Population Dynamics Of Bacteria Research Articles

Mechanisms and rates of bacterial colonization of sinking aggregates.

Quantifying the rate at which bacteria colonize aggregates is a key to understanding microbial turnover of aggregates. We used encounter models based on random walk and advection-diffusion considerations to predict colonization rates from the bacteria's motility patterns (swimming speed, tumbling frequency, and turn angles) and the hydrodynamic environment (stationary versus sinking aggregates). We then experimentally tested the models with 10 strains of bacteria isolated from marine particles: two strains were nonmotile; the rest were swimming at 20 to 60 microm s(-1) with different tumbling frequency (0 to 2 s(-1)). The rates at which these bacteria colonized artificial aggregates (stationary and sinking) largely agreed with model predictions. We report several findings. (i) Motile bacteria rapidly colonize aggregates, whereas nonmotile bacteria do not. (ii) Flow enhances colonization rates. (iii) Tumbling strains colonize aggregates enriched with organic substrates faster than unenriched aggregates, while a nontumbling strain did not. (iv) Once on the aggregates, the bacteria may detach and typical residence time is about 3 h. Thus, there is a rapid exchange between attached and free bacteria. (v) With the motility patterns observed, freely swimming bacteria will encounter an aggregate in <1 day at typical upper-ocean aggregate concentrations. This is faster than even starving bacteria burn up their reserves, and bacteria may therefore rely solely on aggregates for food. (vi) The net result of colonization and detachment leads to a predicted equilibrium abundance of attached bacteria as a function of aggregate size, which is markedly different from field observations. This discrepancy suggests that inter- and intraspecific interactions among bacteria and between bacteria and their predators may be more important than colonization in governing the population dynamics of bacteria on natural aggregates.

A new method for adaptive model-based control of non-linear dynamic plants using a neuro-fuzzy-fractal approach

We describe in this paper a new method for adaptive model-based control of non-linear dynamic plants using Neural Networks, Fuzzy Logic and Fractal Theory. The new neuro-fuzzy-fractal method combines Soft Computing (SC) techniques with the concept of the fractal dimension for the domain of Non-Linear Dynamic Plant Control. The new method for adaptive model-based control has been implemented as a computer program to show that our neuro-fuzzy-fractal approach is a good alternative for controlling non-linear dynamic plants. We illustrate in this paper our new methodology with the case of controlling biochemical reactors in the food industry. For this case, we use mathematical models for the simulation of bacteria growth for several types of food. The goal of constructing these models is to capture the dynamics of bacteria population in food, so as to have a way of controlling this dynamics for industrial purposes.

Effects of Bacterial Density and the Abundance of Limiting Resources for Bacteria on the Removal Process of Bacteria by Predation.

This paper investigated effects of the abundance of total bacterial populations and of limiting resources for bacteria on the removal process of bacteria by predation in a microbial community. For this analysis, an experimental, continuous flow system of a column bed-reactor was employed, to which bacterial suspension containing three species was supplied. The column reactor contains fiber carrier seeded with activated sludge. Population dynamics of bacteria, protozoa, and metazoa in influent and in effluent were examined under several conditions with varying total bacterial density and concentration of limiting resources contained in influent. The experimental results showed the tendency that bacterial density in the effluent was not affected either by the influent total bacterial density or by the resource abundance, which is explained using a mathematical model of one resource, one prey and one predator species. Experimental results suggests that the higher influent abundance of bacteria and/or resources for bacteria raise the size of predacious populations sustained in the community and species richness as well, which keeps the bacterial density in the effluent constant.

Effects of turbulence on bacterial growth mediated through food web interactions

We performed laboratory experiments with natural seawater communities of the Northwestern Mediterranean to test whether turbulence could affect bacterial abundance and activity. There was no direct effect of turbulence on bacteria when they were uncoupled from the remainder of the microbial community. In the presence of the microbial community, bacteria showed higher activity and maintained high abundances for a longer time under turbulence than in still water Thus, turbulence sufficiently altered some microbial component or process in the water samples that indirectly affected bacteria. The population dynamics of bacteria and pigmented eukaryotes suggests that, under turbulence, there is a community grazing shift from smaller to larger prey sizes. This shift can be explained in terms of the advantage to protozoan predators which are able to prey on larger and more nutritious cells when the encounter rates with these cells are increased through the shear present under turbulence. The result is a higher control on phytoplankton and a relaxation of grazing on bacteria. Hence. episodic high turbulence events in coastal systems could accelerate nutrient recycling.

Population dynamics of bacteria including antifungal species in the rhizosphere of oilseed rape during its life cycle

The population dynamics of different bacterial groups with antifungal properties was investigated in comparison with total bacteria based on colony forming units for successful biological control of the soil‐borne pathogen Verticillium dahliae var. longisporum Stark causing tracheomycosis of oilseed rape. This is the first report about bacterial population densities of a plant with a winter annual life cycle. Population densities of colony forming bacteria of oilseed rape (Brassica napus spp. oleifera Metzg. Sinsk.) were significantly lower in autumn and winter than in spring and summer. The number of antifungal bacterial populations like fluorescent pseudomonads, Bacillus spec. (spores) and Stenotrophomonas maltophilia also increased during life cycle. The percentages of antifungal isolates were 7 % on average and relatively stable during time of investigation as estimated by a bioassay in vitro. The antifungal mechanisms of 10 different isolates of each selected taxonomic group were investigated. The mechanisms were specific for each isolate. All of these selected strains showed antifungal activity against V. dahliae var. longisporum in vitro and therefore, they were evaluated as potential biocontrol agents against this pathogen.

Protease and deaminase activities in wheat rhizosphere and their relation to bacterial and protozoan populations

Protease and deaminase activities and population dynamics of bacteria and protozoa were measured in the rhizosphere of wheat to study their interactions with the mineralization of nitrogen. The experimental design allowed the separation of roots and soil material by means of a gauze. The most pronounced “rhizosphere effect” was detected for all the measured variables in the soil closest to the gauze. The number of bacteria was significantly higher in the presence than in the absence of plants up to 4 mm away from the soil-root interface and the closer to this interface the higher the number. Protozoan and bacterial population dynamics were positively correlated; generally, populations of flagellates and amoebae were comparable and their sum accounted for the population of total protozoa. For both enzyme activities the rhizosphere effect extended up to 2 mm away from the soil-root interface. The histidinase activity was of bacterial origin, while it is likely that bacteria, protozoa and root hair all contributed to the overall caseinase activity. Decomposition of root exudates and native organic matter in the rhizosphere, reflected by a growing microbial population, is associated with nitrogen mineralization through increases in caseinhydrolysing and L-histidine-deaminating activities. The adopted soil-plant microcosm is suitable for the study of the rhizosphere effect over time of incubation and distance gradient from the soil-root interface.

Alternative to CBOD 5 -Based Load Allocation Studies on Low-Dilution-Ratio Streams

Carbonaceous BOD5 and ammonia effluent limitations for low-dilution-ratio receiving waters are often determined by using wasteload allocation studies. These studies are labor intensive. They require one-third to one-half a work year to complete. Due to bacteria population dynamics, biological-wastewater treatment plants producing a highly nitrified effluent also produce an effluent low in carbonaceous BOD5. Using the BOD-ammonia relationship, regulators can achieve the same net results as labor-intensive load allocation studies with only 1% or 2% of the labor, if they concentrate on just protecting the receiving water's un-ionized ammonia standard. Four years of monthly effluent reports from 22 nitrifying wastewater treatment facilities were examined. This examination showed that this alternative to time-consuming wasteload allocation studies is practical.

Evolution saisonniere de la structure des communautes microbiennes dans un reservoir d'eau potable

The development of bacterial communities in drinking water supply networks may give rise to bacterial concentrations exceeding drinking water standards and also lead to the establishment of a food chain which allows the growth of macroorganisms incompatible with water quality requirements. Under such circumstances, drinking water reservoirs with relatively long residence times undoubtedly represent a very weak link in efforts to maintain water quality within a distribution network. Nevertheless, very few studies have examined the microbial communities and their trophic relationships in drinking water reservoirs. The goal of this study was to identify and quantify the microbial communities growing in a drinking water reservoir, and to follow their seasonal dynamics. Following cleaning and filling of the reservoir, 15 series of samples were collected between November 1991 and July 1992. Microorganisms of the inflowing water as well as those growing in the reservoir were analyzed. Bacteria were fixed in formaldehyde, stained with 4.6 diamino 2 phenylidole (DAPI) and counted by epifluorescence microscopy (Porter and Feig, 1980). Autotrophic and heterotrophic flagellated protozoa were fixed with glutaraldehyde, stained with primuline and counted by epifluorescence microscopy. Ciliates and amoebae were fixed with mercuric chloride (HgCl 2), microalgae with Lugol's solution, and all three types of organisms were counted with an inverted microscope. Rotifers and crustacea were fixed with formaldehyde and also counted with an inverted microscope. Chlorophyll a was extracted with 90% acetone and analyzed by HPLC according to Mantoura and Llewelyn (1983). The biomass of autotrophic microorganisms (essentially microalgae belonging to the class of Diatomophyceae) was very low and consisted of senescent cells in both, the inflowing water and the reservoir. Heterotrophic microbes were dominated by bacteria. The latter made up 84.5 and 91% of the total biomass of microbial heterotrophs in the reservoir and inflowing water, respectively (Fig. 9). Their concentration was greater in the reservoir ( M = 0.29 · 10 6bact · ml −1) than in the inflowing water ( M = 0.15 · 10 6bact · ml −1). The respective differences in biomass were even more pronounced because the inflowing bacteria were considerably smaller (mean biovolume V = 0.24 μm 3) than the reservoir bacteria (mean biovolume V = 0.53 μm 3) (Table 2). Nevertheless, the respective seasonal variations of the bacterial biomasses were parallel and appeared to relate to the temperature changes between November and May. After, the increase of total and free chlorine concentrations and/or the decline of biodegradable organic carbon (Table 3) led to a dramatic drop of the bacterial biomass. Flagellates numerically dominated the protozoa (98 and 94%, respectively, of total protozoan abundance in the inflowing water and reservoir), followed by ciliates (1.7 and 3%) and by naked amoebae (0.3 and 3%). Ciliates, however, had the greatest biomass (Fig. 10). The biomass of all groups of protozoa was always greater in the reservoir than in the inflowing water (Table 3). The seasonal development of the flagellated protozoa followed that of the bacteria (Figs 2 and 3). Conversely, ciliates and amoebae declined during spring with the growth of rotifers and crustacea (Figs 4, 5 and 8). Predation by the latter two appears to be an important factor limiting the development of protozoa. In conclusion, the drinking water reservoir contains a functional ecosystem with well established and structured microbial communities. The reservoir even appears to further the development of micro-organisms, because, excepting autotrophs, their abundance and biomasses are consistently higher in the reservoir than in the inflowing water (Table 2). The population dynamics of bacteria and flagellated protozoa largely depend on the seasonal changes of temperature. However, during the warm water season, drastic measures of water management (e.g. the increase of free chlorine concentration and the decrease of biodegradable organic carbon) dramatically reduce the biomasses of bacteria and flagellated protozoa in the water.

Soil aggregates as microcosms of bacteria—protozoa biota

Forty-eight air-dried soil aggregates were separately incubated under alternately submerged and dry conditions at 20°C without adding exogenous nutrients. In the course of submersions, the population dynamics of bacteria and protozoa were followed in each aggregate. It was shown that every aggregate accommodated at least three major groups of bacteria as categorized on the basis of colony forming curve (CFC) analysis. The growth of these bacterial groups occurred in sequence during submersion. Three to fourteen protozoan groups from each aggregate were detected as active forms. Distribution patterns of these groups among the 48 aggregates differed. The number of groups which were active simultaneously in each aggregate were small and the composition of groups changed gradually in the course of submersion. Frequency of appearance of each group during submersion was different and most groups appeared sporadically. These observations suggest that, in spite of the microbial diversity among aggregates, only a few groups are active concurrently.

回分式活性汚泥法における脱リンを担う微生物に及ぼす水質および運転変動の影響

回分式活性汚泥法における脱リンを担う微生物に及ぼす水質および運転変動の影響

Identification and population dynamics of bacteria in leaf spots of soybean

The qualitative and quantitative composition of bacterial flora occurring inside the leaf spots of field grown soybeans was studied during the growing seasons (June to October) of 1989 and 1990. As a rule these leaf spots (necrotic lesions with chlorotic haloes) were caused by Pseudomonas syringae pv. glycinea. This pathogenic bacterium was predominantly found during the whole season in the symptomatic leaf tissue. Other species, mainly Erwinia herbicola, were also found in the same habitat. The population sizes of P. s. pv. glycinea increased from the beginning of symptom occurrence until July, stabilized until September, and then decreased a little. In general, the size of saprophytic populations was orders of magnitude lower than that of the pathogenic populations. The number of different bacterial genera per sample increased up to four genera per leaf spot by the end of the season. No significant influence of the occurring saprophytes on the population dynamics of the pathogen in planta could be observed.

Relationship between the immune response of sheep and the population dynamics of bacteria isolated from fleecerot lesions

In sheep wetted by rain, proliferation of bacteria in the skin-fleece microenvironment invariability discolours the fleece and causes a dermatitic condition known as fleecerot. The changes in population dynamics of fleece bacteria were analysed by carrying out skin washings at randomly selected sites on the back of sheep before, and at 48 h and 96 h after exposure to rain. Gram-positive rods belonging to Bacillus species (10 2–10 4 cfu/cm 2) predominated in dry fleece. Gram-positive cocci (e.g. Micrococus and Staphylococcus species) as well as Gram-negative rods (pseudomonads) were also present but in lower abundance (< 10 2 cfu/cm 2). Fleece bacterial populations generally increased in numbers during the first 24–48 h of wetting. By 96 h however, skin washings showed a preponderance of Pseudomonas aeruginosa (10 4–10 6 cfu/cm 2) and to a lesser extent, pigmented Micrococcus species. Growth of fleece bacteria was associated with a characteristic green or yellow/orange staining of fleece. Fewer species of bacteria were isolated from sheep showing green staining while those animals with yellow/orange discolourations appeared to have a more mixed microflora composition. The predominance of P. aeruginosa in the wet fleece of sheep displaying either green or yellow/orange bacterial stain, never been observed to penetrate cutaneously in skin sections biopsied from fleecerot sites, it must be concluded that the sheep skin is sensitized by continuous exposure to antigens that are associated with or released by P. aeruginosa.

Population dynamics of bacteria in Arctic sea ice

The dynamics of bacterial populations in annual sea ice were measured throughout the vernal bloom of ice algae near Resolute in the Canadian Arctic. The maximum concentration of bacteria was 6.0·10(11) cells·m(-2) (about 2.0·10(10) cells·l(-1)) and average cell volume was 0.473 μm(3) in the lower 4 cm of the ice sheet. On average, 37% of the bacteria were epiphytic and were most commonly attached (70%) to the dominant alga,Nitzschia frigida (58% of total algal numbers). Bacterial population dynamics appeared exponential, and specific growth rates were higher in the early season (0.058 day(-1)), when algal biomass was increasing, than in the later season (0.0247 day(-1)), when algal biomass was declining. The proportion of epiphytes and the average number of epiphytes per alga increased significantly (P<0.05) through the course of the algal bloom. The net production of bacteria was 67.1 mgC·m(-2) throughout the algal bloom period, of which 45.5 mgC·m(-2) occurred during the phase of declining algal biomass. Net algal production was 1942 mgC·m(-2). Sea ice bacteria (both arctic and antarctic) are more abundant than expected on the basis of relationships between bacterioplankton and chlorophyll concentrations in temperate waters, but ice bacteria biomass and net production are nonetheless small compared with the ice algal blooms that presumably support them.

Identification and population dynamics of bacteria in symptomatic oat leaves

Bacteria isolated from symptomatic oat leaves included pseudomonads,Erwinia herbicola, and others.Pseudomonas coronafaciens was isolated predominantly from leaves with halo blight symptoms or necrotic spots. Leaves with red leaf symptoms yielded many types of bacteria, including saprophytic pseudomonads,P. syringae, E. herbicola, Bacillus sp.,Micrococcus sp.,Corynebacterium sp., a yeast, and other unidentified species. Only isolates ofP. coronafaciens were pathogenic on the plant hosts tested. The bacteria associated with red leaf symptoms exist as saprophytes and/or epiphytes on leaves with those symptoms. It is concluded that bacteria do not contribute to red leaf symptom development in oats, but symptomatic leaves provide an environment for their growth.

Selbstreinigung und Ciliatenbesiedlung in saurem Milieu (Modellversuche)

It is well known that acid precipitation originating from air pollution may increase the acidity of lakes and rivers. In the present experimental study the effects of acidification on the population dynamics of bacteria and protozoa associated with the decomposition of peptone have been investigated.

A Semi-Continuous Culture Technique for Daphnia pulex

Since its first principles were expounded by Monod (1950) and Novick & Szilard (1950), the technique of continuous culture in the chemostat has been widely employed both as a tool for research and for producing microbes and microbial products. As it provides a highly quantified and constant environment compared with other laboratory culture systems, it also represents an attractive method for ecological study (Smith 1963). Furthermore, it is the only population system for which there is a satisfactory mathematical model providing testable equations (Williamson 1972). The population dynamics of bacteria (Moser 1957, 1958) and of mixtures of bacterial species (Parker 1966) in the chemostat have been described; however, such data cannot be compared with populations of higher organisms because of the absence of birth and death processes. An apparatus developed to employ some of the advantages of continuous culture in growing a laboratory metazoan population will be described.

Automated Mathematical Modelling AndSimulation For Bacteria Growth Control In FoodEngineering

We describe in this paper a computer program for Automated Mathematical Modelling and Simulation (AMMS) for Bacteria growth control in the food industry using Artificial Intelligence (AI) techniques. This computer program is an implementation of a new method for AMMS using Expert Systems technology and Fractal Theory developed by the authors. We show in this paper mathematical models expressed as differential equations, for the simulation of bacteria growth for several types of food. The goal of constructing this models is to capture the dynamics of bacteria population in food, so as to have a way of controlling this dynamics for Industrial purposes. Controlling the growth of bacteria is very important in industrial microbiology in obtaining the food products with the desired chemical and microbiological properties. The goal of controlling the growth of bacteria population can be achieved, by computer simulations and application of the theory of dynamical systems. We also use the fractal dimension as a tool for the identification of bacteria by measuring the geometrical complexity of the colonies. This method of identification is based on the experimental fact that different types of bacteria have colonies of different geometrical form and complexity.