Influence of monoterpenoids on the growth of freshwater cyanobacteria.

Cyanobacteria are characterized by a very high tolerance to environmental factors. They are found in salt water, fresh water, thermal springs, and Antarctic waters. The wide spectrum of habitats suitable for those microorganisms is related to their particularly effective metabolism; resistance to extreme environmental conditions; and the need for only limited environmental resources such as water, carbon dioxide, simple inorganic salts, and light. These metabolic characteristics have led to cyanobacterial blooms and the production of cyanotoxins, justifying research into effective ways to counteract the excessive proliferation of these microorganisms. A new and interesting idea for the immediate reduction of cyanobacterial abundance is to use natural substances with broad-spectrum biological activity to restore phytoplankton diversity. This study describes the effects of selected monoterpenoid derivatives on the development of cyanobacterial cultures. In the course of the study, some compounds ((±)-citronellal, (+)-α-pinene) showed the ability to inhibit the colonization of the tested photosynthetic bacteria, while others (eugenol, eucalyptol) stimulated the growth of these microorganisms. By analyzing the results of these experiments, information was obtained on the mutual relations of cyanobacteria and the tested monoterpenes, which are present in the aquatic environment. KEY POINTS: • Monoterpenoids significantly inhibit the growth of single cyanobacterial strains. • Monoterpenoids can inhibit the growth of cyanobacterial consortia. • Natural substances can control the growth of freshwater cyanobacteria.

Use of High-Resolution Pressure Nephelometry To Measure Gas Vesicle Collapse as a Means of Determining Growth and Turgor Changes in Planktonic Cyanobacteria.

Previous work has demonstrated that the physical properties of intracellular bacterial gas vesicles (GVs) can be analyzed in vivo using pressure nephelometry. In analyzing the buoyant state of GV-containing cyanobacteria, hydrostatic pressure within a sample cell is increased in a stepwise manner, where the concomitant collapse of GVs due to pressure and the resultant decrease in suspended cells are detected by changes in nephelometric scattering. As the relative pressure at which GVs collapse is a function of turgor pressure and cellular osmotic gradients, pressure nephelometry is a powerful tool for assaying changes in metabolism that affect turgor, such as photosynthetic and osmoregulatory processes. We have developed an updated and automated pressure nephelometer that utilizes visible-infrared (Vis-IR) spectra to accurately quantify GV critical collapse pressure, critical collapse pressure distribution, and cell turgor pressure. Here, using the updated pressure nephelometer and axenic cultures of Microcystis aeruginosa PCC7806, we demonstrate that GV critical collapse pressure is stable during mid-exponential growth phase, introduce pressure-sensitive turbidity as a robust metric for the abundance of gas-vacuolate cyanobacteria, and demonstrate that pressure-sensitive turbidity is a more accurate proxy for abundance and growth than photopigment fluorescence. As cyanobacterium-dominated harmful algal bloom (cyanoHAB) formation is dependent on the constituent cells possessing gas vesicles, characterization of environmental cyanobacteria populations via pressure nephelometry is identified as an underutilized monitoring method. Applications of this instrument focus on physiological and ecological studies of cyanobacteria, for example, cyanoHAB dynamics and the drivers associated with cyanotoxin production in aquatic ecosystems.IMPORTANCE The increased prevalence of bloom-forming cyanobacteria and associated risk of exposure to cyanobacterial toxins through drinking water utilities and recreational waterways are growing public health concerns. Cost-effective, early-detection methodologies specific to cyanobacteria are crucial for mitigating these risks, with a gas vesicle-specific signal offering a number of benefits over photopigment fluorescence, including improved detection limits and discrimination against non-gas-vacuolate phototrophs. Here, we present a multiplexed instrument capable of quantifying the relative abundance of cyanobacteria based on the signal generated from the presence of intracellular gas vesicles specific to bloom-forming cyanobacteria. Additionally, as cell turgor can be measured in vivo via pressure nephelometry, the measurement furnishes information about the internal osmotic pressure of gas-vacuolate cyanobacteria, which relates to the metabolic state of the cell. Together these advances may improve routine waterway monitoring and the mitigation of human health threats due to cyanobacterial blooms.

Transition from a mixotrophic/heterotrophic protist community during the dark winter to a photoautotrophic spring community in surface waters of Disko Bay, Greenland.

Unicellular eukaryotic plankton communities (protists) are the major basis of the marine food web. The spring bloom is especially important, because of its high biomass. However, it is poorly described how the protist community composition in Arctic surface waters develops from winter to spring. We show that mixotrophic and parasitic organisms are prominent in the dark winter period. The transition period toward the spring bloom event was characterized by a high relative abundance of mixotrophic dinoflagellates, while centric diatoms and the haptophyte Phaeocystis pouchetii dominated the successive phototrophic spring bloom event during the study. The data shows a continuous community shift from winter to spring, and not just a dormant spring community waiting for the right environmental conditions. The spring bloom initiation commenced while sea ice was still scattering and absorbing the sunlight, inhibiting its penetration into the water column. The initial increase in fluorescence was detected relatively deep in the water column at ~55 m depth at the halocline, at which the photosynthetic cells accumulated, while a thick layer of snow and sea ice was still obstructing sunlight penetration of the surface water. This suggests that water column stratification and a complex interplay of abiotic factors eventually promote the spring bloom initiation.

Physical Properties and Fat Bloom Stability of Compound Chocolates Made with Ternary Fat Blends of Cocoa Butter, 1,3-Dioleoyl-2-stearoyl-triacylglycerol-Fat, and Lauric-Based Cocoa Butter Substitute.

Compound chocolates made of lauric-acid-based cocoa butter substitute (CBS) and cocoa butter (CB) often exhibit serious fat blooms caused by phase separation and polymorphic transformation of CB and CBS triacylglycerols. Herein, we found that the fat bloom of CBS-based chocolates could be completely inhibited by adding fat containing 1,3-dioleoyl-2-stearoyl-triacylglycerol (OSO) to CBS/CB blends. Unlike the CBS/CB chocolates that presented fat blooms within 3 wk under isothermal storage at 15, 20, and 25°C and 15 wk under thermal thawing storage at 15-25°C , no fat blooms appeared in the CBS/CB/OSO compound chocolates under any storage condition up to 6 months. The following key factors are involved in the addition of the OSO fats: the (1) concentration ratio of CB/OSO should be 1/1 such that CB/OSO can form molecular compound crystals and (2) total amount of CB+OSO in the CBS/CB/OSO blends should reach 20%. The solid fat content, hardness, and crystallisation rate of the CBS/CB/OSO blend-based chocolate compound were confirmed to be suitable for chocolate production.

Identification of Candidate Genes for Rind Color and Bloom Formation in Watermelon Fruits Based on a Quantitative Trait Locus-Seq.

Watermelon fruit rind color (RC) and bloom formation (BF) affect product value and consumer preference. However, information on the candidate gene(s) for additional loci involved in dark green (DG) RC and the genetic control of BF and its major chemical components is lacking. Therefore, this study aimed to identify loci controlling RC and BF using QTL-seq of the F2 population derived by crossing 'FD061129' with light-green rind and bloom and 'SIT55616RN' with DG rind and bloomless. Phenotypic evaluation of the F1 and 219 F2 plants indicated the genetic control of two complementary dominant loci, G1 and G2, for DG and a dominant locus, Bf, for BF. QTL-seq identified a genomic region on Chr.6 for G1, Chr.8 for G2, and Chr.1 for Bf. G1 and G2 helped determine RC with possible environmental effects. Chlorophyll a-b binding protein gene-based CAPS (RC-m5) at G1 matched the highest with the RC phenotype. In the 1.4 cM Bf map interval, two additional gene-based CAPS markers were designed, and the CAPS for a nonsynonymous SNP in Cla97C01G020050, encoding a CSC1-like protein, cosegregated with the BF trait in 219 F2 plants. Bloom powder showed a high Ca2+ concentration (16,358 mg·kg-1), indicating that the CSC1-like protein gene is possibly responsible for BF. Our findings provide valuable information for marker-assisted selection for RC and BF and insights into the functional characterization of genes governing these watermelon-fruit-related traits.

Low temperatures can promote cyanobacterial bloom formation by providing refuge from microbial antagonists.

Freshwater cyanobacteria are prone to a wide range of highly potent microbial antagonists. Most of these exploit their prey in a frequency-dependent manner and are therefore particularly well suited to prevent any accumulation of cyanobacteria. Mass developments of cyanobacteria, the so-called blooms, should therefore be rare events, which is in striking contrast to what we actually see in nature. Laboratory experiments of the present study showed that the temperature range 5.8-10 °C forms a thermal refuge, inside which the cyanobacterium Planktothrix can grow without being exploited by two otherwise highly potent microbial antagonists. In nature, access of Planktothrix to this refuge was associated with positive net growth and a high probability of bloom formation, confirming that refuge temperatures indeed allow Planktothrix to grow with a minimum of biomass loss caused by microbial antagonists. Contact to higher temperatures, in contrast, was associated with decreases in net growth rate and in probability of bloom formation, with population collapses and with the occurrence of parasite infection. This is in agreement with the finding of laboratory experiments that above 10 °C exploitation of Planktothrix by multiple microbes increases in a temperature-dependent manner. Taken together, above findings suggest that temperature modulates the microbial control of natural Planktothrix populations. Low temperatures form a thermal refuge that may promote Planktothrix bloom formation by shielding the cyanobacterium from otherwise highly potent microbial antagonists.

Trichodesmium blooms and warm-core ocean surface features in the Arabian Sea and the Bay of Bengal.

Trichodesmium is a bloom-forming, diazotrophic, non-heterocystous cyanobacteria widely distributed in the warmer oceans, and their bloom is considered a 'biological indication' of stratification and nitrogen limitation in the ocean surface layer. In the first part of this paper, based on the retrospective analyses of the ocean surface mesoscale features associated with 59 Trichodesmium bloom incidences recorded in the past, 32 from the Arabian Sea and the Bay of Bengal, and 27 from the rest of the world, we have showed that warm-core features have an inducing effect on bloom formation. In the second part, we have considered the environmental preferences of Trichodesmium bloom based on laboratory and field studies across the globe, and proposed a view about how warm-core features could provide an inducing pre-requisite condition for the bloom formation in the Arabian Sea and the Bay of Bengal. Proposed that the subsurface waters of warm-core features maintain more likely chances for the conducive nutrient and light conditions required for the triggering of the blooms.

In situ dynamics of cyst and vegetative cell populations of the toxic dinoflagellate Alexandrium catenella in Ago Bay, central Japan.

Temporal changes in the in situ germination flux of cysts and the abundance of vegetative cells of the toxic dinoflagellate Alexandrium catenella were investigated in Ago Bay, central Japan from July 2003 to December 2004. The in situ germination flux (cells m-2 day-1) was measured using 'plankton emergence trap/chambers (PET chambers)'. Germination of the cysts in the sediments occurred continuously during the study, ranging from 52 to 1753 cells m-2 day-1, with no temporal trend. This germination pattern appeared to be promoted by a short mandatory dormancy period for newly formed cysts coupled with a broad temperature window for germination. For the vegetative populations, high abundances (>105 cells m-2) were recorded in the water column from spring to summer and from autumn to early winter. The size of the vegetative populations did not correlate with the cyst germination flux but rather larger vegetative populations were often observed when the water temperature was around 20°C, indicating that bloom development was mainly regulated by the temperature. Nonetheless, the continuous germination pattern of A. catenella is advantageous enabling the germinated cells to immediately exploit favorable bloom conditions.