Accelerating ocean deoxygenation driven by anthropogenic warming, eutrophication, and water column stratification poses a global threat to coral reef ecosystems. Several large-scale coral mortality events have been documented on reefs in response to periods of severe hypoxia, wherein environmental dissolved oxygen (DO) levels are insufficient for maintaining physiological homeostasis and supporting coral health. Although adult corals have the capacity for oxyregulation, the extent to which such capacity is affected by reproduction or during coral larval life stages remains poorly understood. Here, we examined oxygen consumption patterns of eight coral species and the offspring of four of these species using closed system respirometry to characterise oxyregulatory performance before and after spawning. Adult corals exhibited a significant increase in oxyregulatory capacity, exerting their maximum regulation capacity (Pcmax) at a lower DO partial pressure (pO2) one week following spawning relative to the 1–2 days preceding gamete release, indicating heightened vulnerability of gravid colonies to hypoxia. Coral larvae also exhibited capacity for oxyregulation, albeit at a lowered capacity (i.e., less regulation possible above oxyconformity based on total positive regulation, Tpos) compared to adults, and larval performance did not correlate with conspecific adult responses. These results highlight ontogenetic and reproductive-state oxyregulation variability, suggesting critical variation in metabolic responses to DO availability across life stages. Characterising coral life stage-specific responses to altered DO availability provides important physiological context for understanding how coral reef organisms may respond to ongoing and future ocean deoxygenation.

Australian breweries produce large volumes of carbon dioxide (CO2) and brewers' spent grain (BSG), presenting an opportunity for sustainable reuse. Microalgae can utilize brewery CO2 and convert it into biomass desirable for ruminant feed applications. However, production costs remain a key limitation, largely influenced by cultivation system design. This techno-economic analysis (TEA) evaluated four systems, including bag photobioreactors (BPBR), vertical tubular photobioreactors (VPBR), thin-layer photobioreactors (TLPBR), and a helical thin-layer photobioreactor (HEPBR), for installation into a small to medium-sized brewery producing 3,000 hectoliters of beer annually and generating 10.2 tons CO2 and 26.4 tons dry BSG. Productivity assumptions were derived from published ranges and applied as baseline values (BPBR: 0.25; VPBR: 1.2; TLPBR: 4.4  kg m-3 d-1). A "what if" scenario assessed three HEPBR productivity cases (5.7, 11.3, and 17  kg m-3 d-1), representing theoretical design potential. Equipment prices were sourced from supplier catalogues, direct quotes, and recent literature. Energy inputs assumed electricity was supplied from solar at 0.20 AUD kWh-1. Results indicate that at this scale, ∼3.41 tons dry algae yr-1 could be cultivated, with standalone algae cultivation economically unviable for feed applications (> $20 AUD kg-1). Integrating algae with BSG reduced total feed costs to < $10 AUD kg-1. The HEPBR scenarios demonstrated that improved reactor design may enhance feasibility, although economic outcomes remain sensitive to productivity assumptions. Overall, the integrated approach evaluated in this TEA aligns with circular bioeconomy principles and provides a pathway for breweries to valorize waste and contribute to more sustainable agricultural practices.

Trophic interactions and nutrient cycling lay at the heart of ecosystem health and biodiversity. In recent years, our understanding of these drivers has been repeatedly challenged by rapid and unanticipated climatic effects, combined with an increasing awareness that carbon acquisition by living organisms often does not meet the textbook duality of autotrophy versus heterotrophy. On coral reefs, mixotrophic feeding that combines these two strategies is widespread. Mixotrophy has been largely overlooked in sponges, which are ecologically important and highly abundant animals that are commonly celebrated both as efficient heterotrophic feeders as well as climate-change winners in these rapidly declining ecosystems. Many Caribbean sponges associate with photosynthetic symbionts, and we here combine oxygen flux measurements with chlorophyll fluorometry in 24 abundant species to show that-in contrast to presumed strict heterotrophy-large portions of their metabolic needs can be covered through symbiont-supplied autotrophic inputs, even when these are in low abundance and when net photosynthesis remains negative. At the ecosystem level, we find that half of the sponge species on the reefs of Cura & ccedil;ao contribute to 11% of gross primary productivity of the entire benthic ecosystem, ranking them the 4th most important producers after macroalgae, hard corals and gorgonians, and higher than crustose-coralline algae, which are well-known phototrophs. Together with their heterotrophic carbon capturing, we argue that the widespread presence and anticipated contribution of photosymbiotic sponges to coastal ecosystem productivity call for further investigation and for revision of benthic food web models and carbon budgets.Read the free for this article on the Journal blog.

Finfish aquaculture is a key contributor to global seafood production, providing quality protein to consumers across the world, however, the search for regenerative, cost-effective and scalable raw materials continues. Alternatives to wild-caught fish have been explored extensively with limited success. Among the most promising alternatives is autotrophic marine microalgae as they produce essential fatty acids, amino acids and bioactive compounds that support fish growth and immune function. However, their development into aquafeed is limited due to cost. By considering the major benefits of microalgae in aquafeed, as well as biotechnological advancements in the industry, this review aims to consolidate multi-disciplinary findings and highlight research opportunities to facilitate widespread adoption of microalgae into aquafeed.

Rheology is crucial for algal cultivation, affecting mixing efficiency and biomass productivity. There is limited research on the rheological aspects of mixed cultures of algae and cyanobacteria. The study aimed to investigate the rheological properties of microalgae and cyanobacteria mixed cultures (Chlorella vulgaris and Microcystis aeruginosa; Nannochloropsis oceanica and Prochlorococcus sp.). While all species were spherical and non-motile with similar aspect ratios, Prochlorococcus sp. exhibited meaningful cell-cell repulsion, increasing its apparent effective volume fraction by 20-40 %. Mixed suspensions of C. vulgaris and M. aeruginosa demonstrated shear thinning at all concentrations, accurately described by a power law model across the explored shear-rate range. The conventional Einstein and Krieger-Dougherty models confirmed that viscosity increased with cell concentration, with Prochlorococcus sp. having the greatest impact. However, these models did not effectively account for mixed suspensions. A novel model, based on Pal (2023) [1] and incorporating two independent parameters, provided a greater reflection of the viscosity in mixed suspensions. Interestingly, parameters for this new mixed culture model could be derived from mono-culture rheological models within the studied concentration range. This first-of-its-kind study highlighted the significance of rheology in optimizing mixed cultures and identifies the need for further research to address rheological challenges, notably towards higher industrial-scale biomass densities.

Understanding how crop varieties acclimate to elevated temperatures is key to priming them for future climates. Here, we imposed a 6 d heat shock treatment (reaching 45 °C) on two genotypes of Sorghum bicolor [one sensitive to heat shock (Sen) and one tolerant (Tol)] growing under two temperature regimes, and carried out a suite of measurements before and during the heat shock. Sen consistently reduced photosynthetic functioning during heat shock, while Tol increased its photosynthetic rate. Higher abundance of heat shock protein transcripts and metabolites related to heat tolerance were noted for Tol when compared with Sen both before and during heat shock, which can be attributed to constitutive and inducible responses to elevated temperatures. In addition, important changes in metabolic pathways were clearly identified for Tol during heat shock (including up-regulation of raffinose family oligosaccharides and down-regulation of the γ-aminobutyric acid catalytic pathway), even as the concentration of hexose sugars became depleted. We infer Tol was able to tolerate elevated temperatures due to up-regulation of osmoprotectants, chaperones, and reactive oxygen species scavengers and by the suppression of SnRK1 via transcripts and metabolites during heat shock. Our results highlight potential targets for attributes of high temperature tolerance that can be utilized in future breeding trials.

Symbiotic cnidarians such as corals and anemones form highly productive and biodiverse coral reef ecosystems in nutrient-poor ocean environments, a phenomenon known as Darwin's paradox. Resolving this paradox requires elucidating the molecular bases of efficient nutrient distribution and recycling in the cnidarian-dinoflagellate symbiosis. Using the sea anemone Aiptasia, we show that during symbiosis, the increased availability of glucose and the presence of the algae jointly induce the coordinated up-regulation and relocalization of glucose and ammonium transporters. These molecular responses are critical to support symbiont functioning and organism-wide nitrogen assimilation through glutamine synthetase/glutamate synthase-mediated amino acid biosynthesis. Our results reveal crucial aspects of the molecular mechanisms underlying nitrogen conservation and recycling in these organisms that allow them to thrive in the nitrogen-poor ocean environments.

Random mutagenesis of microalgae offers a novel solution to improve the biomining efficiency of rare earth elements (REEs). Cold atmospheric plasma is an emerging technology to mutate microalgae strains randomly and enhance their performance. This study aims to (i) investigate the performance of mutant microalgae Chlorella vulgaris for REEs recovery, (ii) assess the stability of mutant traits at different scales, (iii) examine the metabolomic profile of the mutant C. vulgaris, and (iv) explore the potential mechanism behind cold atmospheric plasma mutagenesis. The results show that microalgae mutants exposed to cold atmospheric plasma can recover up to 3 times more REEs from bauxite than the wild type. In the leachate of clay-hosted REEs, mutant microalgae can recover 7 to 25 % more REEs than the wild type. At the bench scale, mutant strains are stable in tissue culture flasks for 3 cycles. Metabolomic analysis shows that most of the pigment, total lipid and fatty acid methyl ester (FAME) produced by mutant microalgae are lower than the wild type from 10 % to 55 %, except methyl arachidate (C20:0) and trans-9-elaidic acid methyl ester (C18:1). The optical emission spectra from plasma discharge shows that plasma discharge consists of excited N2*, N2+ and O species, which might cause microalgae mutagenesis.

Seagrasses are critical global carbon sinks declining at a rapid pace. Phytotoxic hydrogen sulfides (H2S) and light deprivation are known drivers of seagrass loss worldwide; however, the underlying physiological mechanisms are not well understood. To address this knowledge gap, we explored the fate of inorganic carbon (Ci) in Halophila ovalis which were exposed to either low light (88% shade), (ii) sediment H2S stress, or (iii) both stressors combined in a mesocosm setting. Using a novel multidisciplinary approach in combination with a 13C tracer (NaH13CO3), we investigated differences in Ci acquisition, metabolite incorporation, and carbon translocation. Ci acquisition into seagrass leaves was impacted by both H2S and low light stress, synergistically reducing carbon acquisition rates by 10.9-fold. The incorporation of 13C into leaf sugar pools was also affected by both stressors. In addition, low light impacted critical intermediates of both glycolysis and the tricarboxylic acid cycle. Below-ground data suggest that H2S interferes with carbon translocation from the leaf into the rhizome and caused an 85% reduction in rhizome growth, irrespective of light. Overall, this study suggests that it is likely a multilevel (acquisition, metabolism, translocation) disruption of the carbon budget that threatens seagrass health and survival under both H2S and low light stress.

Background Chlamydomonas reinhardtii is gaining recognition as a promising expression system for the production of recombinant proteins. However, its performance as a cellular biofactory remains suboptimal, especially with respect to consistent expression of heterologous genes. Gene silencing mechanisms, position effect, and low nuclear transgene expression are major drawbacks for recombinant protein production in this model system. To unveil the molecular changes following transgene insertion, retention, and expression in this species, we genetically engineered C. reinhardtii wild type strain 137c (strain cc-125 mt+) to express the fluorescent protein mVenus and subsequently analysed its intracellular proteome. Results The obtained transgenic cell lines showed differences in abundance in more than 400 proteins, with multiple pathways altered post-transformation. Proteins involved in chromatin remodelling, translation initiation and elongation, and protein quality control and transport were found in lower abundance. On the other hand, ribosomal proteins showed higher abundance, a signal of ribosomal stress response. Conclusions These results provide new insights into the modifications of C. reinhardtii proteome after transformation, highlighting possible pathways involved in gene silencing. Moreover, this study identifies multiple protein targets for future genetic engineering approaches to improve the prospective use of C. reinhardtii as cell biofactory for industrial applications.

Biomining using microalgae has emerged as a sustainable option to extract rare earth elements (REEs). This study aims to (i) explore the capability of REEs recovery from bauxite by microalgae, (ii) assess the change of biochemical function affected by bauxite, and (iii) investigate the effects of operating conditions (i.e., aeration rate, pH, hydraulic retention time) to REEs recovery. The results showed that increasing bauxite in microalgae culture increases REEs recovery in biomass and production of biochemical compounds (e.g., pigments and Ca-Mg ATPase enzyme) up to 10 %. The optimum pulp ratio of bauxite in the microalgae culture ranges from 0.2 % to 0.6 %. Chlorella vulgaris was the most promising, with two times higher in REEs recovery in biomass than the other species. REEs accumulated in microalgae biomass decreased with increasing pH in the culture. This study establishes a platform to make the scaling up of REEs biomining by microalgae plausible.

Organic pollutants (OPs) discharged via wastewater can severely impact public health, natural habitat, and environment in long term. The microalgae-bacteria consortia (MBC) demonstrates its potential as a sustainable bioremediation method for organic pollutants remediation from wastewater. The overarching goal of this study is to review (i) the formation of microalgae and bacteria consortia, (ii) the mechanism of MBC in OCs removal, (iii) the effects of operating conditions on the treatment efficiency, and (iv) the omics approach of MBC for removing OCs in wastewater. The review provides further insights into the application of omics techniques to identify microalgae-bacteria interaction in the consortia. Transcriptomics and metabolomics have elucidated the response of MBC to the impact of culturing conditions and presence of OCs in wastewater. Metagenomics identifies the four dominating-algal strains and observing microbial dynamics during ciprofloxacin treatment. The data of omics approach provide a strong support for upscaling MBC for OCs remediation in wastewater.

Heat priming improves plants tolerance to a recurring heat stress event. The underlying molecular mechanisms of heat priming are largely unknown in seagrasses. Here, ad hoc mesocosm experiments were conducted with two Mediterranean seagrass species, Posidonia oceanica and Cymodocea nodosa. Plants were first exposed to heat-priming, followed by a heat-triggering event. A comprehensive assessment of plant stress response across different levels of biological organization was performed at the end of the triggering event. Morphological and physiological results showed an improved response of heat-primed P. oceanica plants while in C. nodosa both heat- and non-primed plants enhanced their growth rates at the end of the triggering event. As resulting from whole transcriptome sequencing, molecular functions related to several cellular compartments and processes were involved in the response to warming of non-primed plants, while the response of heat-primed plants involved a limited group of processes. Our results suggest that seagrasses acquire a primed state during the priming event, that eventually gives plants the ability to induce a more energy-effective response when the thermal stress event recurs. Different species may differ in their ability to perform an improved heat stress response after priming. This study provides pioneer molecular insights into the emerging topic of seagrass stress priming and may benefit future studies in the field.

Adaptation to local conditions is known to occur in seagrasses; however, knowledge of the genetic basis underlying this phenomenon remains scarce. Here, we analysed Posidonia oceanica from six sites within and around the Stagnone di Marsala, a semi-enclosed coastal lagoon where salinity and temperature exceed the generally described tolerance thresholds of the species. Sea surface temperatures (SSTs) were measured and plant samples were collected for the assessment of morphology, flowering rate and for screening genome-wide polymorphisms using double digest restriction-site-associated DNA sequencing. Results demonstrated more extreme SSTs and salinity levels inside the lagoon than the outer lagoon regions. Morphological results showed significantly fewer and shorter leaves and reduced rhizome growth of P. oceanica from the inner lagoon and past flowering events were recorded only for a meadow farthest away from the lagoon. Using an array of 51,329 single nucleotide polymorphisms, we revealed a clear genetic structure among the study sites and confirmed the genetic isolation and high clonality of the innermost site. In all, 14 outlier loci were identified and annotated with several proteins including those relate to plant stress response, protein transport and regulators of plant-specific developmental events. Especially, five outlier loci showed maximum allele frequency at the innermost site, likely reflecting adaptation to the extreme temperature and salinity regimes, possibly due to the selection of more resistant genotypes and the progressive restriction of gene flow. Overall, this study helps us to disentangle the genetic basis of seagrass adaptation to local environmental conditions and may support future works on assisted evolution in seagrasses.

AbstractFluorescence-Activated Cell Sorting (FACS) is a powerful method with many applications in microalgal research, especially for screening and selection of cells with improved phenotypes. However, the technology requires further investigation to determine the phenotypic stability of sorted populations.Phaeodactylum tricornutumcells were sorted using FACS with excitation/emission parameters targeted towards favouring the industrially-relevant carotenoid fucoxanthin. The resulting cultures showed significantly higher growth rate (1.10 ×), biomass (1.30 ×), chlorophyllalevels (1.22 ×) and fucoxanthin productivity (1.41 ×) relative to the wild-type strain. RNA-seq was used to elucidate the underlying molecular-level regulatory changes associated with these traits, and represents the first study do so on FACS-sorted microalgal cultures. Transcriptome analysis corroborated evidence of increased chlorophyllaand fucoxanthin, showing enrichment for the genes/pathways for tetrapyrrole biosynthesis and for suites of genes directly related to photosynthesis. Only three genes were upregulated in the MEP (non-mevalonate) pathway to carotenoid biosynthesis pathway, suggesting either a strong influence ofIDI,CRTISO5andZEP1on fucoxanthin biosynthesis or a post-transcriptional or post-translational mechanism for the observed increase in fucoxanthin content.

We investigated two non-ionising mutagens in the form of ultraviolet radiation (UV) and ethyl methanosulfonate (EMS) and an ionising mutagen (X-ray) as methods to increase fucoxanthin content in the model diatom Phaeodactylum tricornutum . We implemented an ultra-high throughput method using fluorescence-activated cell sorting (FACS) and live culture spectral deconvolution for isolation and screening of potential pigment mutants, and assessed phenotype stability by measuring pigment content over 6 months using high-performance liquid chromatography (HPLC) to investigate the viability of long-term mutants. Both UV and EMS resulted in significantly higher fucoxanthin within the 6 month period after treatment, likely as a result of phenotype instability. A maximum fucoxanthin content of 135 ± 10% wild-type found in the EMS strain, a 35% increase. We found mutants generated using all methods underwent reversion to the wild-type phenotype within a 6 month time period. X-ray treatments produced a consistently unstable phenotype even at the maximum treatment of 1000 Grays, while a UV mutant and an EMS mutant reverted to wild-type after 4 months and 6 months, respectively, despite showing previously higher fucoxanthin than wild-type. This work provides new insights into key areas of microalgal biotechnology, by (i) demonstrating the use of an ionising mutagen (X-ray) on a biotechnologically relevant microalga, and by (ii) introducing temporal analysis of mutants which has substantial implications for strain creation and utility for industrial applications.

The marine bacterium Vibrio parahaemolyticus is the leading cause of seafood-related food poisoning worldwide and a pathogen of marine species harvested in aquaculture. An outbreak of pathogenic V. parahaemolyticus within crustacean and bi-valve aquaculture facilities often results in significant loss of farmed product and in the spread of the pathogen into the human population. Evidence shows several marine bacteria and microalgae species have antibacterial effects against marine pathogens, including V. parahaemolyticus . This study explored the potential of combining possible mutualistic species as a consortium to enhance antibacterial properties against V. parahaemolyticus . Marine bacteria and microalgae were screened with the aim of identifying those able to successfully coexist while demonstrating growth suppression of multiple V. parahaemolyticus strains. This trial involved four screening phases to find effective inhibitor species and to gain insight into species-specific influences on cell growth. The combination of Tetraselmis sp. and Pseudoalteromonas peptidolytica achieved the greatest inhibition rate of V. parahaemolyticus of all combinations. This pairing resulted in the significant reduction of up to 24 ± 15% in Vibrio sp. copy number mL −1 day −1 in two of the five examined V. parahaemolyticus strains within five days, compared to control cultures absent of probiotic bacteria. Applying probiotic consortia such as this has the potential for use as a biocontrol technique within mariculture, but it will require additional research into the self-sustainability of successful consortia in natural aquatic conditions.

Global climate change is threatening the persistence of coral reefs as associated summer heatwaves trigger the loss of microalgal endosymbionts (Symbiodiniaceae) from the coral tissues, or coral bleaching. We infected aposymbiotic juveniles of the coral Acropora tenuis with either wildtype (WT10) or heat-evolved (SS1 or SS8) Symbiodiniaceae strains Cladocopium proliferum (formerly referred to as Cladocopium goreaui and Cladocopium C1 acro ). After 10 months at 27 °C, SS8-juveniles were 2 × larger than SS1- or WT10-juveniles. In response to a simulated heatwave (31 °C for 41 days), the WT10-juveniles bleached and showed a decline in respiration while cell densities and respiration in both SS-juvenile groups remained unchanged compared to the controls. These results reveal that some heat-evolved strains can increase the bleaching tolerance of juvenile corals without a trade-off against growth. This response is opposite to the lower nutrient provisioning often reported for naturally thermotolerant Symbiodiniaceae (e.g. genus Durusdinium ) , thereby offering enhanced fitness to the host without the ecological consequences of diminished growth.

Behaviours such as chemotaxis can facilitate metabolic exchanges between phytoplankton and heterotrophic bacteria, which ultimately regulate oceanic productivity and biogeochemistry. However, numerically dominant picophytoplankton have been considered too small to be detected by chemotactic bacteria, implying that cell-cell interactions might not be possible between some of the most abundant organisms in the ocean. Here we examined how bacterial behaviour influences metabolic exchanges at the single-cell level between the ubiquitous picophytoplankton Synechococcus and the heterotrophic bacterium Marinobacter adhaerens, using bacterial mutants deficient in motility and chemotaxis. Stable-isotope tracking revealed that chemotaxis increased nitrogen and carbon uptake of both partners by up to 4.4-fold. A mathematical model following thousands of cells confirmed that short periods of exposure to small but nutrient-rich microenvironments surrounding Synechococcus cells provide a considerable competitive advantage to chemotactic bacteria. These findings reveal that transient interactions mediated by chemotaxis can underpin metabolic relationships among the ocean's most abundant microorganisms.