The current study gives a detailed insight into mutualistic collaboration of microalgae and bacteria, including the involvement of competitive interplay between bacteria. We provide experimental evidence that Gram-negative bacteria belonging to the Dyadobacter , Porphyrobacter , and Variovorax are the key players in a Scenedesmus quadricauda alga-bacteria interaction.

Based on previous research, related to detailed insight into mutualistic collaboration of microalga and its microbiome, we established an artificial plant-bacteria system of the microalga Micrasterias radians MZCH 672 and the bacterial isolate Dyadobacter sp. HH091. The bacteria, affiliated with the phylum Bacteroidota, strongly stimulated growth of the microalga when it was added to axenic algal cultures. For further advances, we studied the isolate HH091 and its interaction with the microalga M. radians using transcriptome and extensive genome analyses. The genome of HH091 contains predicted polysaccharide utilizing gene clusters co-working with the type IX secretion system (T9SS) and conceivably involved in the algae-bacteria liaison. Here, we focus on characterizing the mechanism of T9SS, implementing the attachment and invasion of microalga by Dyadobacter sp. HH091. Omics analysis exposed T9SS genes: gldK, gldL, gldM, gldN, sprA, sprE, sprF, sprT, porU and porV. Besides, gld genes not considered as the T9SS components but required for gliding motility and protein secretion (gldA, gldB, gldD, gldF, gldG, gldH, gldI, gldJ), were also identified at this analysis. A first model of T9SS apparatus of Dyadobacter was proposed in a course of this research. Using the combination of fluorescence labeling of Dyadobacter sp. HH091, we examined the bacterial colonisation and penetration into the cell wall of the algal host M. radians MZCH 672.

Scenedesmus acuminatus, also known as Tetradesmus acuminatus, is a promising green microalga for sustainable production of microalga products, including valuable compounds such as astaxanthin, β-carotene, and lutein, polysaccharides such as β-glucan, and polyunsaturated fatty acids. Here, we report the draft whole-genome sequence of Scenedesmus acuminatus SAG 38.81.