Taxonomic identification of rhizospheric actinobacteria isolated from Algerian semi-arid soil exhibiting antagonistic activities against plant fungal pathogens

Figures & data

Table 1.  Number of actinobacteria isolated from various Algerian rhizospheric soil

		Number of isolates
Site	Rhizospheric soil from	YCED	WYE	Total (%)
Cultivated plots, Batna	Allium cepa L.	1	1	2 (2.77)
	Lactuca sativa L.	8	6	14 (19.44)
	Vicia faba L.	1	2	3 (4.16)
Cultivated fields, Tebéssa	Triticum durum Desf.	10	3	13 (18.05)
	Hordeum vulgare L.	2	2	4 (5.55)
ITCMI	Prunus domestica L.	8	10	18 (25.0)
Forest reserve, Khenchela	Pinus halepensis Mill.	9	9	18 (25.0)
Total		39	33	72
Notes: ITCMI = Institut technique des cultures maraîchères et industrielles.

Table 2.  Fungal plant pathogens used in antagonism assays

Species	Strain designation	Disease	Host plant
Fusarium oxysporum	CIT-4	Fusarium wilt	Citrullus lanatus (Thunb.) Matsum. & Nakai
Fusarium culmorum	TRI-1	Fusarium wilt	Triticum durum Desf.
Microdochium nivale	TRI-2	Fusarium wilt	Triticum durum Desf.
Botrytis fabae	VIC-11	Chocolate spot	Vicia faba L.
Bipolaris sorokiniana	AVE-3	Damping-off	Avena sativa L.
Verticillium dahliae	OLE-2	Verticillium wilt	Olea europa L.
Drechslera teres	HOR-5	Helminthosporiosis	Hordeum vulgare L.

Table 3.  Morphological and physiological characteristics of the six antagonistic actinobacteria isolates

	Strains^a
Characteristics	Lac1	Lac3	Vic8	Pin10	Pru14	Pru16
Morphological characteristics
Colour of spore mass	Yellow	Grey	Light yellow	White	White	Yellow/greenish
Spore chain morphology^b	RF	Spiral	Straight	Straight	RA, spiral	RF
Carbon source utilization^c
L-Arabinose	−	−	−	−	+	+
D-Cellobiose	+	+	−	+	+	+
Dulcitol	−	+	−	−	−	−
D-Fructose	+	+	+	−	+	−
D-Glycerol	−	−	+	+	+	−
myo-Inositol	±	+	−	+	−	+
D-Lactose	+	+	−	−	+	+
Levulose	+	+	−	−	+	+
D-Maltose	−	−	−	+	−	+
D-Mannose	+	−	−	−	−	−
Mannitol	+	+	−	−	+	+
D-Melobiose	+	−	−	−	−	−
Methyl α-D-glucose	±	±	−	+	+	+
Raffinose	−	+	−	−	−	−
L-Rhamnose	−	+	+	−	+	−
Salicin	−	−	−	+	−	+
Sucrose	−	−	+	+	−	−
D-Threhalose	+	+	+	+	+	+
D-Xylose	+	+	+	−	+	+
Acetate	+	+	−	−	+	+
Citrate	+	+	−	+	−	−
Lactate	−	±	−	+	−	+
Oxalate	+	−	+	−	−	+
Propionate	+	+	−	+	+	+
Nitrogen source utilization^d
Alanine	−	+	+	−	−	+
Cysteine	−	+	−	−	−	−
Lysine	−	+	+	−	+	+
Methionine	−	+	−	−	+	−
Phenylalanine	−	+	−	−	−	−
Tryptophan	−	+	−	−	−	−
KNO3	−	+	−	+	+	+
Degradation activities^e
Tyrosine	−	+	+	−	−	+
Casein	+	−	+	+	+	+
Xanthine	−	±	−	+	+	−
Hypoxanthine	−	±	+	−	−	+
Aesculin	+	−	−	−	+	−
Arbutin	−	+	−	+	+	+
Growth in presence of inhibitors^f
NaCl (7%)	+	+	−	−	+	+
Lysozyme (50 μg mL^−1)	+	+	−	−	+	+
Phenol	−	+	−	−	−	−
Potassium tellurite	−	−	−	+	−	−
Environmental characteristics^g
45 °C	−	+	−	−	−	−
pH 4.3	−	+	−	−	−	−
Notes: ‘+’ = positive; ‘−’ = negative; ‘±’ = weakly; RF = rectiflexibiles; RA = retinaculum apertum.
^a All strains were negative for production of melanoid pigments on ISP6 and ISP7 media. Urease, nitrate reductase and ß-galactosidase activities of strains were positive.
^b All strains presented smooth spore ornamentation.
^c All strains were positive for assimilation of glucose, galactose, ribose, pyruvate, succinate, glutamate and negative for assimilation of sorbose, sorbitol, adonitol, melezitose, melibiose and xylitol.
^d All strains were positive for assimilation of proline, arginine and asparagine.
^e All strains were positive for degradation of starch, gelatin, xylan, adenine, chitin, Tween 20 and Tween 80, and negative for degradation of allantoin.
^f All strains were positive for growth in 4% NaCl, 10 μg mL^−1 lysozyme, and negative for growth in sodium azide, thallous acetate, crystal violet, 10% and 13% NaCl and 100 μg mL^−1 lysozyme.
^g All strains were positive for growth at pH 7, at 25 and 37 °C and negative for growth at 4 and 10 °C.

Fig. 1. Effect of antagonistic actinobacterial isolates on mycelium growth of phytopathogenic fungi. Results are the means of triplicates. Values from bars with the same letter do not differ statistically (LSD). (a) Fusarium culmorum, (b) Microdochium nivale, (c) Fusarium oxysporum, (d) Drechslera teres, (e) Verticillium dahliae, (f) Bipolaris sorokiniana and (g) Botrytis fabae.

Fig. 2. Spore chain morphology of (a) Streptomyces griseus Lac1, (b) Streptomyces rochei Lac3, (c) Streptomyces anulatus Pru14, (d) Streptomyces champavatii Pru16, (e) Nocardiopsis dassonvillei subsp. dassonvillei Vic8 and (f) Nocardiopsis alba Pin10 observed with scanning electron microscopy. Bars represent 1 μm.

Fig. 3. Phylogenetic tree based on 16S rRNA gene sequences of the six antagonistic strains isolated in this study and their closest relatives. The tree was constructed using the neighbour-joining algorithm. Bootstrap values based on 1000 replicates are shown at the nodes of the tree. The bar indicates a distance of 0.02 substitutions per nucleotide position. Bacillus subtilis was used as an outgroup.