Esperanza Martinez Romero

Title : Probiotics from plants

Abstract:

Plant bacteria are a valuable source of probiotics. However human pathogens or opportunistic pathogens may be found in healthy plants, and some may be recalcitrant to eliminate, especially when they are inside plant tissues, as endophytes, not easily eliminated with surface disinfection procedures. Endophytes are commonly consumed by animals when eating raw vegetables. Plant-beneficial endophytes may be selected in seeds, as they are transmitted to new plant generations determining their health. Among endophytes, we commonly found Klebsiella variicola.

Objectives:
i) Test seed endophytes from Phaseolus vulgaris in vitro for their capacity to inhibit plant pathogenic fungi.
ii) Analyze the genomes of Klebsiella isolated from animals to try to understand their origins and roles in hosts.

Methods: We identified from seeds of Phaseolus vulgaris (common bean) diverse Bacillus strains and supposed that could help defend plantlets from fungal pathogens. A suspension of fungal spores was inoculated on one side of PY plates and a spot of Bacillus cells on the opposite side. After 1 week at 30ºC, inhibition halos were measured. 
Nitrogen-fixing K. variicola has been proposed to be used as a plant growth promoter and even as a probiotic in baby formulas. We searched this bacterium in association with healthy animals such as the Gopherus berlandieri tortoise, Ross chicken and the larvae of the Comadia redtenbacher moth. Genomes of nitrogen-fixing Klebsiella strains were sequenced and analyzed.

Results and discussion: Antagonism experiments showed that Bacillus endophyticus and Bacillus velezensis decreased, up to 60%, the growth of Botryosphaeria dothidea and Fusarium oxysporum pathogenic fungi. The causal agent of anthracnose, Colletotrichum gloeosporioides, was inhibited up to 50% by Bacillus pumilus and B. velezensis. 

Klebsiella isolates were found in tortoise and chicken feces and in moth larvae. Klebsiella genomes from plants and larva isolates had the basic virulence factor (fimbriae and siderophores) and intrinsic ampicillin resistance genes. We are analyzing the genomes from klebsiellas isolated from chicken feces to try to understand their origin and role in these hosts. Besides being an endophyte, Klebsiella has been found in patients in the clinics and more recently it has been found associated with long COVID 19 patients, thus Klebsiella use should be taken with caution. 

Conclusions: Our results support the use of B. endophyticus, B. pumilus, and B.velezensis as effective antifungals and may be considered as plant probiotics. We found that plant and larva associated K. variicola strains have basic virulence genes or antibiotic resistance genes and maybe they are safe to be used in inoculation assays. In animals, we suppose that the mother to progeny transfer of Klebsiella would ensure that nonpathogenic strains are transmitted. Our genomic results indicate that K. variicola strains vary in gene content and may be adapted to distinct hosts. 

Audience Take Away:

• The audience may search for beneficial bacteria in plants.
• This will enlarge their view of probiotics.
• It will enlarge their teaching and research approaches.
• Yes, considering that there may be pathogens among plant bacteria is essential in designing strategies of use of plant bacteria.
• It provides knowledge on bacterial genomics.

Biography:

Professor Esperanza Martínez-Romero is a professor and head of the Genomic Ecology Program at the Genomic Sciences Center at UNAM. She studies the mutualistic symbioses of bacteria with plants and animals native to Mexico using metagenomic and functional genomics approaches. She was a pioneer in the molecular study of the nitrogen-fixing symbioses of beans and endophytes of corn and beans. She has given workshops and advice to agricultural producers. She described new species of bacteria from plants and insects from Mexico, some of them nitrogen-fixing bacteria. The strains that she obtained have been deposited in official bacterial collections and some of them are used as inoculants or biofertilizers in agriculture. She has received awards and prizes such as the National University Award, the Mexican Academy of Sciences Award and recently, the National Science Award of Mexico in December of 2019 and the UNESCO Prize for Women in Science in March 2020. She has been recognized as a highly cited Mexican scientist. She has published 216 articles in international journals, 23 book chapters and 11 genome announcements. She has received more than 20,400 citations to her published work, with an H-index of 80.