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At least 127 records · Page 7Linked to original sources
PubMed1994

Structural and functional responses of a freshwater plankton community to acute copper stress.

An in-situ experiment was performed to quantify the impacts of copper sulfate on plankton structure and carbon dynamics. Plankton were exposed to 140 microg litre(-1) copper in quadruplicate mesocosms. Community structure was monitored for 14 days by microscopical counts and compared with untreated controls. Carbon dynamics were assessed by tracer studies using (14)C bicarbonate and (14)C glucose, to follow the fate of carbon in the algal- and bacterial-based pathways, respectively. Copper reduced the dry-weight biomass of zooplankton, ciliates, flagellates, and autotrophic phytoplankton. Bacterial biomass was increased by an order of magnitude relative to the controls. The bacterial response was most likely due to reduced grazing pressure and/or nutrient release from dying plankton. Copper reduced the effectiveness of the food web in transporting carbon to the surviving zooplankton. Bacterial-based pathways were more greatly affected than algal-based pathways, because zooplankton in the copper treatment were macro-grazers (cyclopoids), which cannot utilize bacteria.

Journal Article↗
PubMed2005

Inter-annual variations of planktonic food webs in the northern Adriatic Sea.

The temporal dynamics of microphytoplankton, microzooplankton and mesozooplankton were monitored over 37 months in the Adriatic Sea in order to identify alterations in the plankton structures, which can lead to, or enhance the production of macro-aggregates, that affected the entire northern basin in summers 2000 and 2002, and to assess any negative effects of mucilage on plankton temporal patterns. Samples were collected monthly, from June 1999 to July 2002, on three transects at 9 stations across the northern and central Adriatic Sea. Besides the high year-to-year variations in abundances and taxonomical composition, plankton communities only showed a clear seasonal succession during 2001, when since April a grazing food web developed and was able to control large sized phytoplankton increase. In spring-summer 2000 and 2002 consumer abundances remained quite low and the dominant mesozooplankton summer species (Penilia avirostris) did not reach its usual summer maximum. The lack of an efficient top control was more evident on the northernmost transect, where generally grazing food web prevails over the microbial one. A large part of the microphytoplankton blooms, although not particularly intense, was exported to the bottom in the particulate phase, where it was processed by bacteria, enhancing the production of refractory dissolved material.

Animals↗
PubMed2000

Reduced calcification of marine plankton in response to increased atmospheric CO2.

The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments. This is important in regulating marine carbon cycling and ocean-atmosphere CO2 exchange. The present rise in atmospheric CO2 levels causes significant changes in surface ocean pH and carbonate chemistry. Such changes have been shown to slow down calcification in corals and coralline macroalgae, but the majority of marine calcification occurs in planktonic organisms. Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species, the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica. This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres. Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production. Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels. We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean. As the process of calcification releases CO2 to the atmosphere, the response observed here could potentially act as a negative feedback on atmospheric CO2 levels.

Atmosphere↗
PubMed2006

Effect of different iodine formulations on the expression and activity of Streptococcus mutans glucosyltransferase and fructosyltransferase in biofilm and planktonic environments.

OBJECTIVES: The glucosyltransferase (GTF) and fructosyltransferase (FTF) enzymes play a pivotal role in dental biofilm formation as they synthesize polysaccharides that act as the extracellular matrix of the biofilm. Iodine is a unique antibacterial agent that has distinct properties from other conventional antibacterial agents. In this study we have examined the effect of iodine and povidone iodine (PI) on gtf and ftf expression in biofilm and planktonic environments and on immobilized and unbound GTF and FTF activity. METHODS: Real-time reverse transcription-PCR was used to investigate the effect of iodine and PI on ftf, gtfB and gtfC expression. The effect of iodine and PI on GTF and FTF activity was tested using radioactive assays. RESULTS: Our results indicate that iodine and PI in a tetraglycol carrier cause enhancement of expression of gtfB in Streptococcus mutans in biofilms but not in planktonic bacteria. PI in water induced expression of gtfB and gtfC in planktonic bacteria. However, iodine and PI strongly inhibit polysaccharide production by GTF and to a lesser extent by FTF activity. The inhibitory effect on GTF activity was similar in solution compared to its activity in the immobilized environment. This unique effect may be attributed to the distinct chemical properties of iodine compared with other antibacterial agents. CONCLUSIONS: This study indicates that iodine at sub-bactericidal concentrations demonstrates molecular and enzymatic effects that are highly associated with biofilm formation.

Anti-Bacterial Agents↗
PubMed2006

The combination of ultrasound with antibiotics released from bone cement decreases the viability of planktonic and biofilm bacteria: an in vitro study with clinical strains.

OBJECTIVES: Antibiotic-loaded bone cements are used for the permanent fixation of joint prostheses. Antibiotic-loaded cements significantly decrease the incidence of infection. The objective of this study was to investigate whether the viability of bacteria derived from patients with a prosthesis-related infection could be further decreased when antibiotic release from bone cements was combined with application of pulsed ultrasound. METHODS: Escherichia coli ATCC 10798, Staphylococcus aureus 7323, coagulase-negative staphylococci (CoNS 7368 and CoNS 7391) and Pseudomonas aeruginosa 5148 were grown planktonically in suspension and as a biofilm on three different bone cements: Palacos R without gentamicin as control, gentamicin-loaded Palacos R-G and gentamicin/clindamycin-loaded Copal. The viability of planktonic and biofilm bacteria was measured in the absence and presence of pulsed ultrasound for 40 h. RESULTS: Ultrasound itself did not affect bacterial viability. However, application of pulsed ultrasound in combination with antibiotic release by antibiotic-loaded bone cements yielded a reduction of both planktonic and biofilm bacterial viability compared with antibiotic release without application of ultrasound. CONCLUSIONS: This study shows that antibiotic release in combination with ultrasound increases the antimicrobial efficacy further than antibiotic release alone against a variety of clinical isolates. Application of ultrasound in combination with antibiotic release in clinical practice could therefore lead to better prevention or treatment of prosthesis-related infections.

Anti-Bacterial Agents↗
PubMed2000

Mesoscale vortices and the paradox of the plankton.

Coexistence of competitive species is severely limited by the availability of resources and the characteristics of the environment. In particular, the so-called 'competitive exclusion principle' states that, at equilibrium, the number of coexisting species cannot be larger than the number of resources for which they compete. However, many in situ observations have revealed prolonged coexistence of a large number of competitive plankton species, a phenomenon known as 'the paradox of the plankton'. Here we investigate this problem and show that ocean mesoscale vortices generate transport barriers and incomplete horizontal mixing, allowing for a prolonged survival of the less-fit species, even for fully homogeneous resource distributions. In such a situation, the temporarily less-fit plankton species are protected from competition by the action of the vortices.

Animals↗
PubMed1994

Iron chelator, exopolysaccharide and protease production in Staphylococcus epidermidis: a comparative study of the effects of specific growth rate in biofilm and planktonic culture.

The growth rate of Staphylococcus epidermidis was controlled for populations growing as a biofilm and perfused with supplemented, simple-salts medium. Production of iron chelators, extracellular protease and exopolysaccharide (EPS) by these populations was assessed as a function of specific growth rate and compared to that by planktonic populations grown in the same medium within a chemostat. Perfused biofilms increased their iron chelator and protease production with increasing growth rate. Chemostat populations decreased their production of iron chelators with increasing growth rate, whilst showing much enhanced production of proteases at intermediate growth rates (mu 0.15-0.25 h-1). Production of iron chelator and protease was generally 2-50 times higher by biofilms than by planktonic populations. EPS production was low and relatively unaffected by growth rate for the chemostat cultures (about 0.2 micrograms per unit cell mass) but high for the attached biofilms, particularly at slow growth rates (about 4 micrograms per unit cell mass). EPS production within the biofilms decreased markedly with increasing growth rate. At growth rates of 0.35 h-1 and above, the levels of EPS for biofilms and planktonic populations were equivalent. The results of this study clearly indicate that growth as a biofilm markedly influences extracellular virulence factor production by S. epidermidis.

Animals↗
PubMed1992

Polyacrylamide gel electrophoresis analysis of lipopolysaccharide from Pseudomonas aeruginosa growing planktonically and as biofilm.

Lipopolysaccharide (LPS, endotoxin) was extracted from biofilm and planktonically grown monoagglutinable (1118) and polyagglutinable (258 and 15703) strains of Pseudomonas aeruginosa isolated from cystic fibrosis patients with chronic pulmonary infections. Analysis by polyacrylamide gel electrophoresis (PAGE) followed by immune-detection of LPS fractions showed an S-form appearance of strain 1118 and 258 with three distinct clusters of high molecular weight bands, whereas 15703 appeared semi-rough. LPS of semi-rough cells grown planktonically and as biofilm showed a very similar PAGE pattern; however, the core/lipid A R-LPS fraction was more prominent in biofilm-LPS than in planktonic-LPS extracted from the S-form bacteria (1118 and 258). The apparent change in LPS sub-unit components of the bacteria when grown as biofilm may reflect changes in the outer membrane structure that contribute to the altered physico-chemical properties of biofilm bacteria in foreign-device associated infections and chronic P. aeruginosa lung infection in cystic fibrosis patients.

Bacteriological Techniques↗
PubMed2002

Distribution of membrane lipids of planktonic Crenarchaeota in the Arabian Sea.

Intact core tetraether membrane lipids of marine planktonic Crenarchaeota were quantified in water column-suspended particulate matter obtained from four depth intervals ( approximately 70, 500, 1,000 and 1,500 m) at seven stations in the northwestern Arabian Sea to investigate the distribution of the organisms at various depths. Maximum concentrations generally occurred at 500 m, near the top of the oxygen minimum zone, and the concentrations at this depth were, in most cases, slightly higher than those in surface waters. In contrast, lipids derived from eukaryotes (cholesterol) and from eukaryotes and bacteria (fatty acids) were at their highest concentrations in surface waters. This indicates that these crenarchaeotes are not restricted to the photic zone of the ocean, which is consistent with the results of recent molecular biological studies. Since the Arabian Sea has a strong oxygen minimum zone between 100 and 1,000 m, with minimum oxygen levels of <1 microM, the abundance of crenarchaeotal membrane lipids at 500 m suggests that planktonic Crenarchaeota are probably facultative anaerobes. The cell numbers we calculated from the concentrations of membrane lipids are similar to those reported for the Central Pacific Ocean, supporting the recent estimation of M. B. Karner, E. F. DeLong, and D. M. Karl ( Nature 409:507-510, 2001) that the world's oceans contain ca. 10(28) cells of planktonic Crenarchaeota.

Crenarchaeota↗
PubMed1998

Role of Fusobacterium nucleatum and coaggregation in anaerobe survival in planktonic and biofilm oral microbial communities during aeration.

Coaggregation is a well-characterized phenomenon by which specific pairs of oral bacteria interact physically. The aim of this study was to examine the patterns of coaggregation between obligately anaerobic and oxygen-tolerant species that coexist in a model oral microbial community. Obligate anaerobes other than Fusobacterium nucleatum coaggregated only poorly with oxygen-tolerant species. In contrast, F. nucleatum was able to coaggregate not only with both oxygen-tolerant and other obligately anaerobic species but also with otherwise-noncoaggregating obligate anaerobe-oxygen-tolerant species pairs. The effects of the presence or absence of F. nucleatum on anaerobe survival in both the biofilm and planktonic phases of a complex community of oral bacteria grown in an aerated (gas phase, 200 ml of 5% CO2 in air x min-1) chemostat system were then investigated. In the presence of F. nucleatum, anaerobes persisted in high numbers (>10(7) x ml-1 in the planktonic phase and >10(7) x cm-2 in 4-day biofilms). In an equivalent culture in the absence of F. nucleatum, the numbers of black-pigmented anaerobes (Porphyromonas gingivalis and Prevotella nigrescens) were significantly reduced (P </= 0.001) in both the planktonic phase and in 4-day biofilms, while the numbers of facultatively anaerobic bacteria increased in these communities. Coaggregation-mediated interactions between F. nucleatum and other species facilitated the survival of obligate anaerobes in aerated environments.

Actinomyces↗
PubMed2003

Plankton composition, distribution and significance in a tropical integrated pilot constructed treatment wetland in Uganda.

The importance of the plankton community in wastewater treatment has been under-estimated for a long time, simply because of its biomass accumulation resulting in final release of organic matter back into the system after decomposition. In a two-year 3-month periodical study on a tropical integrated wastewater treatment constructed wetland, the phytoplankton role was tested and it has been shown that, through harvesting, the phytoplankton community plays a significant role in municipal wastewater treatment. The high phytobiomass, which was dominated by green algae (Chlorophyta), enhanced high levels of dissolved oxygen and high pH within the open ponds, and because of this, the system was found to be highly efficient in BOD5 (81%) and NH4+-N (93%) removal. The high pH enhanced ammonia volatilization within the open ponds. Regression statistics between the plankton community composition and some of the physicochemical parameters (BOD, NH4+-N, DO, pH) within the wetland system show a significant relationship. In conclusion, open treatment wetlands provide a wide variety of planktonic organisms as water quality improvement systems through the provision of oxygen and alteration of the pH for BOD5 and ammonium reduction respectively.

Biodegradation, Environmental↗
PubMed1994

Effectiveness of antibiotics on the autochthonous Escherichia coli of mice in the intestinal biofilm versus its planktonic phase.

The effectiveness of antibiotics was tested on the autochthonous Escherichia coli in biofilm mode of growth in large bowel pieces as well as on the predominant faecal E. coli isolated from the same SPF mice in planktonic phase of growth. Aminoglycoside antibiotics, chloramphenicol, oxytetracycline, erythromycin and lincomycin-clindamycin treatment had a very limited effect in the intestinal biofilm. Surprising ineffectiveness was found with polymyxins: polymyxin B showed a Minimal Bactericidal Dose of 0.78 microgram in planktonic phase, while it was 400 micrograms for E. coli incorporated in the biofilm matrix. In contrast to the above groups of antibiotics, the beta-lactam drugs were effective both in the biofilm and in the planktonic phase growth of E. coli and their derivatives with broad or broader spectrum exerted an increased biofilm activity. Polymyxin B showed no sign of penetration into the colonic mucus, but on the other side ampicillin concentrated about three-four times in the intestinal matrix.

Aminoglycosides↗
PubMed2002

Effect of insecticides on plankton and fish of Ignacio Ramirez reservoir (Mexico): a biochemical and biomagnification study.

Studies on the limnology, plankton, and biomagnification of pesticides at Ignacio Ramírez (IR) reservoir (Mexico) were undertaken. The reservoir is located in central Mexico, in an agricultural zone with high soil erosion. Acetylcholinesterase (AchE), gamma-glutamyl transpeptidase (GGTP), and lipid peroxidation were assayed in fish. Organochlorines (0.024-0.279 mg/liter) and organophosphates (0.02 x 10(-3)-0.21 x 10(-3) mg/liter) were present at high concentrations in water and the biota assayed. In the IR dam the plankton fluctuated depending on the dry and wet seasons. The dominant group of phytoplankton was Bacillariophyta (20-85%) in May, Cyanophyta (22-65%) in September, and Cyanophycean (10-65%), Chlorophycean (10-60%), and Bacyllariophycean (5-80%) species in March. The zooplankton were dominated by cladoceran species (40-70%). Organochlorine and organophosphate insecticides were bioconcentrated (2- to 10-fold) from water to algae, 10- to 25-fold in zooplankton, and 8- to 140-fold in fish. GGTP activity and lipid peroxidation increased and AchE activity in fish decreased in response to the environmental stress caused by the elevated biomagnification of pesticides. The bioaccumulation of these contaminants in fish and the potential for biomagnification in humans are perceived as threats.

Acetylcholinesterase↗
PubMed1994

NAA methodology for the certification of eight trace elements in a plankton reference material.

Neutron activation analysis (NAA) methodology was applied for the certification of eight trace elements (As, Co, Cr, Cu, Hg, Mn, Se, and Zn) in a plankton reference material (CRM 414) prepared by the BCR of the Commission of the European Communities. Average concentrations (micrograms/g dry wt) and standard deviations found in plankton for the eight trace elements were as follows: As 6.29 +/- 0.19, Co 1.37 +/- 0.05, Cr 23.7 +/- 0.56, Cu 27.1 +/- 0.88, Hg 0.29 +/- 0.02, Mn 285 +/- 4.1, Se 1.62 +/- 0.10, and Zn 114 +/- 3.4. All values found were to be in very good agreement (0.5%-8.1%) with certified values.

Animals↗
PubMed2006

Picoeukaryotic plankton diversity at the Helgoland time series site as assessed by three molecular methods.

We analyzed picoeukaryote assemblages in the German Bight at the Helgoland time series site by sequencing cloned eukaryotic 18S rRNA genes in six genetic libraries plus one library from the Orkney Islands from a cruise of opportunity. The libraries were constructed from environmental samples collected at different periods of the year. The same samples were also analyzed using a fingerprinting technique, single-strand conformational polymorphism (SSCP), and DNA microarrays with class-level oligonucleotide probes. One hundred unique clones were analyzed from each library, thus insuring over 85% coverage of the library. The V4 region of the 18S rRNA gene was sequenced from each of these clones, thus providing the most discrimination among the clones. The nonphotosynthetic picoeukaryotic component dominated over the photosynthetic one and was represented by the ciliates at 45% and group II alveolates at 42%. Prasinophytes dominated the photosynthetic group at 40%, but other picoplankton groups, such as bolidomonads and chrysophytes, were also present. Totally novel groups were found in the cryptomonads and in the dinoflagellates. A new algal group sister to the cryptophyte nuclear gene and the glaucocystophytes was also found. These three groups have been found in other picoeukaryotic planktonic clone libraries. SSCP analyses at closer time intervals suggest that clone libraries should be made at weekly intervals if succession in the picoeukaryotic plankton community is to be monitored accurately. A comparison of annual samples suggests thatthere appears to be an annual cycle with regard to species composition. Microarray analysis supported the clone library data and offered a faster means of community analysis, which can be performed with similar accuracy and with higher throughput for a more in-depth analysis.

Animals↗
PubMed2006

Plankton motility patterns and encounter rates.

Many planktonic organisms have motility patterns with correlation run lengths (distances traversed before direction changes) of the same order as their reaction distances regarding prey, mates and predators (distances at which these organisms are remotely detected). At these scales, the relative measure of run length to reaction distance determines whether the underlying encounter is ballistic or diffusive. Since ballistic interactions are intrinsically more efficient than diffusive, we predict that organisms will display motility with long correlation run lengths compared to their reaction distances to their prey, but short compared to the reaction distances of their predators. We show motility data for planktonic organisms ranging from bacteria to copepods that support this prediction. We also present simple ballistic and diffusive motility models for estimating encounter rates, which lead to radically different predictions, and we present a simple criterion to determine which model is the more appropriate in a given case.

Animals↗
PubMed1984

Fate and effects of 4-chlorophenol and 2,4-dichlorophenol in marine plankton communities in experimental enclosures.

The fate and effects of 4-chlorophenol (4CP) and 2,4-dichlorophenol (DCP) added to North Sea coastal plankton communities enclosed by large plastic bags were studied in three experiments of 4 to 6 weeks duration. The biodegradation of the compounds was studied in laboratory experiments using water from the enclosed ecosystems. 4CP and DCP, added at initial concentrations of 0.1-1.0 mg X liter-1, disappeared from the water in the enclosures in 5 to 23 days, 4CP generally being the less persistent. Degradation rates were generally comparable to those found in laboratory tests with the same water. 4CP was removed by biodegradation, and DCP was probably removed by a combination of biodegradation, photodegradation, and/or chemical degradation. Results indicated that biodegradation rates could be limited by lack of inorganic nutrients, leading to much lower degradation rates than would be expected from routine laboratory tests. Faster degradation after repeated addition of 4CP showed adaption of the bacterial community. Addition of 0.3 mg liter-1 4CP or DCP inhibited the phytoplankton growth rate slightly. The 1 mg liter-1 4CP or DCP inhibited the phytoplankton, changed the species composition, and also influenced the zooplankton. In two of the three experiments 1 mg liter-1 DCP resulted in a temporary lowering of bacterial numbers following the addition. In one experiment inhibitory effects were found after 4CP and DCP had disappeared from the water, pointing to the formation of a more toxic intermediate during the degradation of these compounds. The laboratory tests also indicated the formation of relatively stable intermediates. The concentrations causing the effects in the different bag experiments were quite similar. This indicates that, although the development of the plankton communities during the different experiments was different, the concentrations resulting in ecological effects are quite reproducible.

Animals↗
PubMedDate not supplied

Isolation of intact plankton from drowning lung tissue by centrifugation ina colloidal silica gradient.

Several species of intact phyto- and zooplankton from the homogenate of rat "drowning lung" were separated by centrifugation in a colloidal silica gradient. The plankton, except diatoms, were isolated from a small amount of human "drowning lung" by this procedure. This new method was found to be more useful in detecting plankton in tissues than chemical digestion with strong acid.

Animals↗