Duganella alba sp. nov., Duganella aquatilis sp. nov., Duganella margarita sp. nov. and Duganella levis sp. nov., isolated from subtropical streams in China

The novel application of violacein produced by a marine Duganella strain as a promising agent for controlling Heterosigma akashiwo bloom: Algicidal mechanism, fermentation optimization and agent formulation

Controlling harmful algal blooms with algicidal bacteria is thought to be an efficient and eco-friendly way but lack of comprehensive studies from theory to practice limited the field application. Here we presented a purple bacterial strain Duganella sp. A3 capable of killing several harmful algae, including Heterosigma akashiwo, a world-wide fish-killing microalga. A bioactivity-guided purification and identification approach revealed the major algicidal compound of A3 as the pigment violacein, which was never reported for its algicidal potential before. Violacein rapidly disrupted cell permeability, caused long-term oxidative stress, but mildly affected algal photosystem, which might explain its highly species-specific activity against unarmored H. akashiwo. To explore the application potential of violacein, a fermentation optimization approach combing single-factor and multi-factor experiments was conducted to increase the violacein yield, which finally reached 0.4199 g/L just using a simple medium formula beneficial for compound purification. Finally, taking advantages of the physical and chemical stabilities, we successfully developed the novel application of violacein as a sustained-releasing and easy-to-preserve algicidal agent using alginate-acacia-gum-chitosan encapsulation, which paved the path for its future application in controlling H. akashiwo bloom.

Duganella vulcania sp. nov., Rugamonas fusca sp. nov., Rugamonas brunnea sp. nov. and Rugamonas apoptosis sp. nov., isolated from subtropical streams, and phylogenomic analyses of the genera Janthinobacterium, Duganella, Rugamonas, Pseudoduganella and Massilia

Six Gram-stain-negative, catalase- and oxidase-positive, rod-shaped and motile strains (FT81WT, FT82W, FT107W, FT3ST, LX20WT and LX47WT) sharing high 16S rRNA gene sequence similarities with species of the genera Janthinobacterium (97.0–98.3 %), Duganella (96.3–98.8 %), Rugamonas (97.8–98.6 %), Pseudoduganella (96.8–97.5 %) and Massilia (94.5–98.6 %) were isolated from subtropical streams in PR China. The phylogenetic trees reconstructed using the 16S rRNA gene sequences indicated that the species of above five genera often mix together, indicating that the taxonomic statuses of some species were questionable. Phylogenomic reconstruction based on 369 single-copy orthologous clusters indicated that the species of the genus Janthinobacterium form a distinct cluster, strains FT81WT, FT82W and FT107W form a tight cluster with the species of the genus Duganella , and strains FT3ST, LX20WT and LX47WT form a tight cluster with the species of genus Rugamonas , and the species of genus Pseudoduganella form a tight cluster with Massilia guangdongensis , Massilia ginsengisoli , Massilia rivuli , Massilia namucuonensis , Massilia aquatica sensu Lu et al., Massilia buxea , Massilia armeniaca , Massilia plicata , Massilia flava , Massilia lurida , Massilia dura , Massilia lutea , Massilia umbonata , Massilia albidiflava and Massilia violacea . It should be noted that Massilia aquatica Lu et al. 2020 non Massilia aquatica Holochová et al. 2020 is a later homonym and an illegitimate name. The GTDB Release 202 also supported the proposal that M. guangdongensis , M. ginsengisoli , M. rivuli , M. namucuonensis , M. aquatica sensu Lu et al., M. buxea , M. armeniaca , M. plicata , M. flava , M. lurida , M. dura , M. lutea , M. umbonata , M. albidiflava and M. violacea should be transferred into the genus Pseudoduganella . The calculated pairwise orthologous average nucleotide identity by usearch (OrthoANIu) values were between 95.0 % and 95.6 % among strains FT81WT, FT82W and FT107W, but were less than 91.5 % among strains FT3ST, LX20WT, LX47WT and other related strains. Combining the results of phylogenomic analyses, phenotypic, biochemical and genotypic characteristics, strains FT81WT, FT82W and FT107W should represent a novel species of the genus Duganella , and strains FT3ST, LX20WT and LX47WT should represent three novel species of the genus Rugamonas , for which the names Duganella vulcania sp. nov. (type strain FT81WT=GDMCC 1.1679T =KACC 21471T), Rugamonas fusca sp. nov. (type strain FT3ST=GDMCC 1.1907T =KACC 21952T), Rugamonas brunnea sp. nov. (type strain LX20WT=GDMCC 1.1911T =KACC 21956T) and Rugamonas apoptosis sp. nov. (type strain LX47WT=GDMCC 1.1914T =KACC 21959T) are proposed.

Duganella dendranthematis sp. nov. and Massilia forsythiae sp. nov., isolated from flowers

Two aerobic, Gram-stain-negative, motile, mesophilic, rod-shaped and catalase-positive bacterial strains designated AF9R3T and GN2-R2T were isolated from flowers collected in the Republic of Korea. Strain AF9R3T grew at 4–33 °C, pH 4.0–9.0 and with 0–1 % NaCl (w/v), and strain GN2-R2T grew at 10–33 °C, pH 4.0–9.0 and with 0–1 % NaCl (w/v). Phylogenetic analysis on the basis of 16S rRNA gene sequences indicated that strains AF9R3T and GN2-R2T belonged to the genera Duganella and Massilia , respectively, showing high sequence similarity to Duganella levis CY42WT (99.4 %) and Massilia putida 6 NM-7T (98.0 %), respectively. Both strains contained summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c) and C16 : 0 as the major fatty acids, and ubiquinone Q-8 as the predominant quinone. Strain AF9R3T had diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine, and strain GN2-R2T comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified phospholipid as the major polar lipids. Orthologous average nucleotide identity and digital DNA–DNA hybridization values of strain AF9R3T to its closest relative D. levis CY42WT were 92.6 and 56.5 %, and those of strain GN2-R2T to its closest relative M. putida 6 NM-7T were 81.4 and 24.8 %. Based on genotypic and phenotypic data, strains AF9R3T and GN2-R2T are considered to represent novel species of the genus Duganella and Massilia , respectively, for which the names Duganella dendranthematis sp. nov. (type strain AF9R3T=KACC 21258T=NBRC 114510T) and Massilia forsythiae sp. nov. (type strain GN2-R2T=KACC 21261T=NBRC 114511T) have been proposed.

Duganella aceris sp. nov., isolated from tree sap and proposal to transfer of Rugamonas aquatica and Rugamonas rivuli to the genus Duganella as Duganella aquatica comb. nov., with the emended description of the genus Rugamonas

A Gram-reaction-negative, strictly aerobic, betaproteobacterial strain, designated SAP-35^T, was isolated from sap extracted from Acer pictum in Mt. Halla in Jeju, Republic of Korea, and its taxonomic status was examined by a polyphasic approach. Cells of the organism were non-sporulating, motile rods and grew at 4-30 °C, pH 6-7 and in the absence of NaCl. 16S rRNA gene- and whole genome-based phylogenetic analyses showed that strain SAP-35^T belonged to the family Oxalobacteraceae and was closely related to Rugamonas rivuli (98.9% 16S rRNA gene sequence similarity) and Rugamonas aquatica (98.4%). The phylogenomic clustering and average amino acid identity values supported that strain SAP-35^T belonged to the genus Duganella and two Rugamonas species should be transferred to the genus Duganella. The major isoprenoid quinone of the isolate was Q-8. The major polar lipids were phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and an unidentified aminophospholipid. The predominant fatty acids were summed feature 3, C_16:0 and C_17:0 cyclo. The G + C content of genome was 64.9%. The average nucleotide identity and dDDH values between strain SAP-35^T and the members of the genera Rugamonas and Duganella were < 85.1% and < 49%, respectively. Based on the combined data presented here, strain SAP-35^T (= KCTC 72227^T = NBRC 113903^T) represents a novel species of the genus Duganella, for which the name Duganella aceris sp. nov. is proposed. Also, Rugamonas aquatica Lu et al. (Int J Syst Evol Microbiol 70: 3328-3334, 2020) and Rugamonas aquatica Lu et al. 2020 are reclassified as Duganella aquatica comb. nov., with the emended description of the genus Rugamonas.

Duganella lactea sp. nov., Duganella guangzhouensis sp. nov., Duganella flavida sp. nov. and Massilia rivuli sp. nov., isolated from a subtropical stream in PR China and proposal to reclassify Duganella ginsengisoli as Massilia ginsengisoli comb. nov

Five Gram-stain-negative, catalase- and oxidase-positive, rod-shaped and motile strains (FT50W^T, FT80W^T, FT92W^T, FT94W and FT135W^T) were isolated from a subtropical stream in PR China. Comparisons based on 16S rRNA gene sequences showed that strains FT50W^T, FT94W and FT135W^T take strain Duganella sacchari Sac-22^T, and strains FT80W^T and FT92W^T take strain Duganella ginsengisoli DCY83^T as their closest neighbour in the phylogenetic trees, respectively. The G+C contents of strains FT50W^T, FT80W^T, FT92W^T, FT94W and FT135W^T were 63.3, 62.4, 62.8, 63.8 and 60.8 %, respectively. The reconstructed phylogenomic tree based on concatenated 92 core genes showed that strains FT50W^T, FT80W^T, FT94W and FT135W^T clustered together with species of the genus Duganella, but strains FT92W^T and D. ginsengisoli KCTC 42409^T were located in the clades of the genus Massilia. The calculated pairwise average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values among strains FT50W^T, FT80W^T, FT92W^T, FT94W, FT135W^T and related strains were in the ranges of 75.6-87.8% and 20.3-33.8% except that the values between strains FT50W^T and FT94W were 98.7 and 89.2%, respectively. The respiratory quinone of these five strains was Q-8. The major fatty acids were C_16 : 1  ω7c, C_16 : 0, C_18 : 1  ω7c and C_12 : 0. The polar lipids included phosphatidylethanolamine, phosphatidylglycerol and one unidentified phospholipid. Considering the distinct phylogenetic relationships of D. ginsengisoli with species of the genus Massilia in the phylogenomic tree, it was reasonable to transfer D. ginsengisoli to the genus Massilia as Massilia ginsengisoli comb. nov. Combining the results of phylogenomic analysis, ANI and dDDH data, and a range of physiological and biochemical characteristics together, strains FT50W^T and FT94W should belong to the same species and be assigned to genus Duganella with strains FT80W^T and FT135W^T together, and strain FT92W^T should be assigned to the genus Massilia, for which the names Duganella lactea sp. nov. (type strain FT50W^T=GDMCC 1.1674^T=KACC 21466^T), Duganella guangzhouensis sp. nov. (FT80W^T=GDMCC 1.1678^T=KACC 21470^T), Duganella flavida sp. nov. (FT135W^T=GDMCC 1.1745^T=KACC 21659^T) and Massilia rivuli sp. nov. (FT92W^T=GDMCC 1.1682^T=KACC 21474^T) are proposed.