The feeding rates and efficiencies of a marine ciliate, Strombidium sp., grown under chemostat steady-state conditions

A marine ciliate of the genus Strombidium isolated from a marine rock-pool, was grown bacteriafree in a chemostat continuous culture system and fed on the alga Pavlova (Monochrysis) lutheri Droop, which was also grown in continuous culture. The growth rate of the ciliate was maintained constant whilst the growth rate of the alga was varied, the latter producing little change in its energy content.The specific filtration and ingestion rates of Strombidium were measured and found, in both cases, to vary inversely as a function of the concentration of available algae. The filtration rate showed a range from 2 to 35 μl · ciliate^?1 · day^?1 whilst the ingestion rate varied from 0.8 to 3.4 J · ciliate^?1 · day^?1. The efficiency of ingestion remained constant throughout the experiment with a mean of > 91%, the overall growth efficiency also remained constant but with a mean of only 6.5%.The rates and efficiencies are compared with the results obtained by other workers.     

Pelagic Ciliates in a Large Mesotrophic Lake: Seasonal Succession and Taxon‐Specific Bacterivory in Lake Constance

The taxonomic composition of the ciliate assemblage and their taxon‐specific bacterial grazing rates in Lake Constance were investigated over the course of one year. Bacterial grazing rates were measured using natural fluorescently labelled bacteria (FLB) and compared to bacterial production. Small species such as Balanion planctonicum/Urotricha furcata and Rimostrombidium spp./Halteria sp. were the most numerous ciliates on the annual average. Larger ciliates such as Rimostrombidium lacustris and Limnostrombidium spp. contributed significantly to total ciliate biomass, but were relatively unimportant as bacterial grazers. Per capita ingestion rates ranged from 0–194 bacteria ciliate⁻¹ h⁻¹ and changed seasonally up to a hundredfold within a given taxon. Approximately 1% of the bacterial production were removed by the ciliate community on the annual average. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Size dependence of composition, photosynthesis and growth in the colony-forming freshwater ciliate, Ophrydium versatile

1. Ophrydium versatile is a symbiotic ciliate which forms gelatinous colonies up to several centimetres in diameter in transparent temperate lakes. The ciliates are evenly spaced at the colony surface and constitute a small proportion of the surface area (7%) and volume (3.1%) of the colony, but a large proportion of organic carbon (74%) and nitrogen content (82%) (exemplified for 1 cm³ colonies). The majority of the colony volume is formed by the jelly. The biomass proportion of ciliates scales inversely with colony size, following the decline of surface area to colony volume. The largest colonies found in Danish lakes in early summer contain almost 1 million ciliates, and assuming they derive from a single ciliate undergoing exponential division, they need twenty generations and, presumably, almost a year to reach maximum size. 2. The ciliates contain numerous symbiotic zoochlorellae that constitute about 10% of ciliate volume and more than half of the carbon content. Zoochlorellae dominate oxygen metabolism of the assemblage, resulting in low light compensation points, a large diel photosynthetic surplus, and a marked dependence on light for sustained growth and ciliate metabolism. Estimated gross photosynthesis (7ng C ciliate^?1 day^?1) of Ophnrydium from shallow, clear waters in June greatly exceeded the estimated carbon contained in filtered bacteria and small algae (1.9ng C cilicate^?1 day^?1). Nitrogen and phosphorus content of the prey, however, may provide the main nutrient source consistent with the correspondence between mass-specific rates of nutrient uptake and measured relative growth rates (average 0.067 day^?1, generation time 10 days). 3. The large Ophrydium colonies require increased allocation of photosynthetic carbohydrates with increasing colony size to maintain the jelly. The large colonies tend to become gas-filled, floating, mechanically destroyed and their ciliate inhabitants abandon them as swarmers. Colony formation, however, should offer protection against predators which may be more important for the natural abundance than the costs of growing in a colony.     

The Feeding Ecology of Actinophrys sol (Sarcodina: Heliozoa) in Chesapeake Bay

The occurrence of Actinophrys sol, a planktonic heliozoan, in Chesapeake Bay was monitored over a four-year period (1988–1991). Actinophrys sol was widely-distributed throughout Chesapeake Bay and could exceed densities of 5,000 cells liter ^?1. It was most abundant during the warmer months. Feeding experiments were conducted with field populations of heliozoa using 1-μm fluorescent microspheres to label ciliate prey. Two ciliates, a small Strobilidium sp. (30 μ in diameter) and a Pleuronema sp. (45 μ length), were the primary ciliate-prey items in the water column when the experiments were conducted, although a wide range of ciliate taxa was ingested. Two other ciliates not present in situ, a Cyclidium sp. (20 μ length) and a Uronema sp. (40 μ length), were also labeled and added at various concentrations to field populations of plankton containing A. sol. Heliozoan ingestion rates on in situ prey at concentrations of 30 Strohilidium and one Pleuronema ml^?1 were 0.2 to 0.3 prey heliozoan^?1 hour^?1. Ingestion rates increased to a maximum of 1.2 prey heliozoan ^?1 hour^?1 with additions of 100 Uronema ml^?1. A mean clearance rate of 0.15 ml heliozoan^?1 day^?1 did not change with increasing prey abundance. The abundance and distribution of A. sol suggests that these sarcodines may exert strong grazing pressure on the planktonic ciliate populations of Chesapeake Bay at certain times of the year, and may be important in shaping the ciliate community composition and distribution.     

A Dinoflagellate Amylax triacantha with Plastids of the Cryptophyte Origin: Phylogeny,Feeding Mechanism,and Growth and Grazing Responses

The gonyaulacalean dinoflagellates Amylax spp. were recently found to contain plastids of the cryptophyte origin, more specifically of Teleaulax amphioxeia. However, not only how the dinoflagellates get the plastids of the cryptophyte origin is unknown but also their ecophysiology, including growth and feeding responses as functions of both light and prey concentration, remain unknown. Here, we report the establishment of Amylax triacantha in culture, its feeding mechanism, and its growth rate using the ciliate prey Mesodinium rubrum (= Myrionecta rubra) in light and dark, and growth and grazing responses to prey concentration and light intensity. The strain established in culture in this study was assigned to A. triacantha, based on morphological characteristics (particularly, a prominent apical horn and three antapical spines) and nuclear SSU and LSU rDNA sequences. Amylax triacantha grew well in laboratory culture when supplied with the marine mixotrophic ciliate M. rubrum as prey, reaching densities of over 7.5 × 10³ cells/ml. Amylax triacantha captured its prey using a tow filament, and then ingested the whole prey by direct engulfment through the sulcus. The dinoflagellate was able to grow heterotrophically in the dark, but the growth rate was approximately two times lower than in the light. Although mixotrophic growth rates of A. triacantha increased sharply with mean prey concentrations, with maximum growth rate being 0.68/d, phototrophic growth (i.e. growth in the absence of prey) was ?0.08/d. The maximum ingestion rate was 2.54 ng C/Amylax/d (5.9 cells/Amylax/d). Growth rate also increased with increasing light intensity, but the effect was evident only when prey was supplied. Increased growth with increasing light intensity was accompanied by a corresponding increase in ingestion. In mixed cultures of two predators, A. triacantha and Dinophysis acuminata, with M. rubrum as prey, A. triacantha outgrew D. acuminata due to its approximately three times higher growth rate, suggesting that it can outcompete D. acuminata. Our results would help better understand the ecophysiology of dinoflagellates retaining foreign plastids.     

Use of fluorescently labelled algae to measure the clearance rate of the rotifer Keratella cochlearis

1. Fluorescently labelled algae (FLA) were used to measure clearance rates of the rotifer Keratella cochlearis. The freshwater algae Chlorella vulgaris and Stichococcus bacillaris were labelled with a fluorescent dye, 5-(4,6-dichlorotriazin-2-yl) aminofluorescein (DTAF), following a modified staining procedure. 2. Keratella cochlearis ingested both algal species. Clearance rates on tracer foods varied between 2.4 and 6.9 μl ind^?1 h^?1, which are comparable with those determined using other techniques. 3. The main drawback of the FLA technique was that only a little more than one-third of the total amount of algal cells of both C, vulgaris and S. bacillaris were well stained with the dye (DTAF), despite the use of a higher concentration of dye and a longer staining period than recommended in the literature. 4. The FLA method can be successfully applied in grazing studies involving size selection and competition for food among zooplankton. The method complements existing techniques for measuring the clearance and ingestion rates of filter-feeders.     

Overwintering populations of Mesodinium rubrum (Ciliophora: Haptorida) in lakes of the Vestfold Hills, East Antarctica

 The autotrophic ciliate Mesodinium rubrum Lohmann was observed during winter and spring in saline lakes ranging in salinity from 2 to 78‰ in the Vestfold Hills, Antarctica. The ciliate remained active during winter, and contained chlorophyll even though the level of light available for photosynthesis was minimal. No evidence of encystment as a means of survival during winter was observed. A seasonal study in one of the lakes, Ace Lake, revealed that M. rubrum was present throughout the year at abundances ranging from 1×10⁴ to 3.5×10⁵ cells l^-1. During the winter period, when little light penetrated the lake’s ice cover, cells were most common immediately under the ice at 2 m, where cell numbers were typically 8×10⁴ cells l^-1. Received: 3 January 1996/Accepted: 21 April 1996     

Feeding response of a benthic copepod to ciliate prey type,prey concentration and habitat complexity

1. Protozoans are important consumers within microbial food webs and, in turn, they represent potential prey for small metazoans. However, feeding interactions within these food webs are rarely characterised and this is especially true for freshwater sediments. 2. We aimed to quantify the feeding links between a freshwater meiofaunal copepod and ciliates in two laboratory experiments. The first experiment addressed the response of Eucyclops serrulatus towards ciliate density and type (two ciliate species of the same genus differing in terms of body size). A second experiment assessed the effect of habitat structure on feeding rates by introducing different structural complexity into the feeding arena. In contrast to the first experiment, which was run only for one time period, this experiment also tested three different total feeding times (4, 7 and 9 h). 3. Eucyclops serrulatus exhibited high ingestion rates, with 3–69 ciliates copepod^?1 h^?1 consumed depending on food concentration, food type and habitat complexity. Copepods exhibited a preference for the smaller ciliate when total ciliate concentration was low, but selected both ciliates equally when food concentrations were medium or high. However, at very high food concentration, Eucyclops preferred the larger ciliate (which was 1/3 of its own body size), suggesting that the longer handling times of the larger prey are rewarding when the large prey is present in high numbers. In terms of total numbers consumed, copepods fed on more small ciliates, but in terms of carbon units both ciliates were selected equally when total prey concentration was low or medium. However, copepods derived more carbon from the larger prey at high and very high prey concentrations (up to 0.7 μgC out of a maximum of 1.1 μgC copepod^?1 h^?1). Habitat complexity influenced the feeding of copepods when it was observed over time. 4. The copepod–ciliate link is well known from the pelagic zone of both marine and freshwater habitats. We have shown its potential importance within the benthos, where it can be influenced by food identity, food quantity and possibly by habitat complexity.     

A Kinetic Analysis of 6-[18F]Fluoro-l-Dihydroxyphenylalanine Metabolism in the Rat

Abstract: A previous study of the metabolism of 6-[¹⁸F]-fluoro-l -3,4-dihydroxyphenylalanine (FDOPA) in rats pretreated with carbidopa contained information amenable to kinetic analysis. Using these data, tracer transfer coefficients and metabolic rate constants were estimated. After intravenous injection, FDOPA in circulation was O-methylated (k^D₀ = 0.055 min^?1), and the metabolite (O-methyl-FDOPA) escaped from plasma with a rate constant (k^M_?1) of 0.01 min^?1. The initial clearance of FDOPA to striatum (K^D₁) was 0.07 ml g^?1 min^?1, and the equilibrium distribution volume (V^D_e) was 0.67 ml g^?1. The initial clearance of O-methyl-FDOPA to striatum (K^M₁) was 0.08 ml g^?1 min^?1, and the equilibrium distribution volume (V^M_e) was 0.75 ml g^?1. The rate constant of FDOPA decarboxylation (k^D₃) was 0.17 min^?1 in striatum. The elimination of 6-[¹⁸F]fluorodopamine (FDA) from striatum suggested an apparent rate constant for monoamine oxidase activity (k′₇) of 0.055 min^?1. 6-[¹⁸F]Fluorohomovanillic acid (FHVA) was formed from 6-[¹⁸F]fluoro-l -3,4-dihydroxyphenylacetic acid with a rate constant (k₁₁) of 0.083 min^?1, and FHVA was eliminated from striatum (k₉) with a rate constant of 0.12 min^?1. The steady-state concentration ratios of FDA and its metabolites were shown to be functions of these rate constants.     

An approach to measure ciliate grazing on living heterotrophic nanoflagellates

The complicated routes by which organic material is channelled up to higher trophic levels via bacteria and protozoans is a major issue in aquatic microbial ecology. Because of the fragile nature of protists it is not straightforward to perform experimental studies of prey–predator interactions. Here we present an approach for the assessment of ciliate grazing on living heterotrophic nanoflagellates. Stationary phase cultures of a heterotrophic nanoflagellate (Cafeteria sp.) were live-stained by allowing them to take up fluorescently labelled macromolecules. Controls revealed that this label persisted for several hours. Fluorescently labelled living flagellates (FLLF) were added into enriched natural assemblages of marine oligotrich ciliates and uptake of FLLF was monitored over time. Oligotrich ciliates did not incorporate fluorescent-labelled macromolecules but a linear FLLF uptake over time was observed for 20–30 min at 20°C. Ingestion rates were 21–46 FLLF h^–1 at a concentration of about 2×10⁴ FLLF ml^–1, which corresponded to clearance rates of 0.7–0.8 l ciliate^–1 h^–1. These results are in the same order of reported ciliate grazing on phytoplankton of similar size. This method represents a direct approach to measure ciliate grazing specifically on living heterotrophic nanoflagellates.     

Predator–prey interactions between a planktonic ciliate Strombidium sp. (Ciliophora, Oligotrichida) and the dinoflagellate Pfiesteria piscicida (Dinamoebiales, Pyrrophyta)

The functional response of a planktonic ciliate, Strombidium sp. feeding on the dinoflagellate Pfiesteria piscicida non-toxic zoospores (NTZ) was experimentally studied with four different prey concentrations (43–3153 cells ml⁻¹). Data from direct observations (NTZ inside individual Strombidium sp.) was used to calculate predator–prey specific ingestion and clearance rates. The ingestion rates varied between 0.68 and 14.26 NTZ ind⁻¹ h⁻¹, and with the predator–prey specific handling time of 2.83 min the U_max was 21.18 NTZ ind⁻¹ h⁻¹. The increase in the prey concentration between approximately 700 and 3000 NTZ ml⁻¹ did not increase the uptake of prey, and at the lowest Pfiesteria NTZ concentrations the feeding efficiency of Strombidium sp. was lowered, possibly indicating a situation of threshold feeding. When data from direct observations of ingested Pfiesteria NTZ were compared with values of total NTZ loss from the experimental water during the experiment, ingestion was found to represent only a fraction of the total NTZ loss in the presence of ciliates. This discrepancy was concluded to be due to other grazer related factors than actual ciliate grazing. The control of the initial growth of Pfiesteria community, in a pre-bloom situation, would require only a small ciliate abundance (less than 5 ml⁻¹), but when the Pfiesteria NTZ are scarce, relatively more ciliates are needed to limit the population growth of the dinoflagellate community because of the apparent feeding threshold. It is concluded that the formation of non-toxic P. piscicida blooms require periods of low grazing pressure or a means to escape grazing.     

EVIDENCE FOR A CRYPTOMONAD SYMBIONT IN THE CILIATE,CYCLOTRICHIUM MEUNIERI1

Extracts of the marine ciliate Cyclotrichium meunieri contained chlorophylls a and c, carotenoids, and a phycoerythrin with a single absorbance maximum at 542 nm. This assemblage of pigments suggests that the numerous photosynthetic symbionts present in each ciliate cell belong to the Cryptophyceae.     

Cyclopoids feed selectively on free-living stages of parasites

1. Many aquatic organisms can consume parasite larvae, thus hampering parasite transmission; however, information about feeding on them in the presence of an alternative prey remains scarce. When having a food choice, predators may decrease parasite consumption, therefore, it is important to assess the role of parasites in the diet of predators in natural communities with different types of prey available. Our study aims to test whether common freshwater cyclopoids feed on trematode free-living stages (cercariae) when an alternative food source is present.
2. We experimentally studied ingestion rates of cyclopoids Macrocyclops distinctus fed with cercariae of trematode Diplostomum pseudospathaceum, a common and harmful parasite of freshwater fishes, and ciliates Paramecium caudatum (an alternative prey, known as suitable food for copepods). First, the feeding response of cyclopoids to different densities of each prey was studied. Then, feeding selectivity in the mixtures of cercariae and ciliates was tested.
3. Feeding rates of cyclopoids increased with prey densities (both ciliates and cercariae) but almost stopped growing at high prey densities, which indicated saturation (Holling type II functional response). In most cases, cyclopoids consumed cercariae at higher rates than ciliates. Maximum ingestion rates estimated from the obtained curves were 37 cercariae ind⁻¹ hr⁻¹ and 17 ciliate ind⁻¹ hr⁻¹.
4. When exposed to prey mixtures, cyclopoids fed on cercariae selectively. When cercariae were offered to cyclopoids at concentrations exceeding the saturation level, the ingestion of ciliates remained constantly low at all ciliate densities. In contrast, the ingestion of cercariae increased with rising cercariae densities even when ciliates were presented ad libitum, decreasing only at very high prey densities. Possible reasons of such feeding preferences are discussed.
5. Our study demonstrated that cyclopoids may prefer to feed on cercariae when there is an alternative food choice and can ingest cercariae at high rates. These experimental results could be extended to natural communities, suggesting that cyclopoids can reduce the transmission of parasites and contribute to the incorporation of parasite production in food webs of lentic ecosystems.

     

Participation of a Specific Substrate Degrading Strain in a Mixed Bacteria Culture as a Result of Ciliate Grazing

Participation of nitrilotriacetic acid degrading bacterial strain NTA-1 in the continuous-cultivated mixed culture was studied under different conditions including predation pressure of the ciliate Dexiostoma campyla (STOKES , 1886). From the viewpoint of dispersed/flocculated biomass distribution, significant relationships between NTA-1 and total bacteria ratio, and dispersed and total biomass ratio were proved in the systems without high concentrations of ciliates. The ciliate concentrations reaching 10⁴ ml⁻¹ stabilized flocculated biomass growth without directly affecting NTA-1 portion. Using fluorescently labelled NTA-1 bacteria, filter feeding rates of ciliates were evaluated (maximum individual uptake rate upon NTA-1 bacteria as a number of bacteria per ciliate per hour being 120 h⁻¹ and 260 h⁻¹ under ciliate division rate of 0.3 day⁻¹ and 1 day⁻¹, respectively). Biomass balance showed that dispersed NTA-1 bacteria should not serve as the sole feeding source for these free-swimming ciliates. The role of diversity of mixed bacterial diet in ciliate growth and the role of ciliate predation in stabilizing bacterial assemblage structure was proved.     

Inter-strain differences in nitrogen use by the coccolithophore Emiliania huxleyi, and consequences for predation by a planktonic ciliate

Four strains of the coccolithophore Emiliania huxleyi (CCMP strains 370, 373, 374, 379) were tested for their ability to grow on various nitrogen sources. All strains grew on ammonium, nitrate, and urea, although growth of CCMP379 on urea was low. Responses to other dissolved organic nitrogen (DON) sources varied. CCMP379 did not grow on any DON source other than urea. All other strains grew on one of the two tested amino acids: CCMP370 and CCMP373 on glutamine, and CCMP374 on alanine. All three of these strains also grew on hypoxanthine; in addition, two grew well on acetamide and one on ethanolamine. E. huxleyi strains also differed in their susceptibility to predation by the ciliate Strobilidium sp. CCMP374 was ingested at substantially higher rates than CCMP373 regardless of E. huxleyi growth condition. Ciliate feeding rates also depended on E. huxleyi growth condition. For CCMP374, feeding rates were 2× higher on growing E. huxleyi cells than on non-growing cells (average 27.5 versus 15.6 cells ciliate⁻¹ h⁻¹, respectively). For CCMP373, a relationship between E. huxleyi growth rate and ciliate feeding rate was not evident, but E. huxleyi grown on some N sources (ammonium, nitrate, urea) were ingested at consistently higher rates than E. huxleyi grown on other sources (ethanolamine, glutamine). Interstrain differences in the ability to utilize DON and resist predation may contribute to maintenance of high genetic diversity within this cosmopolitan, bloom-forming species.     

Transient state characteristics of changes in light conditions for the cyanobacterium Oscillatoria agardhii

The cyanobacterium Oscillatoria agardhii was subjected to changes in irradiance and to changes in light period. During transient states parameters as growth rate, pigment contents, photosynthetic activities and pool sizes of carbohydrate and proteins were followed. The changes in pigments and photosynthesis were similar for irradiance transitions and transitions in light period length. Carbohydrates served for the supply of carbon and energy during adaptation to low light conditions until a basal level of 125 g · mg dry wt^-1 was reached. After transfer to high light conditions excess carbon fixation led to the storage of carbohydrate reserve polymers up to 600 g · mg dry wt^-1. During adaptation to longer light periods cells showed an overcapacity for carbohydrate accumulation even in the presence of a high carbohydrate content at the start of the light period. A model for the feed back repression of photosynthesis related to carbohydrate accumulation was presented. In all cases protein synthesis was directly maximized under the given conditions. Growth rate defined as specific rate of change in carbon showed the fastest response after a shift in light conditions. It was concluded that adaptation of O. agardhii to changes in light conditions was directed to the optimization of growth. The observation that carbohydrate is used to supply carbon and/or energy during adaptation leads to the conclusion that changes on survival in low light depend on carbohydrate level, the efficiency of its conversion in cell material and the maintenance requirements. Such a survival strategy enables cyanobacteria to cope succesfully with light limiting conditions.Abbreviations HL high irradiance Em^-2s^-1 - LL low irradiance Em^-2s^-1 - L/D light-dark cycle h - specific growth rate h^-1 - _e specific maintenance coefficient h^-1 - _max maximal specific growth rate h^-1 - _c specific rate of change of carbon h^-1 - _protein specific rate of change of protein h^-1 - Chl a chlorophyll a - CPC C-phycocyanin - dry wt dry weight mg - light utilization efficiency nmol O₂ · mg dry wt^-1 · min^-1/Em^-1 s^-1 - P _max photosynthetic capacity nmol O₂ · mg dry wt^-1 · min^-1 - PSI photosystem I - PS II photosystem II - RC II reaction center of PS II - PQ plastoquinone     

Transport of glycine-betaine by Listeria monocytogenes

Uptake of [¹⁴C]glycine-betaine by Listeria monocytogenes was stimulated by NaCl with optimal stimulation at 0.4–0.5 M. The glycine-betaine transport system had a K _m of 22 M and a V _max of 11.7 nmol^-1 min^-1 mg^-1 protein when grown in the absence of NaCl. When grown in the presence of 0.8 M NaCl the V _max increased to 27.0 nmol^-1 min^-1 mg^-1 protein in 0.8 M NaCl. At NaCl concentrations above 0.5 M the uptake rate of glycine-betaine was reduced. Measurement of intracellular K⁺ concentrations and fluorescent dye quenching indicated that higher NaCl concentrations also led to a decrease in the electrochemical potential difference across the cytoplasmic membrane. Uptake of glycine was also observed, but this was not stimulated by NaCl.     

The Effect of Puromycin and Cycloheximide on the Infection of Algae-Free Paramecium bursaria by Symbiotic Chlorellae1

It has been suggested that the infection of algae-free Paramecium bursaria by symbiotic algae involves an induction in the ciliate. Such a process suggests a need for the synthesis of specific proteins. Therefore, an attempt was made to determine the role of protein synthesis during the initial phases of host-symbiont interaction by examining the capacity of the ciliate to form a stable association with algae when the ciliate is exposed to puromycin (PURO) or cycloheximide (CYC) during the first 1–3 h of algal insestion. Cycloheximide (100 μg/ml) blocked algal but not ciliate growth and protein synthesis while PURO (250 μg/ml) appeared to inhibit these processes in both Puromycin significantly inhibited the infection when presented to the ciliate during the first hour of algal exposure and had little effect when added after that period. Inhibition of ciliate, as compared to the alga, protein synthesis appears to be significant in relationship to those processes leading to infection, as CYC when presented during the first hour of algae-ciliate exposure has no inhibitory effects. Experiments on algal sugar secretion and ciliate ingestion of algae indicated that neither process was significantly affected by these inhibitors. These results point to a need for host protein synthesis during the initial phase of ingestion of algae which appears to be important to establishment of the symbiotic association.     

Biosorption of Malathion using dry cells of Bacillus species S14 in a packed bed column reactor

Abstract

The ability of dried bacterial strain Bacillus sp. S₁₄ to adsorb Malathion in a packed bed column reactor was studied. The effects of important design parameters such as bed height, flow rate and influent Malathion concentration on Malathion removal from an aqueous solution was studied using a packed bed column reactor. The optimised conditions for maximum Malathion removal were found to be: flow rate: 5 mL min^-1, bed height: 6.0 cm and influent Malathion concentration: 25 mg L^-1. The Adams-Bohart model, Wolborska model, Thomas model, Yoon and Nelson Model were employed to determine characteristic parameters such as N₀ (saturation concentration, mg L^-1), β_o (external mass transfer coefficient, min^-1), k _Th(Thomas rate constant, mL min^-1mg^-1), q₀ (maximum solid phase concentration of the solute, mg L^-1), k_YN (rate constant, min^-1) and τ (time required for 50 % adsorbate breakthrough time, min) which are useful for process design. Data were fitted with Adams-Bohart model at lower region of (C/C₀) values but more accurately fitted with Wolborska and Thomas model.     

Effects of prey abundance and light intensity on the mixotrophic chrysophyte Poterioochromonas malhamensis from a mesotrophic lake

1. Previous studies of mixotrophy in the flagellate Poterioochromonas malhamensis (Chrysophyceae) were performed on strains that had been in culture for > 30 years. This study aims to compare mixotrophy in a cultured strain with one recently isolated from a mesotrophic lake (Lacawac) in Pennsylvania, U.S.A. 2. P. malhamensis from the lake exhibited a nutritional flexibility similar to that of the culture strain, growing phototrophically but inefficiently in comparison to other nutritional modes (growth rate (μ) = 0.015 h^?1). Supplementing an inorganic salts medium with 1 mM glucose resulted in a doubling of μ to 0.035 h^?1 and 0.033 h^?1 in the light and the dark, respectively. Addition of an algal prey, Nannochloris, to the inorganic salts medium increased growth to rates similar to those observed with glucose. Maximum growth of the lake strain, 0.095 h^?1, was achieved when bacteria was supplied as food. During growth on bacteria, cellular chlorophyll a (Chl a) decreased from 140 fg cell^?1 to 10 fg cell^?1 over 22 h when cultured either in the light or dark. In illuminated cultures, cell-specific Chl a concentration recovered to 185 fg cell^?1 after bacteria became limiting. 3. In contrast to the cultured strain, however, the lake isolate exhibited an inverse relationship between light intensity and ingestion rate. Calculated grazing rates, based upon the ingestion of fluorescently labeled bacteria, were 3.2, 5.2 and 9.4 bacteria flagellate^?1 h^?1, for P. malhamensis incubated in high light, low light and darkness, respectively. Phagotrophy is thus influenced by a light regime in this predominately heterotrophic mixotroph.