Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

The effect of temperature (26 °C, 28 °C, 30 °C and 35 °C) on the growth of native CAAT-3-2005 Microcystis aeruginosa and the production of Chlorophyll-a (Chl-a) and Microcystin-LR (MC-LR) were examined through laboratory studies. Kinetic parameters such as specific growth rate (μ), lag phase duration (LPD) and maximum population density (MPD) were determined by fitting the modified Gompertz equation to the M. aeruginosa strain cell count (cells mL⁻¹). A 4.8-fold increase in μ values and a 10.8-fold decrease in the LPD values were found for M. aeruginosa growth when the temperature changed from 15 °C to 35 °C. The activation energy of the specific growth rate (Eμ) and of the adaptation rate (E₁/LPD) were significantly correlated (R² = 0.86). The cardinal temperatures estimated by the modified Ratkowsky model were minimum temperature = 8.58 ± 2.34 °C, maximum temperature = 45.04 ± 1.35 °C and optimum temperature = 33.39 ± 0.55 °C.Maximum MC-LR production decreased 9.5-fold when the temperature was increased from 26 °C to 35 °C. The maximum production values were obtained at 26° C and the maximum depletion rate of intracellular MC-LR was observed at 30–35 °C. The MC-LR cell quota was higher at 26 and 28 °C (83 and 80 fg cell⁻¹, respectively) and the MC-LR Chl-a quota was similar at all the different temperatures (0.5–1.5 fg ng⁻¹).The Gompertz equation and dynamic model were found to be the most appropriate approaches to calculate M. aeruginosa growth and production of MC-LR, respectively. Given that toxin production decreased with increasing temperatures but growth increased, this study demonstrates that growth and toxin production processes are uncoupled in M. aeruginosa. These data and models may be useful to predict M. aeruginosa bloom formation in the environment.     

Natural variation in the microcystin synthetase operon mcyABC and impact on microcystin production in Microcystis strains

Toxic Microcystis strains often produce several isoforms of the cyclic hepatotoxin microcystin, and more than 65 isoforms are known. This has been attributed to relaxed substrate specificity of the adenylation domain. Our results show that in addition to this, variability is also caused by genetic variation in the microcystin synthetase genes. Genetic characterization of a region of the adenylation domain in module mcyB1 resulted in identification of two groups of genetic variants in closely related Microcystis strains. Sequence analyses suggested that the genetic variation is due to recombination events between mcyB1 and the corresponding domains in mcyC. Each variant could be correlated to a particular microcystin isoform profile, as identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Among the Microcystis species studied, we found 11 strains containing different variants of the mcyABC gene cluster and 7 strains lacking the genes. Furthermore, there is no concordance between the phylogenies generated with mcyB1, 16S ribosomal DNA, and DNA fingerprinting. Collectively, these results suggest that recombination between imperfect repeats, gene loss, and horizontal gene transfer can explain the distribution and variation within the mcyABC operon.     

Seedling growth of climbing species from a southeast Brazilian tropical forest

Climbers are considered heliophytes. They are copious at the margins of forests and natural and man-made clearings. The objective of this paper was to study the initial growth of seedlings maintained under full sunlight and shaded conditions (under a vegetation canopy). The species studied were: Aristolochia galeata, Arrabidea triplinervia, Bidens brasiliensis, Canavalia parviflora, Chamissoa altissima, Cissus sicyoides, Dalechampia pentaphylla, Dicella bracteosa, Dioscorea sp., Gouania virgata, Mascagnia anisopetala, Mutisia coccinea, Oxypetalum molle, Pithecoctenium crucigerum, Rynchosia phaseoloides, Serjania multiflora and Solanum flaccidum. The initial growth of the seedlings was followed under two conditions: at the margin and under the canopy of a mesophyllous tropical forest (22° 4955S–47° 0633W). The climbers showed high rates of growth in sunlight when compared to those under canopy. Most of the species presented higher growth of the shoot than roots but in general no significative differences between root/shoot were found in both treatments. Bidens, Cissus, Mutisia and Pithecoctenium showed a very high mortality rate under canopy but, most of the studied species survived under deep shaded forest for approximately 100 days.     

Recent growth increase in endemic Juglans boliviana from the tropical Andes

The spatial coverage of tree-ring chronologies in tropical South America is low compared to the extratropics, particularly in remote regions. Tree-ring dating from such tropical sites is limited by the generally weak temperature seasonality, complex coloration, and indistinct anatomical morphology in some tree species. As a result, there is a need to complement traditional methods of dendrochronology with innovative and independent approaches. Here, we supplement traditional tree-ring methods via the use of radiocarbon analyses to detect partial missing rings and/or false rings, and wood anatomical techniques to precisely delineate tree-ring boundaries. In so doing we present and confirm the annual periodicity of the first tree-ring width (TRW) chronology spanning from 1814 to 2017 for Juglans boliviana (‘nogal’), a tree species growing in a mid-elevation tropical moist forest in northern Bolivia. We collected 25 core samples and 4 cross-sections from living and recently harvested canopy-dominant trees, respectively. The sampled trees were growing in the Madidi National Park and had a mean age of 115 years old, with certain trees growing for over 200 years. Comparison of (residual and standard) TRW chronologies to monthly climate variables shows significant negative relationships to prior year May-August maximum temperatures (r = −0.54, p < 0.05) and positive relationships to dry season May-October precipitation (r = 0.60, p < 0.05) before the current year growing season. Additionally, the radial growth of Juglans boliviana shows a significant positive trend since 1979. Our findings describe a new and promising tree species for dendrochronology due to its longevity and highlight interdisciplinary techniques that can be used to expand the current tree-ring network in Bolivia and the greater South American tropics.     

Heptapeptide toxin production during the batch culture of two Microcystis species (Cyanobacteria)

Changes in the content of cyclic heptapeptide hepatotoxins called microcystins were investigated during batch culture of two Microcystis species using high performance liquid chromatography. After adsorption to ODS-silica gel cartridges and elution with methanol, the toxins were analyzed and quantified by HPLC. 35 μg per 100 mg dry cells of microcystin-RR, 34 μg of -YR and 43 μg of -LR were present at the beginning of the exponential growth phase of M. viridis. Microcystin-RR increased markedly towards the end of the exponential phase with the maximum content of 112 μg per 100 mg cells was measured at the late stage of the exponential phase. A remarkable increase of microcystin-YR from 130 μg per 100 mg cells to 1020 μg was observed during the exponential phase of a highly toxic strain of M. aeruginosa. However no clear differences were found in the pattern of change among the three toxins during the growth course.     

Growth rates of selected Australian tropical rainforest tree species under controlled conditions

Controlled environment treatments were applied to assess the effects of temperature on the seedling mortality and growth rates of Toona australis and Flindersia brayleyana, two tropical rainforest tree species from northeast Queensland, Australia. Past workers have assigned these two species to the same ecological niche in terms of their response to canopy disturbance and gap-phase regeneration; however, their geographic ranges are very different. The hypothesis was that the species confined to the warm tropics (F. brayleyana) would have higher seedling mortality and a slower growth rate at lower temperatures than the species that occurs over a wide latitudinal range from the warm tropics to cooler temperate environments (T. australis). Significant differences were found in the growth rates of these two species in the warm (29/22° C) and cool (22/10°C), but not the intermediate (24/16° C), day/night temperature regimes. Their growth rates both decreased with decreasing temperature, but the decrease was significantly less for F. brayleyana which had the faster growth rate and lower seedling mortality in the cool regime. These results led to the rejection of the hypothesis and a test of the assignment of these two species to the same ecological niche. The test involved monitoring their growth to sapling-size in the intermediate temperature regime together with four other co-occurring tropical rainforest tree species belonging to different ecological niches. The growth rates and proportions of above-ground biomass allocated to woody tissue distinguished T. australis and a fast-growing pioneer species from F. brayleyana and three primary forest species. The stem heights and aboveground biomass of T. australis and the pioneer species exceeded the other four species by factors ranging from two to five. It is concluded that T. australis does not belong to the same ecological niche as F. brayleyana, and it is recommended that more research be conducted on the ecotypic temperature responses of the taxon T. australis.     

不同氮、磷浓度对铜绿微囊藻生长、光合及产毒的影响

对一株从野外分离得到的铜绿微囊藻产毒株进行分批培养,在不同的氮磷条件下研究其生长、光合荧光及毒素含量的变化。结果表明:正磷酸盐浓度不变时,铵氮浓度的改变对铜绿微囊藻的生长有明显影响。叶绿素a(Chl.a)含量在铵氮浓度为1.83-18.3mg/L时明显较大;微囊藻毒素(包括MC-LR和MC-RR)的含量在铵氮浓度为1.83mg/L时达到最大;当铵氮浓度为0-1.83mg/L时,随着铵氮浓度升高,可变荧光FV和MC的产量均增大,同时MC异构体的种类增多;铵氮浓度过大对M.aeruginosa的生长、生理和产毒均有抑制作用。在另一组实验中,即铵氮浓度不变而正磷酸盐浓度增大时,Chl.a含量呈总体下降的趋势,并且与FV/Fm呈显著正相关关系(P<0.01,r=0.97),MC(MC-LR和MC-RR)的含量在正磷酸盐浓度小于0.56mg/L时明显升高,MC-LR与FV/Fm呈显著正相关关系(P<0.01,r=0.967)。       

Effects of gibberellin A(3) on growth and microcystin production in Microcystis aeruginosa (cyanophyta)

Environmental factors that affect the growth and microcystin production of microcystis have received worldwide attention because of the hazards microcystin poses to environmental safety and public health. Nevertheless, the effects of organic anthropogenic pollution on microcystis are rarely discussed. Gibberellin A(3) (GA(3)) is a vegetable hormone widely used in agriculture and horticulture that can contaminate water as an anthropogenic pollutant. Because of its common occurrence, we studied the effects of GA(3) on growth and microcystin production of Microcystis aeruginosa (M. aeruginosa) PCC7806 with different concentrations (0.001-25mg/L) in batch culture. The control was obtained without gibberellin under the same culture conditions. Growth, estimated by dry weight and cell number, increased after the GA(3) treatment. GA(3) increased the amounts of chlorophyll a, phycocyanin and cellular-soluble protein in the cells of M. aeruginosa PCC7806, but decreased the accumulation of water-soluble carbohydrates. In addition, GA(3) was observed to affect nitrogen absorption of the test algae, but to have no effect on the absorption of phosphorus. The amount of microcystin measured by enzyme-linked immunosorbent assay (ELISA) increased in GA(3) treatment groups, but the stimulatory effects were different in different culture phases. It is suggested that GA(3) increases M. aeruginosa growth by stimulating its absorbance of nitrogen and increasing its ability to use carbohydrates, accordingly increasing cellular pigments and thus finally inducing accumulation of protein and microcystin.     

全细胞多重PCR检测蓝藻、微囊藻及产毒微囊藻方法初探

选取三对分别针对微囊藻、蓝藻16S rDNA及微囊藻毒素合成酶基因mcyB的保守序列的特异性引物209F/409R、27F1/409R、MTR/MTF,其中409R为一条共用引物。设计并优化了一种可以同时检测蓝藻和微囊藻的两重全细胞PCR方法和一种可以同时检测蓝藻、微囊藻和可产毒微囊藻的三重全细胞PCR方法,并且测试了这两种PCR反应的灵敏度区间,分别为10⁵～10³cell·mL^-1、10⁵～10²cell·mL^-1。对采集水库水样检测结果表明双重全细胞PCR方法可以直接应用于对天然水样的检测,三重全细胞PCR方法可用于实验室培养藻细胞的筛查。全细胞多重PCR方法具有快速、简便、准确等特点,在水体微囊藻毒素检测预警方面具有应用价值。     

Seasonal dynamics of amino acids in two small Siberian reservoirs dominated by prokaryotic and eukaryotic phytoplankton

The comparison of the dynamics of phytoplankton biomass and total amino acid composition was made for two water bodies: in one the phytoplankton were dominated by prokaryotes (i.e., there was a bloom of cyanobacteria) and by eukaryotic microalgae in the other. The dynamics of phytoplankton biomass and of total amino acid composition of water were investigated during the vegetation season. It was found that the only factor that significantly changed the percentages of amino acids in water was the bloom of cyanobacteria in the blooming water body. During the bloom of cyanobacteria, the absolute and relative content of the Leu-Glu group increased, while the contents of other acids generally dropped. Before and after the bloom, no significant variations in the total amino acid composition were recorded. In the reservoir where eukaryotic microalgae dominated, no significant variations in amino acid composition were recorded during the season.     

Responses to light changes in tropical deciduous woody seedlings with contrasting growth rates

We evaluated the responses in growth, biomass allocation, photosynthesis and stomatal conductance, to changes in light in woody seedlings from the tropical deciduous forest in Mexico, which shows a highly seasonal rain pattern. We studied ten species, which differed by 30-fold in relative growth rate (RGR). We analyzed plant growth in two contrasting light levels during 52 days and two transfers: from high to low (HL) and from low to high (LH) light intensity, and the respective controls in high (HH) and low (LL) light for another 52 days. The photosynthetic capacity (A _max) and stomatal conductance were measured at the day of the transfer between light conditions and at the end of the experiment. Species with high RGR showed the largest changes in RGR in response to contrasting light conditions (HH/LL ratio), and species with low RGR showed low responses. The fast-growing species were the most plastic, followed by species with intermediate growth rates, with the slow-growing species being the least plastic. Fast-growing species achieved higher maximum photosynthetic capacities (A _max) and stomatal conductance and higher response to light than slow-growing species. Species with high RGR showed a low RGR HH/LH ratio, suggesting a large response of L plants when transfered to H. The RGR of the species were associated with species specific leaf area and with the response in the leaf area, net assimilation rate and leaf weight ratio, suggesting the importance of the leaf area produced and the leaf characteristics rather than root:shoot ratio in determining RGR. Considering that seed germination is expected at the beginning of the rainy period, seedlings of most of the species will experience high-light conditions during its early growth. There are large annual variations in the time required for canopy closure (35–75 days). The influence of these variations may have different effect on the species studied. Species with intermediate growth rate and intermediate response to light changes were less affected by light reduction than fast-growing species. The intermediate-RGR species Caesalpiniaeriostachys is the most abundant and widely distributed species, perhaps this could be in part due to its ability to acclimate to both light increases and decreases. The fast-growing species studied here can be found in open sites in the forest and in areas cleared for pasture growth. These fast-growing species eventually reach the canopy, although this may require several canopy openings during their lives, which implies juvenile shade tolerance. In the tropical deciduous forest juvenile pioneer trees also benefit from the temporary high light available caused by the dry period during the rainy season. The slow-growing species Celaenodendronmexicanum forms small patches of monospecific forest; the adult trees are not completely deciduous, and they retain their old leaves for a long time period before shedding. Thus seedlings of this species may receive lower levels of light, in agreement with its shade tolerance and its lower response to light increases. Received: 14 April 1997 / Accepted: 29 July 1997     

Resource availability and growth responses to defoliation in seedlings of three early-successional,tropical, woody species

A growth experiment was conducted using seedlings of three early-successional, tropical, woody species:Dillenia suffruticosa (Dilleniaceae),Macaranga heynei (Euphorbiaceae) andTrema tomentosa (Ulmaceae). These species are characteristic of different positions along a soil fertility gradient in Singapore, withD. suffruticosa being the least andT. tomentosa the most demanding of high nutrient availability. The seedlings were grown in vermiculite at either low or high nutrient availabilities supplied by watering with different concentrations of a commercial plant food. Half the seedlings were subjected to a 50% defoliation at the start of the experiment by cutting off the distal half of each leaf. After 9 weeks the plants were harvested.Macaranga heynei andT. tomentosa seedlings showed no significant difference in parameters of growth such as total dry weight and total leaf area between the defoliated and control seedlings. The seedlings compensated completely for the loss of leaf area.Dillenia suffruticosa did show significant reductions in growth in some parameters due to defoliation, and these were more pronounced under the high nutrient treatment. These findings support the hypothesis that plants characteristic of resource-rich sites can readily recover from herbivory through fast growth, probably associated with a rapid turnover of leaves, whereas species of resource-poor habitats cannot easily replace losses due to herbivory and are adversely effected by defoliation.     

Fine-root mass, growth and nitrogen content for six tropical tree species

Although fine roots might account for 50% of the annual net primary productivity in moist tropical forests, there are relatively few studies of fine-root dynamics in this biome. We examined fine-root distributions, mass, growth and tissue N and C concentrations for six tree species established in 16-year-old plantations in the Caribbean lowlands of Costa Rica in a randomized-block design (n = 4). The study included five native species (Hyeronima alchorneoides, Pentaclethra macroloba, Virola koschnyi, Vochysia ferruginea and Vochysia guatemalensis) and one exotic (Pinus patula). Under all species >60% of the total fine-root mass to 1 m deep was located in the uppermost 15 cm of the soil. Fine-root live biomass and necromass (i.e., the mass of dead fine-roots) varied significantly among species but only within the uppermost 15 cm, with biomass values ranging from 182 g m⁻² in Pinus to 433 g m⁻² in Hyeronima plots, and necromass ranging from 48 g m⁻² in Pinus to 183 g m⁻² in Virola plots. Root growth, measured using ingrowth cores, differed significantly among species, ranging from 304 g m⁻² year⁻¹ in Pinus to 1,308 g m⁻² year⁻¹ in Hyeronima. These growth rates were one to five times those reported for moist temperate areas. Turnover rates of fine-root biomass ranged from 1.6 to 3.0 year⁻¹ in Virola and Hyeronima plots, respectively. Fine-root biomass was significantly and positively correlated with fine-root growth (r = 0.79, P < 0.0001), but did not correlate with fine-root turnover (r = 0.10, P = 0.20), suggesting that fine-root accumulation is a function of growth rate rather than mortality. Fine-root longevity was not correlated (r = 0.20, P = 0.34) and growth was negatively correlated with root N concentration across species (r = −0.78, P < 0.0001), contrary to reported trends for leaves, perhaps because N was relatively abundant at this site.     

Effects of seasonal rainfall on radial growth in two tropical tree species

 Seasonal drought may limit primary productivity in most of the tropics, but the determinants of tree growth are not well known. A 10-year study of the deciduous trees Cochlospermum vitifolium (Willd.) Spreng. (Cochlospermaceae) and Cnidoscolus spinosus Lundell (Euphorbiaceae) in southwestern México showed radial growth to be highly correlated (both r>0.85) only with precipitation during an interval of <2 months in the mid-wet season. Growth was not affected by total annual precipitation or by an early starting or late ending of the wet season, or by heavy rainfall in the dry season. Annual mean girth increments ranged from 0.03 to 3.31 cm and −0.1 to 2.01 cm, respectively. The best model for growth (r ²>0.85) was a linear combination of mid-summer precipitation (positive coefficient) and total precipitation over the previous 2 years (negative coefficient). Comparison with other species showed heterogeneous responses of wood production to climate variation, and suggests that the range of functional types of dry forest trees is still unknown. Received: 9 September 1996 / Accepted: 4 March 1997     

Damage segregation at fissioning may increase growth rates: a superprocess model

A fissioning organism may purge unrepairable damage by bequeathing it preferentially to one of its daughters. Using the mathematical formalism of superprocesses, we propose a flexible class of analytically tractable models that allow quite general effects of damage on death rates and splitting rates and similarly general damage segregation mechanisms. We show that, in a suitable regime, the effects of randomness in damage segregation at fissioning are indistinguishable from those of randomness in the mechanism of damage accumulation during the organism's lifetime. Moreover, the optimal population growth is achieved for a particular finite, non-zero level of combined randomness from these two sources. In particular, when damage accumulates deterministically, optimal population growth is achieved by a moderately unequal division of damage between the daughters, while too little or too much division is sub-optimal. Connections are drawn both to recent experimental results on inheritance of damage in protozoans, and to theories of aging and resource division between siblings.     

Fur from Microcystis aeruginosa binds in vitro promoter regions of the microcystin biosynthesis gene cluster

Promoter regions of the mcy operon from Microcystis aeruginosa PCC7806, which is responsible for microcystin synthesis in this organism, exhibit sequences that are similar to the sequences recognized by Fur (ferric uptake regulator). This DNA-binding protein is a sensor of iron availability and oxidative stress. In the presence of Fe(2+), a dimer of Fur binds the iron-boxes in their target genes, repressing their expression. When iron is absent the expression of those gene products is allowed. Here, we show that Fur from M. aeruginosa binds in vitro promoter regions of several mcy genes, which suggests that Fur might regulate, among other factors, microcystin synthesis. The binding affinity is increased by the presence of metal and DTT, suggesting a response to iron availability and redox status of the cell.     

The dynamics of toxic Microcystis strains and microcystin production in two hypertrofic South African reservoirs

The South African impoundments of Hartbeespoort and Roodeplaat experience excessive blooms of Microcystis species each year. Microcystins, produced primarily by strains of cyanobacteria belonging to the genera Microcystis, Anabaena and Planktothrix, are harmful cyanobacterial hepatotoxins. These bloom-forming cyanobacteria form toxic and non-toxic strains that co-occur and are visually indistinguishable, but can be identified and quantified molecularly. We described the relationships between microcystin production and the genotypic composition of the Microcystis community involved together with environmental conditions in both the Roodeplaat and Hartbeespoort reservoirs using quantitative real time PCR. DNA copy number of the Microcystis-specific 16S rRNA and toxin biosynthesis genes, mcyE and mcyB, were measured. Planktothrix spp. occurred in both reservoirs during autumn, but no toxin-producing species was present as measured with mcyE specific primers, whereas both toxic and non-toxic strains of Microcystis were recorded in both reservoirs, with Microcystis spp. dominating in the summer months. Water-surface temperature correlated strongly with microcystin concentration, mcyE and mcyB copy number. Microcystin production was associated by temperatures higher than 23 °C. This suggests that should current environmental trends persist with surface water temperatures continuing to rise and more and more nutrients continued to be loaded into fresh water systems toxic Microcystis may outgrow non-toxic Microcystis and synthesise even more microcystins.     

Tree species richness affects litter production and decomposition rates in a tropical biodiversity experiment

We report data on leaf litter production and decomposition from a manipulative biodiversity experiment with trees in tropical Panama, which has been designed to explore the relationship between tree diversity and ecosystem functioning. A total of 24 plots (2025 m²) were established in 2001 using six native tree species, with 1‐, 3‐, and 6‐species mixtures. We estimated litter production during the dry season 2005 with litter traps; decomposition was assessed with a litter bag approach during the following wet season. Litter production during the course of the dry season was highly variable among the tree species. Tree diversity significantly affected litter production, and the majority of the intermediate diverse mixtures had higher litter yields than expected based on yields in monoculture. In contrast, high diverse mixtures did not show such overyielding in litter production. Litter decomposition rates were also highly species‐specific, and were related to various measures of litter quality (C/N, lignin/N, fibre content). We found no overall effect of litter diversity if the entire litter mixtures were analyzed, i.e. mixing species resulted in pure additive effects and observed decomposition rates were not different from expected rates. However, the individual species changed their decomposition pattern depending on the diversity of the litter mixture, i.e. there were species‐specific responses to mixing litter. The analysis of temporal C and N dynamics within litter mixtures gave only limited evidence for nutrient transfer among litters of different quality. At this early stage of our tree diversity experiment, there are no coherent and general effects of tree species richness on both litter production and decomposition. Within the scope of the biodiversity‐ecosystem functioning relationship, our results therefore highlight the process‐specific effects diversity may have. Additionally, species‐specific effects on ecosystem processes and their temporal dynamics are important, but such effects may change along the gradient of tree diversity.