Characterization of an algicidal bacterium Brevundimonas J4 and chemical defense of Synechococcus sp. BN60 against bacterium J4

As part of efforts to enhance the strategies explored to eliminate the adverse impacts of cyanobacterial blooms, we isolated an algicidal bacterium, J4, from Lake Taihu. Analysis of 16S rDNA sequence revealed that strain J4 belonged to the genus Brevundimonas. Bacterium J4 exhibited algicidal activity mainly through excretion of extracellular algicidal compounds that were further extracted with methanol and purified by silica gel chromatography and high performance liquid chromatography (HPLC). The compounds showed thermal stability, strong polarity and water solubility in J4 cultures. Study on the algicidal activity of J4 against two dominant cyanobacterial bloom-forming species in Lake Taihu showed that J4 exhibited lower algicidal rate against Synechococcus sp. BN60 (48.6%, t = 6 days) than against Microcystis aeruginosa 9110 (91.8%, t = 6 days). Additionally, rapid reduction in cell density of J4 was observed in co-cultures of Synechococcus sp. BN60 and bacterium J4 but not observed in co-cultures of M. aeruginosa 9110 and bacterium J4 during algicidal process, which was the main reason why the algicidal rate of J4 against BN60 was lower than against 9110. The reduction in cell density of J4 resulted from inducible production of antimicrobial-like compound secreted by Synechococcus sp. BN60 in co-cultures of Synechococcus sp. BN60 and bacterium J4, which reflected a kind of chemical defense from cyanobacteria (BN60) against algicidal bacteria (J4). However, M. aeruginosa 9110 had no chemical defense against J4, suggesting that whether cyanobacterial chemical defense occurs or not between cyanobacteria and algicidal bacteria depends on specific cyanobacteria–algicidal bacteria pairs. These results show that not only one-sided algicidal effect but also two-sided reciprocal inhibition interactions exist between algicidal bacteria and cyanobacteria, indicating the complexity of cyanobacteria–algicidal bacteria interactions in Lake Taihu and the need to take the cyanobacterial defensive responses into consideration when assessing potential use of algicidal bacteria.     

Isolation and Identification of Algicidal Compound from Streptomyces and Algicidal Mechanism to Microcystis aeruginosa

The biological control of cyanobacterial harmful algal blooms (cyanoHABs) is important to promote human health, environmental protection, and economic growth. Active algicidal compounds and algicidal mechanisms should be identified and investigated to control cyanoHABs. In this study, the algicidal actinobacterium Streptomyces sp. L74 was isolated from the soil of a nearby pond which located in the center lake of Guanghzou Higher Education Mega Center. Results showed that the algicidal activities of cyanoHABs are mainly achieved via an indirect attack by producing algicidal compounds. All active algicidal compounds are hydrophilic substances that are heat and pH stable. In the present study, an active compound (B3) was isolated and purified by high-performance liquid chromatography and identified as a type of triterpenoid saponin (2-hydroxy-12-oleanene-3, 28-O-D-glucopyranosyl) with a molecular formula of C₄₂H₇₀O₁₃ as determined by infrared spectrometry, electrospray ionization mass spectrometry, and nuclear magnetic resonance. Active algicidal compounds from Streptomyces sp. L74 were shown to disrupt the antioxidant systems of Microcystis aeruginosa cells.     

Toxic Effect of a Marine Bacterium on Aquatic Organisms and Its Algicidal Substances against Phaeocystis globosa

Harmful algal blooms have caused enormous damage to the marine ecosystem and the coastal economy in China. In this paper, a bacterial strain B1, which had strong algicidal activity against Phaeocystis globosa, was isolated from the coastal waters of Zhuhai in China. The strain B1 was identified as Bacillus sp. on the basis of 16S rDNA gene sequence and morphological characteristics. To evaluate the ecological safety of the algicidal substances produced by strain B1, their toxic effects on marine organisms were tested. Results showed that there were no adverse effects observed in the growth of Chlorella vulgaris, Chaetoceros muelleri, and Isochrystis galbana after exposure to the algicidal substances at a concentration of 1.0% (v/v) for 96 h. The 48h LC₅₀ values for Brachionus plicatilis, Moina mongolica Daday and Paralichthys olivaceus were 5.7, 9.0 and 12.1% (v/v), respectively. Subsequently, the algicidal substances from strain B1 culture were isolated and purified by silica gel column, Sephadex G-15 column and high-performance liquid chromatography. Based on quadrupole time-of-flight mass spectrometry and PeakView Software, the purified substances were identified as prolyl-methionine and hypoxanthine. Algicidal mechanism indicated that prolyl-methionine and hypoxanthine inhibited the growth of P. globosa by disrupting the antioxidant systems. In the acute toxicity assessment using M. mongolica, 24h LC₅₀ values of prolyl-methionine and hypoxanthine were 7.0 and 13.8 g/L, respectively. The active substances produced by strain B1 can be considered as ecologically and environmentally biological agents for controlling harmful algal blooms.     

Growth stimulation of Microcystis aeruginosa by a bacterium from hyper-eutrophic water (Taihu Lake, China)

Cyanobacteria are the causative organisms of the algal blooms that occur in Taihu Lake. Dissolved organic nitrogen (DON) comprises a significant composition of nitrogen (N) pool in the water and may increase the nutrient source of microalgae. In the present study, we investigated the relationship between Microcystis aeruginosa, Pseudomonas sp. A3CT isolated from Taihu, and DON compounds. Co-incubation (3 days) of the bacterium with six DON compounds (four free amino acids and two combined amino acids) was collected as six decomposed DON solutions. The decomposed DON solutions of six compounds were used to test the stimulatory effect of nutrient regeneration by the bacterium. The growth of M. aeruginosa was significantly enhanced by the six decomposed DON solutions. M. aeruginosa grew much better under the six decomposed DON solutions than the corresponding undigested DON forms. Especially, the decomposed l-lysine solution, not only avoided the inhibiting effect of lysine on M. aeruginosa, but significantly promoted the cyanobacterial growth. Further chemical tests indicated that A3CT transformed DON into NH₄ ⁺, which was utilized by M. aeruginosa. These results demonstrate that the bacterium plays an important role in decomposing unavailable DON forms into available NH₄ ⁺, which suggests that the bacterium contributes to the fast growth of M. aeruginosa. Moreover, this phenomenon, in conjunction with previous studies, indicates that the responsible and effective way of harmful blooms is reducing the N and P inputs (including DON and DOP).     

The potential use of bacterium strain R219 for controlling of the bloom-forming cyanobacteria in freshwater lake

Cyanobacterial blooms become a serious environmental threat to the freshwater ecosystem, and several physical and chemical methods have been developed for controlling the blooms. In order to develop a biocontrol agent for controlling the blooms, we isolated a bacterial strain R219 that exhibited strong algicidal activity against the dominant bloom-forming species of Microcystis aeruginosa from Lake Tai in China. Based on 16S rDNA sequence analysis we determined the strain R219 to be Pseudomonas aeruginosa by the virtue of its sharing about 99.8% similarity with reference strains in the DNA databases. Biochemical and morphological tests were used to support the accurate identification as that of the bacterium P. aeruginosa. We also tested culture filtrate and ethyl acetate extract of strain R219 and showed both of them exhibited strong algicidal effect on the growth of M. aeruginosa at mid-exponential phase when the R219 filtrate and ethyl acetate extract were applied at various cell densities. Moreover, the P. aeruginosa filtrate showed high potency in removal of the mixed species bloom-forming cyanobacteria collected directly from the Lake Tai. When adding the filtrate of the strain R219 to the mixed-species cyanobacteria, the content of chlorophyll-a of the algae were reduced by as much as 80–90%. Oral acute toxicity assessment for strain R219 demonstrated that all the mice that received the broth or filtrate in doses of 0.5 or 2.0 g kg^?1 were alive without any immediate behavioral changes within 14 days of administration of either broth or filtrate. These results indicate that the strain R219 may have potential for a use in controlling the bloom-forming cyanobacteria in freshwater ecosystems.     

Competition between the cyanobacterium Microcystis aeruginosa and the diatom Cyclotella sp. under nitrogen-limited condition caused by dilution in eutrophic lake

The improvement of water quality in Lake Tega, Japan, has been carried out by dilution, causing the shift of dominant species from Microcystis aeruginosa to Cyclotella sp. in summer. The disappearance of Microcystis blooms would be related to dilution, but the detail effect has not been understood yet. In this study, the effect of nitrate concentration on the competition between M. aeruginosa and Cyclotella sp. was investigated through the single-species and the competitive culture experiments. The single-species culture experiment indicated that the half saturation constants for M. aeruginosa and Cyclotella sp. were 0.016 and 0.234?mg?N L^?1, representing that M. aeruginosa would possess a higher affinity to nitrate. On the other hand, the maximum growth rate for Cyclotella sp. was obtained as 0.418?day^?1, which did not represent a significant difference with 0.366?day^?1 obtained for M. aeruginosa. The competitive culture experiment revealed that Cyclotella sp. completely dominated over M. aeruginosa at the nitrate concentrations of 0.5 and 2.5?mg?N L^?1. The dominance of Cyclotella sp. could be attributed to the difference in the abilities of nitrate storage as well as nitrate uptake. One of the possibilities for the disappearance of Microcystis blooms caused by dilution as observed in Lake Tega could be due to the decrease in nitrate concentration, and the lower N:P ratio seemed not to relate to Microcystis blooms.     

Targeted deep sequencing reveals high diversity and variable dominance of bloom-forming cyanobacteria in eutrophic lakes

Cyanobacterial blooms in eutrophic lakes are severe environmental problems worldwide. To characterize the spatiotemporal heterogeneity of cyanobacterial blooms, a high-throughput method is necessary for the specific detection of cyanobacteria. In this study, the cyanobacterial composition of three eutrophic waters in China (Taihu Lake, Dongqian Lake, and Dongzhen Reservoir) was determined by pyrosequencing the cpcBA intergenic spacer (cpcBA-IGS) of cyanobacteria. A total of 2585 OTUs were obtained from the normalized cpcBA-IGS sequence dataset at a distance of 0.05. The 238 most abundant OTUs contained 92% of the total sequences and were classified into six cyanobacterial groups. The water samples of Taihu Lake were dominated by Microcystis, mixed Nostocales species, Synechococcus, and unclassified cyanobacteria. Besides, all the samples from Taihu Lake were clustered together in the dendrogram based on shared abundant OTUs. The cyanobacterial diversity in Dongqian Lake was dramatically decreased after sediment dredging and Synechococcus became exclusively dominant in this lake. The genus Synechococcus was also dominant in the surface water of Dongzhen Reservoir, while phylogenetically diverse cyanobacteria coexisted at a depth of 10 m in this reservoir. In summary, targeted deep sequencing based on cpcBA-IGS revealed a large diversity of bloom-forming cyanobacteria in eutrophic lakes and spatiotemporal changes in the composition of cyanobacterial communities. The genus Microcystis was the most abundant bloom-forming cyanobacteria in eutrophic lakes, while Synechococcus could be exclusively dominant under appropriate environmental conditions.     

Dual Roles of Cadaverine-Producing Pseudomonas sp. on Microcystis spp. in Hyper-Eutrophic Water

A bacterium isolated from Lake Taihu was identified as Pseudomonas sp. A3CT, which performed different effects on Microcystis spp. Growth of Microcystis flos-aquae and Microcystis aeruginosa was assessed in co-culture with A3CT to determine the stimulatory or inhibitory effects on these toxic, bloom-forming Microcystis strains. Results demonstrated that the impacts of A3CT were species specific. A3CT promoted the growth of M. aeruginosa but inhibited growth of M. flos-aquae. To investigate the cause of this phenomenon, the chemical composition of A3CT exudates and the impact of exposure to A3CT exudates on the two Microcystis species were determined. Results suggested that the observed differential growth responses of the two microalgae to A3CT exposure might be related to two components in A3CT exudates NH₄ ⁺ and cadaverine. Growth stimulation of M. aeruginosa by A3CT was significantly related to NH₄ ⁺ concentration. Cadaverine possibly acted as a growth inhibitor of M. flos-aquae. The different effects of cadaverine on growth of the two Microcystis strains suggested that A3CT might play a role in intrageneric succession patterns observed during Microcystis blooms in Lake Taihu.     

Effects of nitrogen on interspecific competition between two cell-size cyanobacteria: Microcystis aeruginosa and Synechococcus sp.

Micro-cyanobacteria and pico-cyanobacteria coexist in many lakes throughout the world. Their distinct cell sizes and nutrient utilization strategies may lead to dominance of one over the other at varying nutrient levels. In this study, Microcystis aeruginosa and Synechococcus sp. were chosen as representative organisms of micro- and pico-cyanobacteria, respectively. A series of nitrate and ammonia conditions (0.02, 0.1, 0.5, and 2.5 mg N L⁻¹) were designed in mono- or co-cultured systems, respectively. Growth rates of the two species were calculated and fitted by the Monod and Logistic equations. Furthermore, the interspecific competition was analyzed using the Lotka–Volterra model. In mono-cultures, the two cyanobacteria displayed faster growth rates in ammonia than in nitrate. Meanwhile, Synechococcus sp. showed faster growth rates compared to M. aeruginosa in lower N groups (≤ 0.5 mg N L⁻¹). However, in the highest nitrate treatment (2.5 mg N L⁻¹), M. aeruginosa achieved much higher biomass and faster growth rates than Synechococcus sp.. In co-cultures, Synechococcus sp. dominated in the lowest N treatment (0.02 mg N L⁻¹), but M. aeruginosa dominated under the highest nitrate condition (2.5 mg N L⁻¹). Based on the analysis of Raman spectra of living cells in mono-cultures, nitrate (2.5 mg N L⁻¹) upgraded the pigmentary contents of M. aeruginosa better than ammonia (2.5 mg N L⁻¹), but nitrogen in different forms showed little effects on the pigments of Synechococcus sp.. Findings from this study can provide valuable information to predict cyanobacterial community succession and aquatic ecosystem stability.     

Dynamics of cyanophage-like particles and algicidal bacteria causing Microcystis aeruginosa mortality

The dynamics of cyanophage-like particles and algicidal bacteria that infect the bloom-forming cyanobacterium Microcystis aeruginosa was followed in a hyper-eutrophic pond from September 1998 to August 1999. The densities of M. aeruginosa ranged between 4.0 × 10⁵ and 1.9 × 10⁷ cells ml⁻¹, whereas those of algicidal bacteria were between 4.0 and 5.1 × 10² plaque-forming units (PFU) ml⁻¹ and those of cyanophage-like particles were between <5.0 × 10² and 7.1 × 10³ PFU ml⁻¹. A significant relationship was found between the densities of algicidal bacteria and M. aeruginosa (r = 0.81, n = 69, P < 0.001), suggesting that the dynamics of the algicidal bacteria may regulate the abundance of M. aeruginosa. Occasional peaks of density of cyanophage-like particles were detected in October, June, and August, when sharp declines in M. aeruginosa cell densities were also observed. The densities of cyanophage-like particles became undetectable when the abundance of M. aeruginosa was low, suggesting the density-dependent infection of M. aeruginosa by cyanophage-like particles. Thus, we suggest that infections of both algicidal bacteria and cyanophage-like particles are important biological agents that decompose blooms of M. aeruginosa in freshwater environments. Received: August 31, 2000 / Accepted: December 6, 2000     

A novel actinomycete Streptomyces aurantiogriseus with algicidal activity against the toxic cyanobacterium Microcystis aeruginosa

A novel actinomycete strain (PK1) was isolated from soil in Khon Kaen Province, Thailand, and was capable of inhibiting the cyanobacterium Microcystis aeruginosa. The isolate PK1 was identified as Streptomyces aurantiogriseus based on an analysis of biochemical and morphological characteristics and 16S rDNA sequence. The algicidal activity of PK1 against M. aeruginosa depended on the growth phase of PK1, but not on the cyanobacterial growth phase. Stationary growth phase cultures of the strain PK1 exhibited the highest anti-Microcystis activity when co-cultivated with M. aeruginosa. Complete growth inhibition was observed after 8 days of co-cultivation in liquid culture medium. The algicidal compounds were extracted from PK1 with ethyl acetate and then purified by silica gel column chromatography. These partially purified compounds demonstrated algicidal activity against M. aeruginosa, suggesting that the strain PK1 provides a potential source of extracellular compounds for the control of M. aeruginosa bloom. This is the first report of anti-cyanobacterial activity from the soil actinomycete S. aurantiogriseus.     

Application of Bayesian network including Microcystis morphospecies for microcystin risk assessment in three cyanobacterial bloom-plagued lakes,China

Microcystis spp., which occur as colonies of different sizes under natural conditions, have expanded in temperate and tropical freshwater ecosystems and caused seriously environmental and ecological problems. In the current study, a Bayesian network (BN) framework was developed to access the probability of microcystins (MCs) risk in large shallow eutrophic lakes in China, namely, Taihu Lake, Chaohu Lake, and Dianchi Lake. By means of a knowledge-supported way, physicochemical factors, Microcystis morphospecies, and MCs were integrated into different network structures. The sensitive analysis illustrated that Microcystis aeruginosa biomass was overall the best predictor of MCs risk, and its high biomass relied on the combined condition that water temperature exceeded 24 °C and total phosphorus was above 0.2 mg/L. Simulated scenarios suggested that the probability of hazardous MCs (≥1.0 μg/L) was higher under interactive effect of temperature increase and nutrients (nitrogen and phosphorus) imbalance than that of warming alone. Likewise, data-driven model development using a naïve Bayes classifier and equal frequency discretization resulted in a substantial technical performance (CCI = 0.83, K = 0.60), but the performance significantly decreased when model excluded species-specific biomasses from input variables (CCI = 0.76, K = 0.40). The BN framework provided a useful screening tool to evaluate cyanotoxin in three studied lakes in China, and it can also be used in other lakes suffering from cyanobacterial blooms dominated by Microcystis.     

Novel algicidal evidence of a bacterium Bacillus sp. LP-10 killing Phaeocystis globosa,a harmful algal bloom causing species

While searching for effective bio-agents to control harmful algal blooms (HABs), the bacterial strain LP-10, which has strong algicidal activity against Phaeocystis globosa (Prymnesiophyceae), was isolated from surface seawater samples taken from the East China Sea. 16S rDNA sequence analysis and morphological characteristics revealed the strain LP-10 belonged to the genus Bacillus. The lytic effect of Bacillus sp. LP-10 against P. globosa was both concentration- and time-dependent. Algicidal activities of different growth stages of the bacterial culture varied significantly. The lytic effect of different parts of the bacterial cultures indicated that the algal cells were lysed by algicidal active compounds in the cell-free filtrate. Analysis of the properties of the active compounds showed that they had a molecular weight of less than 1000 Da and that the active compounds were stable between −80 and 121 °C. The algicidal range assay indicated that five other algal species were also suppressed by strain LP-10, including: Alexandrium catenella, A. tamarense, A. minutum, Prorocentrum micans and Asterionella japonica. Our results suggested that the algicidal bacterium Bacillus sp. LP-10 could be a potential bio-agent to control the blooms of harmful algal species.     

The Algicidal Characteristics of One Algae-Lysing FDT5 Bacterium on Microcystis aeruginosa

One strain of algicidal bacterium which can inhibit Harmful algal blooms (HABs), FDT5, was isolated from activated sludge and found to have good algicidal effects on Microcystis aeruginosa. It was revealed that: The FDT5 was a Gram-negative bacterium and identified as Ochrobactrum sp.; The greater the initial bacterial cell density, the faster the degradation of chlorophyll a.; The algicidal efficiency was evaluated at the most favorable conditions which were a temperature of 30–35°C, a pH of 7.6 and complete darkness; The FDT5 strain lysed Microcystis aeruginosa not directly but by secreting metabolites which could withstand high temperatures and pressure.     

Novel rhodanine derivatives are selective algicides against <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis>

In this study, a series of rhodanine derivatives containing various substituents was synthesized and tested for in vitro algicidal activity. Among the tested substituent groups, phenyl substituents with halogen groups showed good inhibitory potency. Furthermore, the compound with chlorine at the C2 position of the phenyl ring exhibited a higher algicidal effect than the compound with chlorine at the C3 position of the phenyl ring. Among the various rhodanine derivatives tested, 5-(2,4-dichlorobenzylidene)- rhodanine (compound 20) was the most potent inhibitor against M. aeruginosa with a lethal concentration 50 (LC₅₀) value of 0.65 μM and Selenastrum capricornutum with an LC₅₀ value of 0.82 μM. To verify the feasibility of their use in ecosystems, 25 h of acute ecotoxicity tests were carried out for three derivatives against Danio rerio and Daphnia magna. No mortality was observed in groups exposed to 2.0 μM of compound 20 after 100 h of exposure. Moreover, a survival rate of 100% was observed in D. magna exposed to 2 μM of compound 20 for 100 h. Overall, the results show that rhodanine derivatives are a possible method for controlling and inhibiting harmful algal blooms.     

Growth,death, and photobiology of dinoflagellates (Dinophyceae) under bacterial-algicide control

Naturally occurring allelopathic compounds, specific to some phytoplankton, may be a good source of bio-control agents against microalgae responsible for harmful algal blooms (HABs). Global expansion of HABs has invigorated research into different approaches to control these algae, including the search for naturally derived algicidal compounds. Here, we investigated the effects of a filtrate from the algicidal marine bacterium Shewanella sp. IRI-160 on photochemical function of four cultured dinoflagellates, Karlodinium veneficum, Gyrodinium instriatum, Prorocentrum minimum, and Alexandrium tamarense. The filtrate (designated IRI-160AA) contains bioactive compound(s), which were recently shown to inhibit growth of several dinoflagellate species. Results of this study show that all dinoflagellates but P. minimum exhibited photosystem II (PSII) inhibition, loss of photosynthetic electron transport, and varying degrees of cellular mortality. Exposure assays over 24 h showed that PSII inhibition and loss of cell membrane integrity occurred simultaneously in G. instriatum, but not in K. veneficum, where PSII activity declined prior to losing outer-membrane integrity. In addition, PSII inhibition and population growth inhibition were dose-dependent in K. veneficum, with an average EC-50 of 7.9 % (v/v) IRI-160AA. Application of IRI-160AA induced significantly higher PSII inhibition and cell mortality in K. veneficum subjected to continuous darkness as compared to cells maintained with 12:12 h light/dark cycles, while no such dark effect was noted for G. instriatum. The marked differences in the rate and impact of this algicide suggest that multiple cellular targets and different cascades of cellular dysfunction occur across these dinoflagellates.     

Novel L-amino acid oxidase with algicidal activity against toxic cyanobacterium Microcystis aeruginosa synthesized by a bacterium Aquimarina sp

A brownish yellow pigmented bacterial strain, designated antisso-27, was recently isolated from a water area of saltpan in Southern Taiwan. Phylogenetic analyses based on 16S rRNA gene sequences indicate that strain antisso-27 belongs the genus Aquimarina in the family Flavobacteriacea and its only closest neighbor is Aquimarina spongiae (96.6%). Based on screening for algicidal activity, strain antisso-27 exhibits potent activity against the toxic cyanobacterium Microcystis aeruginosa. Both the strain antisso-27 bacterial culture and its culture filtrate show algicidal activity against the toxic cyanobacterium, indicating that an algicidal substance is released from strain antisso-27. The algicidal activity of strain antisso-27 occurs during the late stationary phase of bacterial growth. Strain antisso-27 can synthesize an algicidal protein with a molecular mass of 190 kDa, and its isoelectric point is approximately 9.4. This study explores the nature of this algicidal protein such as l-amino acid oxidase with broad substrate specificity. The enzyme is most active with l-leucine, l-isoleucine, l-methionine and l-valine and the hydrogen peroxide generated by its catalysis mediates algicidal activity. This is the first report on an Aquimarina strain algicidal to the toxic M. aeruginosa and the algicidal activity is generated through its enzymatic activity of l-amino acid oxidase.     

Quantitative Tracing, by Taq Nuclease Assays, of a Synechococcus Ecotype in a Highly Diversified Natural Population

Quantitative Taq nuclease assays (TNAs) (TaqMan PCR), nested PCR in combination with denaturing gradient gel electrophoresis (DGGE), and epifluorescence microscopy were used to analyze the autotrophic picoplankton (APP) of Lake Constance. Microscopic analysis revealed dominance of phycoerythrin (PE)-rich Synechococcus spp. in the pelagic zone of this lake. Cells passing a 3-μm-pore-size filter were collected during the growth period of the years 1999 and 2000. The diversity of PE-rich Synechococcus spp. was examined using DGGE to analyze GC-clamped amplicons of a noncoding section of the 16S-23S intergenic spacer in the ribosomal operon. In both years, genotypes represented by three closely related PE-rich Synechococcus strains of our culture collection dominated the population, while other isolates were traced sporadically or were not detected in their original habitat by this method. For TNAs, primer-probe combinations for two taxonomic levels were used, one to quantify genomes of all known Synechococcus-type cyanobacteria in the APP of Lake Constance and one to enumerate genomes of a single ecotype represented by the PE-rich isolate Synechococcus sp. strain BO 8807. During the growth period, genome numbers of known Synechococcus spp. varied by 2 orders of magnitude (2.9 × 10³ to 3.1 × 10⁵ genomes per ml). The ecotype Synechococcus sp. strain BO 8807 was detected in every sample at concentrations between 1.6 × 10¹ and 1.3 × 10⁴ genomes per ml, contributing 0.02 to 5.7% of the quantified cyanobacterial picoplankton. Although the quantitative approach taken in this study has disclosed several shortcomings in the sampling and detection methods, this study demonstrated for the first time the extensive internal dynamics that lie beneath the seemingly arbitrary variations of a population of microbial photoautotrophs in the pelagic habitat.