Strain G1 Research Articles

Syntrophic Growth on Formate: a New Microbial Niche in Anoxic Environments

Anaerobic syntrophic associations of fermentative bacteria and methanogenic archaea operate at the thermodynamic limits of life. The interspecies transfer of electrons from formate or hydrogen as a substrate for the methanogens is key. Contrary requirements of syntrophs and methanogens for growth-sustaining product and substrate concentrations keep the formate and hydrogen concentrations low and within a narrow range. Since formate is a direct substrate for methanogens, a niche for microorganisms that grow by the conversion of formate to hydrogen plus bicarbonate--or vice versa--may seem unlikely. Here we report experimental evidence for growth on formate by syntrophic communities of (i) Moorella sp. strain AMP in coculture with a thermophilic hydrogen-consuming Methanothermobacter species and of (ii) Desulfovibrio sp. strain G11 in coculture with a mesophilic hydrogen consumer, Methanobrevibacter arboriphilus AZ. In pure culture, neither Moorella sp. strain AMP, nor Desulfovibrio sp. strain G11, nor the methanogens grow on formate alone. These results imply the existence of a previously unrecognized microbial niche in anoxic environments.

Characterization of the traD Operon of Naphthalene-Catabolic Plasmid NAH7: a Host-Range Modifier in Conjugative Transfer

Pseudomonas putida G7 carries a naphthalene-catabolic and self-transmissible plasmid, NAH7, which belongs to the IncP-9 incompatibility group. Adjacent to the putative origin of conjugative transfer (oriT) of NAH7 are three genes, traD, traE, and traF, whose functions and roles in conjugation were previously unclear. These three genes were transcribed monocistronically and thus were designated the traD operon. Mutation of the three genes in the traD operon resulted in 10- to 10(5)-fold decreases in the transfer frequencies of the plasmids from Pseudomonas to Pseudomonas and Escherichia coli and from E. coli to E. coli. On the other hand, the traD operon was essential for the transfer of NAH7 from E. coli to Pseudomonas strains. These results indicated that the traD operon is a host-range modifier in the conjugative transfer of NAH7. The TraD, TraE, and TraF proteins were localized in the cytoplasm, periplasm, and membrane, respectively, in strain G7 cells. Our use of a bacterial two-hybrid assay system showed that TraE interacted in vivo with other essential components for conjugative transfer, including TraB (coupling protein), TraC (relaxase), and MpfH (a channel subunit in the mating pair formation system).

Adaptation of Soybean mosaic virus Avirulent Chimeras Containing P3 Sequences from Virulent Strains to Rsv1-Genotype Soybeans Is Mediated by Mutations in HC-Pro

In Rsv1-genotype soybean, Soybean mosaic virus (SMV)-N (an avirulent isolate of strain G2) elicits extreme resistance (ER) whereas strain SMV-G7 provokes a lethal systemic hypersensitive response (LSHR). SMV-G7d, an experimentally evolved variant of SMV-G7, induces systemic mosaic. Thus, for Rsv1-genotype soybean, SMV-N is avirulent whereas SMV-G7 and SMV-G7d are both virulent. Exploiting these differential interactions, we recently mapped the elicitor functions of SMV provoking Rsv1-mediated ER and LSHR to the N-terminal 271 amino acids of P3 from SMV-N and SMV-G7, respectively. The phenotype of both SMV-G7 and SMV-G7d were rendered avirulent on Rsv1-genotype soybean when the part of the genome encoding the N-terminus or the entire P3 cistron was replaced with that from SMV-N; however, reciprocal exchanges did not confer virulence to SMV-N-derived P3 chimeras. Here, we describe virulent SMV-N-derived P3 chimeras containing the full-length or the N-terminal P3 from SMV-G7 or SMV-G7d, with or without additional mutations in P3, that were selected on Rsv1-genotype soybean by sequential transfers on rsv1 and Rsv1-genotype soybean. Sequence analyses of the P3 and helper-component proteinase (HC-Pro) cistrons of progeny recovered from Rsv1-genotype soybean consistently revealed the presence of mutations in HC-Pro. Interestingly, the precise mutations in HC-Pro required for the adaptation varied among the chimeras. No mutation was detected in the HC-Pro of progeny passaged continuously in rsv1-genotype soybean, suggesting that selection is a consequence of pressure imposed by Rsv1. Mutations in HC-Pro alone failed to confer virulence to SMV-N; however, reconstruction of mutations in HC-Pro of the SMV-N-derived P3 chimeras resulted in virulence. Taken together, the data suggest that HC-Pro complementation of P3 is essential for SMV virulence on Rsv1-genotype soybean.

Variability in the Echinococcus granulosus Cytochrome C oxidase 1 mitochondrial gene sequence from livestock in Turkey and a re-appraisal of the G1–3 genotype cluster

Investigations into the genetic strains of Echinococcus granulosus parasites occurring in sheep and cattle in Turkey were undertaken. A total of 112 hydatid cysts were investigated from sheep (100 isolates) derived from widely distributed sites within Turkey as well as from cattle (12 isolates) from the Turkish province of Kars. The parasite genotypes in these isolates were determined by DNA sequencing of part of the mitochondrial Cytochrome C oxidase 1 ( cox1) gene. Haplotypes were identified which corresponded clearly to the previously described strain G1 in a total of 107 isolates, including 98 isolates from sheep and 9 isolates from cattle. Five isolates, including 2 sheep and 3 cattle, were determined to belong to the G3 genotype. Parasites of the G3 genotype were identified only in isolates derived from animals in the eastern regions of Turkey. While the majority of the isolates described here had haplotypes corresponding to the G1 genotype, none matched exactly the G1 sequence that was defined in previous studies. Analysis of all GenBank entries for E. granulosus cox1 sequences representing G1, G2 and G3 genotypes identified substantial microsequence variability. G1 and G3 could be distinguished as separate strains, however, the existence of G2 as a separate strain could not be supported. Rather, this can be regarded as a microsequence variation of G3.

Characterization and production of the exopolysaccharide (EPS) from Pseudomonas aeruginosa G1 and Pseudomonas putida G12 strains

In this study, exopolysaccharides (EPSs) production was investigated by growing strains of Pseudomonas aeruginosa G1 and Pseudomonas putida G12 in medium containing various carbon sources such as glucose, mannose, fructose, and xylose. EPS production (192 and 182 mg/L, respectively) of these strains grown in PAP medium with 2% glycerol (v/v) was used as control. The highest EPS production of the two strains was found in the xylose containing medium. The effect of different concentrations [2–6% (w/v)] of xylose on EPS production of both strains was also studied. The maximum EPS yield (368 mg/l −1) of the strain G1 was recorded in 3% (w/v) xylose, while the highest yield EPS yield (262 mg/L −1) of the strain G12 was recorded in 2% (w/v) xylose. The monosaccharide compositions of EPS produced by the two strains were analyzed by HPLC. Strain G1 [2% (w/v) glycerol] was found to compose of neutral sugars (92.0%), acetylated amino sugars (8.0%), while strain G1 [3% (w/v) xylose] contained neutral sugars (99.2%), acetylated amino sugars (0.8%). However, the composition of strain G12 [2% (w/v) glycerol] was neutral sugars (96.8%), acetylated amino sugars (3.2%) and the strain G12 [2% (w/v) xylose] was found to contain neutral sugars (96.1%), acetylated amino sugars (3.9%).

Improvement in the Anti-staling Capability of Beer by Genetically Modifying Industrial Brewing Yeast with High Glutathione Content

On the basis of homologous recombination, recombinant plasmid pRKG was constructed by replacing the internal fragment of 18S rDNA of pRJ-5 with a copy of γ-glutamylcysteine synthetase gene ( GSH1) from the industrial brewing yeast strain G03 and a copy of G418 resistance gene ( Kan) as the dominant selection marker. The fragment 18S rDNA::( Kan-GSH1) obtained through the PCR reaction was integrated to the chromosomal DNA of G03 strain, and the recombinants were screened by G418 resistance. It was shown that the GSH content of beer fermented with the recombinant strain SG1 was 16.6% higher than that of G03, and no significant difference in routine fermentation parameters was found. To test the genetic stability, strains SG1 was inoculated into flasks and continuously transferred five times. The intracellular glutathione content of strain was basically kept as a constant. It is an instructive attempt of genetically modifying industrial brewing yeast, as GSH1 was obtained from the host itself.

Indirect oxidation of Co(II) in the presence of the marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1.

Cobalt(II) oxidation in aquatic environments has been shown to be linked to Mn(II) oxidation, a process primarily mediated by bacteria. This work examines the oxidation of Co(II) by the spore-forming marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1, which enzymatically catalyzes the formation of reactive nanoparticulate Mn(IV) oxides. Preparations of these spores were incubated with radiotracers and various amounts of Co(II) and Mn(II), and the rates of Mn(II) and Co(II) oxidation were measured. Inhibition of Mn(II) oxidation by Co(II) and inhibition of Co(II) oxidation by Mn(II) were both found to be competitive. However, from both radiotracer experiments and X-ray spectroscopic measurements, no Co(II) oxidation occurred in the complete absence of Mn(II), suggesting that the Co(II) oxidation observed in these cultures is indirect and that a previous report of enzymatic Co(II) oxidation may have been due to very low levels of contaminating Mn. Our results indicate that the mechanism by which SG-1 oxidizes Co(II) is through the production of the reactive nanoparticulate Mn oxide.

Improving Sample Treatment for In-Solution Protein Identification by Peptide Mass Fingerprint Using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Three ultrasonic energy sources were studied to speed up the sample treatment for in-solution protein identification by peptide mass fingerprint using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Protein reduction, alkylation, and enzymatic digestion steps were done in 15 min. Nine proteins, including zinc resistance-associated protein precursor from Desulfovibrio desulfuricans strain G20 and split-soret cytochrome c from D. desulfuricans ATCC27774 were successfully identified with the new protocol.

Bacillus pumilusSG2 isolated from saline conditions produces and secretes two chitinases

Isolation and characterization of chitinases from a halotolerant Bacillus pumilus. Bacillus pumilus strain SG2 was isolated from saline conditions. It is able to produce chitinase activity at high salt concentration. SDS-PAGE analysis of the B. pumilus SG2 culture supernatant showed two major bands that were induced by chitin. The amino acid sequence of the two proteins, designated ChiS and ChiL, showed a high homology with the chitinase of B. subtilis CHU26, and chitinase A of B. licheniformis, respectively. N-terminal signal peptide of both proteins was also determined. The molecular weight and isoelectric point of the chitinases were determined to be 63 and 74 kDa, and 4.5 and 5.1, for ChiS and ChiL respectively. The genes encoding for both chitinases were isolated and their sequence determined. The regulation of the chitinase genes is under the control of the catabolite repression system. Secreted chitinase genes and their flanking region on the genome of B. pumilus SG2 have been identified and sequenced. This is the first report of a multiple chitinases-producing B. pumilus halotolerant strain. We have identified two chitinases by using a reverse genetics approach. The chitinases show resistance to salt.

Proteases from Bacillus: a new insight into the mechanism of action for rhizobacterial suppression of nematode populations

The aim of this study was to investigate the role of proteases in Bacillus spp. of rhizobacteria in suppressing nematode populations and to understand their mechanism of action. Rhizobacteria with nematicidal activity were isolated from soil samples of five root knot nematode-infested farms. Among these strains, nematotoxicities of Bacillus strains were intensively analysed. Further assays of nematicidal toxins from Bacillus sp. strain RH219 indicated an extracellular cuticle-degrading protease Apr219 was an important pathogenic factor. The Apr219 shared high similarity with previously reported cuticle-degrading proteases from Brevibacillus laterosporus strain G4 and Bacillus sp. B16 (Bacillus nematocida). The cuticle-degrading protease genes were also amplified from four other nematicidal Bacillus strains isolated from the rhizosphere. In addition to Apr219, a neutral protease Npr219 from Bacillus sp. RH219 was also investigated for activity against nematodes. The wide distribution of cuticle-degrading proteases in Bacillus strains with nematicidal activity suggested that these enzymes likely play an important role in bacteria-nematode-plant-environment interactions and that they may serve as important nematicidal factors in balancing nematode populations in the soil. Increased understanding of the mechanism of action of Bacillus spp. against nematodes could potentially enhance the value of these species as effective nematicidal agents and develop new biological control strategies.

Adhesion characteristics of two Burkholderia cepacia strains examined using colloid probe microscopy and gradient force analysis

Colloid probe atomic force microscopy (CP-AFM) was used to investigate two strains of Burkholderia cepacia in order to determine what molecular scale characteristics of strain Env435 make it less adhesive to surfaces than the parent strain, G4. CP-AFM approach curves analyzed using a gradient force method showed that in a high ionic strength solution (IS = 100 mM, Debye length = 1 nm), the colloid probe was attracted to the surface of strain G4 at a distance of ∼30 nm, but it was repelled over a distance of 25 nm when approaching strain Env435. Adhesion forces measured under the same solution conditions during colloid retraction showed that 1.38 nN of force was required to remove the colloid placed in contact with the surface of strain G4, whereas only 0.58 nN was required using strain Env435. At IS = 1 mM (Debye length = 10 nm), the attractive force observed with G4 was no longer present, and the repulsive force seen with Env435 was extended to ∼250 nm. The adhesion of the bacteria to the probe was much less at low IS solution (1 mM) than at high IS (100 mM). The greater adhesion characteristics of strain G4 compared to Env435 were confirmed in column tests. Strain G4 had a collision efficiency of α = 0.68, while strain Env435 had a much lower collision efficiency of α = 0.01 (IS = 100 mM). These results suggest that the reduced adhesion of strain Env435 measured in column tests is due to the presence of high molecular weight extracellular polymeric substances that extend out from the cell surface, creating long-range steric repulsion between the cell and a surface. Adhesion is reduced as these polymers do not appear to be “sticky” when placed in contact with a surface in AFM tests.

Stable expression of Hantavirus H8205 strain G1/IL-2 gene and immune protection of the fusion gene

To explore the feasibility of stable expression of Hantavirus H8205 strain G1 segment and human IL-2 fusion gene in Vero cells, and to examine the immune protection effects on mice vaccinated with this recombinant eukaryotic expression vector containing Hantavirus G1 gene and IL-2 gene. With the help of lipofectamine, the Vero cells were transfected with pcDNA3.1/HisB-IL-2-G1 and the positive cells were selected by G418. IFAT and SDS-PAGE electrophoresis were used to determine the stable transfection and expression of recombinant protein. Each mouse was inoculated with plasmids intramuscularly (i.m.) three times, 2 boosts were given at 2-week intervals, serum anti-hantavirus antibodies were detected by ELISA and neutralizing antibodies (NAb) were detected by Plaque Reduction Neutralization Test. The fusion protein expressed in Vero cells was 78 kD, corresponding to the estimated molecular size. The neutralizing antibody titers of mice with pcDNA3.1/HisB-IL-2-G1 were 1:20-1:80. IL-2/G1 fusion gene could be transferred in Vero cells and stably express the fusion protein. Specific humeral immune responses in mice can be induced with the recombinant eukaryotic expression vector containing the fusion gene, which lays the foundation for further development of therapeutic HTNV vaccine.

Regulation of Arsenate Resistance in Desulfovibrio desulfuricans G20 by an arsRBCC Operon and an arsC Gene

Desulfovibrio desulfuricans G20 grows and reduces 20 mM arsenate to arsenite in lactate-sulfate media. Sequence analysis and experimental data show that D. desulfuricans G20 has one copy of arsC and a complete arsRBCC operon in different locations within the genome. Two mutants of strain G20 with defects in arsenate resistance were generated by nitrosoguanidine mutagenesis. The arsRBCC operons were intact in both mutant strains, but each mutant had one point mutation in the single arsC gene. Mutants transformed with either the arsC1 gene or the arsRBCC operon displayed wild-type arsenate resistance, indicating that the two arsC genes were equivalently functional in the sulfate reducer. The arsC1 gene and arsRBCC operon were also cloned into Escherichia coli DH5alpha independently, with either DNA fragment conferring increased arsenate resistance. The recombinant arsRBCC operon allowed growth at up to 50 mM arsenate in LB broth. Quantitative PCR analysis of mRNA products showed that the single arsC1 was constitutively expressed, whereas the operon was under the control of the arsR repressor protein. We suggest a model for arsenate detoxification in which the product of the single arsC1 is first used to reduce arsenate. The arsenite formed is then available to induce the arsRBCC operon for more rapid arsenate detoxification.

Selection of nitrogen‐fixing deficient Burkholderia vietnamiensis strains by cystic fibrosis patients: involvement of nif gene deletions and auxotrophic mutations

Burkholderia vietnamiensis is the third most prevalent species of the Burkholderia cepacia complex (Bcc) found in cystic fibrosis (CF) patients. Its ability at fixing nitrogen makes it one of the main Bcc species showing strong filiations with environmental reservoirs. In this study, 83% (29 over 35) of the B. vietnamiensis CF isolates and 100% of the environmental ones (over 29) were found expressing the dinitrogenase complex (encoded by the nif cluster) which is essential in N(2) fixation. Among the deficient strains, two were found growing with ammonium chloride suggesting that they were defective in N(2) fixation, and four with amino acids supplements suggesting that they were harbouring auxotrophic mutations. To get insights about the genetic events that led to the emergence of the N(2)-fixing defective strains, a genetic analysis of B. vietnamiensis nitrogen-fixing property was undertaken. A 40-kb-long nif cluster and nif regulatory genes were identified within the B. vietnamiensis strain G4 genome sequence, and analysed. Transposon mutagenesis and nifH genetic marker exchanges showed the nif cluster and several other genes like gltB (encoding a subunit of the glutamate synthase) to play a key role in B. vietnamiensis ability at growing in nitrogen-free media. nif cluster DNA probings of restricted genomic DNA blots showed a full deletion of the nif cluster for one of the N(2)-fixing defective strain while the other one showed a genetic organization similar to the one of the G4 strain. For 17% of B. vietnamiensis clinical strains, CF lungs appeared to have favoured the selection of mutations or deletions leading to N(2)-fixing deficiencies.

Role of an extracellular neutral protease in infection against nematodes by Brevibacillus laterosporus strain G4

Proteases have been proposed as virulence factors in microbial pathogenicity against nematodes. However, what kinds of extracellular proteases from these pathogens and how they contribute to the pathogenesis of infections against nematode in vivo remain largely unknown. A previous analysis using a strain with a deletion in an extracellular alkaline protease BLG4 gene from Brevibacillus laterosporus demonstrated that BLG4 was responsible for the majority of nematicidal activity by destroying host's cuticle. In recent studies, a neutral protease NPE-4, purified from the mutant BLG4-6, was found to be responsible for the majority of the remaining EDTA-inhibited protease activity. However, the purified NPE-4 and recombinant NPE-4 in a related species Bacillus subtilis showed little nematicidal activity in vitro and were unable to degrade the intact cuticle of the host. It is interesting to note that the addition of NPE-4 improved the pathogenicity of crude enzyme extract from wild-type B. laterosporus but had no effect on the BLG4-deficient mutant. This result suggests that NPE-4 functions in the presence of protease BLG4. Moreover, NPE-4 could degrade proteins from the inner layer of purified cuticles from nematode Panagrellus redivivus in vitro. These results indicated that the two different bacterial extracellular proteases might play differential roles at different stages of infection or a synthetic role in penetration of nematode cuticle in B. laterosporus. This is among the first reports to systematically evaluate and define the roles of different bacterial extracellular proteases in infection against nematodes.

Isolation and partial characterization of pigment-like antibiotics produced by a new strain of Streptosporangium isolated from an Algerian soil

Identification of a new actinomycete strain Sg3, belonging to the genus Streptosporangium and partial characterization of the produced antibacterial activities. The strain Sg3 was isolated from an Algerian Saharan soil and identified by morphological, chemotaxonomic and phylogenetic analyses to the genus Streptosporangium. The comparison of its physiological characteristics with those of known species of Streptosporangium showed significant differences with the nearest species Streptosporangium carneum. Analysis of the 16S rDNA sequence of strain Sg3 showed a similarity level ranging between 97% and 98.8% within Streptosporangium species, with S. carneum the most closely related. Strain Sg3 showed a red coloured antibacterial activity against gram-positive bacteria on several culture media. The purification of the red pigment by chromatographic methods led to the isolation of three active products. The (1)H nuclear magnetic resonance (NMR), mass, infrared (IR) and ultraviolet-visible (UV-VIS) data of these molecules strongly suggested that they belonged to the quinone-anthracycline group with three or more rings. Strain Sg3 represents a distinct phyletic line suggesting a new genomic species. It produces antibacterial activities identified as quinone-anthracycline aromatics. The quinone-anthracycline antibiotics are known for their antimicrobial and antineoplastic activities and are used in chemotherapy for the treatment of many cancer diseases. The present work constitutes the first stage of a whole series of studies to be realized on these antibiotics before arriving at a possible application.

The effect of high magnetic field characterized by kinetics: Enhancing the biodegradation of acid red 1 with a strain of Bacillus sp.

The induced strain HG1 exposed to 10.0 T high magnetic field for 30 min and the original strain G1 ( Bacillus sp.) isolated from soil were used to degrade acid red 1. The degradation process of the azo dye by these microbes was approximated by a reversed S-like curve. A kinetics equation whose parameters reflected the degradation process, was then established. The comparison and analysis of the kinetics parameters showed that the high magnetic field enhanced the biodegradation ability of the exposed strain—increasing the value of A (degradation constant) and V max (maximum reaction rate) to 1.7 and 1.5 times, respectively, and at the same time, reducing the value of t c (time when the maximum reaction rate was reached) to 0.8 times. Additionally, the UV/vis spectra also showed that the degradation ability of Bacillus sp. was improved and the metabolic pathway of the bacteria might be changed after being exposed to the high magnetic field.

Cystic echinococcosis in water buffaloes (Bubalus bubalis)

An epidemiological and molecular survey of cystic echinococcosis (CE) caused by Echinococcus granulosus in the water buffalo (Bubalus bubalis) of the Italian Mediterranean breed was carried out in the Campania region of southern Italy. Out of a total of 799 water buffaloes examined at slaughterhouses, 80 (10.0%) were found infected. The molecular study was performed on 58 hydatid cysts in order to determine the E. granulosus strain(s) present in this host. A region of cytocrome c oxydase 1 gene (CO1) was amplified by polymerase chain reaction and the PCR products were then purified and sequenced. DNA amplification of the partial CO1 gene gave a 446 bp fragment for all isolates examined. After sequencing, a region of 419 bp was identified for each sample. Thirty-two isolates were identified as the common sheep strain G1, 15 as the buffalo strain G3, 3 as the Tasmanian sheep strain G2, and 3 as the G1 c genotype (GenBank AF458873). In addition, 5 isolates presented 99% identity with the G2 genotype (Tasmanian sheep strain).

COMPARATIVE MOLECULAR EVOLUTION OF NEWLY DISCOVERED PICOCYANOBACTERIAL STRAINS REVEALS A PHYLOGENETICALLY INFORMATIVE VARIABLE REGION OF β‐PHYCOERYTHRIN1

The genetic diversity and phylogenetic position of 10 strains of picocyanobacteria from the Arabian Sea were examined using partial sequences from three loci: 16S rDNA, RNA polymerase rpoC1, and two elements of the phycoerythrin (PE) locus, cpeA and cpeB which encode for the α and β subunit of PE. Nine of the strains showed nearly identical spectral phenotypes based on the in vivo excitation spectrum for PE fluorescence emission and appear to be strains synthesizing a phycourobilin (PUB)–lacking PE. These strains include one, Synechococcus sp. G2.1, already known to be closely related to filamentous cyanobacteria and not to the commonly studied 5.1 subcluster of marine Synechococcus. The 10th strain was a PE‐lacking strain that was of interest because it was isolated from open‐ocean conditions where picocyanobacteria with this phenotype are relatively uncommon. Phylogenetic analysis of the concatenated 16S rDNA and rpoC1 data sets showed that none of the previously described strains were members of the 5.1 subcluster of marine Synechococcus, nor were they closely related to strain G2.1. Instead, they form a well‐supported and previously undescribed clade of cyanobacteria that is sister to Cyanobium. Thus, these strains represent the first PE‐containing Cyanobium from oceanic waters, and the lineage they define includes a strain with a PE‐lacking phenotype from the same environment. Analysis of the PE sequence data showed the PE apoprotein has evolved independently in the G2.1 lineage and the Cyanobium‐like lineage represented by the study strains. It also revealed a hypervariable region of the β‐subunit not described previously; variation in this region shows a pattern among a wide range of PE‐containing organisms congruent with the phylogenetic relationships inferred from other genes. This suggests that the PUB‐lacking spectral phenotype is more likely to have evolved in distantly related phylogenetic lineages by either divergent or convergent evolution than by lateral gene transfer. Both the conserved PE gene sequences and the inferred amino acid sequences for the hypervariable region show considerable divergence among Prochlorococcus PEs, red algal PEs, PUB‐containing PEs from the marine Synechococcus 5.1 subcluster, PEs from the Cyanobium‐like strains, and PEs from other cyanobacteria (including strain G2.1). Thus, it appears that the hypervariable region of the PE gene can be used as a taxon‐specific marker.

Evaluation of Soybean Cultivars, ‘Williams’ Isogenic Lines, and Other Selected Soybean Lines for Resistance to Two Soybean Mosaic Virus Strains

Soybean mosaic virus (SMV) is one of the most common soybean viruses worldwide. The resistance or susceptibility of most commercial soybean cultivars to SMV is not known. The objectives of this study were to evaluate resistance to SMV strains G1 and G5 of current soybean cultivars, isogenic lines with different Rsv genes and alleles in ‘Williams’ or ‘Williams 82’ background, and selected soybean lines with reported or observed SMV resistance. Commercial and precommercial soybean cultivars were screened for resistance to SMV strains G1 and G5. Based on multiple tests, 1.5% and 6.7% of the 850 cultivars were resistant to SMV‐G1 and SMV‐G5, respectively. No cultivars were resistant to both strains. Expression of different SMV resistance genes in Williams isogenic lines inoculated with both SMV strains indicated that lines with Rsv1‐y from ‘Dorman’, or unnamed resistance genes from ‘Kosamame’, and ‘Sodendaizu’, were resistant to G1 and susceptible to G5. Lines with Rsv1 alleles from PI 96983, ‘Marshall’, or ‘Ogden’ were resistant to both strains, and lines with Rsv1 alleles from ‘Raiden’, ‘SS 74185’ (PI486355), or ‘Suweon 97’ were resistant to G1 and produced a systemic necrosis reaction with G5. Lines with Rsv3‐h from ‘Hardee’ were susceptible to G1 and resistant to G5. Isogenic lines with SMV resistance genes from ‘Buffalo’ showed either a resistant–resistant or resistant–susceptible reaction to the two SMV strains, suggesting the presence of more than one SMV resistance gene. Ten selected lines with reported or observed resistance to SMV were inoculated with the two SMV strains. Some lines were resistant to either G1 or G5, and some were resistant to both strains.