Abstract
The aim of the study was to explore the relationship between membrane-regulating functional lipids of three fucacean species and their associated epiphytic bacterial communities. The analyzed algae Treptacantha barbata, Carpodesmia crinita and Cystoseira compressa, formerly classified under the Cystoseira genus, are indigenous to the Adriatic Sea. The thalli of sampled Fucales species were divided into perennial and annual parts. T. barbata and C. crinita show high contents of mono- and polyunsaturated fatty acids but, however, show a clear distinction between branches, cauloids and apical parts. Along with the highest unsaturation degree (4.32), the C. crinita branches and apical parts demonstrated high proportion of both C18 and C20 polyunsaturated fatty acids, with eicosapentaenoic (C20:5 n-3) and arachidonic (C20:4 n-6) fatty acids up to 5.46% and 13.82%, respectively. The highest proportion of saturated fatty acids was found in thalli of C. compressa, particularly on cauloids and old branches (≥90%). The similarity profile routine analysis of fatty acids and microbial community structure has shown clear separation of the cauloids and apical parts from the branches of C. crinita and T. barbata. Based on the nonmetric multidimensional scaling analysis several representatives of the Gammaproteobacteria class, identified as Vibrionales (Vibrio), Cellvibrionales and Xanthomonadales, which contributed strongly to the separation of T. barbata apical parts and branches, C. compressa receptacles and C. crinita branches from the T. barbata cauloids and C. crinita apical parts and cauloids. The highest richness in polyunsaturated fatty acids, in particular C18:3(n-3), C20:4(n-6) and C20:5(n-3), was observed on branches, accompanied by a distinctive epiphytic microbial structure dominated by numerous representatives with potentially beneficial biological activity. The results showed a strong relationship between fatty acid profiles of the analyzed species and phycosphere community structure, underlining the host physiological condition in shaping the biological interactions and maintaining a healthy microbiome, as well as compiling the ecophysiological and molecular research in order to better assess the resilience of the ecosystem.
Highlights
Brown macroalgae play a major ecological role in sustaining complex food webs and maintaining high biodiversity in the Adriatic Sea [1]
The fatty acid composition of T. barbata and C. crinita was dominated by C16:0, C18:1 and C20:4 fatty acids, whereas the C. compressa profile was dominated by C14:0, C16:0 and C18:0
Along with the highest unsaturation degree, the C. crinita branches and apical parts demonstrated high proportions of both C18 and C20 polyunsaturated fatty acids (PUFAs), with docosapentaenoic (EPA, C20:5 n-3) and arachidonic (ARA, C20:4 n-6) fatty acid up to 5.46% and 13.82%, respectively
Summary
Brown macroalgae play a major ecological role in sustaining complex food webs and maintaining high biodiversity in the Adriatic Sea [1]. Previous studies have demonstrated that epiphytic bacteria on marine algae, in particular Fucales [4,5], differ significantly from bacterial communities on abiotic surfaces and in the surrounding water [6] and that the anti-fouling activity of secondary metabolites in macroalgae and their biofilms are species specific [7] These findings support the hypothesis that the brown algae use biochemical defense mechanisms in control the fouling processes through the selection of beneficial bacteria in the biofilm, there is still very little knowledge about the diversity, degree of host specificity, functional role or the molecular mechanisms of host–microbe interactions in marine systems. In addition to the species ecology and the vegetative cycling that significantly influence species resilience to the climate and anthropogenic stress and recovery, positive species interactions in the phycosphere can act as a first defense barrier against temperature rises, pH declines or pathogenicity [11,12]
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