Peanut agglutinin-induced structural changes in cowpea Rhizobia as revealed by freeze-etching

The ultrastructure of two strains of cowpeaRhizobium species, JLn(c) and NC-92, was studied especially with regards to the effect of peanut agglutinin on the cell envelope. Freezeetching electron microscopy revealed the structural details of the outer and the cytoplasmic membrane. The topology of both membranes resembled that of other Gram-negative bacteria. The cells displayed marked polarity, expressed in the form of an extracellular polar body (EPB) near one end and a periplasmic bay at the opposite end. The EPB was seen as a polar outgrowth of the outer membrane and resembled in structure the outer membrane. The existence of a polar periplasmic bay as a characteristic feature of cowpea rhizobia is reported here for the first time and has been implicated as a probable site for polysaccharide synthesis. Ruthenium red staining showed a polar mode of capsule initiation in the early exponential phase. Peanut agglutinin was found to enhance the incidence of EPB which is necessary for adhesion of rhizobia to root hairs. This suggests that lectins serve as an important biological stimulus which preconditions the symbiont for successful attachment to root hairs.     

Palmitic acid activation of peroxidase and its possible significance in mango ripening.

Palmitic acid stimulated the activity of mango peroxidase and reversed the inhibition due to the peroxidase inhibitor present in the preclimacteric fruit. The palmitic acid effect appeared to saturate in the range of 45 to 60 muM palmitic acid. Crude fatty acid extract of the mango exerted similar effect. The percentage stimulation was pH-dependent. Palmitic acid stimulated the enzyme by 18 percent at its optimum pH (5) but the stimulation was in excess of 63 percent at pH 2.5. At pH 2.5 the enzyme concentration versus velocity plot was non-linear and the activation by palmitic acid appeared to saturate between 32 and 48 muM concentration of the effector. The inhibition of the enzyme at and above 0.86 muM concentration of substrate (H202) was not found in the presence of palmitic acid. The effector also changed the heat inactivation kinetics of the enzyme and activated only two out of the four peroxidase isoenzymes present in the climacteric fruit extracts. The results presented indicate the regulatory nature of the enzyme and support its significance in fruit ripening.     

Deoxyribonucleate Binding and Transformation in Rhizobium japonicum

Rhizobium japonicum, capable of binding high-molecular-weight donor (32)P-labeled deoxyribonucleic acid (DNA) during late log phase in a competence medium, was transformed for streptomycin resistance with a frequency of transformation ranging between 0.02 and 0.08%. Eight to 10% of the homologous native (32)P-labeled input DNA was bound irreversibly in a temperature-dependent manner. Homologous denatured (32)P-labeled DNA was incapable of binding to the recipient under similar conditions. CsCl density gradient banding of the donor and recipient DNA indicated homology. The low frequency of transformation could be due to one or more steps that occur between DNA uptake and integration.     

A note on the use of cross-linked starch in microbiology with special reference to detecting amylase production

Anilogel-E, a cross-linked starch, can be used with distinct advantages where native starch or soluble starch are conventionally used, e.g. in scoring for amylolytic organisms, as an ingredient of fermentation media, and in enhancing protoplast regeneration. It is particularly useful for the direct visualization of amylase producing micro-organisms on solid media, making prior replication of colonies unnecessary.     

Tunicamycin-resistant mutants of Bacillus amyloliquefaciens are deficient in amylase, protease and penicillinase synthesis and have altered sensitivity to antibiotics and autolysis

Mutants of Bacillus amyloliquefaciens resistant to at least 10 μg/ml of tunicamycin were isolated and shown to be pleiotropic. The mutants were more resistant to streptomycin, chloramphenicol, kanamycin and neomycin than was the parent strain but less resistant to penicillin G and tetracycline. They were more autolytic, presumably due to an altered cell wall. The mutants produced reduced levels of amylase, penicillinase and both metal and serine protease besides having an enhanced sporulation frequency and being more motile.     

Plasmid macro-evolution: selection of deletions during adaptation in a nutrient-limited environment

A study was made of the intra-and inter-population variability of the main traits involved in Trichogramma (T. brassicae and T. cacoeciae) efficiency in host exploitation: longevity, fecundity, progeny viability, progeny sex ratio and progeny allocation. The analysis of isofemale strains shows that differences in progeny viability, progeny sex ratio and progeny allocation are transmissible and relatively stable over two successive generations. Comparison of three strains of T. brassicae originating from different locations, demonstrates differences in fecundity, progeny sex ratio and progeny allocation. Differences in host exploitation strategies also exist between two sympatric populations of T. brassicae and T. cacoeciae. No significant correlation appears between the traits which discriminate populations. The ecological and evolutionary significance and the agronomical importance of the results are discussed.     

Peanut agglutinin induced alterations in capsular and extracellular polysaccharide synthesis andex -planta nitrogenase activity of cowpea rhizobia

The root exudate ofArachis hypogea (groundnut) and its seed lectin peanut agglutinin were found to stimulate the synthesis of exopolysaccharide and capsular polysaccharide of the microsymbiont cowpeaRhizobium strain JLn (c). The synthesis of capsular polysaccharide was enhanced 1.5-fold and 2-fold in the presence of peanut agglutinin and root exudate, respectively. The synthesis of capsular polysaccharide was suppressed in the presence of different forms of combined nitrogen. Quantitative differences were also detected between the exopolysaccharide of cells grown in the presence and absence of root exudate. Electron microscopic examination of negatively stained lectin-treated JLn (c) cells showed an increased deposition of capsular polysaccharide surrounding the cells. Hurthermore,ex planta nitrogenase activity of JLn(c) cells in the presence of lectin was found to be enhanced by 63% in correlation with the increased synthesis of polysaccharides. Part of this work was presented at the colloquium session of the 4th Hederation of Asian and Oceanian Biochemists Congress, held at Singapore, in November 1986.