Invisible microbial language in cyanobacterial blooms should not be overlooked: The potential impact of quorum sensing for cyanobacteria community

Cyanobacterial blooms are becoming more common in freshwater systems, causing ecological degradation and human health risks through exposure to cyanotoxins. The role of phosphorus and nitrogen in cyanobacterial bloom formation is well documented and these are regularly the focus of management plans. There is also strong evidence that trace metals are required for a wide range of cellular processes, however their importance as a limiting factor of cyanobacterial growth in ecological systems is unclear. Furthermore, some studies have suggested a direct link between cyanotoxin production and some trace metals. This review synthesises current knowledge on the following: (1) the biochemical role of trace metals (particularly iron, cobalt, copper, manganese, molybdenum and zinc), (2) the growth limitation of cyanobacteria by trace metals, (3) the trace metal regulation of the phytoplankton community structure and (4) the role of trace metals in cyanotoxin production. Iron dominated the literature and regularly influenced bloom formation, with 15 of 18 studies indicating limitation or colimitation of cyanobacterial growth. A range of other trace metals were found to have a demonstrated capacity to limit cyanobacterial growth, and these metals require further study. The effect of trace metals on cyanotoxin production is equivocal and highly variable. Better understanding the role of trace metals in cyanobacterial growth and bloom formation is an essential component of freshwater management and a direction for future research.

Promoting effect and mechanism of residual feed organic matter on the formation of cyanobacterial blooms in aquaculture waters

藻类生长与营养盐浓度存在藻类几何级数增长的营养盐浓度变化的下限阈值和藻类生长不受氮磷浓度增加影响的上限阈值,但由于蓝藻水华的形成受多种因素的综合影响,不同湖泊、不同区域及不同时段的氮磷浓度对蓝藻水华的影响差别较大,使得蓝藻生长的氮磷控制阈值难以确定.针对控制蓝藻水华暴发的氮磷阈值的研究虽然有所开展,但多集中在实验室研究阶段或对经验值的判断,虽然也有基于野外实测数据的研究,但也限制于某一特定区域,而基于野外长序列实测数据并且覆盖整个湖泊的氮磷阈值研究则是空白.太湖作为具有较高营养背景的富营养化浅水湖泊,蓝藻水华的发生受氮磷影响较大.对太湖总磷(TP)、总氮(TN)和叶绿素a(Chl.a)浓度的时空变化分析发现,太湖西北湖区的TP、TN与Chl.a浓度明显较高,并且TP、TN与Chl.a均呈显著性正相关.为探究太湖蓝藻水华暴发的TP和TN控制阈值,以轻富营养化等级下的Chl.a分级标准(10,26]作为表征水华暴发的条件,采用郑丙辉等的频率分布法,确定了太湖蓝藻水华暴发的TP和TN控制阈值分别为0.05~0.06和1.71~1.72 mg/L;通过空间验证,太湖藻型区TP和TN浓度远高于同级营养水平下全湖区TP和TN控制阈值,表明藻型区高氮磷水平为蓝藻水华发生提供充足营养盐条件,即使氮磷全湖平均浓度控制在蓝藻水华暴发的氮磷阈值水平之下,但在气象水文等因素适宜条件下,藻型区水华发生风险仍然较高;并且在高氮磷背景下,即便在水华发生风险低的季节,水华发生风险仍然较大.近十几年来,虽然太湖经历了大规模的高强度治理,但由于环太湖流域的湖西区入湖负荷占比大,导致太湖藻型区氮磷浓度仍处于高位运行状态,为蓝藻水华的暴发提供了充足的营养盐基础,因此,湖西区的控源减排仍然是太湖富营养化及蓝藻水华防控的重点.;Algae growth and nutrient concentration has a lower threshold for algae affected by nutrient concentration with geometric increase and an upper threshold for algae that is not affected by the increase of nitrogen and phosphorus concentration. However, the formation of cyanobacterial blooms is affected by many factors, the effects of nitrogen and phosphorus on cyanobacterial blooms vary greatly in different lakes, different areas, and different periods, making it difficult to determine the nitrogen and phosphorus control thresholds for cyanobacteria growth. Although studies on nitrogen and phosphorus thresholds for algal growth and control of cyanobacterial blooms have been carried out, they are mostly focused on laboratory studies or empirical judgments. Although there are also studies based on field-measured data, they are also limited to a specific area, while studies on nitrogen and phosphorus thresholds based on long series of field measurements and covering the entire lake are lacking. As a eutrophic shallow lake with a high nutrient background, the occurrence of cyanobacterial blooms in Lake Taihu is strongly influenced by nitrogen and phosphorus. Analyzing the temporal and spatial changes of total phosphorus (TP), total nitrogen (TN) and chlorophyll-a concentration (Chl.a) in Lake Taihu, it is found that TP, TN and Chl.a in the northwestern of the lake were significantly higher, and TP, TN and Chl.a are all positively correlated. To investigate the control thresholds of TP and TN for cyanobacterial bloom outbreaks in Lake Taihu, the Chl.a grading standard (10, 26] under the light eutrophication level was used as the condition to characterize the bloom outbreak, referring to the frequency distribution method put forward by Zheng Binghui, the TP and TN control thresholds were determined to be 0.05-0.06 mg/L and 1.71-1.72 mg/L, respectively. Through spatial verification, the concentration of TP and TN in the phytoplankton-dominated area of Lake Taihu is much higher than the control thresholds of TP and TN in the whole lake area under the same nutritional level. This indicated that the high nitrogen and phosphorus levels in the phytoplankton-dominated area provide sufficient nutrient basis for the occurrence of cyanobacterial blooms. Even if the average concentration of nitrogen and phosphorus in the whole lake is controlled below the threshold level, the risk of algal blooms in the phytoplankton-dominated area is still relatively high under suitable conditions of meteorology and hydrology. In addition, under the background of high nitrogen and phosphorus in the phytoplankton-dominated area, even in the low-risk seasons for cyanobacterial blooms that were once considered, the possibility of blooms is still high. In the past ten years, although Lake Taihu has undergone large-scale and high-intensity treatment, the nitrogen and phosphorus concentrations in the phytoplankton-dominated area of Lake Taihu are still at a high level because of the large proportion of the inflow pollution load from Huxi District around Lake Taihu Basin, which provides sufficient nutrients for the cyanobacterial blooms. In consequence, source control and emission reduction in Huxi District is still the key measurement for the prevention and control of eutrophication and cyanobacterial blooms in Lake Taihu.

Effects of different metal ions (Ca, Cu, Pb, Cd) on formation of cyanobacterial blooms.

Antibiotic-accelerated cyanobacterial growth and aquatic community succession towards the formation of cyanobacterial bloom in eutrophic lake water

Nutrient reduction magnifies the impact of extreme weather on cyanobacterial bloom formation in large shallow Lake Taihu (China)

Cyanobacterial (algal) blooms have by convention been attributed to the excessive level of nutrients from pollution and runoff, which promotes the rapid growth and multiplication of cyanobacteria or algae. The cyanophage (virus) is the natural predator of cyanobacteria (the host). The aim of this review is to unveil certain pressures that disrupt cyanophage-host interactions and the formation of cyanobacterial blooms. This review focuses principally on the impact of greenhouse gases, ozone depletion, solar ultraviolet radiation (SUR) and the role of recently discovered virophages, which coexist with and in turn are the natural predator of phages. The key findings are that the increase in SUR, the mutation of cyanophages and cyanobacteria, along with changing nutrient levels, have combined with virophages to impede cyanophage-host interactions and the resultant viral infection and killing of the cyanobacterial cell, which is a necessary step in controlling cyanobacterial blooms. Consider this a 'call to action' for researchers interested in corrective action aimed at evolving aquatic ecosystems.

Effects of different fluid fields on the formation of cyanobacterial blooms

The influence of weather conditions (temperature and wind) on cyanobacterial bloom development in the Gulf of Finland (Baltic Sea)

Association between trophic state, watershed use, and blooms of cyanobacteria in south-central Chile

Short-term hydrodynamic fluctuations caused by extreme weather events are expected to increase worldwide because of global climate change, and such fluctuations can strongly influence cyanobacterial blooms. In this study, the cyanobacterial bloom disappearance and reappearance in Lake Taihu, China, in response to short-term hydrodynamic fluctuations, was investigated by field sampling, long-term ecological records, high-frequency sensors and MODIS satellite images. The horizontal drift caused by the dominant easterly wind during the phytoplankton growth season was mainly responsible for cyanobacterial biomass accumulation in the western and northern regions of the lake and subsequent bloom formation over relatively long time scales. The cyanobacterial bloom changed slowly under calm or gentle wind conditions. In contrast, the short-term bloom events within a day were mainly caused by entrainment and disentrainment of cyanobacterial colonies by wind-induced hydrodynamics. Observation of a westerly event in Lake Taihu revealed that when the 30 min mean wind speed (flow speed) exceeded the threshold value of 6 m/s (5.7 cm/s), cyanobacteria in colonies were entrained by the wind-induced hydrodynamics. Subsequently, the vertical migration of cyanobacterial colonies was controlled by hydrodynamics, resulting in thorough mixing of algal biomass throughout the water depth and the eventual disappearance of surface blooms. Moreover, the intense mixing can also increase the chance for forming larger and more cyanobacterial colonies, namely, aggregation. Subsequently, when the hydrodynamics became weak, the cyanobacterial colonies continuously float upward without effective buoyancy regulation, and cause cyanobacterial bloom explosive expansion after the westerly. Furthermore, the results of this study indicate that the strong wind happening frequently during April and October can be an important cause of the formation and expansion of cyanobacterial blooms in Lake Taihu.

Denitrification is a major process in aquatic ecosystems, and it competes with cyanobacterial growth for nitrogen. However, the effect of denitrification on cyanobacterial blooms under the background of climate change remains unclear. This study explored the interaction between lake denitrification and formation of cyanobacterial blooms, using the historical water quality monitoring data of North Lake Taihu over five years from 2017 to 2021 and via incubation experiments of cyanobacteria and sediment denitrification. The monitoring data showed that algal biomass (Chla as a proxy) primarily peaked during summer and autumn. The seasonal variations in total N concentration showed a completely opposite trend than that of algal biomass, which peaked in winter and spring. Nitrate was the major component of dissolved inorganic nitrogen, and the nitrate concentration was approximately zero in summer and autumn. The total phosphorus concentration varied in the same way as the Chla concentration. The experimental results showed that Cyanobacteria did not grow when the temperature was below 20℃. In comparison, denitrification showed a significant linear relationship with temperatures between 10-25℃ (R2=0.99) and reached the maximum value of (62.98±21.36) μmol·(kg·h)-1 in Lake Taihu at 25℃. Additionally, the nitrate concentration threshold at the maximum denitrification rate was 4 mg·L-1. Cyanobacteria assimilate nitrate for growth, thereby reducing the concentration of nitrate required for denitrification. This study indicated that the advance in lake temperature warming due to climate change may result in earlier growth of cyanobacteria, thereby leading to large amounts of N being assimilated by algae before denitrification, further affecting the dynamics of cyanobacterial blooms. The present results are scientifically important for explaining the mechanism of cyanobacterial bloom rebound in Lake Taihu under the background of recent climate changes.

The presence of high microcystin concentrations in cyanobacterial blooms additionally affects species diversity. Blooms with high toxin contents can reach higher cell densities, which is also demonstrated by microcystin cell contents. In vitro experiments show that microcystins influence phytoplankton proliferation. The action is strongly dependent on the phytoplankton species tested and light conditions. We propose that the environmental impact of different microcystins depends on their enzymatic inhibition activity and thus could not be measured merely on the basis of their toxicity to vertebrate species. Their role in heavy cyanobacterial bloom and scum formation is discussed, as well as their impact on the massive proliferation of other species following toxic cyanobacterial bloom degradation.

Prediction of the complex cyanobacteria-environment interactions is vital for understanding harmful bloom formation. Most previous studies on these interactions considered specific properties of cyanobacterial cells as representative for the entire population (e.g. growth rate, mortality, and photosynthetic capacity (Pmax)), and assumed that they remained spatiotemporally unchanged. Although, at the population level, the alteration of such traits can be driven by intraspecific competition, little is known about how traits and their plasticity change in response to environmental conditions and affect the bloom formation. Here we test the hypothesis that intraspecific variations in Pmax of cyanobacteria (Microcystis spp.) play an important role in its population dynamics. We coupled a one-dimensional hydrodynamic model with a trait-based phytoplankton model to simulate the effects of physical drivers (turbulence and turbidity) on the Pmax of Microcystis populations for a range of dynamic conditions typical for shallow eutrophic lakes. Our results revealed that turbulence acts as a directional selective driver for changes in Pmax. Depending on the intensity of daily-periodic turbulence, representing wind-driven mixing, a shift in population-averaged phenotypes occurred toward either low Pmax, allowing the population to capture additional light in the upper layers, or high Pmax, enhancing the efficiency of light utilization. Moreover, we observed that a high intraspecific diversity in Pmax accelerated the formation of surface scum by up to more than four times compared to a lower diversity. This study offers insights into mechanisms by which cyanobacteria populations respond to turbulence and underscores the significance of intraspecific variations in cyanobacterial bloom formation. Highlights

Agrochemicals such as herbicides change the physical and chemical conditions of aquatic ecosystems and alter the community structure and dynamics of phytoplankton. Cyanobacteria are photosynthetic organisms found at the base of aquatic food chains. When cyanobacteria form blooms and produce toxins, they harm humans and the environment. Herbicides contaminate the aquatic environment when they are leached and transported via surface runoff from farms and industries. In this review, we show that these compounds have different mechanisms of action, but at high concentrations, they cause oxidative stress, interfere with the normal functioning of enzymes, and change the metabolic profile of microalgae and cyanobacteria. This paper demonstrates that at environmentally relevant concentrations, some herbicides facilitate the formation of cyanobacterial harmful algal blooms (cyanoHABs). The formation of blooms is driven by the tolerance of cyanobacteria to herbicides, where some of these compounds are degraded and converted into non-toxic forms. The degradation by-products are also used as a source of nutrients to support cyanobacterial growth. This adaptation sometimes leads to higher concentrations of bioactive compounds such as cyanotoxins in the aquatic environment. The increased levels of cyanotoxins and herbicides in water bodies can trigger a cascading toxicological effect on non-targeted organisms and the aquatic food chain. Despite the evidence confirming herbicides influence the growth of cyanobacteria and alter the structure of the phytoplankton community toward the formation of cyanoHABs, there is a lot that remains to be done to fully understand their impact on these organisms.