Unveiling metabolic diversity through phylogenetic analysis and carbohydrate composition of microalgae isolated from mangroves in Brazil

Mangroves play a crucial ecological and ecosystem role, strongly linked to their microbial communities. However, their photoautotrophic members, particularly microalgae, remain largely unexplored. The unique natural characteristics of these ecosystems, combined with frequent anthropogenic impacts, impose selective pressures on the local microbiota, yielding strains with significant biotechnological potential. This study aimed to isolate, identify, and biochemically characterize the biomass of five microalgae from a mangrove in Baixada Santista (São Paulo, Brazil), focusing on a comprehensive analysis of carbohydrates. The isolated microalgae were identified using conventional genetic markers (18S and ITS), and their biochemical composition was evaluated after cultivation under stressful conditions. The non-structural and structural carbohydrates were characterized through soluble sugars (1.28–2.35 %), starch (11.90–22.39 %), non-cellulosic cell wall monosaccharides (11.57–18.85 %), and cellulose (0.10–6.53 %). All isolates belonged to the phylum Chlorophyta; one strain was identified as Chlorella, while the others were novel species within Micractinium genus (M. brasiliense and M. mangrovii). Three strains exhibited phylogenetically similar characteristics, but their carbohydrate profiles showed distinct metabolic differences, prompting discussions on diversity and genomic regulation mechanisms. Notably, M. brasiliense strain B2 accumulated 46 % total carbohydrates, with significant fractions being starch (19 %) and non-cellulosic wall monosaccharides (18 %). The responses observed under stressful conditions highlighted relevant aspects of cell wall characteristics, particularly in the genus Micractinium, thereby contributing to a still underexplored field. These findings underscore the biorefinery potential of these microalgae, particularly the applicability of their polysaccharide fractions, and highlight mangroves as promising sources of microbial strains with high biotechnological value.