Cellular Carbohydrate Content Research Articles

Buoyancy control of Microcystis using different light regimes combined with extracellular polysaccharides and cationic ions

ABSTRACT Cyanobacterial blooms are widely known to cause problems in the aquatic environment, and their appearance has become more frequent due to global warming. Microcystis is one of the most widespread and dominant bloom-forming cyanobacterial genera, largely because Microcystis has the ability to control its buoyancy. A buoyancy experiment conducted on Microcystis sp. isolated from cyanobacterial blooms in Lake Senba, Japan, showed that buoyancy could be controlled using a combination of preculture under the dark conditions and the addition of powdered tightly bound extracellular polysaccharides (TB-EPS) and metal cations (Ca2+ and Mg2+). Preculture under the dark conditions, 96 h in length were the most effective treatment to reduce the cellular carbohydrate content of Microcystis and simultaneously increase its buoyancy. The addition of TB-EPS, Ca2+ and Mg2+ ions increased the colony size of Microcystis and enhanced buoyancy in precultures under both dark and light conditions. Thus, the buoyancy of Microcystis can be controlled by reducing its cellular carbohydrate content by preculturing it in dark conditions for 96 h and increasing the colony size with the addition of 100 mg l−1 EPS, 80 mg l−1 Ca2+ and 80 mg l−1 Mg2+. This study contributes to establishing a novel removal method for cyanobacterial blooms dominated by Microcystis, especially in water treatment facilities.

Control of <i>Microcystis</i> Buoyancy by Reducing Cellular Carbohydrate Content at High Temperature

Control of <i>Microcystis</i> Buoyancy by Reducing Cellular Carbohydrate Content at High Temperature

Biocrude oil production from a self-settling marine cyanobacterium, Chroococcidiopsis sp., using a biorefinery approach

Although the whole microalgal biomass is typically used as a feedstock for hydrothermal liquefaction (HTL), the conversion of a primary metabolite (i.e., carbohydrate) to biocrude is very low. In this study, a self-settling cyanobacterium (i.e., Chroococcidiopsis sp.) was used to understand the effect of carbohydrate removal, as a pretreatment, on the net energy recovery from the residual biomass. The optimum biocrude yields from pretreated and control biomass were 50.2% (350 °C) and 41.3% (300 °C), respectively. For the temperature range studied, the biocrude yield from the pretreated biomass was higher compared to that obtained from the control feedstock. Further, maximum alkane formation of 42.7 and 23.3% occurred for pretreated and control biomass, respectively, at 325 °C. Total organic carbon and total nitrogen values in the aqueous phase liquid obtained from pretreated biomass were at least 1.31 and 1.23 times lower when compared to the corresponding values obtained from control biomass. When APL was recycled as a source of nutrients, it reduced the biomass yield (24.1%) and pigment content (68.4%) in Chroococcidiopsis sp. Further, a model was developed to understand how the cellular carbohydrate content would affect the net energy recovery for the proposed biorefinery route.

Colonization and survival of a stress tolerant cyanobacterium on a heritage monument of Santiniketan, India

Colonization of cyanobacteria and associated algae on a heritage monument (Buddha statue) of Santiniketan, India was studied. The dominating biofilms component is a filamentous cyanobacterium, Scytonema millei, which thrives on the monument, even when the surface temperature exceeds 60 °C during summer. The basic adaptive strategy of S. millei was analysed upon exposure to different temperature range and desiccation based on the changes in growth, morphology, and biochemical analysis. Maximum increase of growth (16.2%), chlorophyll-a (42.2%), carotenoids (24.4%), cellular carbohydrate content (102.2%), extracellular carbohydrate content (643.6%), and SOD activity (134.8%) were observed under stress conditions. The organism was found as desiccation and thermo-adaptive species. S. millei was more tolerant to heat soon after exposure in the dry state than in the wet state. Significant increase in carbohydrate content (cellular and extracellular) and SOD activity upon exposure to stress suggests their main importance in the stress tolerance of S. millei. These findings suggest that the dominating cyanobacteria have developed different defense mechanisms enough to survive in extreme natural conditions of tropical regions as well as in lab conditions.

Enhancing the production of a marine diatom (Skeletonema costatum) with low-frequency ultrasonic irradiation

This study evaluated the growth stimulatory effect of low-frequency ultrasound on an ecologically and economically important marine diatom, Skeletonema costatum. To investigate the effect of repeated ultrasonication and the optimum duration of ultrasonication, S. costatum cells were exposed to low-frequency ultrasound (40 kHz) for 0, 2, 30 or 90 s under two sonication conditions: a one-time sonication treatment or a 24-h interval treatment. The cell density and cellular carbohydrate content increased in the ultrasonicated cultures. Similarly, the photosynthetic efficiency, particularly in the exponential growth phase, was enhanced in ultrasonicated cultures, which might account for the enhanced cell growth. At the end of the experiment, compared with the corresponding one-time treatment groups, the cell density in the 30-s sonicated culture and the cellular carbohydrate concentration in the 2-s sonicated culture of the 24-h interval treatment group were increased by 34 ± 4% and 28 ± 3%, respectively. This indicates that, under the same ultrasonic treatment conditions, a higher cellular carbohydrate content can be achieved by repeating the ultrasonication. This study also revealed that, compared with control, the silica/nitrate ratio and silica/phosphate ratio required to produce the same number of S. costatum cells were lower in the sonicated cultures, particularly in the one-time sonicated cultures. This finding indicates that ultrasonic irradiation results in the light silicification of S. costatum cells. This study provides valuable information on the diatom response to low-frequency ultrasonic irradiation and is an important benchmark study for future biotechnological applications of the mass production of S. costatum and other microalgae.

Species-Specific Variations in the Nutritional Quality of Southern Ocean Phytoplankton in Response to Elevated pCO2

Increased seawater pCO2 has the potential to alter phytoplankton biochemistry, which in turn may negatively affect the nutritional quality of phytoplankton as food for grazers. Our aim was to identify how Antarctic phytoplankton, Pyramimonas gelidicola, Phaeocystis antarctica, and Gymnodinium sp., respond to increased pCO2. Cultures were maintained in a continuous culture setup to ensure stable CO2 concentrations. Cells were subjected to a range of pCO2 from ambient to 993 µatm. We measured phytoplankton response in terms of cell size, cellular carbohydrate content, and elemental, pigment and fatty acid composition and content. We observed few changes in phytoplankton biochemistry with increasing CO2 concentration which were species-specific and predominantly included differences in the fatty acid composition. The C:N ratio was unaffected by CO2 concentration in the three species, while carbohydrate content decreased in Pyramimonas gelidicola, but increased in Phaeocystis antarctica. We found a significant reduction in the content of nutritionally important polyunsaturated fatty acids in Pyramimonas gelidicola cultures under high CO2 treatment, while cellular levels of the polyunsaturated fatty acid 20:5ω3, EPA, in Gymnodinium sp. increased. These changes in fatty acid profile could affect the nutritional quality of phytoplankton as food for grazers, however, further research is needed to identify the mechanisms for the observed species-specific changes and to improve our ability to extrapolate laboratory-based experiments on individual species to natural communities.

Effects of nitrogen on growth and carbohydrate formation in Porphyridium cruentum

Abstract The microalga Porphyridium cruentum (Rhodophyta) has several industrial and pharmaceutical uses, especially for its polysaccharide production. This study aimed to investigate the influence of nitrogen levels as reflected by altered N:P ratios on the production and content of biomass and carbohydrate. N:P molar ratios were altered in batch cultures to range from 1.6 to 50 using the Redfield ratio of 1:16 as reference. Algal growth (estimated as final cell number, biomass concentration and maximum specific growth rate) was negatively affected at low N:P ratios. The optimal N:P ratio for growth was identified at 35–50, with specific growth rates of 0.19 day−1 and maximum cell concentrations of 59·108 cells L−1 and 1.2 g dry weight of biomass L−1. In addition, variation in cell size was seen. Cells with larger diameters were at higher N:P ratios and smaller cells at lower ratios. The cellular carbohydrate content increased under reduced nitrogen availability. However, because accumulation was moderate at the lowest N:P ratio, 0.4 g per g dry weight biomass compared to 0.24 at the Redfield ratio of 16:1, conditions for increased total carbohydrate formation were identified at the N:P ratios optimal for growth. Additionally, carbohydrates were largely accumulated in late exponential to stationary phase.

Ecophysiology of the estuarine cyanobacterium Lyngbya aestuarii to varying salinity in vitro

Lyngbya aestuarii, one of the dominant cyanobacterium grows in different salinity gradients of Chilika lagoon. It was isolated in axenic culture and its ecophysiology with response to different concentrations of salinity was studied in vitro to understand its adaptation strategies in the changing salinities of the lagoon. Changes in morphological features of the organism were observed with salinity gradients higher than 28 g/L and lower than 14 g/L salinity. Increase in growth was accompanied by increase of chlorophyll-a, carotenoid and cell protein contents of the organism from 3.5 to 28 g/L. Cellular carbohydrate content was higher with increasing salinity of the medium up to 90 g/L. No detrimental effect on pigment synthesis and macromolecular content of the organism was observed at the salinity level ranging from 7 to 56 g/L salinity. Methanolic extract of L. aestuarii showed prominent absorption at 334 nm in the UV-B region of the spectrum due to mycosporine-like amino acid (MAA) and the quantity of MAA increased with increasing salinity. At 7 g/L salinity 150, 93, 58, 34 and 18 kDa proteins were up-regulated; however, at 14 g/L 37, 26 and 28 kDa proteins and in 0, 3.5 and 90 g/L 122, 32 and 20 kDa proteins were repressed; this shows similarities of salinity-induced protein modifications as observed in higher plants. Super oxide dismutase activity also increased in the cells grown at 56 g/L salinity. We conclude because of having these effective adaptation strategies, L. aestuarii cope very well with the changing salinity in different seasons and grows well in the different sectors of the lagoon.

Rapid Mutation of Spirulina platensis by a New Mutagenesis System of Atmospheric and Room Temperature Plasmas (ARTP) and Generation of a Mutant Library with Diverse Phenotypes

In this paper, we aimed to improve the carbohydrate productivity of Spirulina platensis by generating mutants with increased carbohydrate content and growth rate. ARTP was used as a new mutagenesis tool to generate a mutant library of S. platensis with diverse phenotypes. Protocol for rapid mutation of S. platensis by 60 s treatment with helium driven ARTP and high throughput screening method of the mutants using the 96-well microplate and microplate reader was established. A mutant library of 62 mutants was then constructed and ideal mutants were selected out. The characteristics of the mutants after the mutagenesis inclined to be stable after around 9th subculture, where the total mutation frequency and positive mutation frequency in terms of specific growth rate reached 45% and 25%, respectively. The mutants in mutant library showed diverse phenotypes in terms of cell growth rate, carbohydrate content and flocculation intensity. The positive mutation frequency in terms of cellular carbohydrate content with the increase by more than 20% percent than the wild strain was 32.3%. Compared with the wild strain, the representative mutants 3-A10 and 3-B2 showed 40.3% and 78.0% increase in carbohydrate content, respectively, while the mutant 4-B3 showed 10.5% increase in specific growth rate. The carbohydrate contents of the representative mutants were stable during different subcultures, indicating high genetic stability. ARTP was demonstrated to be an effective and non-GMO mutagenesis tool to generate the mutant library for multicellular microalgae.

Adaptation strategies of the sheathed cyanobacterium Lyngbya majuscula to ultraviolet-B

Lyngbya majuscula is a dominant organism in the east coast of India forming characteristic mat in dried saline soils simultaneously exposed to solar radiation of the tropics. Studies on the growth response, changes in the spectral properties of the methanolic extract and protein profile of this estuarine sheathed cyanobacterium to UV-B revealed existence of effective adaptation mechanism to withstand prolonged UV-B radiation. Carotenoids along with MAAs of the organism was increased with increase in UV irradiation. Increase in thickness of the mucilaginous sheath layer as well as cellular carbohydrate content was observed upon exposure to prolonged UV-B dose. Induction of 21 and 33 kDa low molecular weight proteins, and a 99 kDa protein together with formation of distinct multilayered sheath embedding trichomes with granulated cells were the adaptive features of the organism to cope with UV-B stress. The organism was considerably revived after incubating the irradiated cells in mineral medium under florescent light and in the dark suggesting existence of photoreactivation and dark repair in this cyanobacterium. However more experiments are needed to establish the existence of photoreactivation and dark repair mechanism in the studied cyanobacterium.

Buoyancy regulation of Microcystis flos-aquae during phosphorus-limited and nitrogen-limited growth

The dominance of gas-vacuolate cyanobacteria is often attributed to their buoyancy and to their ability to regulate buoyancy in response to environmental conditions. Changes in absolute gas vesicles volume, carbohydrate content, protein content and colony buoyancy of Microcystis flos-aquae were investigated during nitrogen-limited, phosphorus-limited and nutrient-replete growth. When nutrient-replete, M. flos-aquae cells consistently had excess gas vesicles, which provided sufficient buoyancy that the influence of daily carbohydrate changes on cells upon floatation was negligible. However, during nitrogen-limited growth, gas vesicle volume per cell decreased significantly with nitrogen exhaustion. The maximum decrease of gas vesicle volume was up to 84–88%. At the same time, cellular carbohydrate content had an accumulation trend. The decrease of gas vesicle buoyancy together with the daily increase in carbohydrate are suggested to explain the daily changes in the cell floatation. During phosphorus-limited growth, gas vesicle volume per cell decreased slightly (maximum to 22–32%), and they still provided sufficient buoyancy that most cells kept floating even though there were significant daily carbohydrate changes. Since nitrogen limitation caused more significant buoyancy loss than phosphorus limitation did, surface water blooms may disappear or appear frequently in nitrogen limited water bodies while they may persist a longer time in phosphorus limited water bodies. The quantitative analysis in buoyancy change by gas vesicles, carbohydrate and protein suggested that long-term buoyancy regulation was mainly determined by changes of gas vesicle volume whereas short-term buoyancy regulation was mainly determined by carbohydrate accumulation and consumption. Both long-term and short-term buoyancy regulation were influenced by cell nutrient status. Furthermore, gas vesicle volume per cell and protein content changed in the same way in both nitrogen-limited and phosphorus-limited growth, which implied that the decrease of gas vesicles were associated with controls of total protein synthesis.

The effect of variations in irradiance on buoyancy regulation in Microcystis aeruginosa

A mechanism of buoyancy regulation in cyanobacteria was investigated in a fluctuating light environment typical of the mixed layer in a lake. New measurements of density and cellular carbohydrate content were obtained from a field sample of the cyanobacterium Microcystis aeruginosa. The rate of increase in carbohydrate and density in this cyanobacterium does not instantaneously adjust to an increase in light intensity. There is a time lag, the response time, corresponding to physiological adjustment to the increase in light, before equilibration of the rate of carbohydrate and density increase. Also, the rate of density and carbohydrate increase is nonlinear over the response time. Based on these experimental findings, a new model for buoyancy regulation was developed that includes the response time. This model was applied to two fluctuating light regimes that simulate Langmuir circulation and turbulence. The simulations reveal that the response time is critical in determining if a cell equilibrates its rate of density change to a change in the light that it receives. If the response time is longer than the time scale of the light fluctuation, then the rate of density increase will be less than the optimal equilibrium rate. Models that do not include the response time will not correctly predict the buoyancy of cyanobacteria and their water column position after an episode of mixing.

Diazotrophic synchronous growth of a marine unicellular cyanobacterium, Synechococcus sp. strain Miami BG 043511, under aerobic and microaerobic/anaerobic conditions

The growth attributes of an aerobic nitrogen-fixing Synechococcus strain, Miami BG 043511, under aerobic and microaerobic/anaerobic conditions were examined using conventional batch and synchronous culture methods. Generation times of this strain, estimated from the increase in cell density under aerobic and anaerobic batch culture conditions, were 19-23 h and 15-19 h at 30 °C, respectively. It seems, therefore, that atmospheric oxygen did not seriously affect diazotrophic growth in this strain. Under a periodic light-dark regime, cells grew synchronously even under microaerobic/anaerobic conditions. When the aerobic culture entered the light period, a peak of photosynthetic activity was followed by a peak of nitrogenase activity. In contrast, a peak of nitrogenase activity preceded a peak of photosynthetic activity under microaerobic/anaerobic conditions. In both cases, however, cell division was observed at or just after the peak of photosynthetic activity. The difference in the timing of the appearance of nitrogenase activity in microaerobic/anaerobic cultures was ascribed to the inability of cells to generate sufficient ATP under anaerobic dark conditions. Periodic changes in cellular carbohydrate content, associated with the periodic appearances of photosynthetic and nitrogen-fixing activities, were observed under both aerobic and microaerobic/anaerobic conditions. Cellular carbohydrate content increased from 10% to 60% of cell dry weight during the phase of photosynthesis under aerobic conditions, while it reached only 40% under microaerobic/anaerobic conditions. The amount of reserve polysaccharides required to support nitrogen fixation was larger in aerobic cultures than in microaerobic/anaerobic cultures.

Change in the H2 photoproduction capability in a synchronously grown aerobic nitrogen-fixing cyanobacterium, Synechococcus sp. Miami BG 043511

Synchronously growing cells of nitrogen-fixing Synechococcus sp. Miami BG 043511 were harvested periodically and the capability for hydrogen photoproduction in closed vessels was measured under hydrogen production conditions. The capability for hydrogen photoproduction in cells was correlated with that of cellular carbohydrate content. Cells with a high carbohydrate content exhibited a high capacity for hydrogen production and those with low carbohydrate content exhibited low capacity for hydrogen production. Nitrogenase activity at the onset of incubation did not coincide with a capability for the cells to produce hydrogen during the subsequent incubation period. Interestingly, when cells with a high capacity for hydrogen photoaccumulation were incubated, alternate periods of hydrogen and oxygen accumulation were observed at 12 hour intervals. About 0.5 ml of hydrogen per ml of cell suspension was accumulated in flasks during the initial 12-h incubation period. These observations indicate that the use of synchronous culture can be one of the ways of provide materials suitable not only for basic studies but also for applied aspects of hydrogen photoproduction.

Tatlockia, a Genetically and Chemically Distinct Group of Bacteria. Proposal to Transfer Legionella maceachernii (Brenner et al.) to the Genus Tatlockia, as Tatlockia maceachernii comb. nov.

In addition to the previously reported DNA hybridization and base composition data, comparison of the nucleotide sequence of 16S-ribosomal RNA fragments and the total cellular carbohydrate content of Tatlockia micdadei and Legionella pneumophila strains strongly support their separation into different genera. In the present study Legionella maceachernii was found to be very similar to T. micdadei , and like T. micdadei , it was easily distinguished from the other legionellae. Based on the accumulated phenotypic and genotypic data Legionella maceachernii should be transferred to the genus Tatlockia , as Tatlockia maceachernii comb. nov.

Buoyant density changes in the cyanobacterium Microcystis aeruginosa due to changes in the cellular carbohydrate content

The cyanobacterium Microcystis aeruginosa was grown in light-limited chemostat cultures with various light—dark rhythms providing a total periodicity length of 24 h. The buoyant density of the cells changed in parallel with the carbohydrate content. Short incubation experiments with different light intensities, and experiments with the inhibitors iodoacetic acid and arsenate, showed that the buoyant density changes were due to variations in the cellular carbohydrate content. It seems likely that the low dark-growth yield on carbohydrate, which had been stored during the light period, served to facilitate buoyancy changes.

Buoyant density changes in the cyanobacteriumMicrocystis aeruginosadue to changes in the cellular carbohydrate content

The cyanobacterium Microcystis aeruginosa was grown in light-limited chemostat cultures with various light—dark rhythms providing a total periodicity length of 24 h. The buoyant density of the cells changed in parallel with the carbohydrate content. Short incubation experiments with different light intensities, and experiments with the inhibitors iodoacetic acid and arsenate, showed that the buoyant density changes were due to variations in the cellular carbohydrate content. It seems likely that the low dark-growth yield on carbohydrate, which had been stored during the light period, served to facilitate buoyancy changes.