Abstract
Phycosphere harbors cross-kingdom interactions with significant ecological relevance for harmful algal blooms (HAB) and phycotoxins biosynthesis. Previously, a new red-pigmented bacterium designated as strain LZ-28 was isolated from phycosphere microbiota of typical HAB dinoflagellate Alexandrium catenella LZT09 which is a vitamin B12 auxotroph and produces high levels of paralytic shellfish poisoning toxins (PST). Strain LZ-28 exhibited obvious growth-promoting activity toward its algal host, along with the production of active bioflocculanting exopolysaccharides (EPS). But the phylogenetic affiliation and genomic potential of this versatile bacterium has not yet been elucidated. In this study, we carried out combined taxonomic and phylogenomic analysis to clarify the taxonomic classification of strain LZ-28. The obtained 16S rRNA phylogeny revealed close taxonomic relationship between strain LZ-28 and other Mameliella alba members. Additional calculations of key phylogenomic parameters, average nucleotide identity (ANI), the average amino acid identity (AAI) and the digital DNA-DNA hybridization (dDDH) values based on genomes of strain LZ-28 and type strain of Mameliella alba were all exceeded the limit of species circumscription. Collectively considering the phenotypic and biochemical characterizations, strain LZ-28 was therefore identified as a new member of Mameliella alba. Furthermore, based on the genomic evidence, potential algae-bacteria interactions of strain LZ-28 with host algae LZT09 were elucidated through the associations with photosynthetic and antioxidant carotenoids, supplying of bacterial VB12 to auxotroph host, and versatile EPS serving for bacterial colonization and nutrient exchange during their interactions, along with stress response systems to defense oxidative stress and quorum sensing (QS) signals benefited survival for bacteria in the symbiotic system. Comparative genomics shed light on similar genomic features between M. alba strains, revealed potential close associations of strain LZ-28 with its algae host, and further enriched the genomic repertoire of interactions between phycosphere microbiota and algal host LZT09.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Data Availability: All relevant data are within the manuscript.
Abbreviations
- HAB
- Harmful algal blooms
- EPS
- Exopolysaccharides
- ANI
- Average nucleotide identity
- AAI
- Average amino acid identity
- dDDH
- digital DNA-DNA hybridization
- QS
- Quorum sensing
- GTAs
- Gene transfer agents
- ABI
- Algae-bacteria interactions
- PST
- Paralytic shellfish poisoning toxins
- PMP
- Phycosphere Microbiome Project
- PM
- Phycosphere microbiota
- DMSP
- Dimethylsulfoniopropionate
- MA
- Marine agar
- MGPB
- Microalgae growth-promoting bacterium
- PHB
- Poly-β-hydroxybutyrate
- PG
- Phosphatidylglycerol
- PE
- Phosphatidylethanolamine
- PC
- Phosphatidylcholine
- GL
- Glycolipid
- PL
- Phospholipid
- NJ
- Neighbour joining
- ML
- Maximum likelihood
- MP
- Maximum parsimony
- NCBI
- National center for biotechnology information
- UBCG
- Up-to-date bacterial core gene
- HGT
- Horizontal gene transfer
- BGCs
- Biosynthetic gene clusters
- PKS
- Polyketide synthases
- AHL
- N-acylhomoserine lactone
- PHA
- Polyhydroxyalkanoate
- DMSP
- Dimethylsulfoniopropionate
- TQO
- Thiosulfate, quinone oxidoreductase
- SIR
- Sulfite reductase
- ROS
- Reactive oxygen species
- SOD
- Superoxide dismutase
- CAT
- Catalases
- GPX
- Glutathione peroxidases