@article{mbs:/content/journal/micro/10.1099/00221287-143-6-1959, author = "Parveen, Nikhat and Webb, David T. and Borthakur, Dulal", title = "The symbiotic phenotypes of exopolysaccharide-defective mutants of Rhizobium sp. strain TAL1145 do not differ on determinate- and indeterminate-nodulating tree legumes", journal= "Microbiology", year = "1997", volume = "143", number = "6", pages = "1959-1967", doi = "https://doi.org/10.1099/00221287-143-6-1959", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-143-6-1959", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", keywords = "nodulation", keywords = "exo genes", keywords = "nitrogen fixation", abstract = "Three classes of exopolysaccharide (EPS) defective mutants were isolated by Tn3Hogus -insertion mutagenesis of Rhizobium sp. strain TAL1145, which nodulates tree legumes. The class I and class III mutants produced 10-22% of the EPS produced by TAL1145 and appeared partially mucoid while the class II mutants formed small, opaque and non-mucoid colonies. Size-fractionation of the soluble EPSs made by these mutants in the culture supernatant indicated that the class I and the class III mutants produced reduced levels of both highland low-molecular-mass EPSs while the class II mutants lacked both these EPSs but produced a small amount of a medium-molecular-mass anthrone-reactive EPS. The succinyl and acetyl substituents observed in the TAL1145 EPS were absent in the EPS of the class II mutants. When examined under UV, the class I and class III mutants grown on Calcofluor-containing YEM agar showed dim blue fluorescence, compared to the bright blue fluorescence of the wild-type strain, whereas the class II mutants did not fluoresce. While the dim blue fluorescence of the class III mutants changed to yellow-green after 10 d, the fluorescence of the class I mutants did not change after prolonged incubation. Unlike the EPS-defective mutants of other rhizobia, these mutants did not show different symbiotic phenotypes on determinate- and indeterminate-nodulating tree legumes. The class I and the class III mutants formed small ineffective nodules on both types of legumes whereas the class II mutants formed normal nitrogen-fixing nodules on both types. The genes disrupted in the class I and class III mutants form a single complementation group while those disrupted in the class II mutants constitute another. All the three classes of EPS-defective mutants were located within a 10.8 kb region and complemented by two overlapping cosmids.", }