Biology subjects

Kuntam, S.

Publications and source records attributed to Kuntam, S..

5 recordsLinked to original sources

bioRxiv2026

Coupling microalgal bioremediation of recirculating aquaculture effluents with photobiological hydrogen production

Recirculating aquaculture system (RAS) effluents contain substantial nitrate and phosphate loads, posing a significant eutrophication risk to aquatic ecosystems if left untreated. While microalgal bioremediation is a promising strategy, expanding opportunities for valorisation is crucial for its successful implementation. This study couples the cultivation of nitrate-utilizing Chlamydomonas reinhardtii strain CC-1690 in RAS effluent with photobiological hydrogen (H2) production to achieve nutrient removal, bioenergy production, and high-quality biomass. Within 70 h, CC-1690 achieved near-complete depletion of nitrate and phosphate from the effluent. Subsequently, H2 production was induced via carbon limitation and anoxia, yielding a cumulative 49 {micro}mol H2 mg-1 Chl over 72 h. Although decreased chlorophyll content and Fv/Fm indicated physiological stress, key photosynthetic subunits (PsbA, PSBO, CP47, PetB and PsaA) remained largely stable. Importantly, the process preserved biomass quality; total lipid content increased slightly, enriched in palmitic (16:0) and -linolenic (18:3{omega}-3) fatty acids while protein content was unaffected. These results demonstrate that integrating H2 production with RAS effluent remediation offers a robust circular economy approach, valorising wasted nutrients into bioenergy and high-quality biomass with potential downstream applications.

bioengineering↗

bioRxiv2025

Unprecedented exoelectrogenic activity in Parachlorella kessleri MACC-38: The interplay of photosynthetic electron transport and the oxidative pentose phosphate pathway

Exoelectrogenesis is the ability of living cells to export electrons. In photosynthetic organisms, exoelectrogenesis is of particular interest because it can be used for transduction of solar energy into electric current in biophotovoltaics or reducing power for biocatalysis. Previously, we identified and characterized the green microalga Parachlorella kessleri MACC-38 producing unprecedented current largely dependent on the photosynthetic electron transport chain (PETC). In this study, our comparative photosynthetic characterization demonstrates that chlororespiration is a crucial factor maintaining the PETC redox balance in MACC-38. Our data points that the oxidative pentose phosphate pathway (OPPP) is activated during exoelectrogenesis to meet the increased demand of reducing power. We hypothesize that chlororespitration prevents oversaturation of PETC during OPPP activation. These findings provide valuable insights into the fundamental mechanisms of exoelectrogenesis in green algae. By elucidating the complex interconnection between PETC, OPPP and exoelectrogenesis, our results pave the way towards improved bioelectrochemical and biocatalysis technologies.

plant biology↗

bioRxiv2024

Chloroplastic ascorbate acts as a regulatory hub in plant metabolism regardless of oxidative stress

Ascorbate is a major plant metabolite that plays crucial roles in various processes, from reactive oxygen scavenging to epigenetic regulation. However, to what extent and how ascorbate modulates metabolism is largely unknown. To address this, we investigated the consequences of chloroplastic and total cellular ascorbate-deficiencies by studying chloroplastic ascorbate-transporter pht4;4 mutant lines, and the ascorbate-deficient vtc2-4 mutant of Arabidopsis thaliana. Under regular growth conditions, both ascorbate-deficiencies caused minor alterations in photosynthesis, with no apparent signs of oxidative damage. In contrast, metabolomics analysis revealed a global and largely overlapping metabolome rewiring in both ascorbate-deficiencies, suggesting that chloroplastic ascorbate modulates plant metabolism. We observed significant alterations in amino acid metabolism, particularly in arginine metabolism, activation of nucleotide salvage pathways, and changes in secondary metabolism. In addition, proteome-wide analysis of thermostability revealed that ascorbate may interact with enzymes involved in arginine metabolism, the Calvin-Benson cycle, and several photosynthetic electron transport components. Overall, our results suggest that, independently of oxidative stress, chloroplastic ascorbate interconnects and coordinates diverse metabolic pathways in vascular plants and thus acts as a regulatory hub.

plant biology↗

bioRxiv2023

The chloroplastic phosphate transporter CrPHT4-7 supports phosphate homeostasis and photosynthesis in Chlamydomonas

In eukaryotic cells, phosphorus is assimilated and utilized primarily as phosphate (Pi). Pi homeostasis is mediated by transporters that have not yet been adequately characterized in green algae. This study reports on CrPHT4-7 from Chlamydomonas reinhardtii, a member of the PHT4 transporter family, which exhibits remarkable similarity to AtPHT4;4 from Arabidopsis thaliana, a chloroplastic ascorbate transporter. Using fluorescent protein tagging we show that CrPHT4-7 resides in the chloroplast envelope membrane. Crpht4-7 mutants, generated by the CRISPR/Cas12a-mediated single-strand templated repair, show retarded growth especially in high light, enhanced sensitivity to phosphorus limitation, reduced ATP level, strong ascorbate accumulation and diminished non-photochemical quenching in high light. Conversely, CrPHT4-7 overexpressing lines exhibit enhanced biomass accumulation under high light conditions in comparison with the wild-type strain. Expressing CrPHT4-7 in a yeast strain lacking Pi transporters substantially recovered its slow growth phenotype demonstrating that it transports Pi. Even though CrPHT4-7 shows a high degree of similarity to AtPHT4;4, it does not display any significant ascorbate transport activity in yeast or intact algal cells. Thus, the results demonstrate that CrPHT4-7 functions as a chloroplastic Pi transporter essential for maintaining Pi homeostasis and photosynthesis in Chlamydomonas reinhardtii. One-sentence summaryWe demonstrate that the CrPHT4-7 transporter of Chlamydomonas reinhardtii is located in the chloroplast envelope membrane and contributes to maintaining phosphate homeostasis and photosynthesis.

plant biology↗

bioRxiv2023

Accumulation and light-harvesting function of IsiA in cyanobacterial cells with monomeric and trimeric Photosystem I

The acclimation of cyanobacteria to iron deficiency is crucial for their survival in natural environments. In response to iron deficiency, many cyanobacterial species induce the production of a pigment-protein complex called IsiA. IsiA proteins associate with photosystem I (PSI) and can function as light-harvesting antennas or dissipate excess energy. They may also serve as Chl storage during iron limitation. In this study we examined the functional role of IsiA in cells of Synechocystis sp. PCC 6803 grown under iron limitation conditions by measuring the cellular IsiA content and its capability to transfer energy to PSI. We specifically test the effect of the oligomeric state of PSI by comparing wild-type (WT) Synechocystis sp. PCC 6803 to mutants lacking specific subunits of PSI, namely PsaL/PsaI ({Delta}psaL mutant) and PsaF/PsaJ ({Delta}FIJL). Time-resolved fluorescence spectroscopy revealed that IsiA formed functional PSI3-IsiA18 supercomplexes, wherein IsiA effectively transfers energy to PSI on a timescale of 10 ps at room temperature - measured in isolated complexes and in vivo - confirming the primary role of IsiA as an accessory light-harvesting antenna to PSI. However, a significant fraction (40%) remained unconnected to PSI, supporting the notion of a dual functional role of IsiA. Cells with monomeric PSI under iron deficiency contained only 3-4 IsiA complexes bound to PSI. Together the results show that IsiA is capable of transferring energy to trimeric and monomeric PSI but to varying degrees and that the acclimatory production of IsiA under iron stress is controlled by its ability to perform its light-harvesting function.

biophysics↗