Dear Colleagues,

Photosynthetic microalgae are eukaryotic unicellular organisms that live in aquatic environments and use light energy to bind carbon dioxide (CO₂) to produce biomass. Photosynthesis research on microalgal model systems whose genomes have also been sequenced, such as Chlamydomonas reinhardtii or Phaeodactylum tricornutum, has contributed significantly to our understanding of the basic principles of the photosynthetic process. The light-controlled production of microalgal biomass also holds the potential for the biotechnological use of photosynthetic microalgae for the production of biofuels and high-value raw materials. It is foreseeable that genetic engineering will further develop microalgae as biotechnological hosts for the expression of enzymes and products from natural plant substances as well as for the expression of therapeutic proteins.

In order to use microalgae for biotechnological purposes, the understanding and engineering of photosynthetic bottlenecks and the acclimatization of microalgae to the environment are important goals for the future. The understanding of how photosynthetic performance is maintained under adverse environmental conditions and of how light use efficiency versus stress acclimation responses are balanced are key for the further engineering of photosynthetic efficiency and biotechnological applications.
The purpose of this Special Issue is to discuss how microalgal research has provided insights into identifying photosynthetic bottlenecks with the potential to improve photosynthetic light-to-electron efficiency and thus photosynthetic effectiveness. In this context, aspects of light harvesting to drive photosynthetic charge separation and the dissipation of light to heat to protect the photosynthetic machinery will be addressed. Other topics include the generation, storage, and use of the proton motive force, as well as photosynthetic and alternative electron transfer processes. An additional topic is towards an understanding of how microalgae have evolved acclimation strategies to maintain photosynthetic performance under unfavorable environmental conditions. New structural insights into photosynthetic complexes are also addressed. How improvements in photosynthetic performance can be incorporated into biotechnological applications is another focus. Here, improvements in photosynthetic electron transfer to enhance H2 production and other feedstocks that require additional photosynthetic reducing power are addressed. Novel concepts for the design of photobioreactors and the engineering of microalgae growth, as well as new methods of genetic modification for biotechnological purposes, are also considered.

Prof. Dr. Michael Hippler
Dr. Shin-Ichiro Ozawa
Guest Editors

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Potential of microalgae as a vehicle for sustainable usage of phosphorus 

 Dr. Solovchenko et al.

Phosphorus (P) is a very special irreplaceable macronutrient. It is central to energy and information storage and exchange in living cell. P is an element with “broken geochemical cycle” since it lacks abundant volatile compounds capable of closing the P cycle. P fertilizers are critical for global food security, but the reserves of minable P are scarce and extremely non-evenly distributed. Accordingly, the risks of global crisis due to limited access to P reserves is expected to be graver than those entailed by competition for fossil hydrocarbons. Paradoxically, given the scarcity and value of concentrated P reserves, its usage is extremely inefficient: current waste rate reaches 80% giving rise to a plethora of unwanted consequences such as eutrophication and harmful algal blooms. Microalgal biotechnology and emerging approaches based on microalgal cell cultivation comprise a promising vehicle for responding to this challenge. The proposed review briefly presents the relevant aspects of microalgal biology such as cell P reserve composition and turnover and regulation of P uptake kinetics for maximization of P uptake efficiency with the focus on novel knowledge. Multifaceted role of polyphosphate, the largest cell depot for P, is discussed with emphasis on the P toxicity mediated by “rogue” polyphosphates. Opportunities and hurdles of P bioremoval with microalgal cultures, either suspended or immobilized, uptake from waste streams is discussed along with the role of bacterial components of microalgal-bacterial consortia in these processes. Possible avenues of P-rich microalgal biomass such as biofertilizer production or extraction of valuable polyphosphate and other bio[products are considered. The review concludes with comprehensive assessment of the current potential of microalgal biotechnology for ensuring the sustainable usage of phosphorus.