Biography
Tengxin Cao is a post doctor at Institute of Microbiology, Chinese Academy of Sciences. She was a PHD student at the Research Center for Eco-Environmental Science, Chinese Academy of Sciences (RCEES, CAS), Beijing. She focuses on the harmful cyanobacteria induced MIB problems in drinking water sources. She developed molecular biology methods to identify the odor producers, and revealed the distribution and driving factors of odor problems.
Education
Ph.D. Environmental Engineering | Research Center for Eco-Environmental Sciences, Chinese Academy of Science
B.A. Environmental Engineering | University of Science and Technology Beijing
Selected publications
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026 Controlling filamentous cyanobacterial blooms requires adaptive, weather-informed strategy
The global expansion of filamentous cyanobacteria threatens water security due to their production of toxins and taste-and-odor compounds. As subsurface dwellers, filamentous cyanobacteria are resistant to conventional nutrient and flocculation controls, exposing a management gap. We developed an adaptive, forecast-guided framework that integrates predictive modeling with precision sediment resuspension (SR), in which SR-associated light attenuation likely contributes substantially to bloom suppression. A 2023-2024 survey of 40 reservoirs in eastern China showed filamentous dominance of over 80% biomass in half the systems. An XGBoost model (R² = 0.57) identified September-October as the highest-risk period, with over 80% of reservoirs affected. SR efficacy is light-dependent: it suppresses growth under low irradiance but can promote it under high light if shading shifts irradiance into the optimal range for filamentous taxa. We optimized SR through modulated sediment flux (0.1-5.2 g L⁻¹) to dynamically attenuate light in response to real-time forecasts. Field validation confirmed forecast-guided SR effectively limited Pseudanabaena via light control. This ecology-based management provides a scalable framework for sustainable water security under changing climates.
Sediment stirred up, / light dims, filaments retreat— / forecasts guide the cure. -
025 Spatiotemporal decoupling of littoral and lacustrine geosmin dynamics: Implications for early warning in drinking water reservoirs
The relationship between cyanobacterial niche characteristics and the transport dynamics of harmful metabolites to drinking water intakes remains poorly understood. This study integrated a national survey with a five-year high-frequency monitoring program to characterize these dynamics, focusing on the potent odorant geosmin. The national investigation revealed that 14% of surveyed sites exceeded the odor threshold of 10 ng L-1, indicating a non-negligible risk. In the YQ Reservoir, Planktothrix agardhii was identified as a primary producer. Monitoring revealed a distinct spatiotemporal decoupling: shallow littoral zones functioned as production centers where P. agardhii biomass peaked 8 days prior to the lacustrine intake. Time-lagged correlation analysis indicated that littoral biomass predicts intake geosmin concentrations with a 5-week lead time (R2 = 0.41). Ammonium was identified as the key regulatory factor, exhibiting its strongest correlation with geosmin in littoral zones (R2 = 0.37), though this linkage attenuated during transport. This proposed mechanistic transport model and tiered framework shift surveillance from reactive intake sampling to proactive littoral sentinel stations, establishing a critical predictive window for preventive intervention in reservoir-dependent water supplies.
Littoral bloom foreshadows, / a five-week warning, then taste / downstream borne. -
023 Cyanobacterial crowding-out effects on metabolite partitioning: modeling 2-methylisoborneol (MIB) release dynamics and implications
2-Methylisoborneol (MIB), a potent cyanobacterial metabolite, impairs drinking water quality through taste-and-odor issues at trace concentrations. Despite its significant impact, the intracellular dynamics and environmental release mechanisms of MIB remain poorly characterized. We developed a mechanistic model of growth-phase dependent MIB release through controlled experiments with two producer strains. The model reveals that the extracellular MIB proportion ($f = e_{\text{MIB}}/t_{\text{MIB}}$) follows a consistent pattern: decreasing to a minimum at mid-log phase before rising and stabilizing ($f$: 0.4 to 0.6) during stationary phase, suggesting crowding-induced cell lysis drives release dynamics. Application of the model to Lake Taihu successfully reconstructed two odor events during 2022-2023, elucidating both the spatiotemporal development of MIB producers and identifying critical risk thresholds at ~15°C and >30°C under moderate light (0.1-0.4 mol m-2 d-1) - patterns undetectable by conventional monitoring. Our findings demonstrate that physiological transitions, rather than just biomass accumulation, control odorant release. This framework may extend to other algal metabolites (e.g., geosmin, cyanotoxins), offering broader predictive capability. By linking cellular processes to water quality risks, our approach enables proactive management of cyanobacterial contaminants, informing both early warning systems and operational guidance for oxidant-type optimization to prevent large-scale release of hazardous compounds from algal cells.
A scent on the water, / Born from a crowded cell's burst, / A warning grows cold. -
022 Effects of Oxygenation Resuspension on DOM Composition and Its Role in Reducing Dissolved Manganese in Drinking Water Reservoirs
Anaerobic conditions in source water sediments are a key driver of manganese (Mn) release in drinking water systems. Enhancing sediment oxidation can inhibit Mn release, but the mechanisms of Mn speciation under varying oxidative conditions remain unclear. This study examined sediment exposure to oxygenated water layers at controlled dissolved oxygen levels (0, 2, 5, 7 mg L-1) through laboratory simulations. Results showed Mn release is negatively correlated with DO ($R2=0.93$, $p$=0.034), with oxygen driving reactions between dissolved organic matter (C2 and C3 components) and forming functional groups (-OH, -COOH) that remove Mn through adsorption or complexation (C2: $R2$=0.57, $p$<0.001; C3: $R2$=0.53, $p$<0.001). Field studies in six reservoirs identified operational thresholds for sediment resuspension to mitigate Mn risks (compensation threshold: 17.4 μg L-1; risk threshold: China: 95.5 μg L-1; WHO: 70.8 μg L-1^). These findings clarify Mn-organic matter interactions and can provide practical guidance for Mn and algae removal in source water systems.
Mud whispers iron, / oxygen sings it silent— / clean water follows. -
021 Green Light Suppresses Cell Growth but Enhances Photosynthetic Rate and MIB Biosynthesis in PE-Containing Pseudanabaena
2-Methylisoborneol (MIB) is a notorious musty odorant in drinking water systems, produced by cyanobacteria during the biosynthesis of photosynthetic pigments. This study investigated the physiological adaptation of Pseudanabaena cinerea, a phycoerythrin (PE)-containing and MIB-producing cyanobacterium, by inducing chromatic acclimation under different light color. Our findings revealed that red light enhanced growth rates by stimulating the tricarboxylic acid (TCA) cycle and associated metabolic processes, while green light significantly increased photosynthetic pigment content and electron transport efficiency. MIB yield correlated nonlinearly with chlorophyll a (Chl a) content, modeled by a logarithmic-linear equation (R2 = 0.74, p < 0.01). This was supported by the strong correlation between mic and chlG gene expression at the RNA level (R2 = 0.85, p < 0.01). The model showed that <2% of carbon flux is allocated to MIB biosynthesis compared to Chl a production, indicating that MIB biosynthesis is synergistic, not competitive, with photosynthetic pigment production. The red-shift in light spectra due to increased water turbidity observed in the field led to changes in photosynthetic pigments, which decreased MIB levels. This study improves our understanding of MIB-producing cyanobacteria under variable light conditions and offers insights for mitigating MIB occurrences in surface waters.
Red light fuels the growth, / Green deepens the pigments’ hue, / MIB’s quiet rise. -
020 Mitigating harmful cyanobacterial blooms in drinking water reservoirs through in-situ sediment resuspension
Mitigating harmful cyanobacterial blooms is a global challenge, particularly crucial for safeguarding source water. Given the limitations of current technologies for application in drinking water reservoirs, we propose an innovative strategy based on in-situ sediment resuspension (SR). This method's effectiveness in cyanobacterial control and its potential impacts on water quality were assessed through laboratory culture experiments and further validated via field applications in five drinking water reservoirs. The results revealed that SR could significantly mitigate cyanobacterial growth, evidenced by the treated sets (removal rate: 3.82×106 cells L-1 d-1) compared to the control set (growth rate: 2.22×107 cells L-1 d-1) according to the laboratory experiments. The underlying mechanisms identified included underwater light reduction (2.38× increase in extinction coefficient) and flocculation and entrainment of cells by resuspended particles (30% reduction per operation). Additional contributions were noted in the reduction of bioavailable phosphate and remediation of anaerobic sediment characterized by increased redox potential. This facilitated the oxidation of iron, which in turn promoted the co-precipitation of phosphate (removal rate: 46 μg L-1 d-1) and inhibited its release from the sediment. The SR operation, devoid of importing extra substances, represents a safe and economical technology for controlling harmful cyanobacteria in drinking water reservoirs.
Cyanobacterial bloom in source water? / No solution? Try / in-situ Sediment Resuspension -
019 Early warning of MIB episode based on gene abundance and expression in drinking water reservoirs
Cellular 2-methylisoborneol (MIB) yield of cyanobacteria varies under different conditions according to culture studies and field investigations, the causal mechanism remains unclear and results in ineffective MIB prediction. Through an intensive field survey during an MIB episode produced by Pseudanabaena cinerea in QCS reservoir, we demonstrated that MIB synthesis (mic) gene abundance (DNA) and expression (RNA) might be useful as parameters for early warning of MIB production. It was found that the abundance of mic DNA and RNA peaked ahead of MIB concentrations by 10 and 7 days, respectively. In addition, the RNA abundance (R2 = 0.45, p < 0.01) showed a slightly higher correlation with MIB compared to DNA abundance (R2 = 0.37, p < 0.01), suggesting that the conditions for the growth of Pseudanabaena cinerea might be slightly different from those for mic gene expression, which was verified by a culture experiment. The highest cell growth was obtained under 36 μmol photons m-2 s-1, while the highest cellular MIB yield and mic gene expression level were obtained under 85 μmol photons m-2 s-1. Our results clearly supported that light intensity was the virtual regulator governing the mic gene expression within the controlled culture experiment and the actual MIB episode in the reservoir. Besides these results, we developed an early warning model using mic gene abundance as an indicator of MIB episodes, which was verified in two other reservoirs. Our findings highlight the effect of light intensity on mic gene expression and MIB synthesis and provide an early warning tool targeting MIB episode prediction, which therefore should be of importance for source water authorities.
How to know when MIB episode comes? / Gene may tell you. Try / qPCR with mic gene! -
018 MIB-derived odor management based upon hydraulic regulation in small drinking water reservoirs: Principle and application
The musty odorant (2-methylisoborneol, MIB) is prevalent in source water reservoirs and has become one of the major challenges for drinking water quality. This study proposes an approach to control the growth of MIB-producing cyanobacteria in a small reservoir based on hydraulic regulation, according to the results of long-term field investigations, laboratory culture experiments, model construction, and field application. Field investigations found that longer hydraulic retention time (HRT) is a factor that triggers MIB episodes. The culture study revealed that the maximum cell density, growth rate of MIB-producing Planktothricoides raciborskii, and MIB concentration are determined by the HRT (R2= 0.94, p-value < 0.001) and can be minimized by decreasing the HRT to less than 10 $d$. On this basis, an HRT regulation model was constructed and validated by field investigation, and critical HRT values were evaluated for 14 cyanobacteria genera. By decreasing the HRT to 5.4 ± 0.8 $d$, which is lower than the critical value of 7.5 ~ 15.0 $d$, an MIB episode was successfully terminated in ZXD Reservoir in 2021. The results suggest that the proposed principle can provide a scientific basis for HRT regulation, which has been proved to be effective and feasible. This approach avoids negative impacts on water quality, does not require extra investment in engineering infrastructure, and in some cases may be applied readily by changing existing operational procedures. Therefore, HRT-based regulation is a promising strategy targeting MIB control and possibly for other cyanobacterial-derived water quality problems in small reservoirs.
Small reservoirs / Adjust HRT to halt / MIB odors. -
017 Driving forces for the growth of MIB-producing Planktothricoides raciborskii in a low-latitude reservoir
In comparison with the middle- and high-latitude regions, the low-latitude regions are less associated with the occurrence of 2-methylisoborneol (MIB) episodes, since most of the previously identified MIB producers favor moderate/low light/temperature conditions. Here, we report a serious MIB outbreak over the period from Jul. 2018 to Jun. 2019 in a low-latitude reservoir with a mean annual water temperature of 25.6 °C. The MIB episode lasted for a long period, from Jul. 2018 to Jan. 2019, and Planktothricoides raciborskii was confirmed to be the main MIB producer. The growth characteristics of P. raciborskii were explored through both laboratory culturing and on-site verification experiments. The results indicated that this strain was not nutrient-sensitive at TN > 800 μg L−1 and TP > 10 μg L−1, but favored moderate light intensity (54 μmol photon m−2·s−1) and high temperature (30 °C). The two bloom-forming genera, Limnothrix and Aphanizomenon, favoring lower temperature and similar or relatively higher light intensity, showed much greater proliferation, about 13 folds (Limnothrix) and 58 folds (Aphanizomenon), from Dec. to Jun.; by contrast, the high water temperature (29.9 ± 2.8 °C) and light intensity (189.1 ± 87.6 μmol photon m−2·s−1) from Jul. to Nov. were not favorable to Limnothrix or Aphanizomenon, which might have created an opportunity for the growth of MIB-producing P. raciborskii. In addition, we also found that high temperature could promote the release of MIB from P. raciborskii cells, therefore exerting increased pressure on drinking water treatment processes.
MIB persists long / Warm reservoirs bloom anew / Odor challenges. -
015 Evaluation of the MIB-producing potential based on real-time qPCR in drinking water reservoirs
Cyanobacteria release 2-methylisoborneol (MIB) as a secondary metabolite. Here, we propose a reverse transcription quantitative real-time PCR (RT-qPCR) based method to evaluate the MIB-producing potential in source water by detecting the MIB-synthesis gene (mic). A MIBQSF/R primer set was designed based on 35 mic gene sequences obtained from 12 pure-cultured MIB-producing strains and 23 sequences from the NCBI database. This primer set successfully identified all known 43 MIB-producing cyanobacterial strains (12 from this study and 31 from the NCBI database), belonging to different genera, showing a wider coverage than previous primer sets. The efficiency of the method was proved by the amplification efficiency (E = 91.23%), R2 of the standard curve (0.999), the limit of detection (LOD, 5.7 fg μL−1), and the limit of quantification (LOQ, 1.86 × 104 gene copies μL−1). Further, the method was verified by the correlation between the mic gene abundance and MIB concentration 50 field samples from different reservoirs (R2 = 0.614, p < 0.001) and one reservoir (R2 = 0.752, p < 0.001), suggesting its potential as an alternative warning tool to evaluate the risk of MIB problems in source water.
Green light promotes / MIB synthesis and PE / Odor risks increase -
014 Light-Dominated Selection Shaping Filamentous Cyanobacterial Assemblages Drives Odor Problem in a Drinking Water Reservoir
Filamentous cyanobacteria have substantial niche overlap, and the causal mechanism behind their succession remains unclear. This has practical significance since several filamentous genera are the main producers of the musty odorant 2-methylisoborneol (MIB), which lead to odor problems in drinking water. This study investigates the relationships between two filamentous cyanobacteria, the MIB-producing genus Planktothrix and the non-MIB-producing genus Pseudanabaena, in a drinking water reservoir. We firstly identified their niche characteristics based on a monitoring dataset, combined this information with culture experiments and developed a niche-based model to clarify these processes. The results reveal that the optimal light requirements of Pseudanabaena (1.56 mol m-2d-1) are lower than those of Planktothrix (3.67 mol m-2d-1); their light niche differentiation led to a fundamental replacement of Planktothrix (2013) by Pseudanabaena (2015) along with MIB decreases in this reservoir during 2013 and 2015. This study suggests that light is a major driving force responsible for the succession between filamentous cyanobacteria, and that subtle niche differentiation may play an important role in shaping the filamentous cyanobacterial assemblages that drives the MIB odor problems in drinking water reservoirs.
Light shapes their niche / Pseudanabaena reigns / Odors subside slow
DOI