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Crystal Ball
Next generation of microbial inoculants for agriculture
and bioremediation
Antonino Baez-Rogelio,
1,2
Yolanda Elizabeth
Morales-Garc
ıa,
1,2
Ver
onica Quintero-Hern
andez
1,3
and Jes
us Mu~
noz-Rojas
1,
*
1
Laboratorio de Ecolog
ıa Molecular Microbiana, Centro
de Investigaciones en Ciencias Microbiol
ogicas, Instituto
de Ciencias, Benem
erita Universidad Aut
onoma de
Puebla (BUAP), Puebla, Mexico.
2
Biotecnolog
ıa, Escuela de Biolog
ıa-BUAP, Puebla,
Mexico.
3
CONACYT-BUAP, Puebla, Mexico.
The global population has grown dramatically increasing
the needs for food (Tilman et al., 2002). To satisfy the
food needs, farmers of all countries have implemented
the green revolution technology. However, green revolu-
tion have provoked several adverse effects to the envi-
ronment due to indiscriminate use of pesticides,
herbicides and nitrogen fertilizers; the use of improved
varieties and transgenic, among others (Tilman, 1998).
Many types of herbicides and pesticides have carcino-
genicity potential (Zahn and Ward, 1998; Damalas and
Eleftherohorinos, 2011). Even though some of those toxic
compounds have been prohibited in European countries,
several of them are still being applied to the crops in dif-
ferent regions of the world. In addition, application of
those products can promote the accumulation of toxic
compounds in soils. Although little is known about this
topic, we can infer that the crop plants are able to absorb
these compounds from soil, representing a latent problem
to the human health and environment. In fact, it has been
demonstrated that some pesticides can be absorbed
from soil by potatoes (Juraske et al., 2011) and the
highly recalcitrant compound TNT can be absorbed by
maize plants (Van Dillewijn et al., 2007). Nonetheless,
something even more important, it will be determined if
TNT is able to travel to maize fruits or just stay in the
steam of the plants. In other hand, the indiscriminate use
of chemical fertilizers has negatively affected to the envi-
ronment. Only 30% of nitrogen compounds added to the
crops can be absorbed by plants, the remaining nitrogen
is leached to the groundwater generating eutrophication,
NOx gaseous compounds and the concomitant acid rain
and detrimental effects on ozone layer (Moiser, 2001).
The implementation of improved varieties and transgenic
plants to crops increase the productivity. However, this
practice could have a negatively impact on the future of
the planet, as genetic diversity harboured by those native
plants is being displaced (Evenson and Gollin, 2003). As
a consequence of damage caused by green revolution,
farmers of different places of the world are implementing
organic farming schemes based on the past experiences
of agriculture and also introducing new technologies to
replace the use of chemical fertilizer and toxic pesticides
by organic fertilizers and biological control agents. How-
ever, the majority of crop fields of the world are still oper-
ating under the scheme of intensive agriculture of the
green revolution technology and the organic agriculture
does not impact much on either economic or environ-
mental aspects (Tilman et al., 2002; De Ponti et al.,
2012; Seufert et al., 2012). Therefore, a major effort
should be made to increase the positive impact of
organic farming practices on both aspects. One possibil-
ity could be the synergic effect of combine the organic
technology with the use of microorganisms able to carry
out both the plant growth promotion and the bioremedia-
tion of contaminated soils derived from intensive farming.
This synergy maybe of greater impact on the develop-
ment of sustainable agriculture, farmers could get high
yields and additionally they could restore their damaged
and contaminated soils.
Beneficial bacteria have been isolated and studied
since early nineteenth century and today still exist
research groups working in isolation and description of
new bacterial species with potential for agriculture, biore-
mediation, biomedicine and food industry. Plant growth
promoting bacteria (PGPB) and bioremediation bacteria
have been extensively studied and several molecular
mechanisms have been described (Abraham et al.,
Received 29 September, 2016; accepted 30 September, 2016. *For
correspondence. E-mail joymerre@yahoo.com.mx; Tel. +52 222
2295500 ext. 2557.
Microbial Biotechnology (2017) 10(1), 19–21
doi:10.1111/1751-7915.12448
Funding Information
We are grateful to Apoyo Redes PRODEP 2015-2016 (CA-262 and
CA-244), DITCo2016-3, DITCo2016-4 and VIEP-BUAP-2016
(00450, 00513, 00476, 00510) for the support for authors research.
ª2016 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly cited.
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2002; Ramos et al., 2005; Lugtemberg and Kamilova,
2009; Bhattacharyya and Jha, 2012). Research studies
on molecular dialogue between bacteria and plants has
been carried out by some authors showing the wonderful
interchange of signals that occur between interacting
organisms (Badri et al., 2009; Segura and Ramos,
2013). The ability of bacteria to bioremediate toxic com-
pounds and with potential as PGPB suggests that these
bacteria could interact effectively with plants in agricul-
tural contaminated soils, carrying out the degradation of
pollutants and increasing crop yields.
Despite the large number of reports showing the advan-
tages of the use of PGPB in crops, the application of these
microorganisms on the fields is still little explored in com-
parison to the total amount of agricultural land of the
world. Bacterial formulations with PGPB have not always
the desired effectiveness (Dobbelaere et al., 2001). The
capability of microorganisms to promote the growth of
plants in crop fields dependent of several factors that limit
their effectiveness, for example, soil types, climatic condi-
tions, variety of the crop, bacterial genotype, effectiveness
of the bacterial isolate, the proper inoculation technology
and others (Bashan, 1998; Bashan et al., 2014). When
bacteria are in co-interaction with crop plants, the expres-
sion of genes involved in bioremediation and plant growth
promotion may be fundamental to obtain the beneficial
effect (Segura and Ramos, 2013). In our opinion, these
interesting genes could be turned on or off depending on
environmental conditions, which suggest that different
conditions can occur in the crop fields that may be affect-
ing the gene expression. This could explain why some
bacteria improve the growth of plants under laboratory
conditions but frequently fails under field conditions or in
other cases we observe variable results (Okon and
Labandera-Gonzales, 1994).
In order to ensure the promoting effect of bacteria on
plant growth, better adapted bacteria to the conditions
where they will be applied have been studied, because
they could be more active under that conditions. Authors
are focusing in bacteria bearing diverse beneficial abilities,
for example bacteria containing genes involved in meta-
bolic pathways for plant growth stimulation and bioremedi-
ation. In this regard, Burkholderia unamae represent an
example of adapted bacteria with potential as PGPB to be
applied in Mexican fields. B. unamae has the potential to
fix nitrogen, produce phytohormones, siderophores and
other inhibitory substances, ACC-deaminase activity and
degradation of toxic aromatic compounds (Caballero-
Mellado et al., 2004, 2007; Onofre-Lemus et al., 2009).
Nevertheless, as we mention before, effective bacteria for
the crop field will be those able to express the genes
responsible of the plant growth promotion or bioremedia-
tion in association with plants under real environmental
conditions. However, the key genomic aspects are not
completely understood and they should be explored. For
example, studies of the kind of promoters and transcrip-
tional factors involved in the regulation of the expressed
genes in association with plants are needed. Otherwise,
super-bacteria with the potential to stimulate plant growth
under laboratory conditions could fail to provide their ben-
eficial effects to plants under field conditions.
In other hand, bacteria are not alone in nature, there-
fore a consortium of bacteria could be more effective for
plant growth promotion than a single bacterium (Martinez
de Oliveira et al., 2006; Sundaramoorthy et al., 2012).
However, the design and formulation of bacterial consor-
tia is not a trivial task, members of the bacterial mixture
should be able to coexist without any antagonism among
them. In addition, bacteria chosen for the formulation of
the bacterial mixtures should bear different abilities to
increase the growth of plants, carry out bioremediation,
besides to be tolerant to adverse conditions prevalent in
the crop fields. Other important feature of why bacterial
mixtures could work better than single-bacterium formu-
lations is because there are higher probability than one
member of the bacterial mixture carry out the functional
gene expression required for the plant growth promotion.
Putting both strategies together, we could obtain spe-
cial bacterial mixtures with high probability to obtain a
positive effect for bioremediation and high crop yields. In
this sense, our principal speculation is that in a short
time several authors in the field of PGPB and bioremedi-
ation will be expanding the knowledge on the develop-
ment of different formulations containing super-bacteria
able to provide beneficial effect in association with
plants. In addition, a major development of works related
to the design of bacterial inoculants in mixture, for agri-
culture and bioremediation, will be observed. In both
cases, it will be desirable to demonstrate that the
expression of genes involved in plant growth promotion
and bioremediation are working in association with
plants under different environmental conditions. For bac-
terial mixtures, it will be also necessary to demonstrate
that they work better than mono-species formulations.
If the crop yields are constantly increased after every
inoculation of beneficial microorganisms, it will be easier
to convince farmers around the world to substitute the
green revolution technology by the use of microbial inocu-
lants that are friendlier to human health and environment.
Conflict of Interest
None declared.
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Next generation of microbial inoculants 21
