Lysis of cyanobacteria with volatile organic compounds

The origins of odor (β-cyclocitral) under different water nutrient conditions: Algae or submerged plants?

Among the problems caused by water eutrophication, the issue of odor compounds has attracted notable attention. β-Cyclocitral, a widely distributed and versatile odor compound, is commonly derived from both algae and aquatic plants. Planting aquatic plants is a common method of water purification. However, there is limited study on their impact on β-cyclocitral levels in water. Here, we conducted a study on the β-cyclocitral levels in water and the submerged plant leaves under three nutrient levels and six plant density treatments. Our findings revealed the following: (1) Chlorophyll-a (Chla), β-cyclocitral in the water (Wcyc), β-cyclocitral in Potamogeton lucens leaves (Pcyc) and the biomass of the submerged plants increase with rising nutrient concentration, which increased about 83 %, 95 %, 450 %, 320 % from eutrophic treatment to oligotrophic treatment, respectively. (2) In water, β-cyclocitral is influenced not only by algae but also by submerged plants, with primary influencing factors varying across different nutrient levels and plant densities. The main source of β-cyclocitral in water becomes from plants to algae as the water eutrophication and plant density decrease. (3) As submerged plants have the capability to emit β-cyclocitral, the release of β-cyclocitral increases with the density of submerged plants. Hence, when considering planting submerged plants for water purification purposes, it is crucial to carefully manage submerged plant density to mitigate the risk of odor pollution emanating from aquatic plants. This study offers fresh insights into selecting optimal water density for submerged plants and their role in mitigating the release of β-cyclocitral.

Sphingomonas lacusdianchii sp. nov., an attached bacterium inhibited by metabolites from its symbiotic cyanobacterium

An alpha-proteobacterial strain JXJ CY 53 T was isolated from the cyanosphere of Microcystis sp. FACHB-905 (MF-905) collected from Lake Dianchi, China. JXJ CY 53 T was observed to be an aerobic, Gram-stain-negative, oval shaped, and mucus-secreting bacterium. It had C18:1ω7c and C16:0 as the major cellular fatty acids, Q-10 as the predominant ubiquinone, and sphingoglycolipid, diphosphatidylglycerol, phosphatidylcholine, and phosphatidylmethylethanolamine as the polar lipids. The G + C content of DNA was 65.85%. The bacterium had 16S rRNA gene sequence identities of 98.9% and 98.7% with Sphingomonas panni DSM 15761 T and Sphingomonas hankookensis KCTC 22579 T, respectively, while less than 97.4% identities with other members of the genus. Further taxonomic analysis indicated that JXJ CY 53 T represented a new member of Sphingomonas, and the species epithet was proposed as Sphingomonas lacusdianchii sp. nov. (type strain JXJ CY 53 T = KCTC 72813 T = CGMCC 1.17657 T). JXJ CY 53 T promoted the growth of MF-905 by providing bio-available phosphorus and nitrogen, plant hormones, vitamins, and carotenoids. It could modulate the relative abundances of nonculturable bacteria associated with MF-905 and influence the interactions of MF-905 and other bacteria isolated from the cyanobacterium, in addition to microcystin production characteristics. Meanwhile, MF-905 could provide JXJ CY 53 T dissolved organic carbon for growth, and control the growth of JXJ CY 53 T by secreting specific chemicals other than microcystins. Overall, these results suggest that the interactions between Microcystis and its attached bacteria are complex and dynamic, and may influence the growth characteristics of the cyanobacterium. This study provided new ideas to understand the interactions between Microcystis and its attached bacteria. KEY POINTS: • A novel bacterium (JXJCY 53 T) was isolated from the cyanosphere of Microcystis sp. FACHB-905 (MF-905) • JXJCY 53 T modulated the growth and microcystin production of MF-905 • MF-905 could control the attached bacteria by specific chemicals other than microcystins (MCs).

Spatio-temporal connectivity of a toxic cyanobacterial community and its associated microbiome along a freshwater-marine continuum

Due to climate changes and eutrophication, blooms of predominantly toxic freshwater cyanobacteria are intensifying and are likely to colonize estuaries, thus impacting benthic organisms and shellfish farming representing a major ecological, health and economic risk. In the natural environment, Microcystis form large mucilaginous colonies that influence the development of both cyanobacterial and embedded bacterial communities. However, little is known about the fate of natural colonies of Microcystis by salinity increase. In this study, we monitored the fate of a Microcystis dominated bloom and its microbiome along a French freshwater-marine gradient at different phases of a bloom. We demonstrated changes in the cyanobacterial genotypic composition, in the production of specific metabolites (toxins and compatible solutes) and in the heterotrophic bacteria structure in response to the salinity increase. In particular M. aeruginosa and M. wesenbergii survived salinities up to 20. Based on microcystin gene abundance, the cyanobacteria became more toxic during their estuarine transfer but with no selection of specific microcystin variants. An increase in compatible solutes occurred along the continuum with extensive trehalose and betaine accumulations. Salinity structured most the heterotrophic bacteria community, with an increased in the richness and diversity along the continuum. A core microbiome in the mucilage-associated attached fraction was highly abundant suggesting a strong interaction between Microcystis and its microbiome and a likely protecting role of the mucilage against an osmotic shock. These results underline the need to better determine the interactions between the Microcystis colonies and their microbiome as a likely key to their widespread success and adaptation to various environmental conditions.

The apocarotenoid β-ionone regulates the transcriptome of Arabidopsis thaliana and increases its resistance against Botrytis cinerea

Carotenoids are isoprenoid pigments indispensable for photosynthesis. Moreover, they are the precursor of apocarotenoids, which include the phytohormones abscisic acid (ABA) and strigolactones (SLs) as well as retrograde signaling molecules and growth regulators, such as β-cyclocitral and zaxinone. Here, we show that the application of the volatile apocarotenoid β-ionone (β-I) to Arabidopsis plants at micromolar concentrations caused a global reprogramming of gene expression, affecting thousands of transcripts involved in stress tolerance, growth, hormone metabolism, pathogen defense, and photosynthesis. This transcriptional reprogramming changes, along with induced changes in the level of the phytohormones ABA, jasmonic acid, and salicylic acid, led to enhanced Arabidopsis resistance to the widespread necrotrophic fungus Botrytis cinerea (B.c.) that causes the gray mold disease in many crop species and spoilage of harvested fruits. Pre-treatment of tobacco and tomato plants with β-I followed by inoculation with B.c. confirmed the effect of β-I in increasing the resistance to this pathogen in crop plants. Moreover, we observed reduced susceptibility to B.c. in fruits of transgenic tomato plants overexpressing LYCOPENE β-CYCLASE, which contains elevated levels of endogenous β-I, providing a further evidence for its effect on B.c. infestation. Our work unraveled β-I as a further carotenoid-derived regulatory metabolite and indicates the possibility of establishing this natural volatile as an environmentally friendly bio-fungicide to control B.c.

The volatilome reveals microcystin concentration, microbial composition, and oxidative stress in a critical Oregon freshwater lake

IMPORTANCE

Harmful algal blooms are among the most significant threats to drinking water safety. Blooms dominated by cyanobacteria can produce potentially harmful toxins and, despite intensive research, toxin production remains unpredictable. We measured gaseous molecules in Upper Klamath Lake, Oregon, over 2 years and used them to predict the presence and concentration of the cyanotoxin, microcystin, and microbial community composition. Subsets of gaseous compounds were identified that are associated with microcystin production during oxidative stress, pointing to ecosystem-level interactions leading to microcystin contamination. Our approach shows potential for gaseous molecules to be harnessed in monitoring critical waterways.

Volatile sensation: The chemical ecology of the earthy odorant geosmin

Geosmin may be the most familiar volatile compound, as it lends the earthy smell to soil. The compound is a member of the largest family of natural products, the terpenoids. The broad distribution of geosmin among bacteria in both terrestrial and aquatic environments suggests that this compound has an important ecological function, for example, as a signal (attractant or repellent) or as a protective specialized metabolite against biotic and abiotic stresses. While geosmin is part of our everyday life, scientists still do not understand the exact biological function of this omnipresent natural product. This minireview summarizes the current general observations regarding geosmin in prokaryotes and introduces new insights into its biosynthesis and regulation, as well as its biological roles in terrestrial and aquatic environments.

Electronic nose application for detecting different odorants in source water: Possibility and scenario

The problem of taste and odor (T&O) in drinking water is a widespread societal concern and highlights substantial challenges related to the detection and evaluation of odor in water. In this study, the portable electronic nose PEN3, which is equipped with ten different heated metal sensors, was applied to analyze its applicability, feasibility and application scenarios for the detection of typical odorants, such as 2-methylisobornel (2-MIB), geosmin (GSM), β-cyclocitral, β-ionone, and other T&O compounds in source water, while avoiding uncertainties and instability related to manual inspection. All the T&O compounds could be effectively differentiated by principal component analysis (PCA). Linear discriminant analysis (LDA) showed that the odors varied greatly between different samples and could be effectively distinguished. As the odorant concentration increased, the sensor response intensity of the primary identification sensors R6 and R8 increased with a significant positive correlation. For Microcystis aeruginosa, an algae that produces odorants, PCA could distinguish the odors of algae at a series of densities at different concentrations. The responses of R10 showed a significant increase with increasing algae density, implying the production of more aliphatic hydrocarbons and other odor compounds. The results indicated that the electronic nose could provide a promising alternative to traditional unstable and complex detection methods for the detection of odorous substances in surface water and early warning of odor events. This study aimed to provide technical support for rapid monitoring and early warning of odorants in source water management.

Co-Occurrence of Taste and Odor Compounds and Cyanotoxins in Cyanobacterial Blooms: Emerging Risks to Human Health?

Cyanobacteria commonly form large blooms in waterbodies; they can produce cyanotoxins, with toxic effects on humans and animals, and volatile compounds, causing bad tastes and odors (T&O) at naturally occurring low concentrations. Notwithstanding the large amount of literature on either cyanotoxins or T&O, no review has focused on them at the same time. The present review critically evaluates the recent literature on cyanotoxins and T&O compounds (geosmin, 2-methylisoborneol, β-ionone and β-cyclocitral) to identify research gaps on harmful exposure of humans and animals to both metabolite classes. T&O and cyanotoxins production can be due to the same or common to different cyanobacterial species/strains, with the additional possibility of T&O production by non-cyanobacterial species. The few environmental studies on the co-occurrence of these two groups of metabolites are not sufficient to understand if and how they can co-vary, or influence each other, perhaps stimulating cyanotoxin production. Therefore, T&Os cannot reliably serve as early warning surrogates for cyanotoxins. The scarce data on T&O toxicity seem to indicate a low health risk (but the inhalation of β-cyclocitral deserves more study). However, no data are available on the effects of combined exposure to mixtures of cyanotoxins and T&O compounds and to combinations of T&O compounds; therefore, whether the co-occurrence of cyanotoxins and T&O compounds is a health issue remains an open question.

β-Cyclocitral: Emerging Bioactive Compound in Plants

β-cyclocitral (βCC), a main apocarotenoid of β-carotene, increases plants’ resistance against stresses. It has recently appeared as a novel bioactive composite in a variety of organisms from plants to animals. In plants, βCC marked as stress signals that accrue under adverse ecological conditions. βCC regulates nuclear gene expression through several signaling pathways, leading to stress tolerance. In this review, an attempt has been made to summarize the recent findings of the potential role of βCC. We emphasize the βCC biosynthesis, signaling, and involvement in the regulation of abiotic stresses. From this review, it is clear that discussing compound has great potential against abiotic stress tolerance and be used as photosynthetic rate enhancer. In conclusion, this review establishes a significant reference base for future research.

Algal volatiles - the overlooked chemical language of aquatic primary producers

Volatiles are important 'infochemicals' that play a crucial role in structuring life on our planet, fulfilling diverse functions in natural and artificial systems. Algae contribute significant quantities to the global budget of volatiles, but the ecological roles of aquatic volatiles are not well understood. In this review, we discuss the current knowledge of volatile compounds from freshwater and marine microalgae and marine macroalgae, with a focus on their ecological roles. We highlight the multiple reported functions of biogenic volatiles, ranging from intraspecific communication for reproduction, intra-bloom signalling and antioxidant functions, to various interspecific signal exchanges that may allow herbivores to locate them and function in defence against competitors and predators. Beyond reviewing our current understanding, we specifically highlight major knowledge gaps and emerging questions for algal volatile research. These novel perspectives have the potential to improve our understanding of aquatic ecosystems and thus need to be addressed in future research. Filling these gaps and addressing these questions will facilitate humanity's efforts to exploit aquatic volatiles in various applications.

Effects of different cultivation conditions on the production of β-cyclocitral and β-ionone in Microcystis aeruginosa

Background

Cyanobacteria blooms have become a major environmental problem and concern because of secondary metabolites produced by cyanobacteria released into the water. Cyanobacteria produce volatile organic compounds (VOCs), such as the compounds β-cyclocitral and β-ionone, which comprise odors, off-flavors, defense compounds, as well as growth regulators. Therefore, the general objective of this work was to evaluate the VOCs produced by two strains of Microcystis aeruginosa, differing in their ability to produce microcystins (LTPNA 01—non-producing and LTPNA 08—toxin-producing). The analysis of VOC production was carried out in (1) normal culture conditions, (2) under different light intensities (LI), and (3) after the external application of β-ionone in both cultures.

Results

The results showed that β-cyclocitral and β-ionone are produced in all growth phases of LTPNA 01 and LTPNA 08. Both strains were producers of β-cyclocitral and β-ionone in normal culture conditions. It was observed that the β-cyclocitral concentration was higher than β-ionone in all light intensities investigated in this study. Additionally, the strain LTPNA 01 produced more β-cyclocitral than LTPNA 08 at almost all times and LIs analyzed. However, the strain LTPNA 08 produced more β-ionone, mainly at the initial times. In addition, the experiment results with the external addition of β-ionone in the cultures showed that the strain LTPNA 01 produced more β-cyclocitral in control conditions than in treatment. Nonetheless, β-ionone production was higher in treatment conditions in LTPNA 08, indicating that the addition of β-ionone may favor the production of these compounds and inhibit the production of β-cyclocitral.

Conclusion

Our results showed that some abiotic factors, such as different light intensities and external application of β-ionone, can be triggers that lead to the production of VOCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02473-6.

Off-Flavors in Aquacultured Fish: Origins and Implications for Consumers

Off-flavors in fish and water are considered a worldwide problem. Several factors, such as the presence of phosphorus, micronutrients, and organic matter, contribute to phytoplankton proliferation and the production of off-flavors. Geosmin and 2-methylisoborneol are the most common off-flavors that confer the smell of earth or mold to water and fish. These metabolites are not considered toxic, but they can be easily transferred from water to living organisms and accumulate in the biota, up the trophic levels and to consumers, including fish species. Numerous processes have been studied to eliminate or reduce the presence of off-flavors in recirculating aquaculture systems. Managing off-flavors must be eco-friendly and consumer-friendly. Strategies against off-flavors must be efficient and low-cost. However, these solutions may be different for each fish production system. We review herein the main compounds produced by cyanobacteria that can accumulate in fish used in aquaculture that can affect the quality of food, as well as production costs and consumer preference.

[Elucidation of Phenomena Involving Cyanobacteria in Freshwater Ecosystem by Chemically Ecological Approach]

Lakes Sagami and Tsukui are reservoirs constructed by connecting to the Sagami River. Because of eutrophication of the lakes, cyanobacteria have appeared every year. This review deals with phenomena related to occurrence of cyanobacteria that have been observed for 40 years since 1974 at the lakes. These 40 years of observations raised three interesting issues including the retention of cyanobacteria on their surfaces. These phenomena have been attributed to the usual factors, such as illuminance, nutrition and water temperature, but our research results suggested that they cannot be resolved without the introduction of another factor. We have attempted to elucidate various phenomena involving cyanobacteria in lake ecosystems by chemical ecological methods using volatile organic compounds (VOCs) produced by the cyanobacteria as indicators. One of the VOCs, β-cyclocitral, was significantly involved in the above phenomena, which was considered to be produced by the carotenoid cleavage dioxygenase (CCD) of the cyanobacteria. β-Cyclocitral was not produced in the two known CCDs, but two additional CCDs to Microcystis aeruginosa participated to produce the β-cyclocitral. These CCDs did not directly produce β-cyclocitral, but it was accumulated in cells as their precursors. The released β-cyclocitral underwent a Baeyer-Villiger-like oxidation. It was speculated that Microcystis activated the CCD genes through density stress and produced β-cyclocitral, which acted as an allelopathic substance. As a result, the number of cells of cyanobacteria decreased, and the resulting nitrogen and phosphorus were fed to the living cyanobacteria. It is postulated that this "quorum sensing" was functioning in the above-mentioned issues.

Differences in susceptibility of cyanobacteria species to lytic volatile organic compounds and influence on seasonal succession

Cyanobacteria produce numerous volatile organic compounds (VOCs) that show a lytic activity against other cyanobacteria. We found the lytic phenomenon under natural conditions and during densification experiments, and also observed the species change of the cyanobacteria during the lysis processes, in which Microcystis finally became dominant. The species change of the cyanobacteria was strongly suggested to depend on the susceptibility of the cyanobacteria toward the VOCs. To verify this suggestion, the susceptibility of the species was evaluated by the minimal inhibitory concentration (MIC) using axenic cyanobacterial strains against β-cyclocitral, its oxidation products and β-ionone with the aid of log D. It was found that the difference depended on the susceptibility of the cyanobacteria toward the VOCs, in which β-cyclocitral played a crucial role and Microcystis had a significantly protective ability compared to the other cyanobacteria. In addition, the species change of cyanobacteria was consistent with the cyanobacterial seasonal succession in Lakes Sagami and Tsukui, based on data that had been accumulated for 10 years. Conventionally, although this phenomenon could be explained by nutrient availability or the physical structure of the environment, the results of this study revealed that it was controlled by the VOCs, particularly β-cyclocitral produced by the cyanobacteria.

Involvement of several putative transporters of different families in β-cyclocitral-induced alleviation of cadmium toxicity in quinoa (Chenopodium quinoa) seedlings

Cadmium (Cd) has a serious negative impact on crop growth and human food security. This study investigated the alleviating effect of β-cyclocitral, a potential heavy metal barrier, on Cd stress in quinoa seedlings and the associated mechanisms. Our results showed that β-cyclocitral alleviated Cd stress-induced growth inhibition in quinoa seedlings and promoted quinoa seedling root development under Cd stress. Moreover, it maintained the antioxidant system of quinoa seedlings, including the enzymatic, i.e., superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and nonenzymatic, i.e., reduced glutathione (GSH) and ascorbic acid (ASA), antioxidants, which eliminate the damage from excessive reactive oxygen species (ROS). Our results showed that β-cyclocitral could reduce the amount of Cd absorbed by roots. Furthermore, we systematically identified five transporter families from the quinoa genome, and the RT-qPCR results showed that ZIP, Nramp and YSL gene families were downregulated by β-cyclocitral to reduce Cd uptake by roots. Thus, β-cyclocitral promoted the growth, photosynthetic capacity and antioxidant capacity of the aboveground parts of quinoa seedlings. Taken together, these results suggested that the β-cyclocitral-induced decrease in Cd uptake may be caused by the downregulation of several selected transporter genes.

Antimicrobial activity against Microcystis aeruginosa and degradation of microcystin-LR by bacteria isolated from Antarctica

Cyanobacteria massive proliferations are common in freshwater bodies worldwide, causing adverse effects on aquatic ecosystems and public health. Numerous species develop blooms. Most of them correspond to the toxic microcystin-producing cyanobacterium Microcystis aeruginosa. Microorganisms recovered from Antarctic environment can be considered an unexploited source of antimicrobial compounds. Data about their activity against cyanobacteria are scant or inexistent. This study aimed to evaluate the capacity of Antarctic bacteria to inhibit the proliferation of M. aeruginosa BCPUSP232 and to degrade microcystin-LR (MC-LR). Cell-free extracts of seventy-six bacterial strains were initially tested for antimicrobial activity. Unidentified (UN) strains 62 and ES7 and Psychromonas arctica were able to effectively lyse M. aeruginosa. Eight strains showed MIC ranging from 0.55 to 3.00 mg mL^-1, with ES7 showing the best antimicrobial activity. Arthrobacter sp. 443 and UN 383 were the most efficient in degrading MC-LR, with 24.87 and 23.85% degradation, respectively. To our knowledge, this is the first report of antimicrobial and MC-LR degradation activities by Antarctic bacteria, opening up perspectives for their future application as an alternative or supporting approach to help mitigate cyanobacterial blooms.

Bioprospecting of Coralline Red Alga Amphiroa rigida J.V. Lamouroux: Volatiles, Fatty Acids and Pigments

Due to the lack of phytochemical composition data, the major goals of the present study on Amphiroa rigida J.V. Lamouroux were to: (a) investigate and compare volatilome profiles of fresh and air-dried samples obtained by headspace solid-phase microextraction (HS-SPME) and hydrodistillation (HD) followed by gas chromatography and mass spectrometry (GC/MS) analysis; (b) determine fatty acids profile by gas chromatography with flame ionization detector (GC-FID); (c) obtain the pigment profiles of semipurified extracts by high performance liquid chromatography (HPLC) and (d) evaluate the antioxidant and antimicrobial activities of its less polar fractions. The comparison of headspace of fresh (FrAr) and air-dried (DrAr) samples revealed many similarities regarding the presence and abundance of the major (heptadecane and pentadecane) and minor compounds. The hydrodistillate (HD) of DrAr profile was quite different in comparison to HD-FrAr. The predominant compound in HD-FrAr was (E)-phytol. In HD-DrAr, its percentage was approximately one-half reduced, but the abundance of its degradation product phytone and of unsaturated and oxygenated compounds increased indicating more intense fatty acid decomposition and oxidation during drying. The fatty acid determination revealed that the most dominant was palmitic acid (42.86%) followed by eicosapentaenoic acid (19.14%) and stearic acid (11.65%). Among the pigments, A. rigida contained fucoxanthin (0.63 mg g⁻¹ of dry fraction), lutein (5.83 mg g⁻¹), β-carotene (6.18 mg g⁻¹) and chlorophyll a (13.65 mg g⁻¹). The analyzed less polar fractions of A. rigida exhibited antioxidant scavenging activity with diammonium salt of 2,2′-azino-bis (3-ethylbenzthiazolin-6-yl) sulfonic acid (ABTS) assay up to 3.87 mg g⁻¹ trolox equivalents (TE), and with the oxygen radical absorbance capacity (ORAC) assay up to 825.63 μmol g⁻¹ TE (with carotenoids as the major contributors).

Determination of Volatile Organic Compounds and Antibacterial Activity of the Amazonian Cyanobacterium Synechococcus sp. Strain GFB01

Cyanobacteria exhibit great biotechnological potential due to their capacity to produce compounds with various applicability. Volatile organic compounds (VOCs) possess low molecular weight and high vapor pressure. Many volatiles produced by microorganisms have biotechnological potential, including antimicrobial activity. This study aimed to investigate the VOCs synthesized by cyanobacterium Synechococcus sp. strain GFB01, and the influence of nitrate and phosphate on its antibacterial potential. The strain was isolated from the surface of the freshwater lagoon Lagoa dos Índios, Amapá state, in Northern Brazil. After cultivation, the VOCs were extracted by a simultaneous distillation-extraction process, using a Likens-Nickerson apparatus (2 h), and then identified by GC-MS. The extracts did not display inhibitory activity against the Gram-positive bacteria tested by the disk-diffusion agar method. However, the anti-Salmonella property in both extracts (methanol and aqueous) was detected. The main VOCs identified were heptadecane (81.32%) and octadecyl acetate (11.71%). To the best of our knowledge, this is the first study of VOCs emitted by a cyanobacterium from the Amazon that reports the occurrence of 6-pentadecanol and octadecyl acetate in cyanobacteria.

β-Cyclocitral and derivatives: Emerging molecular signals serving multiple biological functions

β-cyclocitral is a volatile short-chain apocarotenoid generated by enzymatic or non-enzymatic oxidation of the carotenoid β-carotene. β-cyclocitral has recently emerged as a new bioactive compound in various organisms ranging from plants and cyanobacteria to fungi and animals. In vascular plants, β-cyclocitral and its direct oxidation product, β-cyclocitric acid, are stress signals that accumulate under unfavorable environmental conditions such as drought or high light. Both compounds regulate nuclear gene expression through several signaling pathways, leading to stress acclimation. In cyanobacteria, β-cyclocitral functions as an inhibitor of competing microalgae and as a repellent against grazers. As a volatile compound, this apocarotenoid plays also an important role in intra-species and inter-species communication. This review summarizes recent findings on the multiple roles of β-cyclocitral and of some of its derivatives.

Bioaccumulation and Phytotoxicity and Human Health Risk from Microcystin-LR under Various Treatments: A Pot Study

Microcystin-LR (MC-LR) is prevalent in water and can be translocated into soil-crop ecosystem via irrigation, overflow (pollution accident), and cyanobacterial manure applications, threatening agricultural production and human health. However, the effects of various input pathways on the bioaccumulation and toxicity of MCs in terrestrial plants have been hardly reported so far. In the present study, pot experiments were performed to compare the bioaccumulation, toxicity, and health risk of MC-LR as well as its degradation in soils among various treatments with the same total amount of added MC-LR (150 μg/kg). The treatments included irrigation with polluted water (IPW), cultivation with polluted soil (CPS), and application of cyanobacterial manure (ACM). Three common leaf-vegetables in southern China were used in the pot experiments, including Ipomoea batatas L., Brassica juncea L., and Brassica alboglabra L. All leaf vegetables could bioaccumulate MC-LR under the three treatments, with much higher MC-LR bioaccumulation, especially root bioconcentration observed in ACM treatment than IPW and CPS treatments. An opposite trend in MC-LR degradation in soils of these treatments indicated that ACM could limit MC-LR degradation in soils and thus promote its bioaccumulation in the vegetables. MC-LR bioaccumulation could cause toxicity to the vegetables, with the highest toxic effects observed in ACM treatment. Similarly, bioaccumulation of MC-LR in the edible parts of the leaf-vegetables posed 1.1~4.8 fold higher human health risks in ACM treatment than in IPW and CPS treatments. The findings of this study highlighted a great concern on applications of cyanobacterial manure.

Interspecific competition between Microcystis aeruginosa and Pseudanadaena and their production of T&O compounds

Microcystis aeruginosa and Pseudanabaena are two common cyanobacterial species/genus and they can occur coincidently in many eutrophic lakes globally. These two cyanobacteria could produce Taste & Odor (T&O) compounds, and their production of T&O compounds might be changed when they are present coincidently. The amounts of T&O compounds and their producers may influence the effectiveness of water treatment processes. Therefore, the mutual interactions between Microcystis aeruginosa (FACHB-905, M) and Pseudanabaena sp. (FACHB-1277, P) on T&O compounds in co-cultures were evaluated in this study. Different initial cell concentrations of M and P, with ratios of M:P = 1:1, M:P = 1:2 and M:P = 2:1 were applied in the co-cultures. The growth of M was enhanced under all of the cyanobacterial cell ratios. The growth of P was enhanced under the ratio of M:P = 1:1, while it was inhibited under the ratios of M:P = 1:2 and M: P = 2:1. In addition, the growth of the two cyanobacteria and their production of β-cyclocitral and 2-methylisoborneol (2-MIB) in the filtrate of P were higher than those in the filtrate of M, which may be attributed to their associated secondary metabolites. The cell integrity and photosynthetic capacity of the two studied cyanobacteria are greatly affected by exposure to β-cyclocitral and 2-MIB. The results showed that β-cyclocitral and 2-MIB had the allelopathic effects on the two cyanobacteria species which might influence the composition of co-existing cyanobacteria and their production of T&O compounds.

Microbial community analysis and correlation with 2-methylisoborneol occurrence in landscape lakes of Beijing

The microbial community is an important factor influencing the health of the water ecosystem in landscape lakes; in particular, proliferation of some cyanobacteria could cause odor problems. Exploring the microbial community is important for water quality management. In this study, focusing on seven landscape lakes in Beijing, the microbial communities were investigated based on 16S rRNA gene amplicon sequencing, and typical odor-causing compounds and interfering factors were identified. The results showed that 2-methylisoborneol (MIB) was the major odor-causing compound responsible for the earthy/musty odor in landscape lakes. For algal communities, Chlorella and Diatoms were the main eukaryote algae in the water. The bacterial community was dominated by Proteobacteria at the phylum level, and then Cyanobacteria, Actinobacteria, and Firmicutes, etc., most of which were the major phyla of the heterotrophic bacterial population. The richness and diversity of bacteria in natural-water-source lakes were higher than those in reclaimed-water-source lakes. Synechococcus (Cyanobacteria) and GKS98 (Proteobacteria) in reclaimed-water-source lakes were higher than those in natural-water-source lakes, however, CL500-29 (Actinobacteria) in natural-water-source lakes was higher than that in reclaimed-water-source lakes. These bacteria also had significantly positive correlations with MIB. Cyanobacteria and Actinobacteria were the main MIB compound contributors to the variability of MIB in the landscape lakes in Beijing.

Analytical Technique Optimization on the Detection of β-cyclocitral in Microcystis Species

β-Cyclocitral, specifically produced by Microcystis, is one of the volatile organic compounds (VOCs) derived from cyanobacteria and has a lytic activity. It is postulated that β-cyclocitral is a key compound for regulating the occurrence of cyanobacteria and related microorganisms in an aquatic environment. β-Cyclocitral is sensitively detected when a high density of the cells is achieved from late summer to autumn. Moreover, it is expected to be involved in changes in the species composition of cyanobacteria in a lake. Although several analysis methods for β-cyclocitral have already been reported, β-cyclocitral could be detected using only solid phase micro-extraction (SPME), whereas it could not be found at all using the solvent extraction method in a previous study. In this study, we investigated why β-cyclocitral was detected using only SPME GC/MS. Particularly, three operations in SPME, i.e., extraction temperature, sample stirring rate, and the effect of salt, were examined for the production of β-cyclocitral. Among these, heating (60 °C) was critical for the β-cyclocitral formation. Furthermore, acidification with a 1-h storage was more effective than heating when comparing the obtained amounts. The present results indicated that β-cyclocitral did not exist as the intact form in cells, because it was formed by heating or acidification of the resulting intermediates during the analysis by SPME. The obtained results would be helpful to understand the formation and role of β-cyclocitral in an aquatic environment.

Fresh Ideas Bloom in Gut Healthcare to Cross-Fertilize Lake Management

Harmful bacteria may be the most significant threat to human gut and lake ecosystem health, and they are often managed using similar tools, like poisoning with antibiotics or algicides. Out-of-the-box thinking in human microbiome engineering is leading to novel methods, like engineering bacteria to kill pathogens, "persuade" them not to produce toxins, or "mop up" their toxins. The bacterial agent can be given a competitive edge via an exclusive nutrient, and they can be engineered to commit suicide once their work is done. Viruses can kill pathogens with specific DNA sequences or knock out their antibiotic resistance genes using CRISPR technology. Some of these ideas may work for lakes. We critically review novel methods for managing harmful bacteria in the gut from the perspective of managing toxic cyanobacteria in lakes, and discuss practical aspects such as modifying bacteria using genetic engineering or directed evolution, mass culturing and controlling the agents. A key knowledge gap is in the ecology of strains, like toxigenic vs nontoxigenic Microcystis, including allelopathic and Black Queen interactions. Some of the "gut methods" may have future potential for lakes, but there presently is no substitute for established management approaches, including reducing N and P nutrient inputs, and mitigating climate change.

The diversity, origin, and evolutionary analysis of geosmin synthase gene in cyanobacteria

The sesquiterpene geosmin, mainly originating from cyanobacteria, is considered one of the problematic odor compounds responsible for unpleasant-tasting and -smelling water episodes in freshwater supplies. The biochemistry and genetics of geosmin synthesis in cyanobacteria is well-elucidated and the geosmin synthase gene (geo) has been cloned and characterized in recent years. However, understanding the diversity, origin, and evolution of geo has been hindered by the limited availability of geo sequences to date. On the basis of the cloned geo sequences from16 filamentous geosmin-producing cyanobacterial species, representing 11 genera in Nostocales and Oscillatoriales, the diversity and evolution of geo in cyanobacteria was systematically analyzed in this study. Homologous alignment revealed that geo is highly conserved among the examined cyanobacterial species, with DNA sequence identities >0.72. Phylogenetic reconstruction and codon bias analysis based on geo suggest that cyanobacterial geo form a monophyletic branch with a common origin and ancestor for cyanobacteria, actinomycetes, and myxobacteria. The global ratio of nonsynonymous/synonymous nucleotide substitutions (dN/dS) was 0.125, which is substantially <1 and indicates strong purifying selection in the evolution of cyanobacterial geo. To add to further interest, horizontal gene transfer of cyanobacterial geo in evolutionary history was confirmed by the discovery of an incongruent coevolutionary relationship between geo and housekeeping genes 16S rDNA and rpoC. The present study enhances the fundamental understanding of cyanobacterial geo in diversity and evolution, and sheds light on the development of molecular assays for detection and molecular ecology research of geosmin-producing cyanobacteria.

Inhibition of cyanobacterial photosynthetic activity by natural ketones

Microbial volatiles have a significant impact on the physiological functions of prokaryotic and eukaryotic organisms. Various ketones are present in volatile mixtures produced by plants, bacteria, and fungi. Our earlier results demonstrated the inhibitory effects of soil bacteria volatiles, including ketones, on cyanobacteria. In this work, we thoroughly examined the natural ketones, 2-nonanone and 2-undecanone to determine their influence on the photosynthetic activity in Synechococcus sp. PCC 7942. We observed for the first time that the ketones strongly inhibit electron transport through PSII in cyanobacteria cells in vivo. The addition of ketones decreases the quantum yield of primary PSII photoreactions and changes the PSII chlorophyll fluorescence induction curves. There are clear indications that the ketones inhibit electron transfer from Q_A to Q_B , electron transport at the donor side of PSII. The ketones can also modify the process of energy transfer from the antenna complex to the PSII reaction center and, by this means, increase both chlorophyll fluorescence quantum yield and the chlorophyll excited state lifetime. At the highest tested concentration (5 mM) 2-nonanone also induced chlorophyll release from Synechococcus cells that strongly indicates the possible role of the ketones as detergents.

Effects of Bacillus subtilis on the growth, colony maintenance, and attached bacterial community composition of colonial cyanobacteria

In freshwater aquaculture ponds, application of algicidal Bacillus is a promising way in the control of cyanobacterial blooms. To best understand Bacillus algicidal characters and mechanisms in the field, different-sized colonial cyanobacteria were isolated from an aquaculture pond, and the effects of B. subtilis on their growth, colony maintenance, and colony-attached bacterial community composition were investigated. The results showed that B. subtilis could inhibit the growth of colonial cyanobacteria. Bigger-sized colonies isolated from the field could spontaneously disintegrate into smaller-sized colonies in the laboratory. Algicidal B. subtilis could accelerate the disintegration of colonies and decrease colony size. B. subtilis not only decreased the colony-attached bacterial community diversity but also changed its composition. B. subtilis increased the relative abundances of some attached bacterial genera, including Pseudomonas, Shewanella, Bacillus, Shinella, Rhizobium, and Ensifer. These bacteria with algicidal, microcystin-degrading, and flocculating activities might be an important contributor to algicidal effects of B. subtilis on colonial cyanobacteria.

Effects of hairy crab breeding on drinking water quality in a shallow lake

The Yangcheng Lake, connected to Taihu, is partly served as drinking water source for Suzhou, China; the temporal and spatial changes of water quality parameters of it are investigated in this study. The Yangcheng Middle Lake with aquaculture area and the Yangcheng East Lake with important water intake are chosen to make a comparative investigation of the relationship between crab breeding and water quality. Phytoplankton community and the composition of dissolved organic matters (DOM) at different areas of the Yangcheng Lake are characterized with spectral fluorescence signatures. Results reveal that biopolymers and humic substances (HS) are the two major DOM compositions in the Yangcheng Lake. In the Yangcheng Middle Lake, the COD_Mn concentration at the large breeding area was lower than that in most other areas; while the concentration of algae and HS fluorescence intensity are positively correlated with each other in the Yangcheng Middle Lake. Crab breeding could accelerate nitrogen transformation and utilization. In summer and winter, the cumulative risk of building up potential harmful by-products such as DPBs caused by the biopolymers and HS is greater; the breeding of hairy crabs could reduce biopolymers and improve drinking water safety.

Phenol and Cr(VI) removal using materials derived from harmful algal bloom biomass: Characterization and performance assessment for a biosorbent, a porous carbon, and Fe/C composites

Lake Erie experiences annual harmful algal blooms (HAB), but generated HAB biomass may provide a waste-based precursor for environmental remediation materials. Three classes of materials (i.e., algal powder biosorbent, porous carbon, and iron/carbon (Fe/C) composite) are prepared from HAB biomass. Algal powder is nonporous with diverse functional groups. Porous carbon, prepared via one-pot carbonization and activation, has surface area up to 430 m²/g. Fe/Cs are prepared by cultivating HAB biomass in iron-rich media, followed by one-pot pyrolysis. Fe/Cs have over 6 wt% iron (Fe⁰ and Fe₃O₄) and nitrogen doping (up to 4 wt%). Materials were applied in phenol and Cr(VI) removal tests to identify preferred products for use in water treatment applications. In deionized water, porous carbon removes the most phenol (52 mg/g), followed by algal powder (38 mg/g) and Fe/C (33 mg/g). Micropore volume and functional groups improve phenol removal. Cr(VI) removal follows: Fe/C (43 mg/g) > porous carbon (28 mg/g) > algal powder (17 mg/g), with synergistic adsorption and reduction elevating Fe/C's performance. Cr(VI) and phenol removal studies were completed with variable pH, ionic strength, and water composition to highlight application potential. This work proposes HAB biomass reuse for pollution control, investigating interaction mechanisms between materials and contaminants.

Why Algae Release Volatile Organic Compounds-The Emission and Roles

A wide spectrum of volatile organic compounds (VOCs) are released from algae in aquatic ecosystems. Environmental factors such as light, temperature, nutrition conditions and abiotic stresses affect their emission. These VOCs can enhance the resistance to abiotic stresses, transfer information between algae, play allelopathic roles, and protect against predators. For homogeneous algae, the VOCs released from algal cells under stress conditions transfer stress information to other cells, and induce the acceptors to make a preparation for the upcoming stresses. For heterogeneous algae and aquatic macrophytes, the VOCs show allelopathic effects on the heterogeneous neighbors, which benefit to the emitter growth and competing for nutrients. In cyanobacterial VOCs, some compounds such as limonene, eucalyptol, β-cyclocitral, α-ionone, β-ionone and geranylacetone have been detected as the allelopathic agents. In addition, VOCs can protect the emitters from predation by predators. It can be speculated that the emission of VOCs is critical for algae coping with the complicated and changeable aquatic ecosystems.

Rapid detection of taste and odor compounds in water using the newly invented chemi-ionization technique coupled with time-of-flight mass spectrometry

Taste and odor (T&O) compounds are widespread in water environments and have attracted considerable public attention. Nowadays, the standard detections of these chemicals rely mainly on off-line methods such as GC-MS or evaluation by trained analysts' senses. In this study, we report a method for the rapid detection of T&O compounds in water by exploiting a newly invented chemi-ionization source, in combination with headspace vapor measurement at room temperature. The calibrated limits of detection (LODs) of 2-methylbutyraldehyde, methyl tert-butyl ether (MTBE), methyl methacrylate (MMA), 2-isobutyl-3-methyoxypyrazine (IBMP), and 2-isopropyl-3-methoxypyrazine (IPMP) are in the range of 3.5-50.2 ng L^-1, and the estimated LODs of 2-methylisoborneol (2-MIB) and geosmin (GSM) are 0.25 and 0.77 ng L^-1, respectively. The calibration results reveal that the instrumental LODs for 2-methylbutyraldehyde, MTBE, MMA, β-cyclocitral, 2-MIB, and GSM are 1-2 orders of magnitude better than the odor thresholds of humans. The accuracy, precision, recovery, and linearity (R²) of the method are tested. Water samples from city tap water and three rivers in Beijing are assessed using this technique, and the typical T&O compositions are observed with concentrations ranging from 0.2 to 297 ng L^-1. The new ultra-sensitive rapid detection method shows comparable sensitivities to the existing off-line technique and displays great potential for real-time detection of T&O pollution in water environments.

The role of algae and cyanobacteria in the production and release of odorants in water

This review covers literatures pertaining to algal and cyanobacterial odor problems that have been published over the last five decades. Proper evaluation of algal and cyanobacterial odors may help establish removal strategies for hazardous metabolites while enhancing the recyclability of water. A bloom of microalgae is a sign of an anthropogenic disturbance in aquatic systems and can lead to diverse changes in ecosystems along with increased production of odorants. In general, because algal and cyanobacterial odors vary in chemistry and intensity according to blooming pattern, it is necessary to learn more about the related factors and processes (e.g., changes due to differences in taxa). This necessitates systematic and transdisciplinary approaches that require the cooperation of chemists, biologists, engineers, and policy makers.

Relationship of Microbiota and Cyanobacterial Secondary Metabolites in Planktothricoides-Dominated Bloom

The identification of phytoplankton species and microbial biodiversity is necessary to assess water ecosystem health and the quality of water resources. We investigated the short-term (2 days) vertical and diel variations in bacterial community structure and microbially derived secondary metabolites during a cyanobacterial bloom that emerged in a highly urbanized tropical reservoir. The waterbody was largely dominated by the cyanobacteria Planktothricoides spp., together with the Synechococcus, Pseudanabaena, Prochlorothrix, and Limnothrix. Spatial differences (i.e., water depth) rather than temporal differences (i.e., day versus night) better-explained the short-term variability in water quality parameters and bacterial community composition. Difference in bacterial structure suggested a resource-driven distribution pattern for the community. We found that the freshwater bacterial community associated with cyanobacterial blooms is largely conserved at the phylum level, with Proteobacteria (β-proteobateria), Bacteroidetes, and Actinobacteria as the main taxa despite the cyanobacterial species present and geographical (Asia, Europe, Australia, and North America) or climatic distinctions. Through multivariate statistical analyses of the bacterial community, environmental parameters, and secondary metabolite concentrations, we observed positive relationships between the occurrences of cyanobacterial groups and off-flavor compounds (2-methyisoborneol and β-ionone), suggesting a cyanobacterial origin. This study demonstrates the potential of 16S rRNA gene amplicon sequencing as a supporting tool in algal bloom monitoring or water-resource management.

Spatial distributions of β-cyclocitral and β-ionone in the sediment and overlying water of the west shore of Taihu Lake

After large-scale outbreaks of algal blooms in eutrophic water, considerable amounts of algae residue accumulate in near-shore zones before fermenting rapidly and becoming malodorous. Taste and odor pollution caused by secondary metabolites from cyanobacterial blooms has become a serious and widespread environmental problem. Two typical odorous compounds, β-cyclocitral and β-ionone, have gained increasing attention in recent years. In this paper, the spatial distributions of β-cyclocitral and β-ionone in the sediments and overlying water off the west shore of Taihu Lake were investigated. The results showed that β-cyclocitral, β-ionone and nutrients are released during the degradation of fresh cyanobacteria, especially in the early stages. The odorous compounds and nutrients greatly decreased as the depth of sediment increased, indicating that reed roots can absorb β-cyclocitral, β-ionone and nutrients. Furthermore, removing cyanobacteria and dredging sludge might reduce the release of β-cyclocitral and β-ionone.

Characteristic oxidation behavior of β-cyclocitral from the cyanobacterium Microcystis

The cyanobacterium Microcystis produces volatile organic compounds such as β-cyclocitral and 3-methyl-1-butanol. The lysis of cyanobacteria involving the blue color formation has been occasionally observed in a natural environment. In this study, we focused on the oxidation behavior of β-cyclocitral that contributed to the blue color formation in a natural environment and compared β-cyclocitral with a structurally related compound concerning its oxidation, acidification, and lytic behavior. The oxidation products of β-cyclocitral were identified by the addition of β-cyclocitral in water, in which 2,2,6-trimethylcyclohex-1-ene-1-yl formate and 2,2,6-trimethylcyclohexanone were structurally characterized. That is, β-cyclocitral was easily oxidized to produce the corresponding carboxylic acid and the enol ester in water without an oxidizing reagent, suggesting that this oxidation proceeded according to the Baeyer-Villiger oxidation. The oxidation behavior of β-cyclocitral in a laboratory was different from that in the natural environment, in which 2,2,6- trimethylcyclohexanone was detected at the highest amount in the natural environment, whereas the highest amount in the laboratory was β-cyclocitric acid. A comparison of β-cyclocitral with structurally similar aldehydes concerning the lytic behavior of a Microcystis strain and the acidification process indicated that only β-cyclocitral was easily oxidized. Furthermore, it was found that a blue color formation occurred between pH 5.5 and 6.5, suggesting that chlorophyll a and β-carotene are unstable and decomposed, whereas phycocyanin was stable to some extent in this range. The obtained results of the characteristic oxidation behavior of β-cyclocitral would contribute to a better understanding of the cyanobacterial life cycle.

The common bloom-forming cyanobacterium Microcystis is prone to a wide array of microbial antagonists

Many degraded waterbodies around the world are subject to strong proliferations of cyanobacteria - notorious for their toxicity, high biomass build-up and negative impacts on aquatic food webs - the presence of which puts serious limits on the human use of affected water bodies. Cyanobacterial blooms are largely regarded as trophic dead ends since they are a relatively poor food source for zooplankton. As a consequence, their population dynamics are generally attributed to changes in abiotic conditions (bottom-up control). Blooms however generally contain a vast and diverse community of micro-organisms of which some have shown devastating effects on cyanobacterial biomass. For Microcystis, one of the most common bloom-forming cyanobacteria worldwide, a high number of micro-organisms (about 120 taxa) including viruses, bacteria, microfungi, different groups of heterotrophic protists, other cyanobacteria and several eukaryotic microalgal groups are currently known to negatively affect its growth by infection and predation or by the production of allelopathic compounds. Although many of these specifically target Microcystis, sharp declines of Microcystis biomass in nature are only rarely assigned to these antagonistic microbiota. The commonly found strain specificity of their interactions may largely preclude strong antagonistic effects on Microcystis population levels but may however induce compositional shifts that can change ecological properties such as bloom toxicity. These highly specific interactions may form the basis of a continuous arms race (co-evolution) between Microcystis and its antagonists which potentially limits the possibilities for (micro)biological bloom control.

Role of bacteria in the production and degradation of Microcystis cyanopeptides

The freshwater cyanobacteria, Microcystis sp., commonly form large colonies with bacteria embedded in their mucilage. Positive and negative interactions between Microcystis species and their associated bacteria have been reported. However, the potential role of bacteria in the production and degradation of cyanobacterial secondary metabolites has not been investigated. In this study, a Microcystis‐associated bacterial community was isolated and added to the axenic M. aeruginosaPCC7806 liquid culture. After 3 years of cocultivation, we studied the bacterial genetic diversity adapted to the PCC7806 strain and compared the intra‐ and extracellular concentration of major cyanopeptides produced by the cyanobacterial strain under xenic and axenic conditions. Mass spectrometric analyses showed that the intracellular concentration of peptides was not affected by the presence of bacteria. Interestingly, the produced peptides were detected in the axenic media but could not be found in the xenic media. This investigation revealed that a natural bacterial community, dominated by Alpha‐proteobacteria, was able to degrade a wide panel of structurally varying cyclic cyanopeptides.

Spatial and Temporal Variations of Taste and Odor Compounds in Surface Water, Overlying Water and Sediment of the Western Lake Chaohu, China

The seasonal variations of taste and odor (T&O) compounds in western Lake Chaohu were evaluated from July to December 2013. High values were detected in particulate fractions, with peak values 28.25 ng/L for geosmin (GEO), 45.18 ng/L for dimethyltrisulfide (DMTS), 714.77 ng/L for β-cyclocitral, 11.23 ng/L for β-ionone in surface water, and 14.21 ng/L for GEO, 103.68 ng/L for DMTS, 11.97 ng/L for β-ionone in overlying water, all exceeding their odor thresholds. The maximum off-flavor concentrations in sediment ranged from 2010.76 ng/kg for GEO to 1.7 ng/kg for β-ionone. Positive correlations could be found not only between Anabaena and particulate GEO (r = 0.813, p < 0.01), but also between Microcystis and total β-cyclocitral (r = 0.652, p < 0.01) or β-ionone (r = 0.560, p < 0.01) in surface water. TP, TN, PO4-P, Chl-a and organic matter contributed significantly to the variations of T&O compounds in water or sediment. The cause of the variations of T&O compounds was the accumulation and degradation of cyanobacteria in water rather than nutrient-rich sediment.

Microcystis aeruginosa/Pseudomonas pseudoalcaligenes interaction effects on off-flavors in algae/bacteria co-culture system under different temperatures

We conducted an experiment to study the interaction effects of Microcystis aeruginosa and Pseudomonas pseudoalcaligenes on off-flavors in an algae/bacteria co-culture system at three temperatures (24, 28 and 32°C). Gas chromatography-mass spectrometry was applied to measure off-flavor compounds dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), 2-methylisoborneol, geosmin (GEO) and β-cyclocitral. During the lag phase of co-cultured M. aeruginosa (first 15days), P. pseudoalcaligenes significantly increased the production of DMS, DMTS and β-cyclocitral at all three temperatures. In the exponential phase of co-cultured M. aeruginosa (after 15days), M. aeruginosa became the main factor on off-flavors in the co-culture system, and β-cyclocitral turned to the highest off-flavor compound. These results also indicated that DMS, DMTS and β-cyclocitral were the main off-flavor compounds in our M. aeruginosa/P. pseudoalcaligenes co-culture system. Univariate analysis was applied to investigate the effects of M. aeruginosa and P. pseudoalcaligenes on the production of off-flavors. The results demonstrated that both M. aeruginosa and P. pseudoalcaligenes could increase the production of DMS and DMTS, while β-cyclocitral was mainly determined by M. aeruginosa. Our results also provide some insights into understanding the relationship between cyanobacteria and heterotrophic bacteria.

Cyanobacterial blue color formation during lysis under natural conditions

Cyanobacteria produce numerous volatile organic compounds (VOCs), such as β-cyclocitral, geosmin, and 2-methylisoborneol, which show lytic activity against cyanobacteria. Among these compounds, only β-cyclocitral causes a characteristic color change from green to blue (blue color formation) in the culture broth during the lysis process. In August 2008 and September 2010, the lysis of cyanobacteria involving blue color formation was observed at Lake Tsukui in northern Kanagawa Prefecture, Japan. We collected lake water containing the cyanobacteria and investigated the VOCs, such as β-cyclocitral, β-ionone, 1-propanol, 3-methyl-1-butanol, and 2-phenylethanol, as well as the number of cyanobacterial cells and their damage and pH changes. As a result, the following results were confirmed: the detection of several VOCs, including β-cyclocitral and its oxidation product, 2,2,6-trimethylcyclohexene-1-carboxylic acid; the identification of phycocyanin based on its visible spectrum; the lower pH (6.7 and 5.4) of the lysed samples; and characteristic morphological change in the damaged cyanobacterial cells. We also encountered the same phenomenon on 6 September 2013 in Lake Sagami in northern Kanagawa Prefecture and obtained almost the same results, such as blue color formation, decreasing pH, damaged cells, and detection of VOCs, including the oxidation products of β-cyclocitral. β-Cyclocitral derived from Microcystis has lytic activity against Microcystis itself but has stronger inhibitory activity against other cyanobacteria and algae, suggesting that the VOCs play an important role in the ecology of aquatic environments.

Inhibitory and toxic effects of volatiles emitted by strains of Pseudomonas and Serratia on growth and survival of selected microorganisms, Caenorhabditis elegans, and Drosophila melanogaster

In previous research, volatile organic compounds (VOCs) emitted by various bacteria into the chemosphere were suggested to play a significant role in the antagonistic interactions between microorganisms occupying the same ecological niche and between bacteria and target eukaryotes. Moreover, a number of volatiles released by bacteria were reported to suppress quorum-sensing cell-to-cell communication in bacteria, and to stimulate plant growth. Here, volatiles produced by Pseudomonas and Serratia strains isolated mainly from the soil or rhizosphere exhibited bacteriostatic action on phytopathogenic Agrobacterium tumefaciens and fungi and demonstrated a killing effect on cyanobacteria, flies (Drosophila melanogaster), and nematodes (Caenorhabditis elegans). VOCs emitted by the rhizospheric Pseudomonas chlororaphis strain 449 and by Serratia proteamaculans strain 94 isolated from spoiled meat were identified using gas chromatography-mass spectrometry analysis, and the effects of the main headspace compounds--ketones (2-nonanone, 2-heptanone, 2-undecanone) and dimethyl disulfide--were inhibitory toward the tested microorganisms, nematodes, and flies. The data confirmed the role of bacterial volatiles as important compounds involved in interactions between organisms under natural ecological conditions.

Streptomyces alboflavus RPS and its novel and high algicidal activity against harmful algal bloom species Phaeocystis globosa

Phaeocystis globosa blooms have frequently occurred along coastal waters and exerted serious impacts on ecological environments by releasing toxic hemolytic substances, forming nuisance foam, and causing oxygen depletion. An actinomycete strain RPS with high algicidal activity against P. globosa was isolated and identified as Streptomyces alboflavus, based on morphology, physiological and biochemical characteristics, and 16S rDNA sequence analysis. RPS lysed 95% of P. globosa within 48 h by releasing an extracellular active substance into the growth medium. The activity of RPS supernatant was sensitive to temperature at and above 50°C and insensitive to pH from 3 to 11. The molecular weight of the active substance was between 100 Da and 1000 Da, and approximately 90% of it was extracted by ethyl acetate. It was presumed that the active component efficiently inhibited the movement of P. globosa, caused the flagella to fall off the algae, and finally lysed the algal cells. RPS showed a wide target range against harmful algae. S. alboflavus RPS with high algicidal activity and such novel features of temperature and pH sensitivity, low molecular weight, algicidal process, and target range possesses great potential in the biological control of P. globosa blooms.

Streptomyces jiujiangensis sp. nov., isolated from soil in South China

An actinomycete capable of lysing cyanobacteria, strain JXJ 0074(T), was isolated from a soil sample collected from Jiangxi province, south China, and characterized by using polyphasic taxonomy. The new isolate showed morphological and chemotaxonomic properties typical of members of the genus Streptomyces. Phylogenetic analysis of the near-complete 16S rRNA gene sequence indicated that strain JXJ 0074(T) should be affiliated to the genus Streptomyces and exhibited highest similarities to Streptomyces shenzhenensis DSM 42034(T) (98.99 %) and Streptomyces lucensis NBRC 13056(T) (98.60 %), while the similarities to other members of the genus are lower than 98.22 % similarity. However, the DNA-DNA hybridization values between strain JXJ 0074(T) and S. shenzhenensis DSM 42034(T) or S. lucensis NBRC 13056(T) were 46.2 ± 2.6 and 32.6 ± 3.1 %, respectively. Thus, on the basis of the polyphasic data, strain JXJ 0074(T) represents a novel species of the genus Streptomyces, for which the name Streptomyces jiujiangensis sp. nov. is proposed. The type strain is JXJ 0074(T) (= BCRC 16953(T) = KCTC 29262(T)).

Renewable jet fuel

Novel strategies for sustainable replacement of finite fossil fuels are intensely pursued in fundamental research, applied science and industry. In the case of jet fuels used in gas-turbine engine aircrafts, the production and use of synthetic bio-derived kerosenes are advancing rapidly. Microbial biotechnology could potentially also be used to complement the renewable production of jet fuel, as demonstrated by the production of bioethanol and biodiesel for piston engine vehicles. Engineered microbial biosynthesis of medium chain length alkanes, which constitute the major fraction of petroleum-based jet fuels, was recently demonstrated. Although efficiencies currently are far from that needed for commercial application, this discovery has spurred research towards future production platforms using both fermentative and direct photobiological routes.

The biology of habitat dominance; can microbes behave as weeds?

Competition between microbial species is a product of, yet can lead to a reduction in, the microbial diversity of specific habitats. Microbial habitats can resemble ecological battlefields where microbial cells struggle to dominate and/or annihilate each other and we explore the hypothesis that (like plant weeds) some microbes are genetically hard-wired to behave in a vigorous and ecologically aggressive manner. These 'microbial weeds' are able to dominate the communities that develop in fertile but uncolonized--or at least partially vacant--habitats via traits enabling them to out-grow competitors; robust tolerances to habitat-relevant stress parameters and highly efficient energy-generation systems; avoidance of or resistance to viral infection, predation and grazers; potent antimicrobial systems; and exceptional abilities to sequester and store resources. In addition, those associated with nutritionally complex habitats are extraordinarily versatile in their utilization of diverse substrates. Weed species typically deploy multiple types of antimicrobial including toxins; volatile organic compounds that act as either hydrophobic or highly chaotropic stressors; biosurfactants; organic acids; and moderately chaotropic solutes that are produced in bulk quantities (e.g. acetone, ethanol). Whereas ability to dominate communities is habitat-specific we suggest that some microbial species are archetypal weeds including generalists such as: Pichia anomala, Acinetobacter spp. and Pseudomonas putida; specialists such as Dunaliella salina, Saccharomyces cerevisiae, Lactobacillus spp. and other lactic acid bacteria; freshwater autotrophs Gonyostomum semen and Microcystis aeruginosa; obligate anaerobes such as Clostridium acetobutylicum; facultative pathogens such as Rhodotorula mucilaginosa, Pantoea ananatis and Pseudomonas aeruginosa; and other extremotolerant and extremophilic microbes such as Aspergillus spp., Salinibacter ruber and Haloquadratum walsbyi. Some microbes, such as Escherichia coli, Mycobacterium smegmatis and Pseudoxylaria spp., exhibit characteristics of both weed and non-weed species. We propose that the concept of nonweeds represents a 'dustbin' group that includes species such as Synodropsis spp., Polypaecilum pisce, Metschnikowia orientalis, Salmonella spp., and Caulobacter crescentus. We show that microbial weeds are conceptually distinct from plant weeds, microbial copiotrophs, r-strategists, and other ecophysiological groups of microorganism. Microbial weed species are unlikely to emerge from stationary-phase or other types of closed communities; it is open habitats that select for weed phenotypes. Specific characteristics that are common to diverse types of open habitat are identified, and implications of weed biology and open-habitat ecology are discussed in the context of further studies needed in the fields of environmental and applied microbiology.