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1. Photobiological production of high-value pigments via compartmentalized co-cultures using Ca-alginate hydrogels

   https://doi.org/10.1038/s41598-022-26437-y  

   Zhao, Runyu; Sengupta, Annesha; Tan, Albern X.; Whelan, Ryan; Pinkerton, Taylor; Menasalvas, Javier; Eng, Thomas; Mukhopadhyay, Aindrila; Jun, Young-Shin; Pakrasi, Himadri B.; et al (December 2022, Scientific Reports)

   Abstract Engineered cyanobacteriumSynechococcus elongatuscan use light and CO₂to produce sucrose, making it a promising candidate for use in co-cultures with heterotrophic workhorses. However, this process is challenged by the mutual stresses generated from the multispecies microbial culture. Here we demonstrate an ecosystem whereS. elongatusis freely grown in a photo-bioreactor (PBR) containing an engineered heterotrophic workhorse (either β-carotene-producingYarrowia lipolytica or indigoidine-producingPseudomonas putida) encapsulated in calcium-alginate hydrogel beads. The encapsulation prevents growth interference, allowing the cyanobacterial culture to produce high sucrose concentrations enabling the production of indigoidine and β-carotene in the heterotroph. Our experimental PBRs yielded an indigoidine titer of 7.5 g/L hydrogel and a β-carotene titer of 1.3 g/L hydrogel, amounts 15–22-fold higher than in a comparable co-culture without encapsulation. Moreover,¹³C-metabolite analysis and protein overexpression tests indicated that the hydrogel beads provided a favorable microenvironment where the cell metabolism inside the hydrogel was comparable to that in a free culture. Finally, the heterotroph-containing hydrogels were easily harvested and dissolved by EDTA for product recovery, while the cyanobacterial culture itself could be reused for the next batch of immobilized heterotrophs. This co-cultivation and hydrogel encapsulation system is a successful demonstration of bioprocess optimization under photobioreactor conditions. 

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2. Phototaxis in a wild isolate of the cyanobacterium Synechococcus elongatus

   https://doi.org/10.1073/pnas.1812871115  

   Yang, Yiling; Lam, Vinson; Adomako, Marie; Simkovsky, Ryan; Jakob, Annik; Rockwell, Nathan C.; Cohen, Susan E.; Taton, Arnaud; Wang, Jingtong; Lagarias, J. Clark; et al (December 2018, Proceedings of the National Academy of Sciences)

   Many cyanobacteria, which use light as an energy source via photosynthesis, have evolved the ability to guide their movement toward or away from a light source. This process, termed “phototaxis,” enables organisms to localize in optimal light environments for improved growth and fitness. Mechanisms of phototaxis have been studied in the coccoid cyanobacteriumSynechocystissp. strain PCC 6803, but the rod-shapedSynechococcus elongatusPCC 7942, studied for circadian rhythms and metabolic engineering, has no phototactic motility. In this study we report a recent environmental isolate ofS. elongatus, the strain UTEX 3055, whose genome is 98.5% identical to that of PCC 7942 but which is motile and phototactic. A six-gene operon encoding chemotaxis-like proteins was confirmed to be involved in phototaxis. Environmental light signals are perceived by a cyanobacteriochrome, PixJ_Se(Synpcc7942_0858), which carries five GAF domains that are responsive to blue/green light and resemble those of PixJ fromSynechocystis. Plate-based phototaxis assays indicate that UTEX 3055 uses PixJ_Seto sense blue and green light. Mutation of conserved functional cysteine residues in different GAF domains indicates that PixJ_Secontrols both positive and negative phototaxis, in contrast to the multiple proteins that are employed for implementing bidirectional phototaxis inSynechocystis. 

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3. Assembly and Quantification of Co-Cultures Combining Heterotrophic Yeast with Phototrophic Sugar-Secreting Cyanobacteria

   https://doi.org/10.3791/67311  

   Hasenklever, Dennis; Pohlentz, Joana C; Berwanger, Tom; Kokarakis, Emmanuel J; Hassan, Tanvir; Schipper, Kerstin; Matuszyńska, Anna; Axmann, Ilka M; Ducat, Daniel C (January 2024, Journal of Visualized Experiments)

   With the increasing demand for sustainable biotechnologies, mixed consortia containing a phototrophic microbe and heterotrophic partner species are being explored as a method for solar-driven bioproduction. One approach involves the use of CO2-fixing cyanobacteria that secrete organic carbon to support the metabolism of a co-cultivated heterotroph, which in turn transforms the carbon into higher-value goods or services. In this protocol, a technical description to assist the experimentalist in the establishment of a co-culture combining a sucrose-secreting cyanobacterial strain with a fungal partner(s), as represented by model yeast species, is provided. The protocol describes the key prerequisites for co-culture establishment: Defining the media composition, monitoring the growth characteristics of individual partners, and the analysis of mixed cultures with multiple species combined in the same growth vessel. Basic laboratory techniques for co-culture monitoring, including microscopy, cell counter, and single-cell flow cytometry, are summarized, and examples of nonproprietary software to use for data analysis of raw flow cytometry standard (FCS) files in line with FAIR (Findable, Accessible, Interoperable, Reusable) principles are provided. Finally, commentary on the bottlenecks and pitfalls frequently encountered when attempting to establish a co-culture with sugar-secreting cyanobacteria and a novel heterotrophic partner is included. This protocol provides a resource for researchers attempting to establish a new pair of co-cultured microbes that includes a cyanobacterium and a heterotrophic microbe. 

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4. Spawning in the deep: reproductive life history of four mesopelagic fishes of the northwestern Atlantic Ocean

   https://doi.org/10.3389/fmars.2025.1582706  

   Lefebvre, Lyndsey S; Sosik, Heidi M; Llopiz, Joel K (May 2025, Frontiers in Marine Science)

   The biomass of mesopelagic fishes is estimated to be on the order of or to exceed that of fishes in the epipelagic. Despite their abundance and importance as an ecological link between surface and deep ocean habitats, there is a dearth of basic life history data for mesopelagic fishes. Reproductive biology data are critical for understanding population dynamics and estimating production of a species, particularly when age and growth data are lacking. Between July 2018 and August 2022, collections were made in the western North Atlantic utilizing multiple net types to capture a broad size-range of mesopelagic fishes. Histological analysis of gonad tissue from four numerically dominant species—Argyropelecus aculeatus(Sternoptychidae),Benthosema glaciale(Myctophidae),Scopelogadus beanii(Melamphaidae), andSigmops elongatus(Gonostomatidae)—were examined to describe aspects of reproduction. We determined thatA. aculeatusandB. glacialeare gonochoristic batch spawners with indeterminate fecundity, and the standard length at which 50% of females were mature (L₅₀) was 39.45 and 33.77 mm, respectively.S. beaniiwere found to be gonochoristic, iteroparous, and likely have multi-year oocyte development with an L₅₀of 90.38 mm.S. elongatuswas confirmed as a protandrous hermaphrodite, iteroparous, and had an L₅₀of 200.45 mm. This study is the first to present regional maturity ogives for all four species and to describe detailed reproductive patterns inA. aculeatus, S. beanii, andS. elongatus.These results contribute to the data necessary for quantifying the role of mesopelagic fishes in global biogeochemical cycles and for ensuring responsible use of mesopelagic resources. 

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5. Photosynthetic responses of switchgrass to light and CO ₂ under different precipitation treatments

   https://doi.org/10.1111/gcbb.13138  

   Kieffer, Christina; Kaur, Navneet; Li, Jianwei; Matamala, Roser; Fay, Philip A; Hui, Dafeng (August 2024, GCB Bioenergy)

   Abstract Switchgrass (Panicum virgatumL.) is a prominent bioenergy crop with robust resilience to environmental stresses. However, our knowledge regarding how precipitation changes affect switchgrass photosynthesis and its responses to light and CO₂remains limited. To address this knowledge gap, we conducted a field precipitation experiment with five different treatments, including −50%, −33%, 0%, +33%, and +50% of ambient precipitation. To determine the responses of leaf photosynthesis to CO₂concentration and light, we measured leaf net photosynthesis of switchgrass under different CO₂concentrations and light levels in 2020 and 2021 for each of the five precipitation treatments. We first evaluated four light and CO₂response models (i.e., rectangular hyperbola model, nonrectangular hyperbola model, exponential model, and the modified rectangular hyperbola model) using the measurements in the ambient precipitation treatment. Based on the fitting criteria, we selected the nonrectangular hyperbola model as the optimal model and applied it to all precipitation treatments, and estimated model parameters. Overall, the model fit field measurements well for the light and CO₂response curves. Precipitation change did not influence the maximum net photosynthetic rate (P_max) but influenced other model parameters including quantum yield (α), convexity (θ), dark respiration (R_d), light compensation point (LCP), and saturated light point (LSP). Specifically, the meanP_maxof five precipitation treatments was 17.6 μmol CO₂m⁻² s⁻¹, and the ambient treatment tended to have a higherP_max. The +33% treatment had the highestα, and the ambient treatment had lowerθandLCP, higherRd, and relatively lowerLSP. Furthermore, precipitation significantly influenced all model parameters of CO₂response. The ambient treatment had the highestP_max, largestα, and lowestθ,R_d, and CO₂compensation pointLCP. Overall, this study improved our understanding of how switchgrass leaf photosynthesis responds to diverse environmental factors, providing valuable insights for accurately modeling switchgrass ecophysiology and productivity. 

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