Dietary supplementation with Synechococcus elongatus PCC 7942 in zebrafish (Danio rerio): impact on zootechnical performance, brain transcriptome, hepato-intestinal physiology, and gut microbiome
Author: Mirna Leandra Enriquez Reyes (Currículo Lattes)
Advisor: Dr. Luis Fernando Fernandes Marins
Abstract
The search for alternative and sustainable ingredients in aquaculture has led to the use of photosynthetic microorganisms, such as cyanobacteria, due to their high nutritional value and biotechnological potential. Synechococcus elongatus PCC 7942 stands out for its rapid growth rate, ability to produce bioactive compounds, and ease of genetic manipulation. However, its effects as a dietary supplement for fish remain largely unexplored. In this context, this Thesis evaluated the impact of S. elongatus PCC 7942 supplementation in zebrafish (Danio rerio), focusing on zootechnical performance, brain metabolism, hepato-intestinal health, and gut microbiota composition. For this, 120 zebrafish were divided into two groups: a control group, fed with a commercial diet, and an experimental group, fed with the same diet supplemented with S. elongatus PCC 7942 for 35 days. Zootechnical parameters, gene expression in the brain and liver, liver histology, intestinal morphometry, and gut microbiota composition (using third-generation sequencing) were analyzed. The results showed a significant increase in feed intake and condition factor in the supplemented fish, suggesting improved palatability of the diet. Transcriptomic analysis revealed alterations in brain gene expression, with upregulation of genes involved in energy metabolism and antioxidant response, while genes associated with neuroplasticity were downregulated, suggesting a more stable neural metabolic environment. In the liver, a lower incidence of hepatic damage was observed in supplemented fish, indicating a potential hepatoprotective effect of the cyanobacterium. Furthermore, the reduced expression of genes related to xenobiotic metabolism and antioxidant enzymes suggests that supplementation did not induce significant oxidative stress. Morphological analysis of the intestine showed no major structural changes, demonstrating good tolerance to the supplement. Gut microbiota composition remained stable in terms of overall diversity, but specific shifts in bacterial abundance were detected. A reduction in Pirellula abundance and the absence of mycoplasmas in the supplemented fish suggest a beneficial effect on the gut microbiome, potentially limiting the presence of opportunistic pathogenic microorganisms. The findings of this study demonstrate that S. elongatus PCC 7942 is a safe dietary supplement for fish and may act as a metabolic and microbiological modulator without causing adverse effects on hepato-intestinal physiology. Its potential as a delivery vehicle for bioactive compounds opens new perspectives for applications in fish nutrition and health. Future studies should further investigate its digestibility, effects on the immune system, and genetic engineering strategies to enhance its probiotic and nutraceutical benefits in aquaculture.