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Algal carbon concentrating drives fatty acid biosynthesis beyond photosynthesis

ABSTRACT: The global carbon cycle underpins Earth’s sustainability, with algae playing a pivotal role in biological carbon assimilation. Efficient photosynthetic carbon fixation in aquatic environments is facilitated by algal CO2-concentrating mechanisms (CCMs). Despite their importance, the coordination of inorganic carbon demands for photosynthesis with other inorganic carbon-utilizing pathways remains unexplored. Here we use the model green alga Chlamydomonas reinhardtii to demonstrate that under limited-CO2 conditions, the biotin carboxyl-carrier protein subunit of acetyl-CoA carboxylase complex—the rate-limiting enzyme in de novo fatty acid biosynthesis—forms dynamic protein condensates at the pyrenoid periphery, partially co-localizing with the putative carbonic anhydrase LCIB. Furthermore, CCM-deficient mutants exhibit compromised fatty acid biosynthesis capacity. We propose a metabolic interaction between CCM and de novo fatty acid biosynthesis, which potentially optimizes cellular carbon economy, enhances biofuel production yields and, more broadly, reveals a molecular mechanism for coordinating inorganic carbon utilization within global carbon cycle.

INSTRUMENT(S):

ORGANISM(S): Chlamydomonas Reinhardtii

SUBMITTER: Yuqing Yang

LAB HEAD: Xiaobo Li

PROVIDER: PXD066441 | Pride | 2025-08-22

REPOSITORIES: Pride

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			Action	DRS
	YQ480_MSP2500511_BCC1_1.raw	Raw
	YQ480_MSP2500511_BCC1_2.raw	Raw
	YQ480_MSP2500511_BCC1_3.raw	Raw
	YQ480_MSP2500511_CDJ1tp_1.raw	Raw
	YQ480_MSP2500511_CDJ1tp_2.raw	Raw

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Project description:The hydrothermal vent gammaproteobacterium Thiomicrospira crunogena inhabits an unstable environment and must endure dramatic sweeps in habitat chemistry. This sulfur chemolithoautotroph responds to changes in dissolved inorganic carbon (DIC; = CO2 + HCO3- + CO3-2) availability with a carbon concentrating mechanism (CCM), in which whole-cell affinity for DIC, as well as the intracellular DIC concentration, increase substantially under DIC-limitation. To determine whether this CCM is regulated at the level of transcription, cells cultivated under high-DIC conditions in chemostats were resuspended in growth medium with low concentrations of DIC, and CCM development was tracked in the presence and absence of RNA polymerase inhibitor rifampicin. The induction of the CCM, as measured by silicone oil centrifugation, was hindered in the presence of rifampicin. Similar results were observed for carboxysome gene transcription and assembly, as assayed by qRT-PCR and transmission electron microscopy, respectively. Genome-wide transcription patterns, assayed via microarrays, were compared for cells grown under DIC-limitation versus ammonia limitation. In addition to carboxysome genes, two novel genes (Tcr_1019 and Tcr_1315), present in other organisms including chemolithoautotrophs, but whose function(s) have not been elucidated in any organism, were found to be upregulated under low-DIC conditions. Likewise, under ammonia limitation, in addition to the expected enhancement of ammonia transporter and PII-gene transcription, the transcription of two novel genes was measurably enhanced (Tcr_0466 and Tcr_2018). Upregulation of all four genes was verified via qRT-PCR (Tcr_1019: 4-fold; Tcr_1315: ~7-fold; Tcr_0466: >200-fold; Tcr_2018: 7-fold), suggesting novel components are part of the response to nutrient limitation by this organism. In this study Thiomicrospira crunogena cells were grown under inorganic carbon limitation and ammonia limitation (high inorganic carbon concentrations) to examine genome wide transcription responses

Project description:Diatoms are responsible for ~40% of marine primary productivity1, fueling the oceanic carbon cycle and contributing to natural carbon sequestration in the deep ocean2. Diatoms rely on energetically expensive carbon concentrating mechanisms (CCMs) to fix carbon efficiently at modern levels of CO23–5. How diatoms may respond over the short and long-term to rising atmospheric CO2 remains an open question. Here we use nitrate-limited chemostats to show that the model diatom Thalassiosira pseudonana rapidly responds to increasing CO2 by differentially expressing gene clusters that regulate transcription and chromosome folding and subsequently reduces transcription of photosynthesis and respiration gene clusters under steady-state elevated CO2. These results suggest that exposure to elevated CO2 first causes a shift in regulation and then a metabolic rearrangement. Genes in one CO2-responsive cluster included CCM and photorespiration genes that share a putative cyclic-AMP responsive cis-regulatory sequence, implying these genes are co-regulated in response to CO2 with cAMP as an intermediate messenger. We verified cAMP-induced down-regulation of CCM gene ?-CA3 in nutrient-replete diatom cultures by inhibiting the hydrolysis of cAMP. These results indicate an important role for cAMP in down-regulating CCM and photorespiration genes under elevated CO2 and provide insights into mechanisms of diatom acclimation in response to climate change. In steady-state experiments: axenic T. pseudonana cells in four biological replicates (duplicate chemostats x 2 experimental runs) were acclimated to nitrate-limitation at 70% (1.5 day-1) of max growth rate for >10 days (>15 generations) under continuous light of 80 µmol photons·m?2·s?1. Cell biomass was maintained at ~2 x 105 cells·mL?1 by 10 ?M nitrate and carbonate chemistry stabilized to 300, 475 or 800 ?atm CO2, verified by pH and DIC measurements. Transition samples and carbonate chemistry were collected daily from chemostat cultures as CO2 levels were increased from ~300-800 ?atm at a rate ? 0.2 ?atm·min?1 over four consecutive days (6 generations) after pre-acclimation to 300 ?atm CO2 and nitrate-limitation.

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Algal carbon concentrating drives fatty acid biosynthesis beyond photosynthesis

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