Fig 7.

The symbiotic productivity of alfalfa plants inoculated with S. meliloti 1021 strains overexpressing exoY is not significantly different from that of plants inoculated with control strains. exoY-overexpressing strains of S. meliloti 1021 were inoculated onto the host plant alfalfa. Symbiotic productivity is measured as (A) shoot length in cm and (B) shoot fresh weight in grams. This indicates that an increased level of succinoglycan production by the S. meliloti 1021 reference strain does not reduce the efficiency of the symbiosis with the host plant alfalfa. Also, since there is not a significant improvement in symbiotic productivity in exoY overexpression strains, it indicates that succinoglycan production is not a limiting factor for the S. meliloti 1021 reference strain in establishing a functional symbiosis on the host plant alfalfa. Plants inoculated with an exoY::Tn5 null mutant that does not produce any succinoglycan had similar shoot lengths and fresh weight to uninoculated plants. Asterisks over graph bars denote a statistically significant difference from the reference strain in an unpaired t test. ref., reference. Error bars show standard errors of the means.