164
C. C. V. Velloso et al.
Bacillus comprises a heterogeneous group of Gram-positive bacteria widely
distributed in the environment, consisting of approximately 360 species that have
distinct physiological, metabolic, and phenotypic characteristics (www.bacterio.net/
bacillus.html). Numerous Bacillus sp. are known to enhance nutrient solubilization
and facilitate nutrient mobilization in the soil. Our research group reported that maize
plants inoculated separately with different Bacillus strains capable of producing
indole-3-acetic acid (IAA) and solubilizing phosphate enhanced root system, dry
matter, and nutrient accumulation in hydroponics. Under field conditions, strains
increased maize yield and P grain accumulation by around 36 and 58%, and P grain
in 21% in soils with no P added. Even in soils fertilized with triple superphosphate,
maize yield increase and P grain accumulation was observed around 20% after inoculation comparing to non-inoculated control (unpublished results). In another study,
pearl millet (Pennisetum glaucum) seeds inoculated with endophytic Bacillus strains
isolated from maize grown in the Brazilian Cerrado, showed increased shoot and
root dry weight, N and P content in the roots and N, P, and K in the shoot, promoting
growth and nutrient uptake in greenhouse conditions. Probably the main mechanism
involved in these processes are the production of IAA, siderophores, and solubilization of phosphate (Ribeiro et al. 2018). Interestingly, these strains showed high
organic acid production, which is one of the mechanisms involved in solubilization
of mineral phosphates, due to lowering soil pH (Abreu et al. 2017).
Other examples of endophytic Bacillus in tropical soil show that inoculation of
strains isolated from medicinal plants, crops and weed enhanced seed germination,
and seedlings vigor of pearl millet crop plants. In addition, the vegetative (height
of the plant, number of basal tillers, fresh and dry weight) and reproductive growth
parameters (early flowering, length and girth of ear heads, 1000-seed weight, plant
height, and tillering) were higher than control due to the treatment of maize seeds
with the endophytic bacteria (Chandrashekhara et al. 2007). The Bacillus strains
were also efficient in reducing the incidence of downy mildew caused by Sclerospora
graminicola under greenhouse and field condition, demonstrating their potential as
a biocontrol agent (Chandrashekhara et al. 2007).
In addition to agricultural crops, various studies have shown evidence of the
benefits of Bacillus endophytic in forestry of Eucalyptus, particularly in tropical
and subtropical regions, due to its rapid growth, adaptability, and the commercial
value of its wood (Brooker 2000). However, the Eucalyptus–endophytic bacteria
interaction is poorly described, and the majority of previous studies have focused on
rhizosphere microorganisms (Bonito et al. 2014; Silva et al. 2014). One of the first
studies describing Bacillus, including B. licheniformis and B. subtilis, as endophytes
of eucalyptus exhibited an increase of the root and shoot growth of plantlets after
inoculation under greenhouse conditions, during the summer and winter seasons
(Paz et al. 2012). Other studies have shown evidence of the benefits of endophytic
inoculation in eucalyptus plantlets; for instance, increasing the rooting indexes and
vegetative biomass or acting as biocontrol agents in improving plant resistance when
challenged with different pathogens (Ferreira et al. 2008; Mafia et al. 2005; Procópio
et al. 2009). Related to nutrient efficiency, the potential for biological nitrogen fixation
C. C. V. Velloso et al.
Bacillus comprises a heterogeneous group of Gram-positive bacteria widely
distributed in the environment, consisting of approximately 360 species that have
distinct physiological, metabolic, and phenotypic characteristics (www.bacterio.net/
bacillus.html). Numerous Bacillus sp. are known to enhance nutrient solubilization
and facilitate nutrient mobilization in the soil. Our research group reported that maize
plants inoculated separately with different Bacillus strains capable of producing
indole-3-acetic acid (IAA) and solubilizing phosphate enhanced root system, dry
matter, and nutrient accumulation in hydroponics. Under field conditions, strains
increased maize yield and P grain accumulation by around 36 and 58%, and P grain
in 21% in soils with no P added. Even in soils fertilized with triple superphosphate,
maize yield increase and P grain accumulation was observed around 20% after inoculation comparing to non-inoculated control (unpublished results). In another study,
pearl millet (Pennisetum glaucum) seeds inoculated with endophytic Bacillus strains
isolated from maize grown in the Brazilian Cerrado, showed increased shoot and
root dry weight, N and P content in the roots and N, P, and K in the shoot, promoting
growth and nutrient uptake in greenhouse conditions. Probably the main mechanism
involved in these processes are the production of IAA, siderophores, and solubilization of phosphate (Ribeiro et al. 2018). Interestingly, these strains showed high
organic acid production, which is one of the mechanisms involved in solubilization
of mineral phosphates, due to lowering soil pH (Abreu et al. 2017).
Other examples of endophytic Bacillus in tropical soil show that inoculation of
strains isolated from medicinal plants, crops and weed enhanced seed germination,
and seedlings vigor of pearl millet crop plants. In addition, the vegetative (height
of the plant, number of basal tillers, fresh and dry weight) and reproductive growth
parameters (early flowering, length and girth of ear heads, 1000-seed weight, plant
height, and tillering) were higher than control due to the treatment of maize seeds
with the endophytic bacteria (Chandrashekhara et al. 2007). The Bacillus strains
were also efficient in reducing the incidence of downy mildew caused by Sclerospora
graminicola under greenhouse and field condition, demonstrating their potential as
a biocontrol agent (Chandrashekhara et al. 2007).
In addition to agricultural crops, various studies have shown evidence of the
benefits of Bacillus endophytic in forestry of Eucalyptus, particularly in tropical
and subtropical regions, due to its rapid growth, adaptability, and the commercial
value of its wood (Brooker 2000). However, the Eucalyptus–endophytic bacteria
interaction is poorly described, and the majority of previous studies have focused on
rhizosphere microorganisms (Bonito et al. 2014; Silva et al. 2014). One of the first
studies describing Bacillus, including B. licheniformis and B. subtilis, as endophytes
of eucalyptus exhibited an increase of the root and shoot growth of plantlets after
inoculation under greenhouse conditions, during the summer and winter seasons
(Paz et al. 2012). Other studies have shown evidence of the benefits of endophytic
inoculation in eucalyptus plantlets; for instance, increasing the rooting indexes and
vegetative biomass or acting as biocontrol agents in improving plant resistance when
challenged with different pathogens (Ferreira et al. 2008; Mafia et al. 2005; Procópio
et al. 2009). Related to nutrient efficiency, the potential for biological nitrogen fixation