Sj. Beard et al., Gas Vesicle genes in Planktothrix spp. from Nordic lakes: strains with weak gas vesicles possess a longer variant of gvpC, MICROBIO-UK, 146, 2000, pp. 2009-2018
In cyanobacteria of the genus Planktothrix, there are three length Variants
of gvpC, the gene that encodes the outer protein of the gas vesicle. Seque
nce analyses indicated that the three allelic variants of gvpC differ princ
ipally in the presence or absence of a 99 nt and a 213 nt section. Strains
with the new variant, gvpC(28), which encodes a 28 kDa form of GvpC, produc
e 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 an
d in the presence of Omega C, a fragment of gvpC. The gvpC(28) gene was fou
nd to be the most common variant of gvpC amongst 71 strains of Planktothrix
isolated from Nordic lakes: 34 strains contained only gvpC(28); 22 strains
, which possessed only the shorter gvpC(20) gene, produced gas vesicles wit
h a higher p(c) of 0.76-0.91 MPa; and 15 strains, which possessed both gvpC
(20) and gvpC(28), also produced the stronger gas vesicles. Genotypes with
only the gvpC(28) genes were more common amongst green Planktothrix strains
(33 out of 38) than red strains (one out of 33). It is suggested that ther
e is competition between the strains producing the two types of gas vesicle
s, 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 gvpC(16)-cantaining strains that
produce even narrower gas vesicles of p(c) 1.0-1.2 MPa, which are common i
n the much deeper Lake Zurich.