Pseudanabaena minima

Yu, Gongliang, Zhu, Mengling, Chen, Youxin, Pan, Qianqian, Chai, Wenbo & Li, Renhui, 2015, Polyphasic characterization of four species of Pseudanabaena (Oscillatoriales, Cyanobacteria) from China and insights into polyphyletic divergence within the Pseudanabaena genus, Phytotaxa 192 (1), pp. 1-12 : 6-9

Pseudanabaena minima (G.S.An) Anagnostidis (2001: 360)

Basionym: Achroonema minima G.S. An (1992: 412).

Strains:— CHAB705 (KM386847), from Lake Donghu in Wuhan city, Hubei province.

Habitat:— Freshwater, planktonic or epiplanktic.

Description: —Trichomes solitary. Macroscopically, the cultures are blue green ( Fig. 1D ). Trichomes solitary, blue green or pale blue green, few-celled, conspicuous constricted at cross-walls, without sheath. Cells cylindrical, 2.0‒4.2 μm long, 1.7‒2.5 μm wide, 1.1‒2.0 L/W ( Table 1). Cell content homogeneous. Thylakoids with 4‒5 parallel layers ( Fig. 2F, G ).

Pigment composition:— The absorption spectra of four strains selected as representatives of four species from 300 nm to 750 nm are shown in Fig. 3A . Almost all of the strains contained chlorophyll a, xanthophyll, and PC, with absorption peaks at 435‒440 and 667, 480, and 620 nm, respectively. Several strains of Pseudanabaena mucicola and Pseudanabaena galeata (e.g., P. galeata strain CHAB732) exhibited the absorption peaks at 560 nm, indicating the presence of PE ( Fig. 3B ), but PE was not found in the strains of Pseudanabaena limnetica and Pseudanabaena minima ( Table 1).

Phylogenetic analysis:— 16S rRNA gene sequences from the 11 strains of Pseudanabaena were obtained.

These sequences and 62 sequences of the 16S rRNA gene cited in GenBank, including strains of Pseudanabaena and other cyanobacterial genera, such as Limnothrix and Arthrospira Sitzenberger ex Gomont (1892: 246) , were used to construct phylogenetic trees. All sequences used to construct phylogenetic trees were 1124 bp long. Comparison of the phylogenetic relationship between cyanobacteria showed that all Pseudanabaena strains newly isolated in this study gathered tightly with most of the Pseudanabaena strains cited from GenBank in a large cluster (Cluster I) in NJ, ML, and Bayes trees. The cluster I in NJ, ML and Bayes trees was supported by high bootstrap values 75%, 96%, and 100%, respectively. Since all the methods gave similar results, only the NJ tree is shown ( Fig. 4 ). However, bootstrap values>50% are shown. The average similarities of the 16S rRNA gene sequences among the strains of P. catenata , P. mucicola , P. galaeta , P. minima , and P. liminetica were 99.5%, 98.7%, 92.7%, 100%, and 99.9%, respectively ( Table 2). The average similarity of the 16S rRNA gene sequences among the 27 Pseudanabaena strains in cluster I of the phylogenetic tree was 95.7%. Several Pseudanabaena strains, including Pseudanabaena persicina (Reinke ex Gomont 1892: 164) Anagnostidis (2001: 360) ; CCMP638 and SAG80.79), Pseudanabaena tremula Johansen & Casamatta in Casamatta et al. (2005: 430) UTCC471, and P. galeata , were found outside cluster I, forming separate clades with other genera of Oscillatoriales ( Fig. 4 ). The average similarities of the 16S rRNA gene sequences between P. catenata (KM020004, KM020005, and AB039020) and P. tremula or P. persicina were 88.6% and 85.3%, respectively. Similar to the results of a previous study ( Zhu et al. 2012), the findings of the present study revealed that the three strains of Limnothrix redekei mixed with Pseudanabaena strains in cluster I.

Figures

FIGURE 1. Morphological features of Pseudanabaena.A. Pseudanabaena mucicola CHAB1147.B, Pseudanabaena galeata CHAB2916. C. Pseudanabaena limnetica CHAB792. D. Pseudanabaena minima CHAB705. Scale bar = 10μm.

FIGURE 2. Ultrastructure of Pseudanabaena. A. Pseudanabaena mucicola CHAB1147. B–C, Pseudanabaena galeata CHAB2916.. D, E. Pseudanabaena limnetica CHAB792. F, G. Pseudanabaena minima CHAB705. Scale bar = 1μm. Thylakoids are marked with T. Phycocyanin granules are marked with PC, and polyphosphate granules with PP.

FIGURE 3. The absorption spectra of 11 Pseudanabaena strains. A. The absorption spectra of the representative strains (Pseudanabaena mucicola CHAB1147, Pseudanabaena galeata CHAB732, Pseudanabaena minima CHAB705, and Pseudanabaena limnetica CHAB 792). B. The Phycoerythrin (PE) absorption spectrum of the strain Pseudanabaena galeata CHAB732.

FIGURE 4. Neighbor-joining (NJ) tree showing phylogenetic relationships between Pseudanabaena and other cyanobacteria based on 16S rRNA gene sequences of 73 strains of Oscillatoriales with 1124 bp nucleotides. Bootstrap values greater than 50% with NJ/ML/Bayes methods are shown on the tree. New isolated strains in this study are shown in bold. Microcystis aeruginosa NIES843 (NR074314) was used as outgroup. The vertical lines were used to represent species or cluster of Pseudanabaena genus. I: real Pseudanabaena cluster. II, III, and IV: the other Pseudanabaena strains outside the real Pseudanabaena cluster.