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African Journal of Biotechnology

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Volume 2 (1) January 2003
Abstracts

Actinorhizal, mycorhizal and rhizobial symbioses: how much do we know?

Diaga Diouf1,2,*, Tahir A. Diop2,3 and Ibrahima Ndoye2,3

1Laboratoire de Biotechnologies Végétales

2Département de Biologie Végétale, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, BP 5005, Sénégal

3Laboratoire de Microbiologie des Sols, IRD/ISRA/UCAD, B.P. 1386, Dakar, Sénégal

*Corresponding author; e-mail:

In this review, we discuss the recent progress in research on symbiotic association of rhizobia, Frankia and fungi with plant roots. We compare infection processes of symbiotic establishment; structure, functioning and molecular biology of the symbiotic organ including the regulation of genes implicated in rhizobial, actinorhizial and arbuscular mycorhizal symbioses.

Key words: Symbiosis, nodule, mycorrhiza, symbiotic genes.

Effects of mixed nitrogen sources on biodegradation of phenol by immobilized Acinetobacter sp. strain W-17

Desouky Abd-El-Haleem1*, Usama Beshay1, Abdou O. Abdelhamid 2, Hassan Moawad3 and Sahar Zaki1

1Environmental Biotechnology Department & Bioprocess Development Department, Genetic Engineering and Biotechnology Research Institute (GEBRI), Mubarak City for Scientific Research and Technology Applications, New Burg-Elarab City, Alexandria, Egypt.

2Chemistry Department, Faculty of Science, Cairo University, Cairo, Egypt.

3Agricultural Microbiology Department, National Research Centre, Dokki, Cairo, Egypt.

 *Corresponding author; e-mail:

Using Ca-alginate immobilized cells of Acinetobacter sp. strain W-17, the effects of ammonium-N and nitrate-N on the biodegradation of phenol were investigated. Degradation experiments in three different culture media; minimal salts medium (MSM), simulated (SW) and modified simulated wastewater (MSW) were performed. With the freely suspended cells (cell dry weight 0.2 g/l), complete phenol (500 mg/l) degradation was achieved after incubation for 120 h. Using the immobilized cells, the time was reduced to 24 h in MSM medium, and 15 h in the MSW. The results also indicate that strain W-17 can tolerate to high concentrations of NH4+-N (63 mg/l) and NO3--N (1000 mg/l) without a significant loss in the phenol biodegradation rate. Moreover, the presence of 500 mg/l phenol in the MSW had no considerable effect on the removal of both ammonium-N and nitrate-N. Repeated use of immobilized cells revealed that they could be used as much as five times without loss of activity. Our findings could be extended to enhance biotreatment of phenol contamination in a variety of biological treatment processes.

Key words: Phenol, biodegradation, immobilization, Acinetobacter, Ca-alginate, ammonium, nitrate.

Diversity of indigeneous bradyrhizobia associated with three cowpea cultivars (Vigna unguiculata (L.) Walp.) grown under limited and favorable water conditions in Senegal (West Africa)

Tatiana Krasova-Wade1, 2, *, Ibrahima Ndoye1, 2, Serge Braconnier3, Benoit Sarr3, Philippe de Lajudie4 and Marc Neyra1

1Laboratoire de Microbiologie, IRD, BP 1386, Dakar, Senegal

2Département de Biologie Végétale, Université Cheikh Anta Diop, BP 5005, Dakar, Senegal

3Centre d'Etude Régional pour l'Amélioration de l'Adaptation à la Sécheresse (CERAAS), BP 3320, Thiès Escale, Thies

4Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM), Campus de Baillarguet, TA10/J, 34398 Montpellier Cedex 5, France

*Corresponding author; phone: (221) 849 33 19, fax: (221) 832 16 75, e-mail:

The diversity of Bradyrhizobium strains nodulating three cowpea (Vigna unguiculata L. Walp.) cultivars in favorable and water-limited conditions occuring at flowering was analysed. PCR- Restriction Fragment Length Polymorphism (PCR-RFLP) analysis of 16S-23S rDNA intergenic spacer region (IGS) directly applied on 85 crushed nodules distinguished four genetic profiles, IGS types I, II, III and IV. The distribution of these IGS types according to water conditions and cowpea cultivars (B-21, TN 88-63 and Mouride) showed that nodulating strains appeared more diverse in water-limited condition. More than three quarters of prospected nodules presented the IGS type I. They were formed on all three cultivars and in both water conditions. Only a small part of nodules was distributed between the IGS type II, III and IV. Nodules showing the IGS types II and III were found mainly in limited conditions on TN 88-63 and Mouride cultivars, whereas nodules presenting the IGS type IV were collected only from cultivars B-21 and Mouride, in both water conditions. Strains corresponding to the different profiles were isolated. The phylogenetic analysis of 16S rRNA gene sequences showed that they belong to the genus, Bradyrhizobium. The sequence analysis of 16S-23S rDNA IGS revealed that the strains exhibiting IGS types II, III and IV were closely related to some Faidherbia albida isolates from Senegal. IGS type II can be assigned with at least 98% similarity to Bradyrhizobium genospecies IV. IGS types III and IV showed more than 96% similarity with genospecies VII and could belong to the same genospecies. IGS type I, the most frequent, exhibits low IGS similarity with reported sequences in the databases, and could represent a new genospecies.

Key words: Bradyrhizobium, Vigna unguiculata, water-limited condition, PCR-RFLP, 16S rDNA, 16S-23S rDNA IGS.

Pre-harvest deterioration of Sour sop (Annona muricata) at Ibadan Southwestern Nigeria and its effect on nutrient composition

N. A. Amusa*, O. A. Ashaye, M. O. Oladapo and O.O. Kafaru

Institute of Agricultural Research and Training Obafemi, Awolowo University Moor Plantation PMB 5029 Ibadan, Nigeria
*Corresponding author; e-mail:

The etiology of pre-harvest deterioration of Soursop (Annona muricata) fruit in Ibadan, southwestern Nigeria and the effects on its nutrient composition was investigated. Four fungal pathogens including Botryodiplodia theobromae, Fusarium sp., Rhizopus stolonifer and Aspergillus niger were found associated with the pre-harvest deteriorating soursop . B. theobromae was the most prevalent and the most pathogenic inducing rot of 75 mm in diameter within four days of inoculation. There was a remarkable reduction in carbohydrate and protein contents of the fungal infected fruits while all other nutrients and mineral assayed were higher in the infected fruits than the non-infected ones.

Key words: Annona muricata, fungal pathogens, pre-harvest deterioration.

 

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