Whole genome sequence insight of two plant growth-promoting bacteria (B. subtilis BS87 and B. megaterium BM89) isolated and characterized from sugarcane rhizosphere depicting better crop yield potentiality.

Since sugarcane is a ratoon crop, genome analysis of plant growth-promoting bacteria that exist in its soil rhizosphere, can provide opportunity to better understand their characteristics and use of such bacteria in turn, may especially improve perennial crop productivity. In the present study, genome of two bacterial strains, one each of B. megaterium (BM89) and B. subtilis (BS87), isolated and reported earlier (Chandra et al., 2018), were sequenced and characterized. Though both strains have demonstrated plant growth promoting properties and enhanced in-vitro plant growth responses, functional annotation and analysis of genes indicated superiority of BS87 as it possessed more plant growth promotion attributable genes over BM89. Apart from some common genes, trehalose metabolism, glycine betaine production, peroxidases, super oxide dismutase, cold shock proteins and phenazine production associated genes were selectively identified in BS87 genome indicating better plant growth performances and survival potential under harsh environmental conditions. Genes for chitinase, d-cysteine desulfhydrase and γ-aminobutyric acid (GABA), as found in BM89, propose its selective utilization in defense and bio-control measures. Concomitant with better settlings' growth, scanning electron micrographs indicated these isolated and characterized bacteria exhibiting healthy colonization within root of sugarcane crop. Kegg pathways' assignment also revealed added pathways namely carbohydrate and amino acid metabolism attached to B. subtilis strain BS87, a preferable candidate for bio-fertilizer and its utilization to promote growth of both plant and ratoon crops of sugarcane usually experiencing harsh environmental conditions.

Microbiome analysis of rhizospheres of plant and winter-initiated ratoon crops of sugarcane grown in sub-tropical India: utility to improve ratoon crop productivity.

One plant and one to two ratoon crops are the predominant patterns of sugarcane cultivation in sub-tropical part of India. Despite high agricultural inputs, yield of ratoon crop gets dwindled in the subsequent years. The microbial community, particularly bacteria and fungi, in the rhizosphere and their interaction with the root system, in general influences plant productivity. For the present study, an early maturing sugarcane variety (CoLk 94184), was used to establish plant and winter-initiated ratoon crops in 2016-2018. Soils pertaining to both plant and ratoon rhizospheres were subjected to biochemical analysis, microbial DNA isolation and high-throughput sequencing of 16S rRNA genes to assess the microbial diversity and associated characteristics impacting cane yield. Although alpha diversity of bacterial community was observed high in the soils of both plant and ratoon crops, the species richness/diversity was more in plant crop. Bacterial community structure in the rhizosphere of plant crop was predominantly consisted of phyla Actinobacteria (35.68%), Gemmatimonadetes (29.26%), Chloroflexi (26.73%) and Proteobacteria (16.68%), while ratoon rhizosphere revealed dominance of Acidobacteria (20.77%) and Bacteroidetes (10.7%). Though studies revealed the presence of rich bacterial community in the rhizospheres of both plant and ratoon crops of sugarcane, dominance of Acidobacteria and meager proportion of Actinobacteria and Proteobacteria in ratoon crop possibly limited its productivity. Along with high total phenols (7.27 mg/g dry wt), ratoon crop depicted less active root system as revealed by scanning electron microscopy. Dominance of thermophilic bacterial phyla Chloroflexi and Gemmatimonadetes which was observed in sugarcane rhizosphere supports better crop growth in drought. However, management of soil microbial community is required to improve the ratoon crop productivity.