TL;DR
Findings suggest that low-dose ethephon elicitation may be a simple strategy to enhance phycobiliprotein accumulation in Arthrospira platensis.
Microalgal growth-promoting bacteria (MGPBs) represent a promising strategy to enhance biomass productivity, yet the mechanistic basis of these mutualistic interactions remains poorly understood. Here, we isolated a new MGPB, Cupriavidus oxalaticus MEYA8, and characterized its mutualistic interaction with the model microalga Chlamydomonas reinhardtii. Co-cultivation at an optimal MEYA8: Chlamydomonas ratio greatly enhanced microalgal cell density and chlorophyll content, which reached 2.1-fold and 1.6-fold those of the control, respectively, with markedly improved photosynthetic efficiency across both photosystems. Transwell assays confirmed that this promotion is mediated by diffusible metabolites rather than direct cell contact. Metabolites and multi-omics analyses revealed that MEYA8 can produce compounds similar to indole-3-acetic acid (IAA) and is adapted to the microalgal phycosphere by preferentially utilizing organic acids and amino acid derivatives. In response, Chlamydomonas upregulated proteins involved in photosynthetic electron transport, energy metabolism, and nitrogen assimilation, consistent with the observed enhancement in photosynthetic performance. These findings suggest a metabolically reciprocal interaction model: MEYA8 supplies diffusible growth-promoting factors such as IAA-like compounds to enhance Chlamydomonas photosynthesis and growth, while Chlamydomonas provides organic substrates that sustain bacterial proliferation. Our work provides new insights into algal–bacterial mutualism and may provide a new microbial resource for engineering microalgal and beneficial bacterial consortia.
Coinoculation with growth-promoting microorganisms has proven to be an efficient strategy for enhancing the agronomic performance of onion (Allium cepa L.). This study evaluated the effect of inoculating Pantoea phytobeneficialis PF55 and Trichoderma harzianum ESALQ 1306, applied individually and in combination, on agronomic, biochemical, and microbiological variables of the Valessul cultivar. The experiment was conducted in a randomized block design with four treatments (non-inoculated, PF55, ESALQ 1306, and PF55 + ESALQ 1306) and 12 replications in Florianópolis, SC, Brazil. Inoculation was performed 14 days after seedling transplant. Inoculation with PF55 resulted in a measurable increase in productivity. The results indicate that PF55 application increased productivity, biomass, and nutrient accumulation, while coinoculation with T. harzianum ESALQ 1306 promoted specific effects, such as higher carotenoid contents and soil microbial activity. Isolated inoculation with T. harzianum ESALQ 1306 increased chlorophyll b and total contents, as well as soluble solids levels. These results confirm that the bacterium acts as the primary growth-promoting agent, while the fungus plays a modulating role, influencing physiological and edaphic processes in a more restricted manner.
Abstract Gracilariopsis lemaneiformis is cultivated as feed for abalone and raw material for agar, and its economic benefits are strongly correlated with its yield. Plant growth regulators such as α-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (6-BA), can effectively promote plant growth and biomass accumulation, however, their effects on macroalgae remain less thoroughly investigated. This study aimed to evaluate the roles of NAA and 6-BA on the G. lemaneiformis using physiological and transcriptomic analyses. Results showed that both NAA and 6-BA enhanced the relative growth rate, linear growth rate of main and lateral branches, as well as accumulation of phycobiliprotein, soluble polysaccharide and total lipid. Transcriptomic results corroborated the physiological performances. Both NAA and 6-BA upregulated carbohydrate metabolism, photosynthesis-related metabolism, amino acid biosynthesis and purine metabolism. In addition, NAA specifically increased the expression levels of the genes related to cell division process, including CDC20, CDC42 and expansin-like protein, while 6-BA upregulated the expression levels of ABC transporters, including ABCD3 and ABCG2. These findings will not only deepen our understanding of the NAA and 6-BA roles in promoting algal growth, but also be useful in cultivating the seedlings of G. lemaneiformis.
Trade-offs between biomass productivity and metabolite accumulation constrain microalgae cultivation for high-value biomolecules due to nutrient competition and concurrent metabolic pathways. This study evaluated the independent and combined effects of static magnetic fields (SMF) and polymeric nanofibers on growth performance, biomass composition, and exopolysaccharide (EPS) profiles of Porphyridium purpureum. A process intensification strategy was applied by integrating external physical forcing and structured functional materials to enhance mass transfer and carbon utilization efficiency. Cultivations were conducted under controlled photobioreactor conditions using SMF exposure for 1 h d−1 or 24 h d−1, combined with polyacrylonitrile (PAN) nanofibers or monoethanolamine-functionalized nanofibers (MEA). Intermittent SMF increased maximal biomass concentration by 36% compared to the control, whereas continuous SMF, MEA nanofibers, and combined conditions reduced biomass accumulation by up to 45%. SMF promoted metabolic reallocation toward carbon-rich fractions, increasing released polysaccharides by 83% and lipid content by 38%. Nanofibers strongly enhanced pigment biosynthesis, with β-phycoerythrin reaching 41.3 mg g−1, threefold higher than the control. EPS characterization showed increased purity, uronic acid content, and sulfation depending on treatment. Overall, SMF and nanofibers acted as selective intensification tools, enabling tunable modulation of growth, metabolism, and product formation.