福建省豆科植物根瘤菌资源的初步调查

对福建省境内(除东北部少数地区外)的29个县(市)豆科植物根瘤菌资源进行了调查,共采集到36属63种豆科植物的根瘤样品278份,在豆科栽培作物方面有一定代表性.采集到的根瘤形态多样,大小多在1-10 mm之间,以淡黄和淡红色居多.对32种51份根瘤样品用乙炔还原法进行了固氮酶活性测定,不同种和同一种植物在不同生境下的固氮酶活性均有差异,多数根瘤样品的固氮酶活性在1-24 μmol C2H4g-1 fresh nodule h-1之间,其中尖叶长柄山蚂蝗(Podocarpium podocarpum var.oxyphyllum)的固氮酶活性相对最高,达87.29 u mol C2H4 g-1 fresh nodule h-1.从采集到的根瘤中经分离纯化获得了228株根瘤菌,其中155株根瘤菌进行了原寄主回接试验,有138株结瘤,回接成功率为89.0%.调查结果显示福建省有丰富的豆科固氮及其根瘤菌资源.     

Compatibility of Rhizobial Genotypes within Natural Populations of Rhizobium leguminosarum Biovar viciae for Nodulation of Host Legumes

Populations of Rhizobium leguminosarum biovar viciae were sampled from two bulk soils, rhizosphere, and nodules of host legumes, fava bean (Vicia faba) and pea (Pisum sativum) grown in the same soils. Additional populations nodulating peas, fava beans, and vetches (Vicia sativa) grown in other soils and fava bean-nodulating strains from various geographic sites were also analyzed. The rhizobia were characterized by repetitive extragenomic palindromic-PCR fingerprinting and/or PCR-restriction fragment length polymorphism (RFLP) of 16S-23S ribosomal DNA intergenic spacers as markers of the genomic background and PCR-RFLP of a nodulation gene region, nodD, as a marker of the symbiotic component of the genome. Pairwise comparisons showed differences among the genetic structures of the bulk soil, rhizosphere, and nodule populations and in the degree of host specificity within the Vicieae cross-inoculation group. With fava bean, the symbiotic genotype appeared to be the preponderant determinant of the success in nodule occupancy of rhizobial genotypes independently of the associated genomic background, the plant genotype, and the soil sampled. The interaction between one particular rhizobial symbiotic genotype and fava bean seems to be highly specific for nodulation and linked to the efficiency of nitrogen fixation. By contrast with bulk soil and fava bean-nodulating populations, the analysis of pea-nodulating populations showed preferential associations between genomic backgrounds and symbiotic genotypes. Both components of the rhizobial genome may influence competitiveness for nodulation of pea, and rhizosphere colonization may be a decisive step in competition for nodule occupancy.     

Diabetes Mellitus Associated with Epidemic of Infectious Hepatitis in Nigeria

This report concerns nine cases of diabetes mellitus associated with infectious hepatitis, an epidemic of which swept through eastern Nigeria between 1970 and 1972. All the patients showed the classical symptoms and signs of diabetes. They quickly responded to treatment, and after a few months the diabetes completely disappeared. Corticosteroid-glucose tolerance tests in four patients 12 to 30 months after the remission of their diabetes were normal. Contact with the remaining five patients had been lost a few months after clinical remission of their diabetes. The infectious hepatitis virus may have damaged pancreatic islet cells to cause an acute remittant form of diabetes mellitus.     

Influence of the Size of Indigenous Rhizobial Populations on Establishment and Symbiotic Performance of Introduced Rhizobia on Field-Grown Legumes

Indigenous rhizobia in soil present a competition barrier to the establishment of inoculant strains, possibly leading to inoculation failure. In this study, we used the natural diversity of rhizobial species and numbers in our fields to define, in quantitative terms, the relationship between indigenous rhizobial populations and inoculation response. Eight standardized inoculation trials were conducted at five well-characterized field sites on the island of Maui, Hawaii. Soil rhizobial populations ranged from 0 to over 3.5 × 10⁴ g of soil^-1 for the different legumes used. At each site, no less than four but as many as seven legume species were planted from among the following: soybean (Glycine max), lima bean (Phaseolus lunatus), cowpea (Vigna unguiculata), bush bean (Phaseolus vulgaris), peanut (Arachis hypogaea), Leucaena leucocephala, tinga pea (Lathyrus tingeatus), alfalfa (Medicago sativa), and clover (Trifolium repens). Each legume was (i) inoculated with an equal mixture of three effective strains of homologous rhizobia, (ii) fertilized at high rates with urea, or (iii) left uninoculated. For soybeans, a nonnodulating isoline was used in all trials as the rhizobia-negative control. Inoculation increased economic yield for 22 of the 29 (76%) legume species-site combinations. While the yield increase was greater than 100 kg ha^-1 in all cases, in only 11 (38%) of the species-site combinations was the increase statistically significant (P ≤ 0.05). On average, inoculation increased yield by 62%. Soybean (G. max) responded to inoculation most frequently, while cowpea (V. unguiculata) failed to respond in all trials. Inoculation responses in the other legumes were site dependent. The response to inoculation and the competitive success of inoculant rhizobia were inversely related to numbers of indigenous rhizobia. As few as 50 rhizobia g of soil^-1 eliminated inoculation response. When fewer than 10 indigenous rhizobia g of soil^-1 were present, economic yield was significantly increased 85% of the time. Yield was significantly increased in only 6% of the observations when numbers of indigenous rhizobia were greater than 10 cells g of soil^-1. A significant response to N application, significant increases in nodule parameters, and greater than 50% nodule occupancy by inoculant rhizobia did not necessarily coincide with significant inoculation responses. No less than a doubling of nodule mass and 66% nodule occupancy by inoculant rhizobia were required to significantly increase the yield of inoculated crops over that of uninoculated crops. However, lack of an inoculation response was common even when inoculum strains occupied the majority of nodules. In these trials, the symbiotic yield of crops was, on average, only 88% of the maximum yield potential, as defined by the fertilizer N treatment. The difference between the yield of N-fertilized crops and that of N₂-fixing crops indicates a potential for improving inoculation technology, the N₂ fixation capacity of rhizobial strains, and the efficiency of symbiosis. In this study, we show that the probability of enhancing yield with existing inoculation technology decreases dramatically with increasing numbers of indigenous rhizobia.     

Case of Localized Recombination in 23S rRNA Genes from Divergent Bradyrhizobium Lineages Associated with Neotropical Legumes

Enzyme electrophoresis and rRNA sequencing were used to analyze relationships of Bradyrhizobium sp. nodule bacteria from four papilionoid legumes (Clitoria javitensis, Erythrina costaricensis, Rhynchosia pyramidalis, and Desmodium axillare) growing on Barro Colorado Island (BCI), Panama. Bacteria with identical multilocus allele profiles were commonly found in association with two or more legume genera. Among the 16 multilocus genotypes (electrophoretic types [ETs]) detected, six ETs formed a closely related cluster that included isolates from all four legume taxa. Bacteria from two other BCI legumes (Platypodium and Machaerium) sampled in a previous study were also identical to certain ETs in this group. Isolates from different legume genera that had the same ET had identical nucleotide sequences for both a 5′ portion of the 23S rRNA and the nearly full-length 16S rRNA genes. These results suggest that Bradyrhizobium genotypes with low host specificity may be prevalent in this tropical forest. Parsimony analysis of 16S rRNA sequence variation indicated that most isolates were related to Bradyrhizobium japonicum USDA 110, although one ET sampled from C. javitensis had a 16S rRNA gene highly similar to that of Bradyrhizobium elkanii USDA 76. However, this isolate displayed a mosaic structure within the 5′ 23S rRNA region: one 84-bp segment was identical to that of BCI isolate Pe1-3 (a close relative of B. japonicum USDA 110, based on 16S rRNA data), while an adjacent 288-bp segment matched that of B. elkanii USDA 76. This mosaic structure is one of the first observations suggesting recombination in nature between Bradyrhizobium isolates related to B. japonicum versus B. elkanii.     

Rhizobial Association with Non-Legumes: Mechanisms and Applications

It has been known for more than a century that rhizobia can promote the growth of legumes through the formation of nitrogen-fixing nodules, but the interaction of rhizobia with non-legumes has been neglected as an experimental system. During the last couple of decades, work on rhizobial interaction with non-legumes has been done progressively and it has been demonstrated that rhizobia can associate with roots of non-legumes also, without forming true nodules, and can promote their growth by using one or more of the direct or indirect mechanisms of actions. Phytohormone production, secretion of other chemicals like lipo-chito-oligosaccharides (LCOs) and lumichrome, solubilization of precipitated phosphorus and mineralization of organic P, improvement in uptake of plant nutrients by altering root morphology, production of siderophores to meet the iron requirements of the plant under iron-stressed conditions and lowering of ethylene level through ACC deaminase enzyme, are some examples of the rhizobial mechanisms with direct positive effects on non-leguminous plant growth. Indirectly, rhizobia improve the growth of non-legumes through biocontrol of pathogens via antibiosis, parasitism or competition with pathogens for nutrients and space, by inducing systemic resistance in the host plant and through increasing root adhering soil by releasing exopolysaccarides which regulate the water movement and facilitate the root growth. However, no influence or even inhibitory effects of rhizobial inoculation on non-legumes has also been demonstrated in some cases. Plant growth promoting mechanisms of rhizobia and its practical application in non-legumes are the major focus of this review.     

Epidemic Gastroenteritis in Newfoundland During 1963 Associated with E. coli 0111:B4

An epidemic of infantile gastroenteritis occurred in Newfoundland in the year 1963. Cases and deaths were reported from communities in widely separated geographic areas. A total of 1071 cases was reported and there were 100 deaths. The death rate was estimated at 600 per 100,000 live births and exceeded the highest rate noted during any of the preceding 15 years.During 1963 the Newfoundland Public Health Laboratories recorded a high incidence of enteropathogenic Escherichia coli isolations. Over 500 isolations were obtained, of which 76% were E. coli 0111:B4, indicating that this organism was the main offender. The majority of E. coli 0111:B4 isolates were resistant in vitro to chloramphenicol and neomycin.Important among efforts to control this widespread community outbreak was an educational program which made extensive use of television and radio.     

Bathy Phytochromes in Rhizobial Soil Bacteria

Phytochromes are biliprotein photoreceptors that are found in plants, bacteria, and fungi. Prototypical phytochromes have a Pr ground state that absorbs in the red spectral range and is converted by light into the Pfr form, which absorbs longer-wavelength, far-red light. Recently, some bacterial phytochromes have been described that undergo dark conversion of Pr to Pfr and thus have a Pfr ground state. We show here that such so-called bathy phytochromes are widely distributed among bacteria that belong to the order Rhizobiales. We measured in vivo spectral properties and the direction of dark conversion for species which have either one or two phytochrome genes. Agrobacterium tumefaciens C58 contains one bathy phytochrome and a second phytochrome which undergoes dark conversion of Pfr to Pr in vivo. The related species Agrobacterium vitis S4 contains also one bathy phytochrome and another phytochrome with novel spectral properties. Rhizobium leguminosarum 3841, Rhizobium etli CIAT652, and Azorhizobium caulinodans ORS571 contain a single phytochrome of the bathy type, whereas Xanthobacter autotrophicus Py2 contains a single phytochrome with dark conversion of Pfr to Pr. We propose that bathy phytochromes are adaptations to the light regime in the soil. Most bacterial phytochromes are light-regulated histidine kinases, some of which have a C-terminal response regulator subunit on the same protein. According to our phylogenetic studies, the group of phytochromes with this domain arrangement has evolved from a bathy phytochrome progenitor.Phytochromes are biological photoreceptors that were discovered in plants, where they control development throughout the life cycle in manifold ways (21, 33). Today, a large number of homologs are known also from cyanobacteria, other bacteria, and fungi, which are termed cyanobacterial phytochromes (Cphs), bacteriophytochromes (BphPs), and fungal phytochromes (Fphs), respectively (20, 24). The chromophore is autocatalytically assembled within the N-terminal part of the protein, the photosensory core module (PCM), which contains the PAS, GAF, and PHY domains (30). Typically, phytochromes are converted by light between two spectrally different forms, the red-absorbing Pr and the far-red-absorbing Pfr forms. Photoconversion is initiated by an isomerization of the covalently bound bilin chromophore (32).Plant and cyanobacterial phytochromes incorporate phytochromobilin (PΦB) and phycocyanobilin (PCB) as natural chromophores, respectively, which are covalently bound to Cys residues in the GAF domains. All characterized phytochromes that belong to these groups have a Pr ground state. Plant phytochromes can undergo dark conversion of Pfr to Pr (5), whereas the Pfr form of typical cyanobacterial phytochromes is stable in darkness (26).Bacteriophytochromes utilize biliverdin (BV) instead as a natural chromophore (1), which is covalently attached to a Cys residue in the N terminus of the PAS domain (26). Since the conjugated system of BV is longer than that of PΦB or PCB, the absorption maxima of bacteriophytochromes are found at higher wavelengths than those of cyanobacterial or plant homologs.With the discovery of a bacterial phytochrome from Bradyrhizobium sp. strain ORS278, termed BrBphP1, the first phytochrome with a Pfr ground state and dark conversion from Pr to Pfr was found (10). Thereafter, five more phytochromes with dark conversion of Pr to Pfr were described: Rhodopseudomonas palustris BphP1 (RpBphP1) from strain CEA001, RpBphP5, and RpBphP6 from strain CGA009 (11); Agrobacterium tumefaciens Agp2 (or AtBphP2) from strain C58 (18); and Pseudomonas aeruginosa BphP1 (PaBphP1) (40). These phytochromes are now termed bathy phytochromes because the absorption maxima of their ground states are bathochromically (to longer wavelengths) shifted compared to those of all other phytochromes.Moreover, some other bacterial phytochromes with unusual properties have been described. In the Ppr from Rhodospirillum centenum, a photoactive yellow protein (PYP) domain is fused to the N terminus of a phytochrome homolog. The phytochrome part of Ppr assembles with BV to form a Pr adduct. However, irradiation does not result in the formation of Pfr but in a bleaching of the Pr spectrum (23). The BV adduct of RpBphP3 from R. palustris, which has a Pr ground state, photoconverts to the so-called Pnr form with a blue-shifted absorption maximum (12). RpBphP4 from R. palustris strains Ha2 and BisB5 and Bradyrhizobium BphP3 (BrBphP3) from Bradyrhizobium BTAi1, both with a Pr ground state, photoconvert into a long-lived MetaR form (8, 42). MetaRa and MetaRc are intermediates in the photoconversion from Pr to Pfr of prototypical phytochromes (3). BphP3 from the Bradyrhizobium strain ORS 278 is an exception among bacteriophytochromes as it binds PCB as a natural chromophore. This phytochrome adopts a so-called Po (P-orange) ground state with an absorbance maximum in the orange range (11, 15). Upon irradiation, this phytochrome converts into the Pr form. RpBphP4 from R. palustris CGA009 lacks the biliverdin binding cysteine and does not bind a chromophore (42).With the rapidly growing number of bacterial genome sequences, many new bacterial phytochromes are being discovered. Thus, a large and increasing number of newly identified phytochromes remain spectroscopically uncharacterized. We established an in vivo photometry approach which allowed the rapid acquisition of spectral information about phytochromes from intact bacterial cells. In the beginning period of plant phytochrome research, in vivo photometry was extensively applied (4, 6, 29, 34). This method, in fact, allowed the identification of phytochromes for the first time in plant tissues (6), which led to the purification of phytochromes from plant extracts (37). Here, we apply in vivo photometry for the first time to organisms outside the plant kingdom. This method is especially useful for studying species with single phytochrome genes. The approach is also helpful for comparing properties of native phytochromes in vivo and of their recombinant proteins in vitro.In the present study, we concentrate on nonphotosynthetic species of the order Rhizobiales which belongs to the Alphaproteobacteria. The family Rhizobiaceae comprises plant-interacting soil bacteria. A. tumefaciens and Agrobacterium vitis can transfer genes into plants to induce plant tumors, whereas many other Rhizobiaceae can live as plant symbionts in nodules of stems or roots in which they assimilate molecular nitrogen to produce NH₄⁺, which is used by the plant for synthesis of amino acids and other nitrogen-containing molecules. A. tumefaciens C58 contains two phytochromes, termed Agp1 (or AtBphP1) and Agp2 (or AtBphP2), that have been characterized as recombinant proteins (14, 18, 26, 35) and whose spectral activities have been measured in extracts of wild-type and knockout mutants (31). A large number of phytochromes from photosynthetic Bradyrhizobium and Rhodopseudomonas species, which also belong to the order Rhizobiales, have been characterized as recombinant proteins (11), some of which have already been noted above.It turned out that most of our analyzed phytochromes undergo dark conversion of Pr to Pfr and thus belong to the group of bathy phytochromes. Such phytochromes, which absorb at around 750 nm, clearly dominate among Rhizobiales. We propose that this specific property reflects an adaptation to the light regime in the soil. Our studies also suggest that bacterial phytochromes with a C-terminal response regulator have evolved from a bathy phytochrome progenitor.     

Nitrogen Fixation in Wild Legumes

Isolations of the rhizobia from nodules of field plants of Ulexeuropaeus and Medicago lupulina have been examined for effectivenessin fixation of nitrogen by inoculating them into host plantsgrowing in a medium free of combined nitrogen. The results indicatethat vigorous fixation may be presumed to occur in associationwith field plants of the Ulex species, but that fixation inMedicago is probably decreased by the presence of ineffectiverhizobia in some nodules. The general importance of fixationin wild legumes is discussed, and it is pointed out that dueattention must be paid to non-legume genera with root nodules.These genera are locally abundant, and in former periods werestill more prominent in some regions of the world.     

Population Genetic Analysis of Propionibacterium acnes Identifies a Subpopulation and Epidemic Clones Associated with Acne

The involvement of Propionibacterium acnes in the pathogenesis of acne is controversial, mainly owing to its dominance as an inhabitant of healthy skin. This study tested the hypothesis that specific evolutionary lineages of the species are associated with acne while others are compatible with health. Phylogenetic reconstruction based on nine housekeeping genes was performed on 210 isolates of P. acnes from well-characterized patients with acne, various opportunistic infections, and from healthy carriers. Although evidence of recombination was observed, the results showed a basically clonal population structure correlated with allelic variation in the virulence genes tly and camp5, with pulsed field gel electrophoresis (PFGE)- and biotype, and with expressed putative virulence factors. An unexpected geographically and temporal widespread dissemination of some clones was demonstrated. The population comprised three major divisions, one of which, including an epidemic clone, was strongly associated with moderate to severe acne while others were associated with health and opportunistic infections. This dichotomy correlated with previously observed differences in in vitro inflammation-inducing properties. Comparison of five genomes representing acne- and health-associated clones revealed multiple both cluster- and strain-specific genes that suggest major differences in ecological preferences and redefines the spectrum of disease-associated virulence factors. The results of the study indicate that particular clones of P. acnes play an etiologic role in acne while others are associated with health.     

Associations Among Rhizobial Chromosomal Background, nod Genes, and Host Plants Based on the Analysis of Symbiosis of Indigenous Rhizobia and Wild Legumes Native to Xinjiang

The associations among rhizobia chromosomal background, nodulation genes, legume plants, and geographical regions are very attractive but still unclear. To address this question, we analyzed the interactions among rhizobia rDNA genotypes, nodC genotypes, legume genera, as well as geographical regions in the present study. Complex relationships were observed among them, which may be the genuine nature of their associations. The statistical analyses indicate that legume plant is the key factor shaping both rhizobia genetic and symbiotic diversity. In the most cases of our results, the nodC lineages are clearly associated with rhizobial genomic species, demonstrating that nodulation genes have co-evolved with chromosomal background, though the lateral transfer of nodulation genes occurred in some cases in a minority. Our results also support the hypothesis that the endemic rhizobial populations to a certain geographical area prefer to have a wide spectrum of hosts, which might be an important event for the success of both legumes and rhizobia in an isolated region.     

PCR-Based Genotyping of Epidemic and Preepidemic Trichoderma Isolates Associated with Green Mold of Agaricus bisporus

We used randomly amplified polymorphic DNA (RAPD)-PCR to estimate genetic variation among isolates of Trichoderma associated with green mold on the cultivated mushroom Agaricus bisporus. Of 83 isolates examined, 66 were sampled during the recent green mold epidemic, while the remaining 17 isolates were collected just prior to the epidemic and date back to the 1950s. Trichoderma harzianum biotype 4 was identified by RAPD analysis as the cause of almost 90% of the epidemic-related episodes of green mold occurring in the major commercial mushroom-growing region in North America. Biotype 4 was more closely allied to T. harzianum biotype 2, the predominant pathogenic genotype in Europe, than to the less pathogenic biotype 1 and Trichoderma atroviride (formerly T. harzianum biotype 3). No variation in the RAPD patterns was observed among the isolates within biotype 2 or 4, suggesting that the two pathogenic biotypes were populations containing single clones. Considerable genetic variation, however, was noted among isolates of biotype 1 and T. atroviride from Europe. Biotype 4 was not represented by the preepidemic isolates of Trichoderma as determined by RAPD markers and PCR amplification of an arbitrary DNA sequence unique to the genomes of biotypes 2 and 4. Our findings suggest that the onset of the green mold epidemic in North America resulted from the recent introduction of a highly virulent genotype of the pathogen into cultivated mushrooms.     

Diverse Bacteria Associated with Root Nodules of Spontaneous Legumes in Tunisia and First Report for nifH-like Gene within the Genera Microbacterium and Starkeya

We characterized 34 endophytic bacterial isolates associated to root nodules collected from spontaneous legumes in the arid zone of Tunisia by 16S rDNA polymerase chain reaction (PCR)–restriction fragment length polymorphism, whole cell protein sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE), 16S rDNA and 16S–23S rDNA internal transcribed spacer sequencing. Phylogenetically, these isolates belong to the branches containing the genera Inquilinus, Bosea, Rhodopseudomonas, Paracraurococcus, Phyllobacterium, Ochrobactrum, Starkeya, Sphingomonas, Pseudomonas, Agromyces, Microbacterium, Ornithinicoccus, Bacillus, and Paenibacillus. These strains did not induce any nodule formation when inoculated on the wide host spectrum legume species M. atropurpureum (Siratro) and no nodA gene could be amplified by PCR. However, nifH sequences, most similar to those of Sinorhizobium meliloti, were detected within strains related to the genera Microbacterium, Agromyces, Starkeya and Phyllobacterium.     

Stigma Diversity in Tropical Legumes with Considerations on Stigma Classification

The great stigma diversity in angiosperms implies a choice of criteria for stigma classification, which nowadays is characterized as dry (= little or no secretory surface and exudate retained by the cuticle and/or protein pellicle), wet (= conspicuous secretory surface, abundant in fluid exudate) and semidry (exudate retained by cuticle and/or protein pellicle). Despite being a very species-rich family, whose representatives exhibit a wide floral variation, no comparative studies of stigma diversity have been done for the whole Leguminosae. In order to assess the stigma morphological diversity in legumes and to evaluate the criteria used in the main classifications of the stigma, we compared the stigma morphology in 15 distinct legume lineages. In addition, we evaluated the stigma classification in other 152 legume species whose morphology was already described in the literature. Stigmas were removed from floral buds and flowers and processed for analyses under scanning electron and light microscopes. The stigma of the study legumes exhibits quite variable morphology, mainly concerning the diameter, the occurrence of an orifice or a furrow, the coating, the cellular composition, and the occurrence, chemical nature and release mechanism of the exudate. This diversity appears to be related mainly to the evolutionary history of the group and also to the selective pressures exerted by different types of pollen and pollinator. More conflicting criteria for stigma classification lie in defining the semidry type, found mostly in papilionoids. For better stigma classification we suggest that stigma morphology be evaluated at the time prior to anthesis, when the cuticle is not yet broken and the exudate is not exposed or drained. In addition, several techniques should be employed for a better classification.     

Recombination Facilitates Adaptive Evolution in Rhizobial Soil Bacteria

Homologous recombination is expected to increase natural selection efficacy by decoupling the fate of beneficial and deleterious mutations and by readily creating new combinations of beneficial alleles. Here, we investigate how the proportion of amino acid substitutions fixed by adaptive evolution (α) depends on the recombination rate in bacteria. We analyze 3,086 core protein-coding sequences from 196 genomes belonging to five closely related species of the genus Rhizobium. These genes are found in all species and do not display any signs of introgression between species. We estimate α using the site frequency spectrum (SFS) and divergence data for all pairs of species. We evaluate the impact of recombination within each species by dividing genes into three equally sized recombination classes based on their average level of intragenic linkage disequilibrium. We find that α varies from 0.07 to 0.39 across species and is positively correlated with the level of recombination. This is both due to a higher estimated rate of adaptive evolution and a lower estimated rate of nonadaptive evolution, suggesting that recombination both increases the fixation probability of advantageous variants and decreases the probability of fixation of deleterious variants. Our results demonstrate that homologous recombination facilitates adaptive evolution measured by α in the core genome of prokaryote species in agreement with studies in eukaryotes.     

Variability in Xanthomonads of Grain Legumes

Pulse xanthomonads could not be differed on the basis of their bacteriological propertries. Colonies from cowpea, mungbean, guar, and bean showed differences in virulence related to the degree of mucoidness than to the rate of multiplication. Very weakly virulent mutants of the bean fuscous pathogen produced distinctive reaction in bean pods. White mutants were as virulent as their yellow forms.