The Marine Endophytic Polyamine-Producing Streptomyces mutabilis UAE1 Isolated From Extreme Niches in the Arabian Gulf Promotes the Performance of Mangrove (Avicennia marina) Seedlings Under Greenhouse Conditions

Abstract

Mangrove forests in the Arabian Gulf are under continuous threat. To increase plantations of gray mangrove (Avicennia marina) in the United Arab Emirates (UAE), 27 endophytic actinobacterial isolates obtained from mangrove roots were in vitro pre-screened to detect the polyamines (PAs) [putrescine (Put), spermidine (Spd), and spermine (Spm)]. We also determined the abilities of the endophytic PA-producing actinobacterial isolates in enhancing the growth of A. marina under greenhouse conditions. Although three highly PA-producing isolates were recovered from inside mangrove root tissues, Streptomyces mutabilis UAE1 constantly colonized root and stem inner tissues for 12 weeks, suggesting an endophytic association between this actinobacterial isolate and mangrove seedlings. When roots were inoculated with S. mutabilis, mangrove growth was remarkably enhanced under gnotobiotic and greenhouse conditions. This was evident from the significant (P < 0.05) increases in dry weight and length of root (66.7 and 65.5%, respectively) and shoot (64.8 and 58.0%, respectively), number of branches (64.3%), total leaf area (40.2%), and photosynthetic pigments (54.5% chlorophyll a; 40.0% chlorophyll b; and 53.1% carotenoids) of mangrove compared to the PA-non-producing Streptomyces sp. or control treatment. Growth promotion in plants treated with S. mutabilis was also supported by significant (P < 0.05) elevations in the contents of mangrove in planta PAs, auxins, and cytokinins, accompanied by a decrease in abscisic acid levels. No difference was, however, detected in growth and amounts of PAs or any plant growth regulators (PGRs) in plants treated with or without the PA-non-producing isolate. Our findings indicate that plant growth parameters can be enhanced as a consequence of secretion of Put, Spd, and Spm by S. mutabilis resulting in regulation of endogenous PAs and other PGRs in mangrove tissues. This study is the first record that aims to improve sustainable agricultural management practices using plant growth promoting (PGP) actinobacteria, endophytic in mangrove tissues to promote mangrove growth under greenhouse conditions. Such research may allow this region to be a model to study the synergistic S. mutabilis–mangrove interactions and the future impacts on mangrove reforestation in the Arabian Gulf and elsewhere where mangrove forests are in threat.

Effectiveness of Augmentative Biological Control of Streptomyces griseorubens UAE2 Depends on 1-Aminocyclopropane-1-Carboxylic Acid Deaminase Activity against Neoscytalidium dimidiatum

“…Streptomyces spp. may have one or multiple mechanisms to control fungal pathogens [10,14] and to promote growth in plants [21,22]. For instance, pathogen growth can be inhibited by the production of cell-wall-degrading enzymes (CWDEs), antifungal metabolites or siderophores [23,24], hyperparasitism [25] and competition for nutrients [26].…”

A Consortium of Rhizosphere-Competent Actinobacteria Exhibiting Multiple Plant Growth-Promoting Traits Improves the Growth of Avicennia marina in the United Arab Emirates

“…For instance, free-living soil bacteria isolated from the rhizosphere, also referred to as plant growth-promoting (PGP) bacteria (PGPB), have been shown to improve plant growth or increase yield especially in nutrient-impoverished environments (Bashan and de-Bashan, 2005;Hassan et al, 2019;Kumar et al, 2019). Seed or root inoculation with PGPB is a common agricultural practice currently in use to improve the productivity and yields of many plants, including halophytes (El-Tarabily et al, 2019, 2021Mathew et al, 2020;Moretti et al, 2020). PGPB may directly influence plant growth by enhancing the availability of essential nutrients such as phosphorous (P), nitrogen (N), and iron (Fe) (El-Tarabily and Youssef, 2010;Glick, 2015), stimulating transport in plants (Bertrand et al, 2000), and producing plant growth regulators (PGRs) such as auxins [e.g., indole-3-acetic acid (IAA)], cytokinins (CKs), gibberellins (GAs), and polyamines (PAs) (Bashan et al, 2004;Hassan et al, 2019).…”

“…In coastal wetlands, few studies have demonstrated the potential of using the PGPB isolated from mangrove roots and rhizosphere for arid mangrove reforestation (Bashan et al, 2009;El-Tarabily and Youssef, 2010;Castro et al, 2018;El-Tarabily et al, 2021). These reports have linked PGPB to the growth of mangroves through P-solubilization or N-fixation.…”

“…Current mangrove reforestation programs in the UAE may benefit from the deployment of PGPB (El-Tarabily and Youssef, 2010Youssef, , 2011 or PGP actinobacteria (PGPA) (El-Tarabily et al, 2021). In the current study, actinobacteria were intentionally targeted because they are adapted to harsh desert environments of low rainfall, high temperature, and salinity found in the UAE and the Arabian Gulf region (Goodfellow and Williams, 1983;El-Tarabily et al, 2020).…”

Pseudomonas stutzeri and Kushneria marisflavi Alleviate Salinity Stress-Associated Damages in Barley, Lettuce, and Sunflower

“…The application of halotolerant plant growth-promoting endophytes (PGPEs) isolated from halophytes, e.g., Salicornia europaea , seems to be an appropriate solution in sustainable agriculture ( Davy et al, 2001 ; Furtado et al, 2019a , b ; Szymańska et al, 2019 ; Christakis et al, 2021 ; El-Tarabily et al, 2021 ). Endophytes (microorganisms living within plant tissues without causing any negative effect on host plants) associated with crops can directly (e.g., nitrogen fixation and phytohormone and siderophore synthesis) and/or indirectly (e.g., protection against pests and herbivores) stimulate plant growth and protect them against unfavorable environmental conditions ( Khan et al, 2016 ; Rabiey et al, 2019 ; Eid et al, 2021 ).…”