Comparative analyses of H₂ photoproduction in magnesium‐ and sulfur‐starved Chlamydomonas reinhardtii cultures

Abstract

Magnesium (Mg)-deprived Chlamydomonas reinhardtii cells are capable to sustain hydrogen (H ) photoproduction at relatively high photosystem II (PSII) activity levels for an extended time period as compared with sulfur (S)-deprived cells. Herein, we present a comparative study of H photoproduction induced by Mg and S shortage to unravel the specific rearrangements of the photosynthetic machinery and cell metabolism occurring under the two deprivation protocols. The exhaustive analysis of photosynthetic activity and regulatory pathways, respiration and starch metabolism revealed the specific rearrangements of the photosynthetic machinery and cellular metabolism, which occur under the two deprivation conditions. The obtained results allowed us to conclude that the expanded time period of H production upon Mg-deprivation is due to the less harmful effects that Mg-depletion has on viability and metabolic performance of the cells. Unlike S-deprivation, the photosynthetic light and dark reactions in Mg-deprived cells remained active over the whole H production period. However, the elevated PSII activity in Mg-deprived cells was counteracted by the operation of pathways for O consumption that maintain anaerobic conditions in the presence of active water splitting.

Algae-Bacteria Consortia as a Strategy to Enhance H2 Production

“…Different culturing approaches have also been developed to alleviate the identified bottlenecks. Among these approaches are the modulation of the light intensity [ 14 , 27 , 28 , 29 , 30 , 31 ], the optimization of the photosynthetic electrons flow towards the HYDAs [ 29 , 32 , 33 , 34 ], the implementation of nutrient stresses, especially sulfur (S) deprivation, influencing H 2 production [ 35 , 36 , 37 , 38 , 39 ], the addition of O 2 scavengers into the culture media [ 33 , 40 , 41 ], or cell immobilization [ 42 , 43 , 44 ]. Moreover, in recent years, the co-cultivation of alga and bacteria has arisen as an alternative strategy to increase algal H 2 production.…”

Microalgal Hydrogen Production

“…Mg is a key component of chlorophyll molecule, and Mg deprivation is one of the latest strategies for hydrogen production in microalgae . Mg deficiency reduces photosynthetic activity by about 20%, and is accompanied by slow electron transport and excessive reduction of PQ pool, active mitochondrial respiration and increased starch accumulation . Hydrogen is produced for about seven days under Mg deprivation.…”

“…It is also possible to use a medium lacking both phosphorus and sulfur (TA‐S‐P, Tris‐Acetate‐minus‐Sulfate‐minus‐Phosphate) to allow Chlamydomonas to enter anaerobiosis more quickly to generate hydrogen . Mg is a key component of chlorophyll molecule, and Mg deprivation is one of the latest strategies for hydrogen production in microalgae . Mg deficiency reduces photosynthetic activity by about 20%, and is accompanied by slow electron transport and excessive reduction of PQ pool, active mitochondrial respiration and increased starch accumulation .…”

Heterologous Hydrogenase Overproduction Systems for Biotechnology—An Overview

“…So far, a number of strategies have been afforded to use these organisms in H 2 production [170,171]. Sulfur or magnesium deprivation results in the inactivation of photosystem II and subsequently reduced O 2 evolution in order to protect the O 2 -sensitive cyanobacterial [FeFe] hydrogenases and improves hydrogen production [172,173] More recently, co-production of cyanoglobin GlbN from Nostoc commune was used to protect the heterologously produced C. acetobutylicum [FeFe]-hydrogenase HydA from oxidation when produced in Nostoc PCC7120. This resulted in an increased H 2 yield of about 20-fold under aerobic conditions [174].…”