Search Results (50)

Cupriavidus necator is a well-studied microorganism with potential application in bioregenerative life support systems for single-cell protein and bioplastic production. Most studies have been carried out in autotrophy or heterotrophy, requiring O₂ as the final electron acceptor. In the context of inhabited missions, access to O₂ will primarily be limited to the crew. In this study, we investigated the capacity of C. necator to carry out nitrate respiration as a strategy to limit oxygen supply to the cultures by providing nitrate from another compartment of the Bioregenerative Life Support System (BLSS). Batch bioreactor experiments were carried out to determine the best conditions for nitrate utilization in terms of pH and aeration. Continuous cultures were then performed under two carbon sources (glucose vs. acetic acid) and two substrate limitations (nitrate vs. carbon). The optimal conditions were found to be pH 7.5 under anaerobiosis. They were applied in chemostats, where three steady-states were obtained at a low dilution rate. In all cases, the biomass consisted of a mixture of protein (from 29 ± 1% Cell Dry Weight (CDW) to 39 ± 2% CDW) and polyhydroxybutyrate (from 45 ± 2% CDW to 57 ± 3% CDW), which was found to be a key component for nitrate respiration metabolism. Microaerobic conditions were also tested in batch culture, reporting for the first time aerobic nitrate respiration in C. necator. Under these conditions, growth parameters improved during the nitrate phase; however, the specific growth rate during the nitrite phase was lower than that observed under strictly anaerobic conditions. Full article

Eukaryotes use diverse nutrient acquisition strategies, including autotrophy, heterotrophy, mixotrophy, and symbiosis, which shape the evolution of cell regulatory networks. The Target of Rapamycin (TOR) kinase is a conserved growth regulator that in most species functions within two complexes, TORC1 and TORC2. TORC1 is broadly conserved and uniquely sensitive to rapamycin, whereas the evolutionary distribution of TORC2 is less well-defined. We built a sensitive hidden Markov model (HMM)-based pipeline to survey core TORC1 and TORC2 components across more than 800 sequenced eukaryotic genomes spanning multiple major supergroups. Both complexes are present in early-branching lineages, consistent with their presence in the last eukaryotic common ancestor, followed by multiple lineage-specific losses of TORC2 and, more rarely, TORC1. A striking pattern emerges in which TORC2 is uniformly absent from photosynthetic autotrophs derived from primary endosymbiosis and frequently lost in those derived from secondary or tertiary events. In contrast, TORC2 is consistently retained in mixotrophs, which obtain carbon from both photosynthesis and environmental uptake, and in free-living obligate heterotrophs. These findings suggest that TORC2 supports heterotrophic metabolism and is often dispensable under strict autotrophy. Our results provide a framework for the evolutionary divergence of TOR signaling and highlight metabolic and ecological pressures that shape TOR complex retention across eukaryotes. Full article

Cervical cancer (CC), often caused by persistent high-risk HPV infection, is a major health issue for Moroccan women. This study is the first in Morocco to examine how the cervico-vaginal microbiome differs across HPV-related clinical stages. Using 16S rRNA sequencing, the researchers analyzed samples from 247 women—100 healthy controls, 43 hr-HPV⁺ pre-cancer cases, and 104 post-treatment CC cases. In healthy women, Lactobacillus dominated (70%), but it significantly declined in the pre-cancer group (45%, p < 0.01) and remained low post-treatment (50%). Meanwhile, Pseudomonadota and Actinobacteriota increased in pre-cancer samples (up to 25–30%, p < 0.01). Although the alpha diversity remained stable, the beta diversity differed significantly across stages (p = 0.001), but not by HPV status. Post-treatment samples showed a sharp decline in Bacillota (logFC −5, p < 10⁻¹⁵) and increases in Campylobacterota and Fusobacteriota (logFC +6 to +21, p < 10⁻¹⁶). Functionally, chemo-heterotrophy and fermentation declined, while nitrogen fixation and phototrophy rose in pre-cancer cases. Host factors like late menarche, high parity, STIs, and contraceptive use correlated with specific microbiota shifts. Full article

Metabolism, the network of biochemical reactions that powers life, arose under conditions radically different from those on Earth today. Investigating its origins reveals how initially simple chemical processes gradually integrated nucleic acid and then protein catalysts, becoming progressively more complex and regulated until they evolved into the enzyme-rich systems observed in modern organisms. Here, we integrate multiple perspectives on the origin of metabolism, focusing primarily on an evolutionary trajectory from an RNA-based world, where ribozymes, metal ions, coenzymes, small peptides, and other small organic molecules worked in concert, to enzyme-driven metabolic networks. We also address the longstanding debates on whether these early metabolic pathways were largely autotrophic or heterotrophic, and consider so-called “pre-metabolisms” (non-enzymatic networks) as an alternative conceptual framework. We discuss key examples such as the Wood–Ljungdahl (W–L) pathway and the reverse tricarboxylic acid (TCA) cycle, both posited to function under early Earth conditions. Finally, we examine how the environment (e.g., minerals, clays, hydrothermal vents) shaped early metabolism, describe unresolved questions about the Last Common Ancestor’s catalytic repertoire and propose future directions that link geochemical insights with molecular biology and synthetic approaches. Full article

Microbial eukaryotes have essential roles in aquatic ecosystems, yet their diversity and ecological functions in extreme environments remain understudied compared to prokaryotes. This study aims to thoroughly characterize the composition and diversity of microbial eukaryotic communities in 14 geothermal waters across Croatia. Physicochemical analysis revealed significant variations in temperature (36–55 °C), pH (6.5–8.3), and nutrient concentrations, with all sites displaying anoxic conditions except for one. Sequencing of the V9 18S rRNA gene identified 134 taxa, predominantly from the Alveolata, Stramenopiles, and Opisthokonta supergroups. The highest diversity and richness were observed in aquifer groups with moderate temperatures and nutrient levels, while extreme sites exhibited reduced diversity. Among the key environmental factors shaping these communities, temperature, pH, and nitrate concentrations were most significant. Photoautotrophic and mixotrophic taxa, such as Ochrophyta, Dinoflagellata, and Chlorophyta, were prominent, reflecting their roles in primary production and nutrient cycling. Decomposers, including Basidiomycota and Ascomycota, were linked to organic matter degradation. Microeukaryotes showed adaptations to extreme conditions, such as thermotolerance and evolutionary shifts from phototrophy to heterotrophy, highlighting their ecological versatility. These findings underscore the potential of microbial eukaryotes in biotechnological applications, such as bioremediation and biofuel production. Genera like Tribonema and Navicula demonstrated promising capabilities in nutrient removal and CO₂ fixation. However, further research is necessary to investigate and confirm their suitability for these purposes. To summarize, our research provides new insights into understudied microbial eukaryotes in Croatian hot springs that represent a valuable model for exploring microbial diversity, ecological interactions, and industrial applications in extreme environments. Full article

In warm oligotrophic waters, photosymbiotic coral can flourish across a wide depth range (0–170+ m), extending to depths where light attenuates to ~0.1% of surface values. Conventional wisdom has long assumed that mixotrophic corals must increasingly rely on heterotrophy as the ambient light available to drive photosynthesis decreases with depth. However, evidence challenging this traditional dogma has been accumulating in recent years. Although some evidence suggests that some depth-generalist coral species likely increase their reliance on heterotrophy with increasing depth, there is growing evidence that other species do not. Analysis of bulk stable isotopes (δ¹³C and δ¹⁵N) applied to photosymbiotic corals has been used in several ways to infer their trophic ecology and their relative dependence on symbiont photosynthesis versus heterotrophic feeding. However, metrics based on bulk tissue δ¹³C and δ¹⁵N values are subject to considerable uncertainty due to the multiple factors that can affect their values independent of trophic ecology. These competing factors can be quite challenging to disentangle and have led to inconsistent results and conclusions regarding trends in coral heterotrophy with depth. The evidence to date suggests no uniform trophic pattern with increasing depth or decreasing light. Different corals appear to function differently, which is not surprising given their phylogenetic diversity. Full article

Limited research has been conducted on the regulation of light quality on heterotrophy in in vitro-grown potato plantlets. Here, we investigated the effect of light quality on photosynthetic and heterotrophic abilities as well as microtuber formation and growth of potato plantlets (Solanum tuberosum L. cv. Shepody). Potato plantlets pre-cultivated under white light for 30 days were then transferred to grow under blue (B), green (G), red (R), yellow (Y), and white (W) lights, and parameters including dry weight, photosynthetic pigment, medium solute consumption, δ¹³C value, root activity, and sucrose transport (SUT) gene expression of these plantlets were measured. The results showed that B, G, and W were conducive to the rapid induction of microtubers, while R, and especially Y, delayed microtuber formation. Higher photosynthetic ability was observed in the W treatment, whereas the opposite effect was seen in the monochromatic light treatments. Microtuber growth was primarily dependent on heterotrophy, and B was conducive to microtuber growth. The delay in microtuber formation was related to the high expression of StSUT4 in the root, and better microtuber growth was associated with higher root activity, more medium solute consumption, and a higher expression level of StSUT1 in the roots. Full article

Polyhydroxyalkanoates (PHAs) are intracellular biopolymers that microorganisms use for energy and carbon storage. They are mechanically similar to petrochemical plastics when chemically extracted, but are completely biodegradable. While they have potential as a replacement for petrochemical plastics, their high production cost using traditional carbon sources remains a significant challenge. One potential solution is to modify heterotrophic PHA-producing strains to utilize alternative carbon sources. An alternative approach is to utilize methylotrophic or autotrophic strains. This article provides an overview of bacterial strains employed for PHA production, with a particular focus on those exhibiting the highest PHA content in dry cell mass. The strains are organized according to their carbon source utilization, encompassing autotrophy (utilizing CO₂, CO) and methylotrophy (utilizing reduced single-carbon substrates) to heterotrophy (utilizing more traditional and alternative substrates). Full article

Four strains of green microalgae (Scenedesmus acutus, Scenedesmus vacuolatus, Chlorella sorokiniana, and Chlamydomonas reinhardtii) were compared to determine growth and pigment composition under photoautotrophic or heterotrophic conditions. Batch growth experiments were performed in multicultivators with online monitoring of optical density. For photoautotrophic growth, light-limited (CO₂-sufficient) growth was analyzed under different light intensities during the exponential and deceleration growth phases. The specific growth rate, measured during the exponential phase, and the maximal biomass productivity, measured during the deceleration phase, were not related to each other when different light intensities and different species were considered. This indicates species-dependent photoacclimation effects during cultivation time, which was confirmed by light-dependent changes in pigment content and composition when exponential and deceleration phases were compared. Except for C. reinhardtii, which does not grow on glucose, heterotrophic growth was promoted to similar extents by acetate and by glucose; however, these two substrates led to different pigment compositions. Weak light increased the pigment content during heterotrophy in the four species but was efficient in promoting growth only in S. acutus. C. sorokiniana, and S. vacuolatus exhibited the best potential for heterotrophic biomass productivities, both on glucose and acetate, with carotenoid (lutein) content being the highest in the former. Full article

A significant fraction of the food produced worldwide is currently lost or wasted throughout the supply chain, squandering natural and economic resources. Food waste valorization will be an important necessity in the coming years. This work investigates the ability of food waste to serve as a viable nutritional substrate for the heterotrophic growth of Chlorella vulgaris. The impact of different pretreatments on the elemental composition and microbial contamination of seven retail food waste mixtures was evaluated. Among the pretreatment methods applied to the food waste formulations, autoclaving was able to eliminate all microbial contamination and increase the availability of reducing sugars by 30%. Ohmic heating was also able to eliminate most of the contaminations in the food wastes in shorter time periods than autoclave. However, it has reduced the availability of reducing sugars, making it less preferable for microalgae heterotrophic cultivation. The direct utilization of food waste containing essential nutrients from fruits, vegetables, dairy and bakery products, and meat on the heterotrophic growth of microalgae allowed a biomass concentration of 2.2 × 10⁸ cells·mL⁻¹, being the culture able to consume more than 42% of the reducing sugars present in the substrate, thus demonstrating the economic and environmental potential of these wastes. Full article

Since reef-building corals rely on both heterotrophy and endosymbiotic dinoflagellate autotrophy to meet their metabolic needs, it is necessary to consider both food supply and light levels, respectively, when optimizing their cultivation ex situ. Herein nubbins of the model reef coral Pocillopora acuta cultured in recirculating aquaculture systems at photosynthetically active radiation levels of 370 or 670 μmol quanta m⁻² s⁻¹ were fed Artemia nauplii at concentrations of either 33 or 78 individuals mL⁻¹ in a separate feeding tank for 6 hr in the dark thrice weekly. A subset of nubbins was experimentally wounded at the outset of the 84-day experiment to assess recovery, and 100% fully healed within 2–4 weeks. All cultured corals survived, and unwounded corals (1) grew at a specific growth rate approaching 0.5% day⁻¹ and (2) demonstrated a mean total linear extension of 0.2% day⁻¹ (~6–8 cm year⁻¹); these are far higher than growth rates normally documented in situ. In the feeding tank, corals tolerated nitrate levels up to 25 mg L⁻¹, but once concentrations reached 50 mg L⁻¹ by day 84, tissue necrosis began to occur in nubbins of one tank. This highlights the importance of feeding in separate tanks during long-term culture of corals, and bio-filtration could reduce the possibility of organic matter accumulation in future coral culture studies. Full article

This study aimed to examine the impact of crude glycerol as the main carbon source on the growth, cell morphology, and production of high-value-added metabolites of two microalgal species, namely Chlorella vulgaris and Scenedesmus quadricauda, under heterotrophic and mixotrophic conditions, using monochromatic illumination from light-emitting diodes (LEDs) emitting blue, red, yellow, and white (control) light. The findings indicated that both microalgae strains exhibited higher biomass yield on the mixotrophic growth system when compared to the heterotrophic one, while S. quadricauda generally performed better than C. vulgaris. In mixotrophic mode, the use of different monochromatic illumination affected biomass production differently on both strains. In S. quadricauda, growth rate was higher under red light (μ_max = 0.89 d⁻¹), while the highest biomass concentration and yield per gram of consumed glycerol were achieved under yellow light, reaching 1.86 g/L and Y_x/s = 0.18, respectively. On the other hand, C. vulgaris demonstrated a higher growth rate on blue light (μ_max = 0.45 d⁻¹) and a higher biomass production on white (control) lighting (1.34 g/L). Regarding the production of metabolites, higher yields were achieved during mixotrophic mode in both strains. In C. vulgaris, the highest lipid (26.5% of dry cell weight), protein (63%), and carbohydrate (20.3%) contents were obtained under blue, red, and yellow light, respectively, thus indicating that different light wavelengths probably activate different metabolic pathways. Similar results were obtained for S. quadricauda with red light leading to higher lipid content, while white lighting caused higher production of proteins and carbohydrates. Overall, the study demonstrated the potential of utilizing crude glycerol as a carbon source for the growth and metabolite production of microalgae and, furthermore, revealed that the strains’ behavior varied depending on lighting conditions. Full article

Microalgae attract interest worldwide due to their potential for several applications. Scenedesmus is one of the first in vitro cultured algae due to their rapid growth and handling easiness. Within this genus, cells exhibit a highly resistant wall and propagate both auto- and heterotrophically. The main goal of the present work is to find scalable ways to produce a highly concentrated biomass of Scenedesmus rubescens in heterotrophic conditions. Scenedesmus rubescens growth was improved at the lab-scale by 3.2-fold (from 4.1 to 13 g/L of dry weight) through medium optimization by response surface methodology. Afterwards, scale-up was evaluated in 7 L stirred-tank reactor under fed-batch operation. Then, the optimized medium resulted in an overall productivity of 8.63 g/L/day and a maximum biomass concentration of 69.5 g/L. S. rubescens protein content achieved approximately 31% of dry weight, similar to the protein content of Chlorella vulgaris in heterotrophy. Full article

Chlamydomonas reinhardtii is a unicellular green alga that can grow heterotrophically by using acetate as a carbon source. Carotenoids are natural pigments with biological activity and color, which have functions such as antioxidant, anti-inflammatory, vision protection, etc., and have high commercial value and prospects. We transformed Chlamydomonas reinhardtii with the BKT genes from Phaffia rhodozyma (PrBKT) and Chlamydomonas reinhardtii (CrBKT) via plasmid vector, and screened out the stable transformed algal strains C18 and P1. Under the condition that the cell density of growth was not affected, the total carotenoid content of C18 and P1 was 2.13-fold and 2.20-fold higher than that of the WT, respectively. CrBKT increased the levels of β-carotene and astaxanthin by 1.84-fold and 1.21-fold, respectively, while PrBKT increased them by 1.11-fold and 1.27-fold, respectively. Transcriptome and metabolome analysis of C18 and P1 showed that the overexpression of CrBKT only up-regulated the transcription level of BKT and LCYE (the gene of lycopene e-cyclase). However, in P1, overexpression of PrBKT also led to the up-regulation of ZDS (the gene of ζ-carotene desaturase) and CHYB (the gene of β-carotene hydroxylase). Metabolome results showed that the relative content of canthaxanthin, an intermediate metabolite of astaxanthin synthesis in C18 and P1, decreased. The overall results indicate that there is a structural difference between CrBKT and PrBKT, and overexpression of PrBKT in Chlamydomonas reinhardtii seems to cause more genes in carotenoid pathway metabolism to be up-regulated. Full article

The aim of this study was to improve the protein content and yield of heterotrophic microalgal cultivation and establish a simple, economical, and efficient method for microalgal protein production using the novel green alga, Graesiella emersonii WBG-1, which has not been previously reported for heterotrophic cultivation. Through batch heterotrophic cultivation of this alga, we observed that glucose was the optimal carbon source, while it could not use sucrose as a carbon source. Biomass production and protein content were significantly reduced when sodium acetate was used as the carbon source. Compared with nitrate, protein content increased by 93% when urea was used as the nitrogen source. Cultivation temperature had a significant impact on biomass production and protein content. The optimal conditions were glucose as the carbon source at an initial concentration of 10 g/L, urea as the nitrogen source at an initial concentration of 1.62 g/L, and a culture temperature of 35 °C. On the second day of batch cultivation, the highest protein content (66.14%) was achieved, which was significantly higher than that reported in heterotrophic cultures of Chlorella and much higher than that reported for specially established technologies aimed at increasing the protein content, such as two-stage heterotrophic, heterotrophy–dilution–photoinduction, and mixotrophic processes. These results demonstrate the great potential of the heterotrophic cultivation of G. emersonii WBG-1 for protein production. Full article