Phagotrophic Algae Research Articles

Assemblage Patterns of Microalgae along the Upstream to Downstream Gradient of the Okavango Delta: Abundance, Taxonomic Diversity, and Functional Diversity

This study addresses the gap in understanding the diversity, species, and functional trait distribution of different algal groups that occur in the Okavango Delta (a near-pristine subtropical wetland in northwestern Botswana) across hydrological and habitat gradients. We systematically characterize the delta’s algal flora, addressing the gap left by previous research that was limited to single algal groups (e.g., diatoms) and/or only looking at upstream areas in the Okavango River basin. We analyzed 130 algal samples from 49 upstream and downstream sites with higher and lower flooding frequency, respectively, across a river-to-floodplain habitat gradient. Chlorophyta and Bacillariophyta dominated both abundance and taxon richness (>80%) of the total 494 taxa found from 49,158 algal units counted (cells, colonies, coenobia, and filaments). Smaller algae were more abundant in downstream floodplains than in upstream channels and lagoons. Motile and siliceous algae were much more abundant than non-motile, nitrogen fixing, and phagotrophic algae. The frequency of these traits was associated more with flooding frequency than habitat type. The highest algal richness and diversity were found downstream, where shallow floodplain ecosystems with seasonally fluctuating water depths offer greater habitat heterogeneity, and macronutrients are resuspended. The increasing threats from upstream water abstraction plans, fracking, and climate change require enhanced protection and monitoring of the Okavango Delta’s natural annual flood-pulse to maintain the high species and functional diversity of this unique wetland’s microalgae.

Responses of Phytoplanktonic Chlorophyll-a Composition to Inorganic Turbidity Caused by Mine Tailings

Inorganic turbidity can limit light penetration in water and reduce phytoplankton photosynthesis. Anthropogenic activities such as mining can produce or augment the amount of suspended inorganic particles in water. Recent mining disasters in Brazil have released tons of mine tailings into aquatic ecosystems, with known and unknown negative consequences for aquatic life, biodiversity, and ecosystem services beyond the human and material losses. Here, we investigated the effects of inorganic turbidity on phytoplankton chlorophyll content and composition caused by sediments from two areas in Lake Batata, one natural and the other impacted by bauxite tailings. We experimentally compared the effects of different levels of turbidity (12, 50, and 300 NTU) caused by the addition of sediments from the two lake areas on a chlorophyll-a gradient (5, 15, and 25 μg/L). Inorganic turbidity did not consistently reduce chlorophyll-a concentrations. In treatments with high chlorophyll-a, high turbidity was associated with lower chlorophyll-a concentrations at the end of the experiment. On the other hand, in low-chlorophyll treatments, high turbidity was associated with higher chlorophyll-a concentrations. In treatments with sediments from the natural area, overall chlorophyll-a levels were higher than in treatments with sediments from the impacted area. Phagotrophic algae dominated both in treatments with sediments from the impacted area (Chrysophyceae 34%, Chlorophyceae 26%, and Cyanobacteria 22% of total density) and in treatments with sediment from the natural area (Euglenophyceae 26%, Chrysophyceae 23%, and Chlorophyceae 20%). We conclude that high turbidity does not lead to a reduction in chlorophyll-a concentrations and sediment from the natural area allowed higher chlorophyll-a levels, indicating that impacted area sediment affected more phytoplankton.

Application of phagotrophic algae in waste activated sludge conversion and stabilization.

Phagotrophic algae can consume bacteria that are the predominant microorganisms present in the waste activated sludge (WAS) generated from municipal wastewater treatment processes. In this study, we developed a combined ultrasonication-phagotrophic algal process for WAS conversion. The ultrasonic pretreatment released small volatile solids (VS) including bacteria from WAS flocs. A phagotrophic alga Ochromonas danica then grew by consuming more than 80% of the released VS, with approximately 30% (w/w) algal cell yield. The process reduced the overall WAS VS by 42.4% in 1day, comparing very favorably with the 27% reduction in 10days by aerobic digestion. For stabilizing the solids remaining from the ultrasonic step, the total oxygen uptake required was 65%-92% lower than that for the original WAS, indicating substantially reduced aeration cost. Overall, this novel process enhanced the WAS digestion at lower energy requirements and produced microalgae for other potential uses. © 2021 Water Environment Federation PRACTITIONER POINTS: At least 80% of released VS from WAS can be processed by phagotrophic algae. Significant amounts of algae can be produced from WAS. Ultrasonication-phagotrophic algal process can make sludge management more sustainable.

Cultivation of phagotrophic algae with microbial cells released from waste activated sludge: An evaluation of different pretreatment methods to enhance release of microbial cells from sludge flocs

The application of phagotrophic algae in waste activate sludge (WAS) treatment can largely accelerate WAS organics reclamation rate, because the phagotrophic capability of phagotrophic algae on intact microbial cells provides an efficient and fast way to digest microbial cells, which eliminate the need of the time-consuming hydrolysis of WAS solid organics. In this research work, different pretreatment methods of anoxia, alkali, and ultrasound were compared in terms of efficiency in releasing microbial cells from WAS flocs and subsequent growth of phagotrophic algae. Results show that ultrasonic pretreatment was the most efficient method since it yielded the highest microbial cell release and subsequent algae growth, while requiring the shortest pretreatment time. Mathematical modelling shows that the release of microbial cells in anoxic and ultrasonic pretreatment was achieved mainly through breaking physical forces of attraction, while the release of microbial cells in alkali pretreatment was achieved through breaking ionic bonds. Re-floc of released microbial cells was observed during algae growth, and the microbial cells released through breaking ionic bonds were less liable to reform floc. The electricity consumption of ultrasonic pretreatment was the highest, which was 6.9 times and 17.9 times of that of alkali and anoxic pretreatment. The electricity consumption of ultrasonic pretreatment can be reduced by performing alkali pretreatment prior to ultrasonic pretreatment.

Phagotrophic algae in a wastewater stabilization pond

In the course of evolution, phagotrophic euglenoids developed before the phototrophic species. Most phagotrophic euglenoids have a robust feeding apparatus. Members of the algal genus Peranema are able to eat a wide variety of living organisms that have little or no mobility, such as other unicellular algae and live yeasts. Stabilization ponds are artificial environments rich in organic matter, nutrients and microorganisms, and are therefore suitable environments for growing species of Euglenophyta. This contribution records, through photographs and videos, the operation of the feeding apparatus of Peranema collected in a wastewater stabilization pond. The mean pheophytin content of the water was higher than the mean chlorophyll a content, which indicates a non-ideal environment for the growth of microalgae. Thus, Peranema can be used as a bioindicator of the quality of wastewater stabilization pond. The operation of the feeding apparatus of Peranema sp. and the strategy for phagocytizing plastids of Lepocinclis sp. are described.

Reclamation of wastewater organics via two-stage growth of bacteria-then-oleaginous phagotrophic algae.

A substantial amount of organic matter is wasted in current wastewater treatment processes. To reclaim the value of organic matter, a two-stage continuous-flow open process has been developed by utilizing the capability of phagotrophic algae in ingesting bacterial cells. In this process, wastewater is first pumped into a bacteria tank to grow bacterial cells, and then the effluent containing grown bacteria cells is fed to an algae tank to grow phagotrophic algae. The operation conditions such as dilution rate, pH, and dissolved oxygen level were comprehensively investigated and optimized with long-term tests. Results show that phagotrophic algae can be stably cultivated with wastewater organics through this open process without costly chemical/physical sterilization. The produced phagotrophic algae had high lipid content and can be potentially used as biofuel feedstock.

Linking patterns of net community production and marine microbial community structure in the western North Atlantic.

Marine net community production (NCP) tracks uptake of carbon by plankton communities and its potential transport to depth. Relationships between marine microbial community composition and NCP currently remain unclear despite their importance for assessing how different taxa impact carbon export. We conducted 16 and 18S rRNA gene (rDNA) sequencing on samples collected across the Western North Atlantic in parallel with high-resolution O2/Ar-derived NCP measurements. Using an internal standard technique to estimate in-situ prokaryotic and eukaryotic rDNA abundances per liter, we employed statistical approaches to relate patterns of microbial diversity to NCP. Taxonomic abundances calculated using internal standards provided valuable context to traditional relative abundance metrics. A bloom in the Mid-Atlantic Bight featured high eukaryote abundances with low eukaryotic diversity and was associated with the harmful algal bloom-forming Aureococcus anophagefferens, phagotrophic algae, heterotrophic flagellates, and particle-associated bacteria. These results show that coastal Aureococcus blooms host a distinct community associated with regionally significant peaks in NCP. Meanwhile, weak relationships between taxonomy and NCP in less-productive waters suggest that productivity across much of this region is not linked to specific microplankton taxa.

Energy-efficient ultrasonic release of bacteria and particulates to facilitate ingestion by phagotrophic algae for waste sludge treatment and algal biomass and lipid production

Wastewater treatment generates large amounts of waste activated sludge (WAS) that contains concentrated bacteria and particulate organics and requires costly treatment prior to disposal. This study develops an approach to harness the unique capability of oleaginous phagotrophic microalgae for treating WAS and producing algal biomass and lipids. WAS ultrasonication is studied for releasing particulates and bacteria suitable for direct ingestion by phagotrophic microalgae, without bacterial destruction/lysis, and thus minimizing energy requirement. Particle release into supernatant was followed by optical density at 610 nm (OD610) and volatile solid concentration (VS); OD610 correlated well with micron-size particle count rates measured by dynamic light scattering. Microalgae (Ochromonas danica) grew with a 7.6-h doubling time in sonication-generated WAS supernatant alone, giving approximately 66% (w/w) cell yield from consumed VS and ∼30% intracellular lipids. Effects of sonication power (P in W), WAS volume (V in mL) and sonication duration (t in s) were studied with a 3 × 3 × 6 factorial design. Supernatant OD610 increased with increasing P and t and decreasing V. Multiple linear regression gave the following equation with only significant terms: OD610TS=−0.0536+0.000592P−0.000213t+0.000003P×t+0.000274P×tV (R2 = 0.94). Sonicating 500-mL WAS at 180 W for 240 s was selected for giving high particulate release (∼29% VS) with maximal energy efficiency, corresponding to a specific energy input of 4320 kJ (kg TS)−1, which was much lower than the range (15,000–250,000 kJ (kg TS)−1) reported previously for WAS ultrasonication. The results supported development of new ultrasonication-phagotrophic algae processes for WAS treatment and algae production.

Enhancement of resource recovery and sludge digestion by cultivation of phagotrophic algae with alkali-pretreated waste activated sludge and waste ketchup

Abstract The reclamation of waste activated sludge (WAS) organics is often impeded by the long time required for the solid organic matter to solubilize. Here we introduce a fast approach to reclaim WAS by using phagotrophic algae. Phagotrophic algae have unique ability of growing by ingesting insoluble organic particles, which makes the solubilization of WAS organic matter unnecessary and largely accelerates the WAS digestion rate. To facilitate this approach, alkali treatment was evaluated at different pH and time and optimized at pH 10 for 6 h to release microbial cells and other organics from the WAS flocs. Then the alkali-treated WAS was fed to phagotrophic algae. In later experiments, the addition of readily consumable organics, such as waste ketchup (WK), was found to enhance the percentage reduction of WAS organics and algae yield. With WK addition at 0.118:1 (w/w) WK-to-WAS organics, 46–49% of the WAS organic matter was digested within 22 h. The lipid content was 20.8% in the treated biosolids, increased from 6.8% in the original WAS. With the fast digestion rate and high lipid production ability, this new approach has strong potential to improve WAS digestion and utilization.

Growth and Lipid Production of a Phagotrophic Alga Feeding on Escherichia coli Cells: A New Approach for Algal Biomass and Lipid Production from Wastewater Bacteria

Abstract Production of algae as renewable resources has been pursued actively. Attention has so far been focused on phototrophic algae. Explored here is a completely different approach that harnesses the growth ability of phagotrophic algae on microorganisms such as bacteria, which are abundantly present in waste, including activated sludge generated in wastewater treatment plants. Escherichia coli, a common bacterium, was used as an example of bacterial feed for the oleaginous phagotrophic alga Ochromonas danica. Growth characteristics and lipid contents of O. danica were determined under various conditions. Algal doubling time could be as short as 7 h, but increased to >20 h at low starting E. coli-to-O. danica ratios. The alga was also sensitive to step changes of pH and darkness. Without these factors, phagotrophic growth was similar in a wide range of conditions, even under total darkness and in deionized water with washed E. coli as the only food source. O. danica grew on E. coli with an average yie...

Autotrophic and heterotrophic acquisition of carbon and nitrogen by a mixotrophic chrysophyte established through stable isotope analysis

Collectively, phagotrophic algae (mixotrophs) form a functional continuum of nutritional modes between autotrophy and heterotrophy, but the specific physiological benefits of mixotrophic nutrition differ among taxa. Ochromonas spp. are ubiquitous chrysophytes that exhibit high nutritional flexibility, although most species generally fall towards the heterotrophic end of the mixotrophy spectrum. We assessed the sources of carbon and nitrogen in Ochromonas sp. strain BG-1 growing mixotrophically via short-term stable isotope probing. An axenic culture was grown in the presence of either heat-killed bacteria enriched with 15N and 13C, or unlabeled heat-killed bacteria and labeled inorganic substrates (13C-bicarbonate and 15N-ammonium). The alga exhibited high growth rates (up to 2 divisions per day) only until heat-killed bacteria were depleted. NanoSIMS and bulk IRMS isotope analyses revealed that Ochromonas obtained 84–99% of its carbon and 88–95% of its nitrogen from consumed bacteria. The chrysophyte assimilated inorganic 13C-carbon and 15N-nitrogen when bacterial abundances were very low, but autotrophic (photosynthetic) activity was insufficient to support net population growth of the alga. Our use of nanoSIMS represents its first application towards the study of a mixotrophic alga, enabling a better understanding and quantitative assessment of carbon and nutrient acquisition by this species.

Cultivation of phagotrophic algae with waste activated sludge as a fast approach to reclaim waste organics

Substantial energy is reserved in waste activated sludge (WAS) organics but much of it is difficult to recover because the solid organics require long time to solubilize. In this work we introduced the new approach of recovering WAS organics into the biomass of phagotrophic algae. Phagotrophic algae have the unique ability to grow by ingesting insoluble organic particles including microbial cells. This phagotrophic ability renders the solubilization of WAS organics unnecessary and makes this approach remarkably fast. The approach consists of two stages: a short anaerobic digestion treatment followed by the algal growth on treated WAS. The short anaerobic digestion was exploited to release discrete bacteria from WAS flocs. Phagotrophic algae could then grow rapidly with the released bacteria as well as the solubilized nutrients in the treated WAS. The results showed that WAS organics could be quickly consumed by phagotrophic algae. Among all studied conditions the highest WAS volatile solids (VS) reduction was achieved with 72 h anaerobic digestion and 24 h algal growth. In this optimal process, 28% of WAS VS was reduced, and 41% and 20% of the reduced VS were converted into algal biomass and lipids, respectively. In comparison, only 18% WAS VS were reduced after the same time of aerobic digestion without algae addition. Through this approach, the amount of WAS organics requiring further treatment for final disposal is significantly reduced. With the production of significant amounts of algal biomass and lipids, WAS treatment is expected to be more economical and sustainable in material recycling.

Mixotrophy, allelopathy and the population dynamics of phagotrophic algae (cryptophytes) in the Darss Zingst Bodden estuary, southern Baltic

Seasonal plankton dynamics in the Darss Zingst Bodden Chain (DZBC), a southern Baltic estuary, are characterised by summer cyanophyte/chlorophyte dominance, but with winter blooms of mixotrophic cryptophytes, particularly associated with periods of ice cover. Analysis and simulation of a mixotrophic Lotka-Volterra competition model shows that coexistence of algae and cryptophytes is unlikely under static conditions, with seasonal or stochastic variation in parameters, as well as with time lags. However, incorporating production by cyanophytes/chlorophytes of non- toxic allelopathic substances allows stable coexistence of algae and mixotrophs. When parameterised using empirical DZBC data for light, temperature and ice cover, the model gives a good represen- tation of cryptophyte dynamics and bloom formation. We conclude that both mixotrophy and allelopathy are necessary ingredients of community coexistence and dynamics in the DZBC.

Life-stage differences in the diet of Parabroteas sarsi ( Daday) (Copepoda, Calanoida): A field study

The diet of P. sarsi in different life-stages from copepodid I to adult was investigated. Gut contents of copepodid I to II consisted mainly of algae such as diatoms and dinoflagellates. From copepodid III to adult stages the composition of the diet changed towards the inclusion of nauplii, cladocerans and copepods. The importance of the algae on the diet decreased with the inclusion of the prey items. Copepods were the most important components of the diet from C V to adult. Differences in the capture and ingestion of cladocerans and copepods were found. Diet of P. sarsi can be characterized as diverse consisting of diatoms, phagotrophic algae, protozoans, rotifers and nauplii from C I to C III and consisting mainly of carnivorous items from C IV to adult. The ability to eat a variety of food allows the copepods to modify their diet with varying conditions in the food environment. The effect of these diversity in the diet seems to be advantageous, specially in stressed environments imposed by episodes of drying.

The role of C, N and P in dissolved and particulate organic matter as a nutrient source for phytoplankton growth, including toxic species

Phytoplankton have traditionally been regarded as strictly phototrophic, with a well defined position at the base of pelagic food webs. However, recently we have learned that the nutritional demands of a growing number of phytoplankton species can be met, at least partially, or under specific environmental conditions, through heterotrophy. Mixotrophy is the ability of an organism to be both phototrophic and heterotrophic, in the latter case utilizing either organic particles (phagotrophy) or dissolved organic substances (osmotrophy). This finding has direct implications for our view on algal survival strategies, particularly for harmful species, and energy- and nutrient flow in pelagic food webs. Mixotrophic species may outcompete strict autotrophs, e.g. in waters poor in inorganic nutrients or under low light. In the traditional view of the ‘microbial loop’ DOC is thought to be channeled from algal photosynthesis to bacteria and then up the food chain through heterotrophic flagellates, ciliates and mesozooplankton. Are mixotrophic phytoplankton that feed on bacteria also significantly contributing to this transport of photosynthetic carbon up the food chain? How can we estimate the fluxes of carbon and nutrients between different trophic levels in the plankton food web involving phagotrophic algae? These questions largely remain unanswered. In this review we treat evidence for both osmotrophy and phagotrophy in phytoplankton, especially toxic marine species, and some ecological implications of mixotrophy.