Borja Torres

Laura Toral, Miguel Rodríguez, Victoria Béjar and Inmaculada Sampedro
This work aims to explore the capacity of a Bacillus methylotrophicus (later heterotypic
synonym of Bacillus velezensis) strain named XT1 CECT 8661 against the necrotrophic
plant pathogen Botrytis cinerea and to identify the compounds responsible for its
activity. Q_TOF electrospray mass spectrometry analysis allows us to detect several
lipopeptides – surfactin, bacillomycin, and fengycin – in XT1 cultures. In vitro antibiosis
studies demonstrated the efficiency of the lipopeptide fraction for the inhibition of
fungal growth. In fact, microscopy studies (SEM/TEM) revealed, an alteration of the
morphology of the phytopathogen in interaction with lipopeptides, with resistance
structures appearing in the early stages of growth of the fungus. Our studies, carried out
with tomatoes, grapes, and strawberries have demonstrated the efficiency of Bacillus
XT1 CECT 8661 lipopeptides against B. cinerea infection and it capability to trigger
the antioxidant activity in fruit. Overall, the results of this study highlight the potential of
lipopeptides of this strain as an effective biological control agent against the colonisation
of B. cinerea.

Marta Torres In,maculada Llamas, Borja Torres, Laura Toral, Inmaculada Sampedro, Victoria Béjar
Bacillus velezensis XT1 is a halotolerant bacterium isolated from a saline habitat in Spain. The objective of this
work was to evaluate its plant growth promotion capacity on horticultural crops and its in vitro antifungal
activity. The biochemical properties related to both of these characteristics were identified. When applied directly
in the soil, strain XT1 significantly increased aerial fresh weight of tomato, pepper, pumpkin and cucumber
plants by 53%, 63.6%, 129.2% and 100.8%, respectively, as compared to the control. Plant height,
number of flowers and number of fruits increased more significantly in tomato plants treated with strain XT1.
Under sterile conditions, strain XT1 significantly increased shoot and root biomass, height and number of leaves
of tomato plants showing that its plant growth-promoting properties were independent of soil microbiota. In
greenhouse and field experiments, addition of strain XT1 increased aerial biomass between 37 and 43.8% and
height of tomato plants by 20.1 and 22.2%, respectively. Metabolic features associated with the properties of
strain XT1 included nitrogen-fixing capacity; organic and inorganic phosphate solubilization; siderophore production,
enzymes (e.g. urease and 1-aminocyclopropane-1-carboxylate deaminase) and volatile metabolites
(such as acetoin and 2,3-butanediol). It produced endospores, had a high motility, synthesized high yields of
exopolysacharides and formed biofilms. Strain XT1 displayed in vitro antifungal activity (over 40% of mycelium
inhibition) against the phytopathogens Alternaria alternata, Fusarium oxysporum, Monilinia fructicola,
Magnaporthe oryzae, Thanatephorus cucumeris and Sclerotinia sclerotiorum. All the characteristics described above
showed a high potential of Bacillus velezensis XT1 to be used in agriculture.