Metabolic relationships between marine red algae and algae-associated bacteria

Mutualistic interactions between marine phototrophs and associated bacteria are an important strategy for their successful survival in the ocean, but little is known about their metabolic relationships. Here, bacterial communities in the algal sphere (AS) and bulk solution (BS) of nine marine red algal cultures were analyzed, and Roseibium and Phycisphaera were identified significantly more abundantly in AS than in BS. The metabolic features of Roseibium RMAR6-6 (isolated and genome-sequenced), Phycisphaera MAG 12 (obtained by metagenomic sequencing), and a marine red alga, Porphyridium purpureum CCMP1328 (from GenBank), were analyzed bioinformatically. RMAR6-6 has the genetic capability to fix nitrogen and produce B vitamins (B1, B2, B5, B6, B9, and B12), bacterioferritin, dimethylsulfoniopropionate (DMSP), and phenylacetate that may enhance algal growth, whereas MAG 12 may have a limited metabolic capability, not producing vitamins B9 and B12, DMSP, phenylacetate, and siderophores, but with the ability to produce bacitracin, possibly modulating algal microbiome. P. purpureum CCMP1328 lacks the genetic capability to fix nitrogen and produce vitamin B12, DMSP, phenylacetate, and siderophore. It was shown that the nitrogen-fixing ability of RMAR6-6 promoted the growth of P. purpureum, and DMSP reduced the oxidative stress of P. purpureum. The metabolic interactions between strain RMAR6-6 and P. purpureum CCMP1328 were also investigated by the transcriptomic analyses of their monoculture and co-culture. Taken together, potential metabolic relationships between Roseibium and P. purpureum were proposed. This study provides a better understanding of the metabolic relationships between marine algae and algae-associated bacteria for successful growth.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00227-z.

Particle-attached bacteria act as gatekeepers in the decomposition of complex phytoplankton polysaccharides

BACKGROUND

Marine microalgae (phytoplankton) mediate almost half of the worldwide photosynthetic carbon dioxide fixation and therefore play a pivotal role in global carbon cycling, most prominently during massive phytoplankton blooms. Phytoplankton biomass consists of considerable proportions of polysaccharides, substantial parts of which are rapidly remineralized by heterotrophic bacteria. We analyzed the diversity, activity, and functional potential of such polysaccharide-degrading bacteria in different size fractions during a diverse spring phytoplankton bloom at Helgoland Roads (southern North Sea) at high temporal resolution using microscopic, physicochemical, biodiversity, metagenome, and metaproteome analyses.

RESULTS

Prominent active 0.2-3 µm free-living clades comprised Aurantivirga, "Formosa", Cd. Prosiliicoccus, NS4, NS5, Amylibacter, Planktomarina, SAR11 Ia, SAR92, and SAR86, whereas BD1-7, Stappiaceae, Nitrincolaceae, Methylophagaceae, Sulfitobacter, NS9, Polaribacter, Lentimonas, CL500-3, Algibacter, and Glaciecola dominated 3-10 µm and > 10 µm particles. Particle-attached bacteria were more diverse and exhibited more dynamic adaptive shifts over time in terms of taxonomic composition and repertoires of encoded polysaccharide-targeting enzymes. In total, 305 species-level metagenome-assembled genomes were obtained, including 152 particle-attached bacteria, 100 of which were novel for the sampling site with 76 representing new species. Compared to free-living bacteria, they featured on average larger metagenome-assembled genomes with higher proportions of polysaccharide utilization loci. The latter were predicted to target a broader spectrum of polysaccharide substrates, ranging from readily soluble, simple structured storage polysaccharides (e.g., laminarin, α-glucans) to less soluble, complex structural, or secreted polysaccharides (e.g., xylans, cellulose, pectins). In particular, the potential to target poorly soluble or complex polysaccharides was more widespread among abundant and active particle-attached bacteria.

CONCLUSIONS

Particle-attached bacteria represented only 1% of all bloom-associated bacteria, yet our data suggest that many abundant active clades played a pivotal gatekeeping role in the solubilization and subsequent degradation of numerous important classes of algal glycans. The high diversity of polysaccharide niches among the most active particle-attached clades therefore is a determining factor for the proportion of algal polysaccharides that can be rapidly remineralized during generally short-lived phytoplankton bloom events. Video Abstract.

Algicella marina gen. nov., sp. nov., a novel marine bacterium isolated from a Pacific red alga

A novel Gram-staining negative, strictly aerobic, rod-shaped, and non-motile bacterium, designated strain 9Alg 56^T, was isolated from the red alga Tichocarpus crinitus. The phylogenetic analysis based on 16S rRNA gene sequences placed the novel strain within the family Rhodobacteraceae, the order Rhodobacterales, the class Alphaproteobacteria, the phylum Pseudomonadota. The nearest neighbors of the new strain were Pontivivens insulae KCTC 42458^T, Oceanibium sediminis KCTC 62076^T, Halovulum dunhuangense YYQ-30^T and Monaibacterium marinum C7^T with 16S rRNA gene sequence similarity of 94.7, 94.4%, 93.1 and 92.7%, respectively. The AAI/ANI/dDDH values between 9Alg 56^T and the five species of the closest genera (Pontivivens, Oceanibium, Halovulum, Monaibacterium, and 'Oceanomicrobium') were 58.63-63.91%/ 75.91-77.37%/ 19.3-20.4%. The prevalent fatty acids of strain 9Alg 56^T were C_18:1 ω7c, C_18:0 and C_14:0 3-OH. The polar lipid profile consisted of phosphatidylethanolamine, phosphatidylglycerol, phosphatidic acid, phosphatidylcholine, and two unidentified lipids. The DNA G+C content of strain 9Alg 56^T was 61.5 mol%. A combination of the genotypic and phenotypic data showed that the algal isolate represents a novel genus and species, for which the name Algicella marina gen. nov., sp. nov. is proposed. The type strain is 9Alg 56^T (= KCTC 72005^T = KMM 6775^T).

Parasphingopyxis marina sp. nov. isolated from coastal seawater

A Gram-stain-negative, aerobic, yellow-pigmented and non-motile rod-shaped bacterium, designated as GrpM-11^T, was isolated from coastal seawater collected from the East Sea, Republic of Korea. Strain GrpM-11^T could grow at 10-40 °C (optimum, 35 °C), at pH 5.5-9.5 (optimum, pH 7.0) and in the presence of 0-8 % (w/v) NaCl (optimum, 3-4 %). Cells hydrolysed aesculin, gelatin and casein, but could not reduce nitrate to nitrite. The 16S rRNA gene sequence analysis showed that this strain formed a distinct phylogenic lineage with Parasphingopyxis algicola ATAX6-5^T (96.2 % sequence identity) and Parasphingopyxis lamellibrachiae DSM 26725^T (96.2 % identity) and belonged to the genus Parasphingopyxis. The predominant isoprenoid quinone was ubiquinone-10. The polar lipid profile of strain GrpM-11^T consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, sphingoglycolipid and three unknown glycolipids. Cellular fatty acid analysis indicated that summed feature 8 (C_18 : 1 ω7c and/or C_18 : 1 ω6c; 42.8 %), C_16 : 0 (19.0 %), C_18 : 1 ω7c 11-methyl (13.3 %) and C_18 : 1 ω7c (8.0 %) were the major fatty acids. The DNA G+C content of strain GrpM-11^T was 63.7 mol%. Through whole genome sequence comparisons, the digital DNA-DNA hybridization and average nucleotide identity values between strain GrpM-11^T and two species of the genus Parasphingopyxis were revealed to be in the ranges of 19.0-22.0 % and 76.3-79.7 %, respectively. Based on the results of polyphasic analysis, strain GrpM-11^T represents a novel species of the genus Parasphingopyxis, for which the name Parasphingopyxis marina sp. nov. is proposed. The type strain is GrpM-11^T (KCCM 43343^T=JCM 34665^T).

Transfer of Sphingorhabdus marina, Sphingorhabdus litoris, Sphingorhabdus flavimaris and Sphingorhabdus pacifica corrig. into the novel genus Parasphingorhabdus gen. nov. and Sphingopyxis baekryungensis into the novel genus Novosphingopyxis gen. nov. within the family Sphingomonadaceae

During a phylogenetic analysis of Sphingorhabdus and its closely related genera in the family Sphingomonadaceae, we found that the genus Sphingorhabdus and the species Sphingopyxis baekryungensis might not be properly assigned in the taxonomy. Phylogenetic, phenotypic and chemotaxonomic characterizations clearly showed that the genus Sphingorhabdus should be reclassified into two genera (Clade I and Clade II), for which the original genus name, Sphingorhabdus, is proposed to be retained only for Clade I, and a new genus named as Parasphingorhabdus gen. nov. is proposed for Clade II with four new combinations: Parasphingorhabdus marina comb. nov., Parasphingorhabdus litoris comb. nov., Parasphingorhabdus flavimaris comb. nov. and Parasphingorhabdus pacifica comb. nov. Moreover, Sphingopyxis baekryungensis should represent a novel genus in the family Sphingomonadaceae, for which the name Novosphingopyxis gen. nov. is proposed, with a combination of Novosphingopyxis baekryungensis comb. nov. The study provides a new insight into the taxonomy of closely related genera in the family Sphingomonadaceae.

Rhodophyticola porphyridii gen. nov., sp. nov., isolated from a red alga, Porphyridium marinum

A Gram-stain-negative, strictly aerobic and moderately halophilic bacterium, designated strain MA-7-27^T, was isolated from a marine red alga, Porphyridium marinum, in the Republic of Korea. The cells of strain MA-7-27^T were non-motile rods showing oxidase- and catalase-positive activities. Growth of strain MA-7-27^T was observed at 15-45 °C (optimum, 30 °C), pH 5.0-9.0 (pH 7.0) and in the presence of 0.0-5.0 % (w/v) NaCl (2.0 %). Strain MA-7-27^T contained C10 : 0, summed feature 1 (comprising iso-C15 : 1 h and/or C13 : 1 3-OH) and summed feature 8 (comprising C18 : 1 ω7c and/or C18 : 1 ω6c) as the major fatty acids. The only isoprenoid quinone detected was ubiquinone-10. The major polar lipids of strain MA-7-27^T were phosphatidylglycerol, two unidentified phospholipids and two unidentified aminolipids. The G+C content of the genomic DNA was approximately 63.6 mol%. Strain MA-7-27^T was most closely related to the type strains of Boseongicola aestuarii BS-W15^T and Nioella nitratireducens SSW136^T with 96.98 % and 96.12 % 16S rRNA gene sequence similarities, respectively, but phylogenetic analyses showed that strain MA-7-27^T formed a clearly distinct phylogenic lineage from the closely related strains. The phenotypic, chemotaxonomic and molecular properties support that strain MA-7-27^T represents a novel genus of the family Rhodobacteraceae, for which the name Rhodophyticola porphyridii gen. nov., sp. nov. is proposed. The type strain is MA-7-27^T (=KACC 18805^T=JCM 31537^T).

Cohnella algarum sp. nov., isolated from a freshwater green alga Paulinella chromatophora

A Gram-stain-positive, facultatively aerobic and endospore-forming bacterium, designated strain Pch-40^T, was isolated from a freshwater green alga, Paulinella chromatophora. Cells were motile rods with a monotrichous polar flagellum showing catalase- and oxidase-positive reactions. Strain Pch-40^T grew at 20-50 °C (optimum, 37-40 °C), at pH 5.0-11.0 (optimum, pH 7.0) and in the presence of 0-4.0 % (w/v) NaCl (optimum, 0 %). Menaquinone-7 was detected as the sole isoprenoid quinone. The genomic DNA G+C content of strain Pch-40^T was 55.6 mol%. The major cellular fatty acids of strain Pch-40^T were C16 : 0, iso-C16 : 0, anteiso-C15 : 0 and anteiso-C17 : 0. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain Pch-40^T clearly belonged to the genus Cohnella of the family Paenibacillaceae. Strain Pch-40^T was most closely related to Cohnella rhizosphaerae CSE-5610^T with a 96.1 % 16S rRNA gene sequence similarity. The phenotypic and chemotaxonomic features and the phylogenetic inference clearly suggested that strain Pch-40^T represents a novel species of the genus Cohnella, for which the name Cohnellaalgarum sp. nov. is proposed. The type strain is strain Pch-40^T (=KACC 19279^T=JCM 32033^T).