Cassava leaf harvesting as vegetables; a cause of vulnerability of cassava plant to cassava mosaic disease and eventual yield reduction: Ernte von cassavablättern als gemüse; eine ursache für die anfälligkeit der cassavapflanze für die cassava-mosaikkrankheit und für spätere ertragseinbußen

The consequence of harvesting young leaves of cassava as vegetable on the vulnerability of the crop to cassava mosaic disease (CMD) and on storage root yield was investigated using 30 cassava genotypes planted in IITA fields located in the humid forest (Port Harcourt?:?Onne), forest-savannah transition (Ibadan), southern guinea savannah (Mokwa) and northern guinea savannah (Zaria) agroecologies in Nigeria. Tender apical leaves and shoots of the cassava genotypes were removed from forty plants per cassava genotype with the same number of plants considered as control. Whitefly infestation, disease incidence (DI) and symptom severity (ISS) of the disease were assessed at monthly interval for six months and also at the ninth month after planting (MAP). Yield reduction due to this treatment was calculated as percentage harvest index (HI). Whitefly population fluctuated throughout the period of observation at all locations with higher population obtained generally for treated plants compared to control plants. Sprouting leaves of some treated genotypes were observed with severe mosaic symptoms, while corresponding control showed no mosaic symptoms. Contrarily, no remarkable difference was observed in Zaria between the mean ISS of treated and control cassava genotypes. There was a highly significant difference (P?<?0.01) in DI and ISS among cassava genotypes across all locations. Also, there was a highly significant interaction (P?<?0.01) in symptom severity between location (loc) and genotype, genotype and treatment (trt), loc and trt. Interaction between loc, genotypes and trt with regard to DI was highly significant at 2, 3 and 4 MAP, while with ISS, the interaction was highly significant all through the counting period. There was a positive relationship between DI and ISS on plants of genotypes 96/1039 and ISU. The percentage HI (27.4) of treated plants of genotype 95/0166 in Ibadan was remarkably lower than the value obtained for corresponding control (41.9) plants. Also, sharp distinction in% HI of treated (39.5) and control (43.8) ISU was observed in Onne with their respective ISS values as 3.7 and 3.2. Therefore, harvesting tender apical leaves and shoots of cassava as vegetables should be discouraged as it increases the severity of CMD infection in the regenerating shoots of cassava with attendant storage root yield reduction.     

The Effect of the Extracellular Bacteriolytic Enzymes of Lysobacter sp. on Gram-Negative Bacteria

The effect of the extracellular bacteriolytic enzymes of Lysobacter sp. on gram-negative bacteria was studied. These enzymes were found to be able to hydrolyze the peptidoglycan that was isolated from the gram-negative bacteria, the hydrolysis being completely inhibited by the cell wall lipopolysaccharide of these bacteria. The native cells of the gram-negative bacteria became susceptible to the bacteriolytic enzymes after the permeability of the outer membrane of the cells was altered by treating them with polymyxin B.     

Specificity of the action of lysoamidase on Staphylococcus aureus 209P cell walls

Specificity of Staphylococcus aureus 209P cell wall hydrolysis by the L1 and L2-bacteriolytic enzymes from lysoamidase lytic complex was studied. L1-peptidase was shown to display both glycyl-glycine endopeptidase and N-acetylmuramyl-L-alanine amidase enzymatic activities on the S. aureus peptidoglycan molecule, whereas L2-peptidase acts as N-acetylmuramyl-L-alanine amidase.     

Detection of propeptides of AlpA and AlpB lytic endopeptidases from Lysobacter sp. XL1 by the sandwich enzyme immunoassay based on monoclonal antibodies

Extracellular lytic endopeptidases AlpA and AlpB of the Gram-negative bacterium Lysobacter sp. XL1 have a high degree of homology and are synthesized as preproproteins consisting of a signal peptide, a propeptide, and the mature protein. In the present work, two monoclonal antibodies against the AlpA propeptide (ProA) and eleven antibodies against the AlpB propeptide (ProB) have been obtained. The affinity constants for antibodies to ProA were 2.9 × 10⁹ and 3.5 × 10⁹ M^?1, and those for antibodies to ProB were from 1.5 × 10⁸ to 2.2 × 10⁹ M^?1. The antibodies showed no immune cross-reactivity with each other and with mature forms of the enzymes. On the basis of monoclonal antibodies, a sandwich enzyme immunoassay has been developed, which makes it possible to detect these propeptides in the dissolved native form. The linear range of the detection of ProA was 1.5–100.0 ng/mL with an error of measurement of 6%, and that of the determination of ProA was 0.2–6.25 ng/mL with an error of measurement of 6%. By using the assay, propeptides ProA and ProB were detected in cell lysates of Lysobacter sp. XL1 in an amount of 1.18 ± 0.03 and 0.096 ± 0.002 ng per 1 OD540 of bacterial culture, respectively. The immunochemical assay for the detection of different forms of AlpA and AlpB can be useful in solving the problems associated with their secretion into environment.     

Secretion of bacteriolytic endopeptidase L5 of Lysobacter sp. XL1 into the medium by means of outer membrane vesicles

The Gram-negative bacterium Lysobacter sp. XL1 secretes various proteins, including bacteriolytic enzymes (L1-L5), into the culture medium. These proteins are able to degrade Gram-positive bacteria. The mechanism of secretion of extracellular proteins by Lysobacter sp. XL1 has not been studied hitherto. Electron microscopic investigations revealed the phenomenon of the formation of extracellular vesicles by Lysobacter sp. XL1. These vesicles contained components of the Lysobacter sp. XL1 outer membrane, and demonstrated bacteriolytic activity against Gram-positive and Gram-negative bacteria: Staphylococcus aureus 209-P and Erwinia marcescens EC1, respectively. Western blotting analysis with antibodies to homologous bacteriolytic endopeptidases L1 and L5 showed that endopeptidase L5 was secreted into the culture medium by means of vesicles, unlike its homolog, endopeptidase L1. When inside the vesicles, endopeptidase L5 actively lysed the Gram-negative bacterium Erwinia marcescens; outside the vesicles, it lost this ability. The secretion of bacteriolytic endopeptidase L5 through the outer membrane vesicles is of great biological significance: because of this ability, Lysobacter sp. XL1 can compete in nature with both Gram-positive and Gram-negative bacteria.