Detection of Karenia brevis blooms on the west Florida shelf using in situ backscattering and fluorescence data

Using shipboard data collected from the central west Florida shelf (WFS) between 2000 and 2001, an optical classification algorithm was developed to differentiate toxic Karenia brevis blooms (>10⁴ cells l⁻¹) from other waters (including non-blooms and blooms of other phytoplankton species). The identification of K. brevis blooms is based on two criteria: (1) chlorophyll a concentration ≥1.5 mg m⁻³ and (2) chlorophyll-specific particulate backscattering at 550 nm ≤ 0.0045 m² mg⁻¹. The classification criteria yielded an overall accuracy of 99% in identifying both K. brevis blooms and other waters from 194 cruise stations. The algorithm was validated using an independent dataset collected from both the central and south WFS between 2005 and 2006. After excluding data from estuarine and post-hurricane turbid waters, an overall accuracy of 94% was achieved with 86% of all K. brevis bloom data points identified successfully. Satisfactory algorithm performance (88% overall accuracy) was also achieved when using underway chlorophyll fluorescence and backscattering data collected during a repeated alongshore transect between Tampa Bay and Florida Bay in 2005 and 2006. These results suggest that it may be possible to use presently available, commercial optical backscattering instrumentation on autonomous platforms (e.g. moorings, gliders, and AUVs) for rapid and timely detection and monitoring of K. brevis blooms on the WFS.     

Vertical migration of Karenia brevis in the northeastern Gulf of Mexico observed from glider measurements

The toxic marine dinoflagellate, Karenia brevis (the species responsible for most of red tides or harmful algal blooms in the Gulf of Mexico), is known to be able to swim vertically to adapt to the light and nutrient environments, nearly all such observations have been made through controlled experiments using cultures. Here, using continuous 3-dimensional measurements by an ocean glider across a K. brevis bloom in the northeastern Gulf of Mexico between 1 and 8 August 2014, we show the vertical migration behavior of K. brevis. Within the bloom where K. brevis concentration is between 100,000 and 1,000,000 cells L⁻¹, the stratified water shows a two-layer system with the depth of pycnocline ranging between 14–20 m and salinity and temperature in the surface layer being <34.8 and >28 °C, respectively. The bottom layer shows the salinity of >36 and temperature of <26 °C. The low salinity is apparently due to coastal runoff, as the top layer also shows high amount of colored dissolved organic matter (CDOM). Within the top layer, chlorophyll-a fluorescence shows clear diel changes in the vertical structure, an indication of K. brevis vertical migration at a mean speed of 0.5–1 m h⁻¹. The upward migration appears to start at sunrise at a depth of 8–10 m, while the downward migration appears to start at sunset (or when surface light approaches 0) at a depth of ∼2 m. These vertical migrations are believed to be a result of the need of K. brevis cells for light and nutrients in a stable, stratified, and CDOM-rich environment.     

Nitrogen uptake kinetics in field populations and cultured strains of Karenia brevis

This study represents the most comprehensive assessment of kinetic parameters for Karenia brevis to date as it encompasses natural populations sampled during three different bloom years in addition to cultured strains under controlled conditions. Nitrogen (N) uptake kinetics for ammonium (NH₄⁺), nitrate (NO₃⁻), urea, an amino acid mixture, individual amino acids (glutamate and alanine), and humic substrates were examined for the toxic red tide dinoflagellate, K. brevis, during short term incubations (0.5–1 h) using ¹⁵N tracer techniques. Experiments were conducted using natural populations collected during extensive blooms along the West Florida Shelf in October 2001, 2002, and 2007, and in cultured strains (CCFWC 251 and CCFWC 267) obtained from the Florida Fish and Wildlife Institute culture collection. Kinetic parameters for the maximum uptake velocity (V_max), half-saturation concentration (K_s), and the affinity constant (α) were determined. The affinity constant is considered a more accurate indicator of substrate affinity at low concentrations. K. brevis took up all organic substrates tested, including N derived from humic substances. Uptake rates of the amino acid mixture and some NO₃⁻ incubations did not saturate even at the highest substrate additions (50–200 μmol N L⁻¹). Based upon the calculated α values, the greatest substrate preference was for NH₄⁺ followed by NO₃⁻ ≥ urea, humic compounds and amino acids. The ability of K. brevis to utilize a variety of inorganic and organic substrates likely helps it flourish under a wide range of nutrient conditions from bloom initiation in oligotrophic waters offshore to bloom maintenance near shore where ambient nutrient concentrations may be orders of magnitude greater.     

The P170 expression system enhances hyaluronan molecular weight and production in metabolically-engineered Lactococcus lactis

Recombinant Lactococcus lactis strains based on the P170 expression system were developed for hyaluronan (HA) production, by incorporating genes from the has operon of Streptococcus zooepidemicus and compared with nisin-inducible recombinant L. lactis strains containing the hasABC and hasABD constructs. It was found across all batch and fed-batch experimental studies that HA concentration and molecular weight (MW) were higher for the P170 expression systems than the corresponding NICE-based strains. The highest hyaluronan MW was obtained for all constructs in batch studies at 60 g/L initial glucose concentration, the highest being 2.94 MDa for the P170 strains with hasABC construct (L. lactis APJ3). In fed-batch studies with constant feed rate, the L. lactis APJ3 gave better HA yield (0.03 g/g) than the NICE-based strain. A higher hyaluronan MW was obtained for all strains in pulse fed-batch compared to constant feed experiments, the highest being 2.52 MDa for L. lactis APJ3.     

Contribution of diazotrophy to nitrogen inputs supporting Karenia brevis blooms in the Gulf of Mexico

Blooms of Karenia brevis plague the West Florida Shelf (WFS) region in the Gulf of Mexico (GOM) where they exert harmful effects on aquatic biota and humans. Because productivity on the WFS is N limited, new N inputs into the region are thought to trigger blooms of K. brevis. Here we examine the potential for new N inputs via N₂ fixation by Trichodesmium and other diazotrophic plankton to contribute to the N demand of K. brevis. Because of possible methodological biases, we also compared N₂ fixation rates by cultured Trichodesmium using the ¹⁵N₂ bubble addition method and the ¹⁵N₂ saturated seawater. Both methods yielded identical results in 12 and 24 h incubations; however, there was more variability in rate estimates made using the bubble addition method. Pelagic N₂ fixation rates by other planktonic diazotrophs ranged from 0 to 13.6 nmol N L⁻¹ d⁻¹, comparable to or higher than rates observed in oligotrophic gyres. These rates should be considered conservative estimates because they were made using the bubble addition method. Integrating over our study area, we estimate that new inputs of N to the WFS via N₂ fixation are on the order of 0.011 Tmol N annually. Further, we measured directly the trophic transfer of recently fixed N₂ to co-occurring plankton that included K. brevis and found that up to 47% of N₂ fixed was transferred to non-diazotrophic plankton even in short (<6 h) incubations where N₂ fixation was likely underestimated.     

Zooplankton community composition and copepod grazing on the West Florida Shelf in relation to blooms of Karenia brevis

Blooms of the toxin producing dinoflagellate Karenia brevis occur routinely on the West Florida Shelf of the Gulf of Mexico. Nutrient supplies are thought to play a large role in the formation and maintenance of these blooms. The role of top-down control has been less well studied, but grazing, or the lack thereof, on these toxic species may also enhance the formation of large biomass blooms in this region. Zooplankton community structure and copepod species composition were analyzed from samples collected on the West Florida Shelf (WFS) during a NOAA funded ECOHAB regional Karenia Nutrient Dynamics project during October 2007–2010. In 2008 there was no statistical difference in the abundance of zooplankton at bloom and non-bloom stations, however in 2009 there was a statistically significant difference (p < 0.05) between the abundance of zooplankton at stations with Karenia present. To investigate copepod ingestion rates in relation to K. brevis, shipboard and laboratory experiments of the single label method of ¹⁴C labeled phytoplankton culture, and time course ingestion experiments with isolated copepods were performed. Calculated ingestion rates suggest that the copepod species Centropages velificatus, and Acartia tonsa ingested K. brevis, however rates were variable among collection sites and K. brevis strains. Parvocalanus crassirostris did not ingest K. brevis in any of the experiments.     

Characterization of the LP28 strain-specific exopolysaccharide biosynthetic gene cluster found in the whole circular genome of Pediococcus pentosaceus

We have previously isolated a lactic acid bacterium (LAB), Pediococcus pentosaceus LP28, from the longan fruit Euphoria longana. Since the plant-derived LAB strain produces an extracellular polysaccharide (EPS), in this study, we analyzed the chemical structure and the biosynthesizing genes for the EPS.The EPS, which was purified from the LP28 culture broth, was classified into acidic and neutral EPSs with a molecular mass of about 50 kDa and 40 kDa, respectively. The acidic EPS consisted of glucose, galactose, mannose, and N-acetylglucosamine moieties. Interestingly, since pyruvate residue was detected in the hydrolyzed acidic EPS, one of the four sugars may be modified with pyruvate. On the other hand, the neutral EPS consisted of glucose, mannose, and N-acetylglucosamine; pyruvate was scarcely detected in the polysaccharide molecule.As a first step to deduce the probiotic function of the EPS together with the biosynthesis, we determined the whole genome sequence of the LP28 strain, demonstrating that the genome is a circular DNA, which is composed of 1,774,865 bp (1683 ORFs) with a GC content of 37.1%. We also found that the LP28 strain harbors a plasmid carrying 6 ORFs composed of 5366 bp with a GC content of 36.5%. By comparing all of the genome sequences among the LP28 strain and four strains of P. pentosaceus reported previously, we found that 53 proteins in the LP28 strain display a similarity of less than 50% with those in the four P. pentosaceus strains. Significantly, 4 of the 53 proteins, which may be enzymes necessary for the EPS production on the LP28 strain, were absent in the other four P. pentosaceus strains and displayed less than 50% similarity with other LAB species. The EPS-biosynthetic gene cluster detected only in the LP28 genome consisted of 12 ORFs containing a priming enzyme, five glycosyltransferases, and a putative polysaccharide pyruvyltransferase.     

Brevenal,a brevetoxin antagonist from Karenia brevis,binds to a previously unreported site on mammalian sodium channels

Brevetoxins are a family of ladder-frame polyether toxins produced by the marine dinoflagellate Karenia brevis. During blooms of K. brevis, inhalation of brevetoxins aerosolized by wind and wave action can lead to asthma-like symptoms in persons at the beach. Consumption of either shellfish or finfish contaminated by K. brevis blooms can lead to the development of neurotoxic shellfish poisoning. The toxic effects of brevetoxins are due to binding at a defined site on, and subsequent activation of, voltage-sensitive sodium channels (VSSCs) in cell membranes (site 5). In addition to brevetoxins, K. brevis produces several other ladder-frame compounds. One of these compounds, brevenal, has been shown to antagonize the effects of brevetoxin. In an effort to further characterize the effects of brevenal, a radioactive analog ([³H]-brevenol) was produced by reducing the terminal aldehyde moiety of brevenal to an alcohol using tritiated sodium borohydride. A K_D of 67 nM and B_max of 7.1 pmol/mg protein were obtained for [³H]-brevenol in rat brain synaptosomes, suggesting a 1:1 matching with VSSCs. Brevenal and brevenol competed for [³H]-brevenol binding with K_i values of 75 nM and 56 nM, respectively. However, although both brevenal and brevenol inhibited brevetoxin binding, brevetoxin was completely ineffective at competition for [³H]-brevenol binding. After examining other site-specific compounds, it was determined that [³H]-brevenol binds to a site that is distinct from the other known sites on the sodium channel, including the brevetoxin site, (site 5) although some interaction with site 5 is apparent.     

Selenium nanoparticles from Lactobacillus paracasei HM1 capable of antagonizing animal pathogenic fungi as a new source from human breast milk

The current study was performed to develop a simple, safe, and cost-effective technique for the biosynthesis of selenium nanoparticles (SeNPs) from lactic acid bacteria (LAB) isolated from human breast milk with antifungal activity against animal pathogenic fungi. The LAB was selected based on their speed of transforming sodium selenite (Na₂SeO₃) to SeNPs. Out of the four identified LAB isolates, only one strain produced dark red color within 32 h of incubation, indicating that this isolate was the fastest in transforming Na₂SeO₃ to SeNPs; and was chosen for the biosynthesis of LAB-SeNPs. The superior isolate was further identified as Lactobacillus paracasei HM1 (MW390875) based on matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and phylogenetic tree analysis of 16S rRNA sequence alignments. The optimum experimental conditions for the biosynthesis of SeNPs by L. paracasei HM1 were found to be pH (6.0), temperature (35˚C), Na₂SeO₃ (4.0 mM), reaction time (32 h), and agitation speed (160 rpm). The ultraviolet absorbance of L. paracasei-SeNPs was detected at 300 nm, and the transmission electron microscopy (TEM) captured a diameter range between 3.0 and 50.0 nm. The energy-dispersive X-ray spectroscopy (EDX) and the Fourier-transform infrared spectroscopy (FTIR) provided a clear image of the active groups associated with the stability of L. paracasei-SeNPs. The size of L. paracasei-SeNPs using dynamic light scattering technique was 56.91 ± 1.8 nm, and zeta potential value was −20.1 ± 0.6 mV in one peak. The data also revealed that L. paracasei-SeNPs effectively inhibited the growth of Candida and Fusarium species, and this was further confirmed by scanning electron microscopy (SEM). The current study concluded that the SeNPs obtained from L. paracasei HM1 could be used to prepare biological antifungal formulations effective against major animal pathogenic fungi. The antifungal activity of the biologically synthesized SeNPs using L. paracasei HM1 outperforms the chemically produced SeNPs. In vivo studies showing the antagonistic effect of SeNPs on pathogenic fungi are underway to demonstrate the potential of a therapeutic agent to treat animals against major infectious fungal diseases.     

Three-dimensional structure of a Karenia brevis bloom: Observations from gliders,satellites, and field measurements

Autonomous underwater gliders with customized sensors were deployed in October 2011 on the central West Florida Shelf to measure a Karenia brevis bloom, which was captured in satellite imagery since late September 2011. Combined with in situ taxonomy data, satellite measurements, and numerical circulation models, the glider measurements provided information on the three-dimensional structure of the bloom. Temperature, salinity, fluorescence of colored dissolved organic matter (CDOM) and chlorophyll-a, particulate backscattering coefficient, and K. brevis-specific chlorophyll-a concentrations were measured by the gliders over >250 km from the surface to about 30-m water depth on the shallow shelf. At the time of sampling the bloom was characterized by uniform vertical structures, with relatively high chlorophyll-a and CDOM fluorescence, low temperature, and high salinity. Satellite data extracted along the glider tracks demonstrated coherent spatial variations as observed by the gliders. Further, the synoptic satellite observations revealed the bloom evolution during the 7 months between late September 2011 and mid April 2012, and showed the maximum bloom size of ∼3000 km² around 23 November. The combined satellite and in situ data also confirmed that the ratio of satellite-derived fluorescence line height (FLH) to particulate backscattering coefficient at 547 nm (b_bp(547)) could be used as a better index than FLH alone to detect K. brevis blooms. Numerical circulation models further suggested that the bloom could have been initiated offshore and advected onshore via the bottom Ekman layer. The case study here demonstrates the unique value of an integrated coastal ocean observing system in studying harmful algal blooms (HABs).     

Influence of daylight surface aggregation behavior on nutrient cycling during a Karenia brevis (Davis) G. Hansen & Ø. Moestrup bloom: Migration to the surface as a nutrient acquisition strategy

The toxic HAB dinoflagellate Karenia brevis (Davis) G. Hansen & Ø. Moestrup (formerly Gymnodinium breve) exhibits a migratory pattern atypical of dinoflagellates: cells concentrate in a narrow (∼0–5 cm) band at the water surface during daylight hours due to phototactic and negative geotactic responses, then disperse downward at night via non-tactic, random swimming. The hypothesis that this daylight surface aggregation behavior significantly influences bacterial and algal productivity and nutrient cycling within blooms was tested during a large, high biomass (chlorophyll a >19 μg L⁻¹) K. brevis bloom in October of 2001 by examining the effects of this surface layer aggregation on inorganic and organic nutrient concentrations, cellular nitrogen uptake, primary and bacterial productivity and the stable isotopic signature (δ¹⁵N, δ¹³C) of particulate material. During daylight hours, concentrations of K. brevis and chlorophyll a in the 0–5 cm surface layer were enhanced by 131% (±241%) and 32.1% (±86.1%) respectively compared with an integrated water sample collection over a 0–1 m depth. Inorganic (NH₄, NO₃₊₂, PO₄, SiO₄) and organic (DOP, DON) nutrient concentrations were also elevated within the surface layer as was both bacterial and primary productivity. Uptake of nitrogen (NH₄⁺, NO₃⁻, urea, dissolved primary amines, glutamine and alanine) compounds by K. brevis was greatest in the surface layer for all compounds tested, with the greatest enhancement evident in urea uptake rates, from 0.08 × 10⁻⁵ ng N K. brevis cell⁻¹ h⁻¹ to 3.1 × 10⁻⁵ ng N K. brevis cell⁻¹ h⁻¹. These data suggests that this surface aggregation layer is not only an area of concentrated cells within K. brevis blooms, but also an area of increased biological activity and nutrient cycling, especially of nitrogen. Additionally, the classic dinoflagellate migration paradigm of a downward migration for access to elevated NO₃⁻ concentrations during the dark period may not apply to certain dinoflagellates such as K. brevis in oligotrophic nearshore areas with no significant nitricline. For these dinoflagellates, concentration within a narrow surface layer in blooms during daylight hours may enhance nutrient supply through biological cycling and photochemical nutrient regeneration.     

Effect of probiotic L. plantarum IS-10506 and zinc supplementation on humoral immune response and zinc status of Indonesian pre-school children

A 90-day randomized, double-blind, placebo-controlled, pre-post trial was conducted in four groups of Indonesian children aged 12–24 months: placebo, probiotic, zinc, and a combination of probiotic and zinc (n = 12 per group). Microencapsulated Lactobacillus plantarum IS-10506 of dadih origin was supplemented at a dose of 10¹⁰ CFU/day as a probiotic. Zinc was supplemented as 20 mg zinc sulfate monohydrate (8 mg zinc elemental). Blood and stool samples were collected at baseline and at the end of the study period. Fecal sIgA was assessed by ELISA and serum zinc concentrations by ICP-MS. Fecal sIgA increased significantly in the probiotic group (30.33 ± 3.32 μg/g; p < 0.01) and in the combination probiotic and zinc group (27.55 ± 2.28 μg/g; p < 0.027), as compared with the placebo group (13.58 ± 2.26 μg/g). Changes in serum zinc concentrations in the combination probiotic and zinc group showed the highest elevation at the end of the study period. A combination of probiotic L. plantarum IS-10506 at a dose of 10¹⁰ CFU/day and 8 mg of elemental zinc supplementation showed a potential ability to improve the zinc status of pre-school children. Taken together, supplementation with the probiotic L. plantarum IS-10506 and zinc for 90 days resulted in a significantly increased humoral immune response, as well as improved zinc status, in young children.     

Toxic and essential elements in children's blood (<6 years) from Kinshasa,DRC (the Democratic Republic of Congo)

In this study we determined the concentration of 9 trace elements (As, Cd, Cu, Hg, Mn, Mo, Pb, Se and Zn) in whole blood of children (n = 100, 64 girls, 36 boys and median age: 36 months) using inductively coupled plasma mass spectrometry (ICP-MS). The proportion of children potentially deficient in essential elements or poisoned by toxic elements was evaluated. The aging effects on the concentration of these elements were also investigated. The median values were 3.17 μg/L (As), 0.15 μg/L (Cd), 1.1 mg/L (Cu), 2.1 μg/L (Hg), 10.4 μg/L (Mn), 17.7 μg/L (Mo), 8.7 μg/dL (Pb), 10.7 μg/L (Se) and 5.0 mg/L (Zn). The concentration of many elements (As, Cd, Hg, Mn, Pb and Zn) showed significant age variations but not sex influence. Regarding levels of the essential elements (Cu, Mn, Mo, Se and Zn), B-Cu, B-Mn, B-Se and B-Zn were in the normal range, whereas exceeded levels were observed for B-Mo. None of these children was deficient in essential elements. Except B-Cd, all toxic elements showed exceeded blood levels. The proportion of children potentially poisoned by toxic elements varies from 10% (n = 10) to 95% (n = 95) and depends on toxic element: 95% for As, 10% for Hg and 35% for Pb. The main health concerns emerging from this study are the high As, Hg and Pb exposures of the Kinshasan children requiring further documentation, corrective actions and the implementation of appropriate regulations.     

Antimicrobial activity against Shigella sonnei and probiotic properties of wild lactobacilli from fermented food

Four lactobacilli strains (Lactobacillus paracasei subp. paracasei M5-L, Lactobacillus rhamnosus J10-L, Lactobacillus casei Q8-L and L. rhamnosus GG (LGG), were systematically assessed for the production of antimicrobial substances active towards Shigella sonnei, Escherichia coli and Salmonella typhimurium. Agar-well assay showed that the four lactobacilli strains displayed strong antibacterial activity towards S. sonnei. The nature of antimicrobial substances was also investigated and shown to be dependent on the production of organic acids, in particular the lactic acid. Time-kill assay showed that the viability of the S. sonnei was decreased by 2.7–3.6 log CFU/ml after contact with CFCS (cell-free culture supernatants) of four lactobacilli for 2 h, which confirmed the result of the agar-well assay. Further analysis of the organic acid composition in the CFCS revealed that the content of lactic acid range from 227 to 293 mM. In addition, the aggregations properties, adherence properties and tolerance to simulated gastrointestinal conditions were also investigated in vitro tests. The result suggested that the M5-L, J10-L and Q8-L strains possess desirable antimicrobial activity towards S. sonnei and probiotic properties as LGG and could be potentially used as novel probiotic strains in the food industry.     

Use of Spirulina platensis micro and nanoparticles for the removal synthetic dyes from aqueous solutions by biosorption

In this research, micro and nanoparticles of Spirulina platensis dead biomass were obtained, characterized and employed to removal FD&C red no. 40 and acid blue 9 synthetic dyes from aqueous solutions. The effects of particle size (micro and nano) and biosorbent dosage (from 50 to 750 mg) were studied. Pseudo-first order, pseudo-second order and Elovich models were used to evaluate the biosorption kinetics. The biosorption nature was verified using energy dispersive X-ray spectroscopy (EDS). The best results for both dyes were found using 250 mg of nanoparticles, in these conditions, the biosorption capacities were 295 mg g^?1 and 1450 mg g^?1, and the percentages of dye removal were 15.0 and 72.5% for the FD&C red no. 40 and acid blue 9, respectively. Pseudo-first order model was the more adequate to represent the biosorption of both dyes onto microparticles, and Elovich model was more appropriate to the biosorption onto nanoparticles. The EDS results suggested that the dyes biosorption onto microparticles occurred mainly by physical interactions, and for the nanoparticles, chemisorption was dominant.     

Effects of nutrient-limiting supply ratios on toxin content of Karenia brevis grown in continuous culture

Toxins produced as secondary metabolites can play important roles in phytoplankton communities and contribute to the ecological success of harmful algal bloom (HAB) taxa. Toxin composition and content in phytoplankton are affected by a suite of environmental factors, including nutrient availability. Changes in nutrient availability can increase or decrease toxin content and alter toxin composition, depending on toxin stoichiometry and the mechanisms by which nutrient limitation affects toxin production. The studies that have assessed the effects of nutrient availability on brevetoxin content of the HAB species Karenia brevis have reported contradictory results, although there is growing support that nutrient limitation increases brevetoxin content. In this study, we assessed the effects of decreased nitrogen (N) and phosphorus (P) availability on brevetoxin content and composition of K. brevis grown in chemostats at steady state by altering the nutrient supply ratios of incoming media from the Redfield Ratio. Overall, brevetoxin content was greatest in cultures grown at the lowest rate, regardless of the nutrient supply ratio (i.e., under both Redfield and N-limiting supply ratios). Compared to cultures grown at 0.2 d⁻¹, cultures grown at 0.1 d⁻¹ exhibited 5-fold increases in intracellular toxin content. In contrast, at constant growth rates, N-limiting supply ratios decreased intracellular brevetoxin content by approximately one-third, although this result was significant only in cultures growing at the fastest rate of 0.23 d⁻¹. P-limiting supply ratios had no effect on brevetoxin content or composition. In addition, when cultures grown at rates of 0.2 d⁻¹ were supplied with balanced/Redfield N:P supply ratios, but different absolute nutrient concentrations, toxin content was greater under greater nutrient concentrations. These findings suggest that when growth rate is not nutrient limited, there is a positive relationship between nutrient availability and brevetoxin content. This work contributes to previous studies by demonstrating strong growth rates effects on brevetoxin content and that growth rate and nutrient availability can independently or together affect toxin content of K. brevis. Moreover, our work underscores the value of the chemostat as a tool to elucidate the mechanisms by which nutrient availability and growth rate affect toxin production and content of HAB species.     

Biosorption kinetics and isotherm studies of Acid Red 57 by dried Cephalosporium aphidicola cells from aqueous solutions

Equilibrium, kinetics and thermodynamic studies on the removal of Acid Red 57 (AR57) by biosorption onto dried Cephalosporium aphidicola (C. aphidicola) cells have been investigated in a batch system with respect to pH, contact time and temperature. The results showed that the equilibrium time was attained within 40 min and the maximum biosorption capacity of AR57 dye onto C. aphidicola cells was 2.08 × 10⁻⁴ mol g⁻¹ or 109.41 mg g⁻¹ obtained after contact with 0.4 g dm⁻³ biosorbent concentration, pH₀ of 1 and at a temperature of 20 °C. The pseudo-second-order kinetic model was observed to provide the best correlation of the experimental data among the kinetic models studied. Biosorption isotherm models were developed and the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were conformed well to the experimental data. The changes of free energy, enthalpy and entropy of biosorption were also evaluated for the biosorption of AR57 dye onto C. aphidicola cells.     

Production and characterization of curdlan by Agrobacterium sp.

Agrobacterium sp. was studied for the production of curdlan by conventional one-factor-at-a-time technique and response surface methodology. Factors such as initial pH, urea concentration, sucrose concentration having the greatest influence on the curdlan production were identified. By using response surface methodology (RSM), the curdlan production by Agrobacterium sp. was increased significantly by 109%, from 2.4 g/L to 5.02 g/L when the strain was cultivated in the optimal medium developed by RSM as compared to conventional one-factor-at-a-time technique. The curdlan production rate of 0.84 g/(L h) was obtained when Agrobacterium sp. was cultivated in the optimal medium developed by RSM, which was the highest curdlan production rate reported to date. The infrared (IR) and NMR spectra, the thermogram of DSC and pattern of X-ray diffraction for the curdlan of the present study were almost identical to those of the authentic curdlan sample (from Alcaligenes faecalis; Sigma). The purified curdlan was a linear polysaccharide composed of exclusively β-(1,3)-glucosidic linkages with the molecular weight of 160,000 Da by GPC. The crystalline melting point (T_m), glass transition temperature (T_g) and X-ray diffraction of the sample indicated low crystallinity in the structure.     

Biosorption of Basic Orange using dried A. filiculoides

In order to understand the biosorption of Basic Organic (BO) textile dye on dried Azolla filiculoides (A. filiculoides), batch experiments were conducted under various conditions. The results show that biosorption of BO on dried A. filiculoides was dependent on the initial solution pH, biosorbent dosage, contact time and the initial BO concentration. Using the Langmuir equation, the biosorption capacity (q_m) for BO was 833 mg/g at 303 K. The kinetic study suggested that the mechanism of biosorption was due to ion-exchange physisorption via the intra-particle diffusion and chemisorption on the external surface of dried A. filiculoides. Different techniques were used to characterize dried A. filiculoides and indicated that the biomass had a high cation exchange capacity (93.6 mmol/100 g), a large specific surface area (80.35–422.89 m²/g) and contained various functional groups which may play an important role in the physisorption and chemisorption of BO on the surface of A. filiculoides. The results showed that the removal ratio of BO reached 79.3% from wastewater containing 100 mg/L BO, indicating that the biomass could be used as a potential biosorbent for the removal of BO from industrial wastewater.