The culture medium volume and the inoculation method should be considered in semi-quantitative screening of calcium phosphate solubilization by bacteria

Agar media with insoluble phosphates are used for semi-quantitative screening of phosphate-solubilizing bacteria based on the solubilization halo formed around the colonies. We show that the volume of the culture medium (15, 20, and 30 mL) and the inoculation method (toothpick vs microdrop) strongly influence the diameter of the solubilization halo, and this should be considered in advance selection of the isolates most efficient in this process.

Keywords:
insoluble phosphate; plant growth-promoting rhizobacteria; solubilization halo; microdrop; toothpick

Authorship

Silvia Maria de Oliveira-Longatti

Departamento de Ciência do Solo, Setor de Biologia, Microbiologia e Processos Biológicos do Solo, Universidade Federal de Lavras, Cx. Postal 3037, 37200-000, Lavras, Minas Gerais, Brazil.Universidade Federal de LavrasBrazilLavras, Minas Gerais, BrazilDepartamento de Ciência do Solo, Setor de Biologia, Microbiologia e Processos Biológicos do Solo, Universidade Federal de Lavras, Cx. Postal 3037, 37200-000, Lavras, Minas Gerais, Brazil.

Leandro Marciano Marra

Universidade Estadual de Mato Grosso do Sul, Mundo Novo, Mato Grosso do Sul, Brazil.Universidade Estadual de Mato Grosso do SulBrazilMundo Novo, Mato Grosso do Sul, Brazil Universidade Estadual de Mato Grosso do Sul, Mundo Novo, Mato Grosso do Sul, Brazil.

Teotonio Soares de Carvalho

Fatima Maria de Souza Moreira ^** Author for correspondence. E-mail: fmoreira@dcs.ufla.br

http://orcid.org/0000-0003-0159-5811

* Author for correspondence. E-mail: fmoreira@dcs.ufla.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (2)
Tables (2)

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Figure 1
Colonies of phosphate solubilizing bacteria of the strain UFLA 04-155 obtained after inoculation by two methods in 30 mL of NBRIP medium. A - Inoculation by the microdrop method. B - Inoculation by the toothpick method.

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Figure 2
Linear regression analyses for slicing the interaction between volume of culture medium and inoculation method: A) Toothpick, *significant at p = 0.05, and B) Microdrop.

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Table 1
Results of analyses of variance showing the interaction between volume of culture medium vs inoculation method for 3 strains of phosphate solubilizing bacteria in all the periods evaluated.

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Table 2
Solubilization index of 3 bacterial strains inoculated by the toothpick and microdrop methods at different volumes of NBRIP culture medium in Petri dishes.

Figure 1 Colonies of phosphate solubilizing bacteria of the strain UFLA 04-155 obtained after inoculation by two methods in 30 mL of NBRIP medium. A - Inoculation by the microdrop method. B - Inoculation by the toothpick method.

Figure 2 Linear regression analyses for slicing the interaction between volume of culture medium and inoculation method: A) Toothpick, *significant at p = 0.05, and B) Microdrop.

Table 1 Results of analyses of variance showing the interaction between volume of culture medium vs inoculation method for 3 strains of phosphate solubilizing bacteria in all the periods evaluated.

DAI	UFLA04-155	CV%	UFLA04-232	CV%	UFLA04-233	CV%
6	F_2,18 = 33.43, P = 0.0000	11.57	F_2,18 = 27.79, P = 0.0000	9.47	F_2,18 = 27.79, P = 0.0000	9.47
12	F_2,18 = 17.80, P = 0.0001	7.00	F_2,18 = 41.67, P = 0.0000	7.71	F_2,18 = 23.35, P = 0.0000	7.71
15	F_2,18 = 10.16, P = 0.0011	13.60	F_2,18 = 6.56, P = 0.0073	18.31	F_2,18 = 285.24, P = 0.6175^*	15.75
30	F_2,18 = 16.80, P = 0.0001	7.72	F_2,18 = 25.24, P = 0.0000	11.60	F_2,18 = 25.24, P = 0.0000	11.60

DAI: days after inoculation. CV: coefficient of variation. *: Not significant at 5% probability.

Table 2 Solubilization index of 3 bacterial strains inoculated by the toothpick and microdrop methods at different volumes of NBRIP culture medium in Petri dishes.

Strain	DAI	Inoculation method	Volume (mL)
Strain	DAI	Inoculation method	15	20	30
UFLA04-155	6	Toothpick	8.84aA	5.66bA	4.35cA
	6	Microdrop	2.89aB	2.88aB	2.42aB
	12	Toothpick	9.26aA	8.07bA	6.18cA
	12	Microdrop	3.69aB	3.63aB	3.32aB
	15	Toothpick	9.56aA	8.04bA	5.93cA
	15	Microdrop	3.55aB	3.77aB	3.42aB
	30	Toothpick	12.64aA	10.00bA	9.30cA
	30	Microdrop	4.32aB	4.36aB	4.01aB
UFLA04-232	6	Toothpick	9.51aA	7.90bA	5.26cA
	6	Microdrop	3.03aB	2.87aB	2.41aB
	12	Toothpick	10.92aA	8.16bA	6.42cA
	12	Microdrop	3.56aB	3.52aB	3.21aB
	15	Toothpick	12.65aA	9.76bA	7.59cA
	15	Microdrop	3.99B	3.83B	3.48B
	30	Toothpick	15.03aA	13.53bA	8.72cA
	30	Microdrop	3.74aB	4.49aB	4.13aB
UFLA04-233	6	Toothpick	9.51aA	7.90bA	5.26cA
	6	Microdrop	3.03aB	2.88aB	2.41aB
	12	Toothpick	10.77aA	9.69bA	7.43cA
	12	Microdrop	3.21aB	3.61aB	3.19aB
	30	Toothpick	15.03aA	13.53bA	8.72cA
	30	Microdrop	3.74aB	4.49aB	4.13aB

DAI: days after inoculation. Means followed by the same lowercase letters in the same row or by same uppercase letters in the same column do not differ from each other by the Scott-Knott test at 5% probability. UFLA04-233: Non-significant interaction at 5% probability at 15 DAI.

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The culture medium volume and the inoculation method should be considered in semi-quantitative screening of calcium phosphate solubilization by bacteria

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[1] * Author for correspondence. E-mail: fmoreira@dcs.ufla.br