Microseira minor Geng et Yu, 2021

Geng, Ruozhen, Wen, Qianzhi, Wang, Yilang, Yang, Ping, Dai, Guofei, Li, Renhui & Yu, Gongliang, 2021, A novel filamentous cyanobacterium Microseira minor sp. nov. (Oscillatoriaceae, Cyanobacteria) from the Ganfu Channel, Jiangxi, China, Phytotaxa 524 (3), pp. 178-190 : 180-183

Microseira minor Geng et Yu sp. nov. ( Fig. 1 )

Diagnosis: —This species is morphologically similar to the genus Microseira but differs from M. wollei in the lack of false branching, much narrower filaments and trichomes, smaller ratio of cell length and width under the light microscopy. The phylogenetic analysis based on 16S rRNA gene, partial 16S-23S rRNA operon and nifH gene showed that this species was formed a well-supported clade, closest to other Microseira species , far away from other close genera. In addition, the non-producing of neurotoxins and hepatotoxins is also a major difference.

Description: —Filaments unbranched, long, 13.73–(16.04)–18.58 μm broad, forming densely aggregations, blueblack, brown-black, yellowed when old, straight or slightly flexuous. Trichomes cylindrical, isopolar, not attenuated to the ends, not or slightly constricted at the cross-walls. Cells discoid, 3.12–(5.03)–7.70 μm long, 9.02–(11.05)–13.33 μm broad, 2–3 × broader than long, with granular content, not aerotopes. Apical cells rounded, without calyptra or thickened outer cell wall. Sheath usually present, colorless, hyaline, firm, lamellated when old, and open at the apex. Reproduction by motile hormogonia formed by help of necridia. Thylakoids irregularly arranged.

Etymology: —The name of species “ minor ” was chosen because of its small and thin discoid cells.

Type locality: — In the Ganfu Channel, Jiangxi Province, China. (August 2019, site one 28°11’8.2” N, 116°10’2.56” E and October 2019, site two 28°14’7.70” N, 116°6’38.21” E) .

Holotype here designated: —Dry material of strain CHAB 4136 was stored at the Freshwater Algae Biology Herbarium ( HBI), Institute of Hydrobiology , Chinese Academy of Science, Wuhan, Hubei Province, China, as specimen No. JXGF201901 .

Reference strain: — CHAB 4136 and CHAB 4163 (the additional strain) were deposited at the CHAB, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei Province, China.

Habitat: —Rock surface in freshwater rivers and channels in subtropical region.

Molecular and phylogeny analyses: —The 16S rRNA gene sequences of Microseira minor strains CHAB 4136 and CHAB 4163 obtained in this study shared 98.90%–99.92% similarities among all six clones by calculating p-distance with pairwise deletion of gaps using MEGA software v7.0. These clones shared 95.00%–96.01% with other Microseira species , less than 97% which was regarded as the cutoff for bacterial species delimitation. These clones had a maximum similarity of 16S rRNA gene sequences as 95.50% with their closest filamentous genera (sharing similarities to Potamosiphon, Aerosakkonema , Phormidium, Potamolinea and Oscillatoria as 93.98%–95.50%, 92.78%–92.95%, 92.28%–92.44%, 92.11%–92.44% and 91.92%–92.60%, respectively) ( Table 1 ). The 16S rRNA gene phylogenetic trees based on ML and BI methods showed that the six clones of Microseira minor clustered a unique clade (cluster A) together with other Microseira species ( Fig. 3 and Fig. 4 ), supported by ML and BI calculations with high bootstrap values of 100% and 1.000.

In the nifH phylogeny ( Fig. 5 and Fig. 6 ), the eight clones obtained from the two strains of Microseira minor in this study formed a well-supported freshwater clade together with all environmental clones of Microseira wollei (cluster M, cluster N and cluster L). The nifH gene sequences of CHAB 4136 (cluster S1) and CHAB 4163 (cluster S2) divided into two distinct sub-groups with cluster M and cluster N, and sequence similarities were 94.28%–95.96% and 96.97%–98.32%, respectively ( Table 2 ). The whole clade formed by Microseira clones including the two strains of Microseira minor were supported by ML and BI methods with high bootstrap values of 85% and 0.90, supporting the two strains as a new species Microseira minor within the genus Microseira .

Genes associated with four types of toxins of microcystins, cylindrospermopsin, paralytic shellfish toxins and anatoxin were not detected in any of these Microseira minor strains.

Analyses of ITS between 16S and 23S rRNA gene: —The ITS sequences of the six clones from the two strains of Microseira minor , shared 96.05-96.26% similarities with each other, and contained both tRNA Ile and tRNA Ala, ranging from 485 to 499 bp.

Figures

Fig. 1. Lightmicroscopy of Microseira minor strains.A–C. Immature filaments with colourlesssheaths (Arrow indicates sheath). D–G. Trichome fragmentation and formation of necridia (Arrows indicate fragmentation of trichomes and formation of necridias). H–I. Old filaments with lamellated sheaths (Arrows indicate lamellated sheaths). Scale bars: 20 μm.

Fig. 3. Phylogenetic tree of 16S rRNA gene sequences (1208bp) with maximum-likelihood (ML) analysis. Bootstrap values greater than 50% are showed on the ML tree. The novel filamentous strains of this study is indicated in bold. Bar, 0.03.

Fig. 4. Bayesian inference (BI) phylogenetic tree based on 16S rRNA gene sequences. Bootstrap values of Bayesian posterior probabilities greater than 0.50 are showed on the BI tree. The novel filamentous strains of this study is indicated in bold. Bar, 0.03.

Fig. 5. Phylogenetic tree based on nifH gene sequences (298bp) with maximum-likelihood (ML) analysis. Bootstrap values greater than 50% are showed on the ML tree. The novel filamentous species of this study is indicated in bold. Bar, 0.07.

Fig. 6. Bayesian inference (BI) phylogenetic tree based on nifH gene sequences. Bootstrap values of Bayesian posterior probabilities greater than 0.50 are showed on the BI tree. The novel filamentous species of this study is indicated in bold. Bar, 0.05.

Tables

TABLE 1. Sequence similarity comparison of the 16S rRNA gene between Microseira minor strains and its closed species and genera. Similarity= [1-(p-distance)]*100.

Strains	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
1. Microseira minor CHAB
4136-4
2. Microseira minor CHAB	99.83
4136-5
3. Microseira minor CHAB	99.92	99.92
4136-6
4. Microseira minor CHAB	98.90	98.90	98.98
4163-5
5. Microseira minor CHAB	99.07	99.07	99.15	99.83
4163-6
6. Microseira minor CHAB	98.98	98.98	99.07	99.75	99.92
4163-7
7. Microseira wollei NIES-	95.42	95.50	95.50	95.08	95.08	95.00
4236
8. Microseira wollei AW2009	95.76	95.84	95.84	95.25	95.25	95.17	98.64
clone B19
9. Microseira wollei YC 0404	95.93	96.01	96.01	95.42	95.42	95.34	98.81	99.49
clone E43
10. Microseira wollei YC1109	95.84	95.93	95.93	95.42	95.42	95.34	98.56	99.41	99.58
clone A45
11. Microseira wollei AW2009	95.93	96.01	96.01	95.42	95.42	95.34	98.81	99.83	99.66	99.58
clone B37
12. Microseira wollei AW2009	95.93	96.01	96.01	95.42	95.42	95.34	98.81	99.83	99.66	99.58	100.00
clone B35
13. Microseira wollei YC2010	95.67	95.76	95.76	95.25	95.25	95.17	98.47	99.15	99.66	99.58	99.32	99.32
clone B9
14. Microseira wollei str.	94.83	94.91	94.91	95.59	95.59	95.50	97.63	97.12	97.63	97.29	97.29	97.29	97.37
Carmichael/Alabama
15. Potamosiphon austaliensis	93.98	94.06	94.06	94.23	94.40	94.32	93.64	93.30	93.81	93.47	93.47	93.47	93.72	93.98
FHC0914.01
16. Potamosiphon austaliensis	95.08	95.17	95.17	95.34	95.50	95.42	94.40	94.23	94.74	94.40	94.40	94.40	94.57	95.00	98.56
FHC0914.02
17. Potamosiphon austaliensis	94.15	94.23	94.23	94.40	94.57	94.49	93.81	93.47	93.98	93.64	93.64	93.64	93.89	94.15	99.66	98.73
FHC0914.03
18. Phormidium uncinatum	92.28	92.36	92.36	92.28	92.44	92.36	92.02	91.85	92.36	92.02	92.02	92.02	92.19	92.78	93.63	94.40	93.80
SAG 81.79
19. Oscillatoria princeps	92.52	92.52	92.60	92.01	92.01	91.92	91.92	92.01	92.26	92.09	92.18	92.18	92.01	91.58	90.82	91.67	90.99	91.49
CCALA 1115 clone K1
20. Aerosakkonema funiforme	92.78	92.87	92.87	92.95	92.95	92.87	92.61	93.04	93.38	93.21	93.21	93.21	93.21	93.29	92.62	93.80	92.79	92.61	91.76
Lao26
21. Potamolinea magna 47PC	92.36	92.44	92.44	92.19	92.19	92.11	92.28	92.28	92.53	92.28	92.44	92.44	92.28	92.78	91.26	92.19	91.43	91.25	91.16	92.11