Arabidopsis thaliana Seedlings Influence Bacillus subtilis Spore Formation

Abstract

Bacillus subtilis is a Gram-positive plant-growth-promoting rhizobacterium exerting many beneficial effects on plant health. Because they secrete antimicrobial compounds and elicit induced systemic resistance, B. subtilis and phylogenetically related species are of particular interest as antifungals in organic agriculture. These bacteria are also known for their capacity to differentiate phenotypically into endospores able to withstand many environmental stresses. However, although B. subtilis is often inoculated on plants as spores, dynamics of germination and sporulation on roots remain unexplored. Using a hydroponic culture system and a soil system for Arabidopsis thaliana, we observed that B. subtilis spores germinate rapidly on contact with plants. However, the vegetative cells are abundant on roots for only a few days before reversing back to spores. We observed that the germinant receptor GerK and sporulation kinases KinA and KinB identified in vitro control sporulation dynamics on plants. Surprisingly, when plants are inoculated with B. subtilis, free-living cells sporulate more rapidly than plant-associated cells. However, direct contact between plant and bacteria is required for the induction of sporulation in the surrounding B. subtilis. This study has fundamental implications for our understanding of interactions between Bacillus spp. and plants, and particularly for a more efficient usage of B. subtilis as a biofertilizer or biofungicide.

Adaptation of Bacillus thuringiensis to Plant Colonization Affects Differentiation and Toxicity

“…Colonization of the rhizosphere by Bacilli depends on various multicellular traits ( 46 , 51 , 52 ). We specifically examined the evolved isolates from lineages E and F and compared the differentiation properties to the ancestor and the isolates from other evolved lineages (lineages A, C, and D).…”

A spore quality–quantity tradeoff favors diverse sporulation strategies in Bacillus subtilis

“…Endospores of the model organism Bacillus subtilis have been isolated from almost every niche on Earth, but primarily from the soil and from the gut flora of organisms that (partially) feed directly from the ground, including chickens, pigs, mice, and also humans [1]. B. subtilis sporulates both in the rhizosphere environment of soil [2] and in the gut [3][4][5], and spores also revive there [2,5,6]. Diverse natural isolates have been characterized, and it was noted repeatedly that their sporulation kinetics is strikingly variable [4,7,8].…”

Biofilm Dispersal for Spore Release in Bacillus subtilis

“…What could facilitate B. subtilis cells' dispersal from a biofilm in addition to reduced matrix expression? B. subtilis, when colonizing plant roots under hydroponic conditions, first produces the biofilm matrix followed by robust spore formation (22). Spore are anticipated to survive the harsh conditions in the soil, including predation by protozoans, nematodes, or other microbes (23)(24)(25).…”