Tuning photosynthetic oxygen for hydrogen evolution in synergistically integrated, sulfur deprived consortia of Coccomyxa chodatii and Rhodobium gokarnense at dim and high light

Abstract

In this work, tuning oxygen tension was targeted to improve hydrogen evolution. To achieve such target, various consortia of the chlorophyte Coccomyxa chodatii with a newly isolated photosynthetic purple non-sulfur bacterium (PNSB) strain Rhodobium gokarnense were set up, sulfur replete/deprived, malate/acetate fed, bicarbonate/sulfur added at dim/high light. C. chodatii and R. gokarnense are newly introduced to biohydrogen studies for the first time. Dim light was applied to avoid the inhibitory drawbacks of photosynthetic oxygen evolution, values of hydrogen are comparable with high light or even more and thus economically feasible to eliminate the costs of artificial illumination. Particularly, the consortium of 2n− (n = 1.9 × 105 cell/ml, sulfur deprived) demonstrated its perfection for the target, i.e., the highest possible cumulative hydrogen. This consortium exhibited negative photosynthesis, i.e., oxygen uptake in the light. Most hydrogen in consortia is from bacterial origin, although algae evolved much more hydrogen than bacteria on per cell basis, but for only one day (the second 24 h), as kinetics revealed. The higher hydrogen in unibacterial culture or consortia results from higher bacterial cell density (20 times). Consortia evolved more hydrogen than their respective separate cultures, further enhanced when bicarbonate and sulfur were supplemented at higher light. The share of algae relatively increased as bicarbonate or sulfur were added at higher light intensity, i.e., PSII activity partially recovered, resulting in a transient autotrophic hydrogen evolution. The addition of acetic acid in mixture with malic acid significantly enhanced the cumulative hydrogen levels, mostly decreased cellular ascorbic acid indicating less oxidative stress and relief of PSII, relative to malic acid alone. Starch, however, decreased, indicating the specificity of acetic acid. Exudates (reducing sugars, amino acids, and soluble proteins) were detected, indicating mutual utilization. Yet, hydrogen evolution is limited; tuning PSII activity remains a target for sustainable hydrogen production.

Amelioration of NaCl stress on germination, growth, and nitrogen fixation of Vicia faba at isosmotic Na–Ca combinations and Rhizobium

“…Chlorophyll contents in faba leaves were also lowered as salinity was increased while was enhanced by calcium addition. Chlorophyll plays a crucial role in the absorption and transmission of light quanta and chlorophyll concentration is an indicator of a plant's capacity to utilize light for photosynthesis (Zhang et al 2018 ; Danial et al 2023 ). Under saline conditions the reduction of seedling shoot, and root lengths FW, and DW is a common phenomenon in many plants.…”

From Microalgae to Bioenergy: Recent Advances in Biochemical Conversion Processes

“…To induce anaerobiosis in the second stage, nutrient (sulfur, nitrogen, and phosphorus) deprivation has been extensively studied, where cells are first cultivated under nutrient-replete conditions (first stage) and then subjected to nutrientdeprived conditions in the second stage [141]. Daniel et al [142], Maswanna et al [135], and Pongpadung et al [143] deprived the Coccomyxa chodatii, Tetraspora sp., and Chlorella sorokiniana cultures of sulfur and reported a 4-, 1.2-, and 69-fold increase in biohydrogen production, respectively. Sulfur is an essential component of amino acids, cysteine, and methionine, which play a vital role in protein synthesis during the PSII repair cycle [125].…”