Characterization of a new species in the genus Didymosphenia and of Cymbella janischii (Bacillariophyta) from Connecticut, USA

Abstract

Two non-native stalk-forming diatoms that were recently observed in the West Branch of the Farmington River, a tributary of the Connecticut River in Connecticut (USA), are characterized morphologically and barcode marker sequences were obtained for each of them. Cymbella janischii, the dominant stalk-forming species during the summer of 2012, previously had not been found in the northeastern USA. Samples of C. janischii were examined microscopically and used to obtain four sequences of the barcode marker, the V4 region of the 18S rDNA gene. Phylogenetic analysis indicated that the four independent sequences of C. janischii were distinct from, but most closely related to, published sequences of C. janischii from Idaho and C. mexicana from Texas, USA. A second non-native stalk-producing diatom, resembling Didymosphenia geminata, was found in November 2012 – June 2013 and first reported as Didymosphenia sp. Over this period, the observed cells had a compressed morphology and were consistently small compared with D. geminata. Sequences of the V4 region, obtained from three independent direct polymerase chain reactions (PCR) of single cells isolated from the Connecticut samples, indicated a close relationship to three published sequences of D. geminata from Italy, New Zealand and the USA, and to D. siberica and D. dentata from Russia. Frustules of the cells used in the PCR reactions were recovered and examined using scanning electron microscopy, providing a direct link between the observed morphology and sequence data. The morphology of the novel Connecticut Didymosphenia taxon was compared with that of other Didymosphenia taxa, being most similar to D. pumila, D. laticollis, D. grunowii and smaller cells of D. geminata. Didymosphenia sp. had a triundulate morphology with a consistent length of 40–60 µm. Given the unique morphological features of this diatom, it is proposed as a new species, Didymosphenia hullii Khan-Bureau, sp. nov.

Key words:

• 18S V4 rDNA
• benthic diatoms
• cymbelloid diatoms
• Didymosphenia geminata
• gomphonemoid diatoms
• invasive species
• nuisance species
• USA

ACKNOWLEDGEMENTS

We thank the Connecticut Institute of Water Resources (CTIWR) for funding this research.

We thank K. Fučíková, S. Olm, C. Lo, M. Letsch, H. McManus and acknowledge the late F. Trainor for helpful discussion. This work made use of the computer cluster maintained by the Bioinformatics Facility (Biotechnology/Bioservices Center) at the University of Connecticut. We are grateful for D. Metzeltin’s expert opinion and H. Lange-Bertalot for the use of their D. geminata images. Thanks to S. Spaulding for access to her D. geminata image. We thank Three Rivers Community College’s Dean of Information Technology S. Goetchius, K. Barfield, S. Cohen, D. Jewett, and retired President G. S. Jones for providing continual support for this project, J. Sgro, John Carroll University, for providing his input and continual support, for the expert assistance of M. Cantino and S. Daniels of the EM lab at UCONN, NSF 1126100 supporting the purchase of the Nova Nano SEM, V. Kask scientific illustrator in Biological Central Services at UCONN, J. Morrison, East Hartford, USGS, L. Matthews VT DEC, M. Becker and C. Bellucci, CT DEEP for their assistance. We thank the reviewers for their helpful comments.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at http://dx.doi.org/10.1080/09670262.2015.1126361

Supplementary table 1: Taxon list and source page numbers of images used for morphological comparisons of D. geminata and D. hullii.

Supplementary figs 1–4: LM images offield-collected C. janischii cells showing size distribution. Fig. 3: Central valve illustrates the distinct radiated striae with striae more closely together and longer pointed areolae in the central area, differentiating between other larger Cymbella taxa and C. janischii. Figs 1–3: Scale bars = 10 μm. Fig. 4: LM image of cell on its stalk prior to acid cleaning. Scale bar = 20 μm.

Supplementary fig. 5: LM image of D. geminata from Massachusetts. Scale bar = 10 μm.

Additional information

Notes on contributors

Diba A. Khan-Bureau

D.A. Khan-Bureau: original concept, LM and SEM and molecular analyses, drafting and editing the manuscript; E.A. Morales: reviewed LM and SEM images and edited the manuscript; L. Ector reviewed the LM and SEM images and edited the manuscript; M.S. Beauchene, provided water quality data and historical information and edited the manuscript; L.A. Lewis reviewed molecular, SEM, and LM analyses, and edited the manuscript.

Eduardo A. Morales

D.A. Khan-Bureau: original concept, LM and SEM and molecular analyses, drafting and editing the manuscript; E.A. Morales: reviewed LM and SEM images and edited the manuscript; L. Ector reviewed the LM and SEM images and edited the manuscript; M.S. Beauchene, provided water quality data and historical information and edited the manuscript; L.A. Lewis reviewed molecular, SEM, and LM analyses, and edited the manuscript.

Luc Ector

D.A. Khan-Bureau: original concept, LM and SEM and molecular analyses, drafting and editing the manuscript; E.A. Morales: reviewed LM and SEM images and edited the manuscript; L. Ector reviewed the LM and SEM images and edited the manuscript; M.S. Beauchene, provided water quality data and historical information and edited the manuscript; L.A. Lewis reviewed molecular, SEM, and LM analyses, and edited the manuscript.

Michael S. Beauchene

D.A. Khan-Bureau: original concept, LM and SEM and molecular analyses, drafting and editing the manuscript; E.A. Morales: reviewed LM and SEM images and edited the manuscript; L. Ector reviewed the LM and SEM images and edited the manuscript; M.S. Beauchene, provided water quality data and historical information and edited the manuscript; L.A. Lewis reviewed molecular, SEM, and LM analyses, and edited the manuscript.

Louise A. Lewis

D.A. Khan-Bureau: original concept, LM and SEM and molecular analyses, drafting and editing the manuscript; E.A. Morales: reviewed LM and SEM images and edited the manuscript; L. Ector reviewed the LM and SEM images and edited the manuscript; M.S. Beauchene, provided water quality data and historical information and edited the manuscript; L.A. Lewis reviewed molecular, SEM, and LM analyses, and edited the manuscript.