Effect of an overproduction of accessory Gvp proteins on gas vesicle formation in Haloferax volcanii

Gas vesicle formation in haloarchaea requires the expression of the p-vac region consisting of 14 genes, gvpACNO and gvpDEFGHIJKLM. Expression of gvpFGHIJKLM leads to essential accessory proteins formed in minor amounts. An overexpression of gvpG, gvpH or gvpM in addition to p-vac inhibited gas vesicle formation, whereas large amounts of all other Gvp proteins did not disturb the synthesis. The unbalanced expression and in particular an aggregation of the overproduced Gvp with other accessory Gvp derived from p-vac could be a reason for the inhibition. Western analyses demonstrated that the hydrophobic GvpM (and GvpJ) indeed form multimers. Fluorescent dots of GvpM–GFP were seen in cells in vivo underlining an aggregation of GvpM. In search for proteins neutralizing the inhibitory effect in case of GvpM, p-vac +pGM^ex, +pHM^ex, +pJM^ex, and +pLM^ex transformants were constructed. The inhibitory effect of GvpM on gas vesicle formation was suppressed by GvpH, GvpJ or GvpL, but not by GvpG. Western analyses demonstrated that pHM^ex and pJM^ex transformants contained additional larger protein bands when probed with an antiserum raised against GvpH or GvpJ, implying interactions. The balanced amount of GvpM–GvpH and GvpM–GvpJ appears to be important during gas vesicle genesis.