Diversity of Root Nodule-Associated Bacteria of Diverse Legumes Along an Elevation Gradient in the Kunlun Mountains, China

Abstract

Bacteria in root nodules of legumes play important roles in promoting plant growth. In this study, we investigated root nodule-associated bacteria isolated from leguminous plants along an elevation gradient on the northern slope of the Kunlun Mountains, China, using a cultivation approach. In total, 300 isolates were obtained from seven legume species within six ecological zones. Isolates were identified based on 16S rRNA gene phylogenetic analysis and potential rhizobia were further identified using a recA gene phylogeny. Among the isolates, Bacillales (particularly Bacillus) were the dominant isolates from all host legumes and all elevations (63.5%), followed by Rhizobiales (13%) and Pseudomonadales (11.7%). Less than 3% of the isolates belonged to Burkholderiales, Paenibacillales, Enterobacteriales, Actinomycetales, Sphingomonadales, Xanthomonadales, Chitinophagales, Brevibacillales, Staphylococcales, or Mycobacteriales. A few elevation-specific patterns emerged within the Bacillales and Pseudomonadales. For example, isolates related to the psychrotroph Bacillus psychrosaccharolyticus were only isolated from the highest elevation sites (>3,500 m) whereas those related to the mesophile Bacillus endophyticus were only isolated from lowest elevation sites (1,350 m), suggestive of a role of soil temperature in their distribution. Similarly, isolates related to Pseudomonas brassicacearum were the dominant Pseudomonadales isolates, but they were only isolated from middle and low elevations (<3,200 m). A total of 39 isolates belonged to the Rhizobiales, 36 of which were confirmed to the genus level using the recA gene. In all, Rhizobiales isolates were obtained from five different host legumes spanning the entire elevation gradient. Those from the low-elevation Qira Desert-Oasis Transition Zone (1,350–1,960 m) suggested some patterns of host preference. For example, most isolates from Albizia julibrissin formed a monophyletic group related to Rhizobium lemnae and most from Alhagi sparsifolia were closely related to Ensifer kummerowiae. In general, this study shows that most bacteria associated with root nodules of legumes are widely distributed in distinct ecological zones within a single geographic region but suggests that both climate and host interactions may influence their distributions.

Apple-marigold intercropping improves soil properties by changing soil metabolomics and bacterial community structures

“…The orders Rhizobiales and Pseudomonadales, which belong to the Proteobacteria phylum, were improved in apple-marigold intercropping system rhizosphere soils, as well as the order Bacillales ( Figure 2A ). These orders are mainly enriched in the rhizosphere and decompose organic matter to promote soil carbon and nitrogen cycles ( Zhou J. et al, 2020 ; Pang et al, 2021 ). Thus, their enrichment may improve soil nutrients and promote plant growth.…”

Authentication of putative competitive bacterial endophytes of rice by re-isolation and DNA fingerprinting assay

“…To validate our hypothesis, the ecological niches of these endophytes, as reported earlier, were correlated with our data. Bacillus endophyticus was first reported as an endophyte of the cotton plant (Reva et al, 2002) and later found as an endophyte of several plants, including sugarcane (Pirhadi et al, 2018), cotton (Vinodkumar et al, 2018), onion (Ibrahim et al, 2020), mung bean, cowpea and soybean nodules (Bakhtiyarifar et al, 2021), Chinese mountain legumes (Pang et al, 2021), groundnut (Pal et al, 2021), medicinal plants like Salvadora persica (Moustafa et al, 2016), Vernonia anthelmintica (Rustamova et al, 2020), Gloriosa superba (Das et al, 2021) and halophyte Salicornia europaea (Zhao et al, 2016). This species was also isolated from wheat rhizosphere (Ibarra‐Villarreal et al, 2021; Verma et al, 2016), sugarcane rhizosphere (Mukhtar et al, 2017), rice phyllosphere (Devarajan Arun et al, 2020), termatorium soil (Chauhan et al, 2016), and honeydew of cotton whitefly (Roopa et al, 2014).…”

Seasonal Shifts in Soil Microbiome Structure Are Associated with the Cultivation of the Local Runner Bean Variety around the Lake Mikri Prespa

“…In our study, non-rhizobial endophytes and rhizoplane bacteria were mainly the genus Bacillus , unclassified Bacillales , Sphingomonas, Burkholderiaceae , which include known nitrogen-fixing bacteria [ 74 ], and Massilia, a major rhizosphere and root-colonizing bacteria of many plant species [ 75 ], in higher abundances during runner bean cultivation in summer along with Candidatus alysiosphaera , which was solely detected during the runner bean cultivation. Research has shown that both climate and host interactions may influence root nodule-associated bacteria isolated from leguminous plants [ 37 ]. Nevertheless, the rhizobia genera identified were the unclassified Burkholderiaceae, present in higher abundances during summer cultivation, yet the Rhizobiales spp.…”

“…The symbiotic relationships of leguminous crops with soil nitrogen-fixing bacteria [ 31 ] and other endophytic [ 32 , 33 ] and non-endophytic bacteria [ 34 , 35 , 36 , 37 ] have been extensively studied in the literature, given their contribution to agricultural sustainability and productivity [ 38 , 39 , 40 ] by initiating nutrient cycling in nutrient-depleted soils [ 41 ]. Agronomically important examples of nitrogen-fixing symbiosis in the Fabaceae family, include the common bean ( Phaseolus vulgaris L.) with Rhizobium etli , and lentils ( Lens culinaris Medik.)…”