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Gas vesicle genes in Planktothrix spp. from Nordic lakes: strains with weak gas vesicles possess a longer variant of gvpC

School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK¹
Norwegian Institute for Water Research, PO Box 173 Kjelsas, N-0411 Oslo, Norway²

Author for correspondence: A. E. Walsby. Tel: +44 117 928 7490. e-mail: A. E.Walsby{at}bristol.ac.uk

In cyanobacteria of the genus Planktothrix, there are three length variants of gvpC, the gene that encodes the outer protein of the gas vesicle. Sequence analyses indicated that the three allelic variants of gvpC differ principally in the presence or absence of a 99 nt and a 213 nt section. Strains with the new variant, gvpC²⁸, which encodes a 28 kDa form of GvpC, produce gas vesicles that collapse at the relatively low critical pressure (p_c) of 0·61–0·75 MPa. The authors have identified 12 classes of gvp genotypes that differ in the number and arrangement of alternating gvpA–gvpC genes and in the presence of C, a fragment of gvpC. The gvpC²⁸ gene was found to be the most common variant of gvpC amongst 71 strains of Planktothrix isolated from Nordic lakes: 34 strains contained only gvpC²⁸; 22 strains, which possessed only the shorter gvpC²⁰ gene, produced gas vesicles with a higher p_c of 0·76–0·91 MPa; and 15 strains, which possessed both gvpC²⁰ and gvpC²⁸, also produced the stronger gas vesicles. Genotypes with only the gvpC²⁸ genes were more common amongst green Planktothrix strains (33 out of 38) than red strains (one out of 33). It is suggested that there is competition between the strains producing the two types of gas vesicles, with the stronger forms favoured in lakes deeper than 60 m, in which the combination of cell turgor pressure and hydrostatic pressure can collapse the weaker gas vesicles. The fact that none of the Nordic lakes are deeper than 67 m would explain the absence of the gvpC¹⁶-containing strains that produce even narrower gas vesicles of p_c 1·0–1·2 MPa, which are common in the much deeper Lake Zürich.

Keywords: cyanobacterial genetics, gas vesicles, Planktothrix

Abbreviations: 33RR, 33-residue repeat; p_c, critical pressure; p_t, turgor pressure; p_h, hydrostatic pressure.

The GenBank accession numbers for the new sequences in this paper are AJ253125–253133.

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