Microbial Inoculants and Their Impact on Soil Microbial Communities: A Review

Table 2

The most significant studies addressing the impact of inoculation on soil microbial communities.

Inoculant type	Species	Techniques	Major results
Rhizobia	S. meliloti L33	SSCP	The bacterial diversity in the rhizosphere of Medicago sativa was qualitatively and quantitatively affected. While the number of members of 𝛾-proteobacteria decreased, the number of members of 𝛼-proteobacteria increased.	[14]
	Cocktail of Ensifer strains	DGGE	Field inoculation showed a significant increase of total bacterial diversity due to seasonal changes, but no effect of rhizobial inoculation was observed. DGGE offered little information about bacterial communities.	[17]
	S. meliloti M401/M403	TGGE	The persistence of certain 𝛾-proteobacterial populations in the rhizosphere of alfalfa could be affected. TGGE proved to be better for identifying specific M403-dependent changes.	[18]
	R. gallicum 8a3; E. meliloti 4H41	T-RFLP	Field inoculation showed significant effects on bacterial structure and diversity in the bulk soil of common bean. Both 𝛼- and 𝛾-proteobacteria together with Firmicutes and Actinobacteria were enhanced, including beneficial bacterial communities with PGPM potentialities. Dual inoculation was less effective than simple inoculation and induced distinct effects.	[22, 23]
	S. meliloti S26/OS6	qPCR	The bacterial genes involved in nitrogen turnover were affected by inoculation. The effectiveness of inoculation was related to the abundance of nifH genes in the late flowering phase. A higher number of amoA copies were observed during flowering.	[26]
Azospirillum	A. brasilense Cd/Sp245	DGGE; RISA	Field inoculation showed no prominent effects on bacterial communities of maize in two different soils and in different growth systems.	[21]
	A. lipoferum CRT1	RISA	Field inoculation of maize increased the intersample variability of the bacterial community between individual plants and sampling times without modifying the total number of root bacteria.	[19, 20]
	A. brasilense 40M/42M	CLPPs	Inoculation changed the community-level physiological profiles of the cultivable microbial communities associated with rice roots.	[29]
AMF	G. intraradices	DGGE	Inoculation affected the composition of the rhizosphere bacterial community of pea. Four to five specific bands were suppressed. Before flowering, the AMF decreased rhizosphere respiration and number of protozoa, but it did not affect bacterial number. During flowering and pod formation, the AMF stimulated rhizosphere respiration and the negative effect on protozoa decreased.	[46]
	G. mosseae; G. intraradices	DGGE	Inoculation significantly modified the rhizosphere bacterial composition of tomato. The two AMFs had had similar bacterial communities; however, specific species-dependent effects were observed.	[47]
Biocontrol agents	P.  fluorescens 2P24	T-RFLP; DGGE	Inoculation induced a transient effect on fungal community in the rhizosphere of cucumber suggesting that this biocontrol agent has a limited validity. DGGE and T-RFLP showed similar results.	[25]
	P. chlororaphis IDV1; P. putida RA2	FAME	Inoculation induced shifts in fatty acid methyl ester profiles of cultivable bacteria fractions, as well as total microbial communities in the rhizosphere of maize. The rhizosphere composition shifted from a Gram-positive-dominated community to more Gram-negative populations.	[27]
Coinoculation	Pseudomonas spp. AMF	DGGE	Inoculation induced a significant modification in the bacterial community structure. The type of PGPM consortium had more impact on the bacterial community structure than the presence of AMF. A synergistic effect of coinoculation was observed.	[15]
	B. subtilis 101; A. brasilense Sp245	DGGE	Inoculation with the biocontrol agent did not show significant effects on fungal (18S rRNA) and bacterial (16S rRNA) communities in the rhizosphere of tomato. Combination of the two rhizobacteria had no synergistic or comparable effects on plant biomass, with respect to their single applications.	[16]
	A. brasilense; P.  fluorescens	T-RFLP; CLPPs	Inoculation did not show significant impact on cultivable communities and nifH T-RFLP-patterns of diazotrophic bacteria associated with rice roots. A synergistic effect of coinoculation was found.	[24]