Abstract
Bacillus velezensis gram-positive bacterium, is frequently isolated from diverse niches mainly soil, water, plant roots, and fermented foods. B. velezensis is ubiquitous, non-pathogenic and endospore forming. Being frequently isolated from diverse plant holobionts it is considered host adapted microorganism and recognized of high economic importance given its ability to promote plant growth under diverse biotic and abiotic stress conditions. Additionally, the species suppress many plant diseases, including bacterial, oomycete, and fungal diseases. It is also able after plant host root colonization to induce unique physiological situation of host plant called primed state. Primed host plants are able to respond more rapidly and/or effectively to biotic or abiotic stress. Moreover, B. velezenis have the ability to resist diverse environmental stresses and help host plants to cope with, including metal and xenobiotic stresses. Within species B. velezensis strains have unique abilities allowing them to adopt different life styles. Strain level abilities knowledge is warranted and could be inferred using the ever-expanding new genomes list available in genomes databases. Pangenome analysis and subsequent identification of core, accessory and unique genomes is actually of paramount importance to decipher species full metabolic capacities and fitness across diverse environmental conditions shaping its life style. Despite the crucial importance of the pan genome, its assessment among large number of strains remains sparse and systematic studies still needed. Extensive knowledge of the pan genome is needed to translate genome sequencing efforts into developing more efficient biocontrol agents and bio-fertilizers. In this study, a genome survey of B. velezensis allowed us to (a) highlight B. velezensis species boundaries and show that Bacillus suffers taxonomic imprecision that blurs the debate over species pangenome; (b) identify drivers of their successful acquisition of specific life styles and colonization of new niches; (c) describe strategies they use to promote plant growth and development; (d) reveal the unlocked strain specific orphan secondary metabolite gene clusters (biosynthetic clusters with corresponding metabolites unknown) that product identification is still awaiting to amend our knowledge of their putative role in suppression of pathogens and plant growth promotion, and (e) to describe a dynamic pangenome with a secondary metabolite rich accessory genome.
Highlights
The genus Bacillus include ubiquitous bacteria having countless advantages in industrial, medicinal and especially in agricultural sectors [1,2,3,4,5,6]
Bacterial genome size was in the range of 3.38 to 4.97 Mb and the average GC content was between 45.23%
B. velezensis collection were isolated from various substrates (Figure 1D), almost half of them originated from soil (44%), 6% came from the above ground parts of plants, 4% from either slow sand biofilter or uncut heroin sample, 3% of the totality of Bv bacteria were originally isolated from water or plants roots and bulbs or as endophytes, 1% originated from air, and the remaining 32% came from other different sources
Summary
The genus Bacillus include ubiquitous bacteria having countless advantages in industrial, medicinal and especially in agricultural sectors [1,2,3,4,5,6]. The extensive use of Bacillus strains was documented by several reasons such as the facility of isolation, replication and cultivation, biofilm formation, and resistance to harsh environmental conditions through spore forming potentials [7,8,9,10,11,12]. A massive amount of B. velezensis strains have been the focus of numerous studies [13,14,15,16,17,18]. B. velezensis is a Gram-positive, aerobic, endospore-forming beneficial bacterium inhabiting diverse environments (soil, water, air, plant rhizosphere, human, animal, fermented food, etc.). B. velezensis strains have been especially applied for plant growth promotion and biocontrol of phypathogens (fungi, bacteria, virus, nematodes, oomycetes, etc.) [19,20,21,22,23,24].
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