Complete genome sequence analysis of a plant growth-promoting phylloplane Bacillus altitudinis FD48 offers mechanistic insights into priming drought stress tolerance in rice.

Bacillus altitudinis FD48 is a multifunctional plant growth-promoting bacterium isolated from the phylloplane of rice and survives at --10 bars of osmotic potential (--1.0 MPa). It also serves as an ideal PGPM against drought stress by triggering antioxidant defense mechanisms in rice. To further unravel the genetic determinants of osmotic stress tolerance and plant growth-promoting traits, the whole genome sequence of FD48 was compared with its related strains. The whole genome analysis revealed a single chromosome with a total length of 3,752,533 bp (3.7 Mb) and an average G + C ratio of 41.19%. A total of 4029 genes were predicted, of which 3964 (98.4%) were protein-encoding genes (PEGs) and 65 (1.6%) were non-protein-coding genes. The interaction of FD48 with the host plants is associated with many chemotactic and motility-related genes. The ability of FD48 to colonize plants and maintain plant growth under adverse environmental conditions was evidenced by the presence of genes for plant nutrient acquisition, phytohormone synthesis, trehalose, choline, and glycine betaine biosynthesis, microbial volatile organic compounds (acetoin synthesis), heat and cold shock chaperones, translation elongation factor TU (Ef-Tu), siderophore production, DEAD/DEAH boxes, and non- ribosomal peptide synthase clusters (bacilysin, fengycin, and bacitracin). This study sheds light on the drought stress-resilient mechanism, metabolic pathways and potential activity, and plant growth-promoting traits of B. altitudinis FD48 at the genetic level.

Plant Growth-Promoting Bacillus sp. Cahoots Moisture Stress Alleviation in Rice Genotypes by Triggering Antioxidant Defense System.

Drought is considered one of the major obstacles for agricultural productivity worldwide such that greater efforts are required to boost crop production under this stress. One of the methods to overcome this obstacle is to harness the potential of microbe-induced systemic tolerance against moisture stress. The present work evaluated the potential role of two bacterial strains, namely Bacillus altitudinis FD48 and Bacillus methylotrophicus RABA6 and their combination as a co-inoculant for promoting plant growth and moisture stress resilience in two contrast cultivars of Oryza sativa L: CO51 (moderately drought tolerant) and IR64 (drought susceptible) under conditions of terminal moisture stress. B. altitudinis FD48- and B. methylotrophicus-primed rice seeds (CO51 and IR64) significantly influenced the source-sink relationship and reduced the relative water content (RWC). While photosynthetic pigments and proline showed a steady increase owing to the co-inoculant priming, the activity of reactive oxygen species (ROS)-quenching enzymes, such as catalase, superoxide dismutase, ascorbate peroxidase, and peroxidase constitutively increased in plants treated with co-inoculant besides,reducing the trend during the recovery phase. The productive tillers and grain weight were further augmented by the co-inoculant under induced moisture stress. Moreover, the results revealed a 14% and 19% increase in the harvest index (HI) in CO51 and IR64, respectively, attenuated with Bacillus sp. as a co-inoculant. The key mechanism in augmenting energy metabolism by B. altitudinis FD48 and B. methylotrophicus RABA6 could be attributed to the regulation of ROS-quenching enzymes that aid in moisture stress resilience. The results of the present study conclude that these strains may be used as a novel bioinoculant for enhancing the drought tolerance in rice grown under moisture stress regimes.