Ability of Bacillus velezensis EM-A8, a biocontrol agent for Northern Corn Leaf Blight (NCLB), to colonize maize leaves under different environmental conditions.

AIMS: Bacillus velezensis EM-A8 has shown antagonism against Exserohilum turcicum, a foliar pathogen that causes Northern Corn Leaf Blight. The present study aimed to: (a) analyze biofilm formation and motility by the bacterium in a low-cost medium (YMM) under different water potential values and light qualities; (b) evaluate the expression of genes related to biofilm formation and motility in vitro and in planta, and (c) assess the strain's ability to colonize maize leaves in planta.

METHODS AND RESULTS: EM-A8 was similarly able to form biofilm in YMM and in a biofilm-inducing medium. Moreover, it was able to swim and swarm after growth in YMM and exposure to either red or white light. The genes evaluated were differentially expressed in the strain after 8 h of incubation in vitro under the different light qualities, e.g. tasA and epsA were upregulated after exposure to white light. On the other hand, EM-A8 colonized maize leaves in planta. The morphological characteristics of the colonies formed by the strain indicated that the inoculum concentration and its endophytic presence were maintained for up to 720 h postinoculation (HPI).

CONCLUSIONS: Bacillus velezensis EM-A8 was able to produce biofilm and be motile after being grown in YMM. It also showed tolerance to different light qualities and water potentials, both of which are important environmental factors at field level. After having grown in YMM, the strain colonized maize leaves both epi- and endophytically in chamber assays.