Hassallia littoralis González-Resendiz & León-Tejera, 2013

González-Resendiz, Laura, León-Tejera, Hilda P., Díaz-Larrea, Jhoana, Alba-Lois, Luisa & Segal-Kischinevzky, Claudia, 2013, Hassallia littoralis sp. nov. (Cyanobacteria, Microchaetaceae) from Mexico’s marine supralittoral based on morphological and molecular evidence, Phytotaxa 137 (1), pp. 35-47 : 37-41

Hassallia littoralis González-Resendiz & León-Tejera , sp. nov. ( Figs. 1–25 )

Cespitose short mats brown to blackish ( Figs. 1, 2 ), filaments cylindrical ( Fig. 13 ), straight or curved; parallely oriented or intermingled, sometimes forming fascicles 200–300 µm long and 5–12 µm in diameter, without a common sheath ( Figs. 2, 3 , 20, 21 ). Falsely branched, branches tightly joined or irregularly divaricated to the main filament ( Figs. 4, 8 , 11 , 21, 24 ). Trichomes 3–6 µm wide ( Figs. 3, 5 ), constricted at cross-walls ( Figs. 15, 16 ). Cells cylindrical to barrel-shaped ( Figs. 15, 16 ), shorter than wide, 3–6 µm wide, 1–3 µm long, with slightly granulated content. Terminal cells widely rounded, sometimes nearly spherical, hyaline to greenish or yellowish ( Figs. 12, 15, 16 ) (2-4 µm long × 3–6 µm wide). Sheaths firm, stratified, slender, hyaline ( Fig. 16 ) to thick and amber or dark yellowishbrown, often widening with pronounced, rounded terminals (3–7 µm in diameter) ( Figs. 11, 12, 16 ), generally closed and rarely opened at the apex ( Figs. 10, 14 ). Heterocytes spherical, ovoid to cylindrical ( Figs. 4, 5, 9 , 11 ), 4–6 µm in diameter, 4–8 µm long ( Fig. 5 ), one basal ( Figs. 4, 8 , 11 , 19 ), rarely two ( Fig. 9 ), and less frequently intercalary. Akinetes not detected. Reproduction by hormogonia ( Figs. 6, 7 , 18 , 22, 23 ).

Type: — MEXICO. Oaxaca: Tangolunda bay, 15° 46’ 24.79” N, 96° 5’ 28.32” W. Marine supralittoral, León-Tejera , 2-2- 2011 (holotype FCME! PTM9586 , GenBank sequence access number KF017617, isotype UAMIZ! 1225, paratypes FCME! PTM9587 , PTM9588 ) .

Etymology: —The species epithet was selected according to the specific environment (marine littoral).

Habitat: —In Tangolunda Bay, supralittoral black mats of Hassallia dominate this habitat and the three collected populations were epilithic mats from the rocky marine littoral. They were found growing on nearly vertical igneous rocks 7 m from the seaside and approximately 4–5 m above sea level, facing the sea. The rocks are only slightly wetted by the sea breeze and totally exposed to sunlight. Considering the maximal tidal heights of 2.4 m, probably they are never covered by the sea but grains of salt were found intermingled among filaments due to the sea breeze water evaporation. This species was found growing with several undescribed coccoid and LPP species ( Fig. 1 ) but not with common filamentous non-heterocystous ( Oscillatoria , Lyngbya , Microcoleus , Phormidium , Schizothrix ) or heterocystous genera ( Rivularia , Calothrix , Scytonema ) typically described for intertidal biotopes ( Brito et al. 2012).

Observations: —Cells appearing as monocytes and short hormogonia of 2 to 10 (15) cells long ( Fig. 25 ), are sometimes liberated. Young filaments and hormogonia are either isopolar ( Figs. 6, 7 , 24 ) or heteropolar ( Figs. 9 , 22 ). Isopolar hormogonia formation through necridic cells ( Fig. 23 ) develop later terminal/basal heterocytes ( Figs. 6, 7, 9 , 17, 18 , 22 ). Sheath becomes lighter or darker toward the extremes, probably due to terminal gelatinization ( Figs. 10, 14, 15 ). Populations morphologically characterized are C76 (PTM9586 and UAMIZ1225), C77 (PTM9587) and C78 (PTM9588). The sequence was obtained from sample C76.

Molecular and phylogenetic analyses: —A total of 24 sequences of representative taxa from available sequences of Microchaetaceae and Scytonemataceae deposited at GenBank were analyzed, including Brasilonema bromeliae DQ 486055, Scytonema sp. AB093483 and Brasilonema tolantongensis JN 676147 as outgroups and our strain. The three approaches used (MP, B and ML), produced similar clustering, therefore only the ML tree, with support values of ML, B and MP is shown in Fig. 26 . Topology of the ML tree showed that the Hassallia assemblages including seven taxa are segregated into two clades supported by modest bootstrap values. The earliest diverging clade included H. byssoidea . The second clade included two sister groups: one defined by H. antarctica Komárek, Nedbalová et Hauer (2012: 770) assemblage, and the other by H. littoralis , H. andreassenii Komárek, Nedbalová et Hauer (2012: 768) and Coleodesmium sp. ANT ( Fig. 26 ). Hassallia littoralis is moderately supported by bootstrap values in ML and MP topologies, but with a higher value in Bayesian analysis (0.97), forming a distinct sister clade to H. andreassenii and Coleodesmium sp. ANT. Molecular data confirmed the distinctiveness of our tropical populations that show similarity values of 98.4% with H. andreassenii , 97.8-98.1% with the H. antarctica assemblage, 97.8% with H. byssoidea , and finally 98.5% with Coleodesmium sp. ANT.

Figures

FIGURE 26. Maximum-likelihood tree based on the analysis of 16S rRNA gene of representatives of the families Scytonemataceae and Microchaetaceae showing the position of the sequence obtained in the present study (in bold). Numbers at nodes indicate bootstrap values ≥ 50% for Maximum Parsimony (left), Maximum Likelihood analysis (medium) and Bayesian posterior probabilities (right) values.

FIGURES 1–9. Morphological features of Hassallia littoralis. Fig. 1. Intermingled filaments as seen with epifluorescence. Fig. 2. Erect fascicle growth form with lighter terminal parts. Fig. 3. Straight or curved filament growth forms. Fig. 4. False branching with basal heterocytes. Fig. 5. Trichomes with evident intercalar heterocytes and polar nodules. Fig. 6. Release of short isopolar trichome with evident nodal constrictions. Fig. 7. Series of heteropolar and isopolar hormogones. Fig. 8. Divaricated pseudobranch with basal heterocyte and stratified sheath. Fig. 9. False branching with single and paired heterocytes. Scale bars: Figs 1–3: 30 µm, Figs 4–9: 6µm.

FIGURES 10–16. Morphological features of Hassallia littoralis. Fig. 10. Terminal widening of the sheath. Fig. 11. Branched filament with evident cytoplasmic granules. Fig. 12. A trichome with variations in diameter bearing a darker, shortened necridial cell. Fig. 13. Plane view of a cylindrical trichome and filament. Fig. 14. Intense terminal EPS production by highly granulosed trichome with an open sheath. Fig. 15. Darkening of hyaline sheath produced probably by gelatinization. Fig. 16. A trichome of a young filament with necridic cells and sheath widening. Scale bars: 6 µm.

FIGURES 17–19. Hassallia littoralis TEM images. Fig. 17. Hormogonia formation through a necridic cell. Fig. 18. Young isopolar hormogonium with a wide stratified sheath. Fig. 19. Evident polar nodule in a basal heterocyte. Scale bars: Fig. 17: 3 µm, Fig. 18: 5 µm, Fig. 19: 1 µm.

FIGURES 20–25. Hassallia littoralis habitus. Figs 20, 21. Fasciculated growth form. Figs 22, 23. Formation of hormogonia. Fig. 24. Hormogonia and branch formation. Fig. 25. Production of monocyte-like cells. Scale bars: Figs 20, 21: 30 µm, Figs 22–25: 6 µm.