Spatial structure facilitates the accumulation and persistence of antibiotic‐resistant mutants in biofilms

Spontaneous mutants (3/parental strain) of soybean bradyrhizobia resistant to streptomycin and erythromycin were selected from strains isolated from bradyrhizobial populations indigenous to Cape Fear and Dothan soils. These were used to evaluate (i) the validity of using antibiotic-resistant mutants to make inferences about the competitiveness of parental strains in soil environments and (ii) the recovery of strains in nodules after inoculation of soybeans grown in soils with indigenous bradyrhizobial populations. Streptomycin and erythromycin resistances of all mutants were stable after approximately 27 generations of growth in yeast extract - mannitol medium, but 33% of the mutants lost resistance to erythromycin upon passage through nodules. Only 17% of the mutants were as competitive as their parental strain when inoculated in a ratio near 1:1 in vermiculite. Four of 10 mutants, which differed in competitiveness from their parental strain in vermiculite, had competitiveness against the soil populations equal to that of their parental strain. Therefore, assessment of competitiveness of mutants and parental strains in non-soil media may not accurately reflect their competitiveness in soil systems. For both the Cape Fear and Dothan soils, recovery of a given mutant from nodules of field-grown plants was always lower than from nodules of plants grown in the greenhouse. Inoculation of the entire rooting zone in the greenhouse experiment and of only a portion of the rooting zone in the field experiments may account for this difference in recovery. Techniques that increase the volume of soil inoculated may enhance nodulation by inoculant strains.Key words: Bradyrizobium, antibiotic resistance, competition.

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Slow growth determines nonheritable antibiotic resistance in Salmonella enterica

Science Signaling ◽

10.1126/scisignal.aax3938 ◽

2019 ◽

Vol 12 (592) ◽

pp. eaax3938 ◽

Cited By ~ 48

Author(s):

Mauricio H. Pontes ◽

Eduardo A. Groisman

Keyword(s):

Bacterial Population ◽

Slow Growth ◽

Large Fraction ◽

Signaling Molecules ◽

Antibiotic Resistant ◽

Phenotypic Changes ◽

Resistant Mutants ◽

Persistent Bacteria ◽

Small Subpopulation ◽

Antibiotic Resistant Mutants

Bacteria can withstand killing by bactericidal antibiotics through phenotypic changes mediated by their preexisting genetic repertoire. These changes can be exhibited transiently by a large fraction of the bacterial population, giving rise to tolerance, or displayed by a small subpopulation, giving rise to persistence. Apart from undermining the use of antibiotics, tolerant and persistent bacteria foster the emergence of antibiotic-resistant mutants. Persister formation has been attributed to alterations in the abundance of particular proteins, metabolites, and signaling molecules, including toxin-antitoxin modules, adenosine triphosphate, and guanosine (penta) tetraphosphate, respectively. Here, we report that persistent bacteria form as a result of slow growth alone, despite opposite changes in the abundance of such proteins, metabolites, and signaling molecules. Our findings argue that transitory disturbances to core activities, which are often linked to cell growth, promote a persister state regardless of the underlying physiological process responsible for the change in growth.

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A Rapid Technique for Obtaining One-step or Multi-step Antibiotic Resistant Mutants Employing Mutator Strains ofEscherichia coliK12

Journal of Applied Bacteriology ◽

10.1111/j.1365-2672.1973.tb04097.x ◽

1973 ◽

Vol 36 (2) ◽

pp. 241-243

Author(s):

D. W. Mount ◽

E. E. M. Moody ◽

N. Lew ◽

A. Walker

Keyword(s):

Antibiotic Resistant ◽

Rapid Technique ◽

Mutator Strains ◽

One Step ◽

Resistant Mutants ◽

Antibiotic Resistant Mutants

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Competition for nodulation of field-grown soybeans by strains of Rhizobium fredii

Canadian Journal of Microbiology ◽

10.1139/m86-037 ◽

1986 ◽

Vol 32 (2) ◽

pp. 183-186 ◽

Cited By ~ 4

Author(s):

Thomas J. McLoughlin ◽

Scott G. Alt ◽

P. Ann Owens ◽

Corrine Fetherston

Keyword(s):

Bradyrhizobium Japonicum ◽

Indigenous Population ◽

Growing Season ◽

Indigenous Populations ◽

First Year ◽

Antibiotic Resistant ◽

Rhizobium Fredii ◽

Glycine Max L ◽

Resistant Mutants ◽

Antibiotic Resistant Mutants

Nodulation of Glycine max (L) Merr. by six Rhizobium fredii strains was measured in two Midwestern fields containing high indigenous populations of Bradyrhizobium japonicum (3 × 105/gm soil). The soils were inoculated with antibiotic-resistant mutants using liquid inoculum at two levels on soybean cv. Peking and cv. Jacques 130. Strain establishment was measured 40 days after planting. In the first year, USDA206, USDA217, and USDA257 were the most competitive strains, occupying greater than 50% of the nodules on cv. Peking in both soils. None of the strains were competitive on Jacques 130. In the second growing season, all nodules were formed by the indigenous population on both cultivars, suggesting that these fast-growing strains do not persist in Midwestern soils.

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Studies on associative nitrogen fixation by antibiotic-resistant mutants ofAzospirillum brasilensewith genotypes of lentil (Lens culinaris)Rhizobiumstrains in calcareous soil

The Journal of Agricultural Science ◽

10.1017/s0021859600043136 ◽

1985 ◽

Vol 104 (1) ◽

pp. 207-215 ◽

Cited By ~ 1

Author(s):

R. Rai

Keyword(s):

Nitrogen Fixation ◽

Azospirillum Brasilense ◽

Calcareous Soil ◽

Lens Culinaris ◽

Nitrogenase Activity ◽

Dry Weight ◽

Antibiotic Resistant ◽

Uninoculated Control ◽

Resistant Mutants ◽

Antibiotic Resistant Mutants

SummaryNitrosoguanidine-induced mutation frequencies for resistance to streptomycin, spectinomycin, erythromycin and novomycin were studied inAzospirillum brasilense.Lentil inoculated withA. brasilenseand its mutants andRhizobiumstrains produced increased nodule dry weight, nitrogenase activity of nodules and roots and grain yield compared with an uninoculated control.

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