Evaluation of secretion reporters to microalgae biotechnology: Blue to red fluorescent proteins

Biohybrid microswimmers against bacterial infections

Biohybrid microswimmers exploit the natural abilities of motile microorganisms e.g. in releasing cargo on-demand. However, using such engineered swarms to release antibiotics addressing bacterial infections has not yet been realized. Herein, a design strategy for biohybrid microswimmers is reported, which features the covalent attachment of antibiotics with a photo-cleavable linker to the algae Chlamydomonas reinhardtii via two synthetic steps. This surface engineering does not rely on genetic manipulations, proceeds with high efficiency, and retains the viability or phototaxis of microalgae. Two different antibiotics have been separately utilized, which result in activity against both gram-positive and gram-negative strains. Guiding the biohybrid microswimmers by an external beacon, and on-demand delivery of the drugs by light with high spatial and temporal control, allowed for strong inhibition of bacterial growth. This efficient strategy could potentially allow for the selective treatment of bacterial infections by engineered algal microrobots with high precision in space and time. STATEMENT OF SIGNIFICANCE: Biological swimmers with innate sensing and actuation capabilities and integrated components have been widely investigated to create autonomous microsystems. The use of natural swimmers as cargo delivery systems presents an alternative strategy to transport therapeutics to the required locations with the difficult access by traditional strategies. Although the transfer of various therapeutic cargo has shown promising results, the utilization of microswimmers for the delivery of antimicrobials was barely covered. Therefore, we present biohybrid microalga-powered swimmers designed and engineered to carry antibiotic cargo against both Gram-positive and Gram-negative bacteria. Guided by an external beacon, these microhybrids deliver the antibiotic payload to the site of bacterial infection, with high spatial and temporal precision, released on-demand by an external trigger to inhibit bacterial growth.

Application of Fluorescence Microscopy and Behavioral Assays to Demonstrating Neuronal Connectomes and Neurotransmitter Systems in C. elegans

The nematode Caenorhabditis elegans (C. elegans) is a prevailing model which is commonly utilized in a variety of biomedical research arenas, including neuroscience. Due to its transparency and simplicity, it is becoming a choice model organism for conducting imaging and behavioral assessment crucial to understanding the intricacies of the nervous system. Here, the methods required for neuronal characterization using fluorescent proteins and behavioral tasks are described. These are simplified protocols using fluorescent microscopy and behavioral assays to examine neuronal connections and associated neurotransmitter systems involved in normal physiology and aberrant pathology of the nervous system. Our aim is to make available to readers some streamlined and replicable procedures using C. elegans models as well as highlighting some of the limitations.

Metabolic Engineering of Chlamydomonas reinhardtii for Enhanced β-Carotene and Lutein Production

The metabolic engineering of Chlamydomonas reinhardtii, one of the fastest-growing microalgae, is a potential alternative for enhanced carotenoid productivity. CrtYB (phytoene-β-carotene synthase - PBS) gene from red yeast Xanthophyllomyces dendrorhous encodes for a bifunctional enzyme that harbours both phytoene synthase (psy) and lycopene cyclization (lcyb) activities. Heterologous expression of this bifunctional PBS gene led to 38% enhancement in β-carotene along with 60% increase in the lutein yields under low light conditions of 75 μmol photons m^-2 s^-1. Short Duration-High Light induction strategy led to overall 72% and 83% increase in β-carotene and lutein yield reaching up to 22.8 mg g^-1 and 8.9 mg g^-1, respectively. This is the first report of expression of heterologous bifunctional PBS gene resulting in simultaneous enhancement in β-carotene and lutein content in phototrophic engineered cells. Graphical Abstract.

Engineered Fusion Proteins for Efficient Protein Secretion and Purification of a Human Growth Factor from the Green Microalga Chlamydomonas reinhardtii

Light-driven recombinant protein (RP) production in eukaryotic microalgae offers a sustainable alternative to other established cell-culture systems. RP production via secretion into the culture medium enables simple product separation from the cells adding a layer of process value in addition to the algal biomass, which can be separately harvested. For the model microalga Chlamydomonas reinhardtii, a broad range of molecular tools have been established to enable heterologous gene expression; however, low RP production levels and unreliable purification from secretion concepts have been reported. Domesticated C. reinhardtii strains used for genetic engineering are often cell-wall deficient. These strains nevertheless secrete cell-wall components such as insoluble (hydroxy)proline-rich glycoproteins into the culture media, which hinder downstream purification processes. Here, we attempted to overcome limitations in secretion titers and improve protein purification by combining fusion partners that enhance RP secretion and enable alternative aqueous two-phase (ATPS) RP extraction from the culture medium. Protein fusions were strategically designed to contain a stably folded peptide, which enhanced secretion capacities and gave insights into (some) regulatory mechanisms responsible for this process in the algal host. The elevated protein titers mediated by this fusion were then successfully applied in combination with a fungal hydrophobin tag, which enabled protein purification from the complex microalgal extracellular environment by ATPS, to yield functional recombinant human epidermal growth factor (hEGF) from the algal host.