scholarly journals Role of galactosyltransferase activity in phage sensitivity and nodulation competitiveness of Rhizobium meliloti.

1986 ◽  
Vol 166 (1) ◽  
pp. 148-154 ◽  
Author(s):  
R A Ugalde ◽  
J Handelsman ◽  
W J Brill
Keyword(s):  
Rhizobium Meliloti ◽  
Nodulation Competitiveness ◽  
Phage Sensitivity

scholarly journals Long-term persistence of crAss-like phage crAss001 is associated with phase variation in Bacteroides intestinalis

2020 ◽  
Author(s):  
Andrey N Shkoporov ◽  
Ekaterina V Khokhlova ◽  
Niamh Stephens ◽  
Cara Hueston ◽  
Samuel Seymour ◽  
...  
Keyword(s):  
Dynamic Equilibrium ◽  
Phase Variation ◽  
Carrier State ◽  
Human Gut ◽  
Rapid Phase ◽  
Host Interaction ◽  
Infected Cells ◽  
Phage Sensitivity

The crAss-like phages are ubiquitous and highly abundant members of the human gut virome that infect commensal bacteria of the order Bacteroidales. Although incapable of classical lysogeny, these viruses demonstrate unexplained long-term persistence in the human gut microbiome, dominating the virome in some individuals. Here we demonstrate that rapid phase variation of alternate capsular polysaccharides plays an important role in dynamic equilibrium between phage sensitivity and resistance in B. intestinalis cultures, allowing phage and bacteria to multiply in parallel. The data also suggests the role of concomitant phage persistence mechanisms associated with delayed lysis of infected cells, such as carrier state infection. From an ecological and evolutionary standpoint this type of phage-host interaction is consistent with the Piggyback-the-Winner model, which suggests a preference towards lysogenic or other 'benign' forms of phage infection when the host is stably present at high abundance.

Nodulation competitiveness of Tn5-induced mutants of Rhizobium fredii USDA208 that are altered in motility and extracellular polysaccharide production

1991 ◽  
Vol 37 (1) ◽  
pp. 52-58 ◽  
Author(s):  
Robert E. Zdor ◽  
Steven G. Pueppke
Keyword(s):  
Parental Strain ◽  
Extracellular Polysaccharide ◽  
Triphenyltetrazolium Chloride ◽  
Polysaccharide Production ◽  
Production Type ◽  
Rhizobium Fredii ◽  
Induced Mutants ◽  
Nodulation Competitiveness

The role of motility and extracellular polysaccharide production in nodulation competitiveness of Rhizobium fredii was examined. Transposon Tn5 was used to mutagenize strain USDA208, and mutants with reduced motility on semisolid agar medium were isolated. One such mutant, 208M3, migrated to only one-seventh the distance of the parental strain. Solid medium amended with triphenyltetrazolium chloride was used to identify mutants altered in extracellular polysaccharide production. Type 1 colonies, typified by mutant 208T13, were heavily mucoid, while type 2 colonies, represented by mutant 208T3, were dry and nonmucoid. Compared with strain USDA208, these mutants produced 4- to 5-fold more extracellular polysaccharide and 20% as much extracellular polysaccharide, respectively. Marker exchange of 208T3 genomic DNA containing Tn5 into strain USDA208 resulted in a mutant, 208K1, that produced extracellular polysaccharide levels similar to mutant 208T3. Mutants 208M3, 208T3, and 208T13 contained single Tn5 insertions. All formed pink nodules on 'Peking' soybean that were structurally indistinguishable and contained proteins with similar profiles. Rates of nodulation were similar in the mutants and the parental strain. Mutants 208M3 and 208T13 were as competitive against an isolate of Bradyrhizobium japonicum serogroup 123 as was strain USDA208. In contrast, mutants 208T3 and 208K1 were competitively superior. Key words: nodulation competition, motility, extracellular polysaccharide, Rhizobium.

Denitrification activity of phage types representative of two populations of indigenous Rhizobium meliloti

1989 ◽  
Vol 35 (7) ◽  
pp. 737-740 ◽  
Author(s):  
Y.-K. Chan ◽  
L. R. Barran ◽  
E. S. P. Bromfield
Keyword(s):  
Medicago Sativa ◽  
Rhizobium Meliloti ◽  
Previous History ◽  
Indigenous Populations ◽  
Frequency Of Occurrence ◽  
Phage Types ◽  
Denitrification Activity ◽  
History Of ◽  
Phage Sensitivity ◽  
Two Populations

Isolates of Rhizobium meliloti from indigenous populations at two sites were previously characterized according to phage sensitivity. Isolates representative of the 55 and 65 phage types comprising these two populations, respectively, were tested for denitrification activity with nitrate or nitrite as substrate. Fifty-seven of 120 isolates were capable of denitrification with activities varying considerably between phage types. Only one isolate was able to denitrify nitrite but not nitrate, indicating the presence of a truncated denitrification pathway. Each of five phage types showed variation in denitrification ability between isolates from different sites, indicating possible adaptation of indigenous R. meliloti to their respective environments. The estimated frequency of occurrence of denitrifiers in the two indigenous populations of R. meliloti (9 and 13%) differed significantly between sites with and without a previous history of Medicago sativa cultivation, respectively.Key words: Rhizobium, denitrification, populations, phage.

A cryptic plasmid of indigenous Rhizobium meliloti possesses reiterated nodC and nifE genes and undergoes DNA rearrangement

1992 ◽  
Vol 38 (6) ◽  
pp. 563-568 ◽  
Author(s):  
V. K. Rastogi ◽  
E. S. P. Bromfield ◽  
S. T. Whitwill ◽  
L. R. Barran
Keyword(s):  
Genomic Dna ◽  
Rhizobium Meliloti ◽  
Phage Type ◽  
Cryptic Plasmid ◽  
Dna Rearrangement ◽  
Homologous Sequences ◽  
Phage Types ◽  
Phage Sensitivity ◽  
Cryptic Plasmids ◽  
Free Strain

Indigenous Rhizobium meliloti were previously characterized on the basis of plasmid profiles and phage sensitivity patterns (phage types). Rhizobium meliloti 1076, which contained two cryptic plasmids, was one of four isolates comprising phage type 23. In this study, the large cryptic plasmid pVS1(size >500 b) was transferred from isolate 1076 into the plasmid-free strain of Agrobacterium tumefaciens UBAPF1. This plasmid contained nucleotide sequences homologous to genes for nodulation (nodB, nodC) and nitrogen fixation (nifH, nifD, nifK, nifE). Cosmid clones possessing the nod and nif homologous sequences, which had been selected from a genomic bank of A. tumefaciens UBAPF1 containing pVS1, complemented R. meliloti nodC and nifE mutants, respectively. These results demonstrate that the nodC and nifE homologous sequences are functionally expressed. Three of four isolates comprising phage type 23 possessed a megaplasmid band in agarose gels characteristic of R. meliloti, as well as two cryptic plasmids. The fourth isolate (No. 323) lacked the large cryptic plasmid corresponding to pVS1, but instead showed a band of lesser mobility than that of the megaplasmids. Nevertheless, its restricted genomic DNA retained the nodC and nifE hybridizing fragments characteristic of pVS1, indicating that the cryptic plasmid has undergone DNA rearrangement. Key words: Rhizobium, plasmid, reiteration, genes, rearrangement.

scholarly journals rosR, a Determinant of Nodulation Competitiveness in Rhizobium etli

1997 ◽  
Vol 10 (2) ◽  
pp. 180-186 ◽  
Author(s):  
Mark A. Bittinger ◽  
Jocelyn L. Milner ◽  
Barry J. Saville ◽  
Jo Handelsman
Keyword(s):  
Cell Surface ◽  
Rhizobium Meliloti ◽  
Single Gene ◽  
Cell Surface Hydrophobicity ◽  
Surface Hydrophobicity ◽  
Competitive Growth ◽  
Rhizobium Etli ◽  
Reading Frame ◽  
Nodulation Competitiveness ◽  
Mutant Phenotypes

We previously described a Tn5 mutant of Rhizobium etli strain CE3, designated CE3003, that is decreased in nodulation competitiveness, reduced in competitive growth in the rhizosphere, and has a hydrophobic cell surface (R. S. Araujo, E. A. Robleto, and J. Handelsman, Appl. Environ. Microbiol., 60:1430–1436, 1994). To determine the molecular basis for the mutant phenotypes, we identified a 1.2-kb fragment of DNA derived from the parent that restored the wild-type phenotypes to the mutant. DNA sequence analysis indicated that this 1.2-kb fragment contained a single open reading frame that we designated rosR. The Tn5 insertion in CE3003 was within rosR. We constructed a derivative of CE3 that contained a deletion in rosR, and this mutant was phenotypically indistinguishable from CE3003 in cell surface and competitive characteristics. Based on the nucleotide sequence, the deduced RosR amino acid sequence is 80% identical to that of the Ros protein from Agrobacterium tumefaciens and the MucR protein from Rhizobium meliloti. Both Ros and MucR are transcriptional repressors that contain a putative zinc-finger DNA-binding domain. This study defines a gene, rosR, that is homologous to a family of transcriptional regulators and contributes to nodulation competitiveness of R. etli. Moreover, we established that a single gene affects nodulation competitiveness, competitive growth in the rhizosphere, and cell surface hydrophobicity.

Does siderophore production influence the relative abundance of Rhizobium meliloti in two field populations?

1993 ◽  
Vol 39 (3) ◽  
pp. 348-351 ◽  
Author(s):  
L. R. Barran ◽  
E. S. P. Bromfield
Keyword(s):  
Soil Ph ◽  
Relative Abundance ◽  
Iron Content ◽  
Direct Relationship ◽  
Rhizobium Meliloti ◽  
Siderophore Production ◽  
Frequency Of Occurrence ◽  
Apparent Absence ◽  
Phage Types ◽  
Phage Sensitivity

Populations of indigenous Rhizobium meliloti isolated from nodules of alfalfa grown at sites A and B (soil pH, 7.0 and 6.1, respectively) were previously characterized on the basis of phage sensitivity and divided into 55 and 65 phage types. The available iron content of soil at site B was significantly higher than that at site A. Isolates representing the phage types comprising each of these populations were tested for the production of siderophores. The frequency of siderophore-producing (sid+) phage types of R. meliloti, estimated from the distribution of types in the two field populations, was significantly higher at site A (54%), where iron was less available, than at site B (18%). The distributions of frequency for sid+ and sid− phage types were similar at site A but differed (P < 0.005) at site B, where the soil was slightly acidic and contained more available iron. The apparent absence of a direct relationship between siderophore production and frequency of occurrence suggests that siderophore production may not influence the relative abundance of R. meliloti in these populations at sites differing in iron availability.Key words: siderophore, iron, Rhizobium meliloti, populations.

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