Endophytic culturable bacteria colonizing Lavandula dentata L. plants: Isolation, characterization and evaluation of their plant growth-promoting activities

Abstract

Aromatic plants such as lavender are stirring the attention of many researchers due to their content in bioactive secondary metabolites that can be used in traditional medicine. However, information regarding naturally occurring lavender associated bacterial endophytes (BE) is limited. To the best of our knowledge, this is the first study which aims to assess the phylogenetic diversity of the culturable endophytic bacteria of Lavandula dentata cultivated under organic management and to evaluate their potential as plant growth promoting (PGP) agents. BE were grouped by random amplified polymorphic DNA and identified by 16S ribosomal RNA gene sequencing. Endophytes were further characterized for the ability to produce several PGP substances, like ammonia, siderophores, indol-3-acetic acid, hydrogen cyanide and for the ability to solubilize phosphate. Plant cell-wall degrading enzymes were also determined. Densities of BE were higher in roots (log 6.39 CFU g-1 fresh weight) than in shoots (log 5.56 CFU g-1 fresh weight). Phylogenetic analysis showed that BE were affiliated to two major groups: γ-Proteobacteria (50%) and Firmicutes (31.6%) and a small part belonged to α-(7.9%) and β-Proteobacteria (10.5%), being Pseudomonas and Bacillus the most highly represented genera. Higher bacterial diversity was found in the lavender roots, with endophytes belonging to 6 different genera (Pseudomonas, Variovorax, Rhizobium, Caulobacter, Bacillus and Paenibacillus), than in shoots where only 3 genera (Bacillus, Pseudomonas and Xanthomonas) were found. Overall, BE showed ability to produce extracellular enzymes and multiple PGP traits, suggesting their potential use as efficient bioinoculants in sustainable cultivation of medicinal and aromatic plants.

Hydrocarbon degradation potential and plant growth-promoting activity of culturable endophytic bacteria of Lotus corniculatus and Oenothera biennis from a long-term polluted site

“…All strains that we isolated were IAA producers (Table 2 ). Similarly, other authors observed that a vast majority of endophytic bacteria synthesized IAA (Etesami et al 2014 ; Kukla et al 2014 ; Pawlik and Piotrowska-Seget 2015 ; Pereira et al 2016 ; Xu et al 2016 ). The application of these strains could contribute to improve root proliferation and elongation that is crucial during phytoremediation as well as in growth and development of economical important crops such as potatoes, maize, and rice (Garbeva et al 2001 ; Ikeda et al 2010 ; Seghers et al 2004 ).…”

“…The cellulase secretion and motility of endophytic bacteria may help in the process of plant colonization and spread of bacteria in the host plant. Verma et al ( 2001 ) and Pereira et al ( 2016 ) described the cell wall-degrading enzymes from endophytic bacteria, demonstrating their potential for plant tissues colonization. The ability of bacterial strains to colonize roots appears to be crucial for a close interaction between plants and bacteria especially in hazardous environments.…”

Linking belowground microbial network changes to different tolerance level towards Verticillium wilt of olive

“…Concerning fungi, the genus Acremonium is worth mentioning for its involvement in plant growth [40]. On the other hand, in the Frantoio endosphere, the bacterial genera Neorhizobium, Bradyrhizobium (able to form nitrogen fixing nodules in legumes and nodule-like structure in radish, tomato, and rice [41]), Sphingomonas (reported to increase Chinese medicinal plant [42] biomass), Actinoplanes (involved in cucumber [39] growth promotion), and Caulobacter (reported as phytohormones producer in lavender [43]) were significantly more abundant. With regard to fungi and as reported for the rhizosphere, the genera Trichoderma, a wellknown PGPM and BCA, and Acremonium were also found (e.g., [44]).…”

Phytohormones and Beneficial Microbes: Essential Components for Plants to Balance Stress and Fitness

“…Plant-associated microbes live in plant tissue endophytically or symbiotically or they colonize the root surface and cooperate with each other by producing various metabolically active substances ( Egamberdieva, 2011 , 2012 ; Berg et al, 2013 ; Asaf et al, 2017 ). The stimulation of plant growth and nutrient acquisition by beneficial rhizobacteria has been correlated to the biosynthesis of plant growth regulators, including auxins ( Etesami et al, 2015 ; Pereira et al, 2016 ), gibberellins ( Khan et al, 2014 ), cytokinins ( Kudoyarova et al, 2014 ), and ABA ( Sgroy et al, 2009 ). The microbial regulators modulate plant hormone levels in plant tissue, and they have been found to have effects that are similar to exogenous phytohormone application ( Egamberdieva, 2009 ; Turan et al, 2014 ; Shahzad et al, 2016 ).…”