This generally applicable soft-sensor, based on first principles, was used for the quantification of biomass in induced recombinant fed-batch processes. Results were compared with “state of the art” methods to estimate the biomass concentration and the specific growth rate µ. Gross errors such as wrong stoichiometric assumptions or sensor failure were detected automatically. This method allows for variable model coefficients such as yields in contrast to other process models, hence does not require prior experiments. It can be easily adapted to a different growth stoichiometry; hence the method provides good generalization, also for induced culture mode. This approach estimates the biomass (or anabolic bioconversion) in induced fed-batch cultures in real-time and provides this key variable for process development for control purposes.     

The effect of resuspension on algal production in a shallow lake

Waves cause erosion and resuspension of bottom sediments. In shallow lakes resuspension can take place over most of the lake area and the resuspended matter can stay in suspension for such a long time that the mean light intensity in the lake is reduced, causing reduced algal growth. The increase of suspended matter and light attenuation in the water of lake Tämnaren, Sweden, was found to be proportional to wind velocity to the third power. After each storm increased attenuation of light lasted for a week. The algal production was estimated to be reduced to only 15 % of what it would have been without increased turbidity due to resuspension.     

The effect of temperature on the growth and hydrogen production by Citrobacter intermedius

Summary Citrobacter intermedius was grown batchwise in a mineral salts medium with glucose as a carbon and energy source under anaerobic conditions and at different temperatures. The effect of temperature on the following parameters was studied: maximum specific growth rate, max, maximum rate of hydrogen gas production and maximum rate of total gas (H₂ + CO₂) production. Arrhenius plots were used to determine the activation energies associated with max and maximum rates of hydrogen gas production.     

Effects of pH on biomass, maximum specific growth rate and extracellular enzyme production by three species of cutaneous propionibacteria grown in continuous culture

Three cutaneous propionibacteria, Propionibacterium acnes, Propionibacterium avidum and Propionibacterium granulosum, were grown in chemostats using semi-synthetic medium at various pH values. Growth occurred between pH 4.5 and 7.5 for P. acnes and pH 5.0 and 8.0 for P. avidum and P. granulosum. The highest mumax was at pH 6.0 for the three species. Maximum biomass production was obtained at pH 6.0 for P. acnes and P. avidum and at pH 7.5 for P. granulosum. Extracellular enzyme production occurred over the entire pH growth range when denaturation of the enzymes was taken into account. However, detectable activity of the enzymes was found in a narrower range of pH due to the denaturation of the enzymes at low or high pH values. The highest production of enzymes occurred at pH values between 5.0 and 6.0, apart from the production of hyaluronate lyase of P. granulosum (pH 6.0 to 7.0) and the proteinase of P. acnes and P. avidum (pH 5.0 to 7.5). Propionibacterium acnes produced a lipase, hyaluronate lyase, phosphatase and proteinase activity. Propionibacterium avidum produced a lipase and proteinase activity. Propionibacterium granulosum produced a lipase and hyaluronate lyase.     

Stimulatory effect of aerosil on algal growth

Unicellular green alga represents not only a convenient model for its biochemical and physiological studies but also a sensitive system to test the effects of various environmental factors. Algae cells of two strains, SA-3 strain (exsymbiotic from Paramecium bursaria) and Chlorella vulgaris c-27, were asynchronously cultured in the presence of 0.01% Aerosil A-300. Aerosil effects on algae were monitored at logarithmic and stationary phases of their growth by flow cytometry and microscopic counting of algal numbers. The growth patterns of algae were evaluated by their forward light scatter versus fluorescence of endogenous chlorophyll (FL3-height) signal distributions. Although aerosil itself did not cause any direct effects on algal morphology, it affected the growth patterns and the numbers of algae of both strains. Their growth patterns were remarkably altered in the late logarithmic phase cultures (6-day cultures). However, a significant increase of cell numbers was found in the stationary phase cultures (9- and 12-day cultures). While C. vulgaris c-27 demonstrated an increase of cell numbers by approximately 11% in the 9- and 12-day cultures, the amounts of SA-3 cells in the 9- and 12-days cultures were increased by 16% and 35%, respectively. Our study shows aerosil in its colloidal form stimulates proliferation of algae mainly via an acceleration of their life cycles. The stimulatory effect of silica on the growth of algae, the mechanism of which remains to be clarified, might have a practical (e.g., ecological) interest for regulation of algal expansion.     

On-line estimation of the specific growth rate based on viable biomass measurements: experimental validation

The application of model based control techniques to biotechnological processes is often hampered due to the lack of reliable on-line sensors. This problem can be tackled by the application of software sensors, in which the available hardware measurements are combined with the model equations. The resulting estimates serve as additional measurements useful for process monitoring and control. In this paper, an observer based estimator for the specific growth rate based on on-line viable biomass measurements is studied. Several fed-batch experiments with baker's yeast in a stirred tank bioreactor illustrate the design, tuning, and implementation from a practical point of view. The main contributions of this paper are to illustrate (i) the implementation and validation of the presented algorithm in real-time, (ii) the use of an advanced on-line biomass measurement, and (iii) the design and tuning of the algorithm from a practical point of view. Real-time knowledge of the specific growth rate is important because it yields information on the viability of the cells and it can be used in real-time feedback control algorithms.     

The dependence of reproductive rate on cell size and temperature in freshwater ciliated protozoa

Summary Reproductive rates have been calculated for ten species of ciliated protozoa in defined conditions. Interspecific double log regressions of generation time vs. cell volume have been computed at each of three temperatures (8.5° C, 15° C, and 20° C) indicating a significant dependence of reproductive rate on cell size. Recorded generation times varied from 6.38 h in Vorticella microstoma at 20° C to 1004 h in Spirostomum teres at 8.5° C. These values correspond to a range in r _m (day)^-1 of 2.607 to 0.017 and (day)^-1 of 13.554 to 1.017. The relationship between these data and similar published data for marine ciliates is examined and the value of such regressions in ecological studies of the protozoa is discussed.     

Determination of bacterial number and biomass in the marine environment.

Three techniques for the measurement of bacterial numbers and biomass in the marine environment are described. Two are direct methods for counting bacteria. The first employs an epifluorescence microscope to view bacteria that have been concentrated on membrane filters and stained with acridine orange. The second uses a transmission electron microscope for observing replicas of bacteria that are concentrated on membrane filters. The other technique uses Limulus amebocyte lysate, an aqueous extract from the amebocytes of the horseshoe crab, Limulus polyphemus, to quantitate lipopolysaccharide (LPS) in seawater samples. The biomass of gram-negative (LPS containing) bacteria was shown to be related to the LPS content of the samples. A factor of 6.35 was determined for converting LPS to bacterial carbon.     

Determination of bacterial number and biomass in the marine environment.

Three techniques for the measurement of bacterial numbers and biomass in the marine environment are described. Two are direct methods for counting bacteria. The first employs an epifluorescence microscope to view bacteria that have been concentrated on membrane filters and stained with acridine orange. The second uses a transmission electron microscope for observing replicas of bacteria that are concentrated on membrane filters. The other technique uses Limulus amebocyte lysate, an aqueous extract from the amebocytes of the horseshoe crab, Limulus polyphemus, to quantitate lipopolysaccharide (LPS) in seawater samples. The biomass of gram-negative (LPS containing) bacteria was shown to be related to the LPS content of the samples. A factor of 6.35 was determined for converting LPS to bacterial carbon.