Saturday, 29 August 2015

Nisada stipitata: A new species of Cyanobacteria from the coast of Oaxaca State, Mexico.


Cyanobacteria are filament-forming photosynthetic Bacteria which often form dense mats by extruding polysaccharide films, which bind the individual filamentous colonies together as well as attaching them to surfaces. These mats are among the first biological traces found in the geological record, with stromatolites (deposits in which thin layers of microbial mat alternate with other sedimentary deposits such as limestone or sands) being found in some of oldest sedimentary formations on Earth. Modern Cyanobacteria are found in all modern ecosystems where there is light, including desert sands and the surfaces of glaciers, but their full diversity is poorly understood, though the group is no longer thought to be monophyletic (it is no longer thought that all members of the group are descended from a single common ancestor) and there are likely to be many undiscovered species living in poorly explored environments.

In a paper published in the journal Phytotaxa on 24 July 2015, Michelle Gold-Morgan, Laura González-Resendiz, Hilda León-Tejera and Gustavo Montejano of the Departamento de Biología Comparada at the Universidad Nacional Autónoma de México describe a new species of Cyanobacteria from rocky shores on the coast of Oaxaca State, Mexico.

The new species is named Nisada stipitata, where ‘Nisada’ means ‘marine’ in the indigenous Zapotec language spoken in parts of Oaxaca State and ‘stipitata’ meand ‘stipulate’ (having dots) in Latin. The species is described from colonies found living on granitic rocks on the coast of Oaxaca near San Agustín in Huatulco, where the Sierra Madre del Sur mountains meat the sea in a series of rocky bays and cliffs. Nisada stipitata forms colonies up to 5 mm thick, with each colony consisting of a biofilm to which numerous coccoid (spherical) cells are attached by short stipes (stems).

Morphology of Nisada stipitata. (A) Macroscopic view of partially covered rock (black portion). (B) Macroscopic view of strip of biofilm on rock. (C) Pseudofilament apices in fluorescent microscopy. (D) Edge of biofilm with pseudofilaments in a row. (E) Apices of morph 2 before cell division (single arrow) and after division but before separation (double arrow). Gold-Morgan et al. (2015).

The coccoid cells show distinct polarity, which is to say that they have distinct ends, despite being spherical. The stipes of the cells form distinct rows in on the biofilm, with each stipe supporting one-to-three cells; this is connected to the way in which the cells divide, either in or at 90˚ to the plane of the stipe-row, with each parent cell apparently splitting into two daughter cells, one of which then itself splits in two, resulting in three cells on the stipe. Further divisions after this are not seen, and numerous stipes were found without cells, suggesting a distributive phase (cells leaving the stipe and either settling in the biofilm or forming new colonies).

Line drawings of Nisada stipitata. (A) Edge of biofilm with pseudofilaments in a row. (B) Complete pseudofilament of morph 1. (C) Complete pseudofilament of morph 2. Ps, pseudofilament sheath; dc, daughter cell; c, cup; mc, mother cell; st, stipe; p, pad; cs, colonial sheath. Scale bars: (A) 8 μm, (B, C) 6 μm. Gold-Morgan et al. (2015).

Insufficient material of Nisada stipitata was recovered to allow a DNA comparison to other Cyanobacteria (which is generally considered the best way to compare and classify any Bacterium), and it did not prove possible to cultivate the species in the lab. However reproductive strategies and in particular splitting plains are considered significant in the classification of these organisms, and the pattern of splitting seen in Nisada stipitata is sufficiently unique that Gold-Morgan et al. are confident in their diagnosis of the colonies as a new species.

(Top) Line drawing of life cycle of morph 1. (Bottom) Line drawing of life cycle of morph 2. . Gold-Morgan et al. (2015).

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