Recent advances in PGPR-mediated resilience toward interactive effects of drought and salt stress in plants

The present crisis at hand revolves around the need to enhance plant resilience to various environmental stresses, including abiotic and biotic stresses, to ensure sustainable agriculture and mitigate the impact of climate change on crop production. One such promising approach is the utilization of plant growth-promoting rhizobacteria (PGPR) to mediate plant resilience to these stresses. Plants are constantly exposed to various stress factors, such as drought, salinity, pathogens, and nutrient deficiencies, which can significantly reduce crop yield and quality. The PGPR are beneficial microbes that reside in the rhizosphere of plants and have been shown to positively influence plant growth and stress tolerance through various mechanisms, including nutrient solubilization, phytohormone production, and induction of systemic resistance. The review comprehensively examines the various mechanisms through which PGPR promotes plant resilience, including nutrient acquisition, hormonal regulation, and defense induction, focusing on recent research findings. The advancements made in the field of PGPR-mediated resilience through multi-omics approaches (viz., genomics, transcriptomics, proteomics, and metabolomics) to unravel the intricate interactions between PGPR and plants have been discussed including their molecular pathways involved in stress tolerance. Besides, the review also emphasizes the importance of continued research and implementation of PGPR-based strategies to address the pressing challenges facing global food security including commercialization of PGPR-based bio-formulations for sustainable agricultural.

Thermal Endurance by a Hot-Spring-Dwelling Phylogenetic Relative of the Mesophilic Paracoccus

High temperature growth/survival was revealed in a phylogenetic relative (SMMA_5) of the mesophilic Paracoccus isolated from the 78 to 85°C water of a Trans-Himalayan sulfur-borax spring. After 12 h at 50°C, or 45 min at 70°C, in mineral salts thiosulfate (MST) medium, SMMA_5 retained ~2% colony forming units (CFUs), whereas comparator Paracoccus had 1.5% and 0% CFU left at 50°C and 70°C, respectively. After 12 h at 50°C, the thermally conditioned sibling SMMA_5_TC exhibited an ~1.5 time increase in CFU count; after 45 min at 70°C, SMMA_5_TC had 7% of the initial CFU count. 1,000-times diluted Reasoner's 2A medium, and MST supplemented with lithium, boron, or glycine-betaine, supported higher CFU-retention/CFU-growth than MST. Furthermore, with or without lithium/boron/glycine-betaine, a higher percentage of cells always remained metabolically active, compared with what percentage formed single colonies. SMMA_5, compared with other Paracoccus, contained 335 unique genes: of these, 186 encoded hypothetical proteins, and 83 belonged to orthology groups, which again corresponded mostly to DNA replication/recombination/repair, transcription, secondary metabolism, and inorganic ion transport/metabolism. The SMMA_5 genome was relatively enriched in cell wall/membrane/envelope biogenesis, and amino acid metabolism. SMMA_5 and SMMA_5_TC mutually possessed 43 nucleotide polymorphisms, of which 18 were in protein-coding genes with 13 nonsynonymous and seven radical amino acid replacements. Such biochemical and biophysical mechanisms could be involved in thermal stress mitigation which streamline the cells' energy and resources toward system-maintenance and macromolecule-stabilization, thereby relinquishing cell-division for cell-viability. Thermal conditioning apparently helped inherit those potential metabolic states which are crucial for cell-system maintenance, while environmental solutes augmented the indigenous stability-conferring mechanisms. IMPORTANCE For a holistic understanding of microbial life's high-temperature adaptation, it is imperative to explore the biology of the phylogenetic relatives of mesophilic bacteria which get stochastically introduced to geographically and geologically diverse hot spring systems by local geodynamic forces. Here, in vitro endurance of high heat up to the extent of growth under special (habitat-inspired) conditions was discovered in a hot-spring-dwelling phylogenetic relative of the mesophilic Paracoccus species. Thermal conditioning, extreme oligotrophy, metabolic deceleration, presence of certain habitat-specific inorganic/organic solutes, and potential genomic specializations were found to be the major enablers of this conditional (acquired) thermophilicity. Feasibility of such phenomena across the taxonomic spectrum can well be paradigm changing for the established scopes of microbial adaptation to the physicochemical extremes. Applications of conditional thermophilicity in microbial process biotechnology may be far reaching and multifaceted.

Glycine-betaine ionic liquid analogues as novel phase-forming components of aqueous biphasic systems

Given the biotechnology advances observed in recent years in terms of upstream, the development of effective downstream processes becomes mandatory to decrease the associated costs of biotechnological-based products. Although a large interest has been devoted to ionic-liquid-based aqueous biphasic systems (IL-based ABS) as tailored separation platforms, imidazolium-based ILs have been the preferred choice as phase-forming agents. To overcome some toxicity and biodegradability issues associated to imidazolium-based ILs, novel ABS composed of ILs analogues of glycine-betaine (AGB-ILs) are here proposed and investigated. Five AGB-ILs were synthesized, characterized in terms of ecotoxicity, and applied toward the development of novel ABS formed with Na₂ SO₄ . Three commercial ILs were also investigated for comparison purposes. The respective ABS ternary phase diagrams, as well as the tie-lines and tie-line lengths, were determined at 25°C. Finally, their performance as extraction strategies was evaluated with five amino acids (L-tryptophan, L-phenylalanine, D-phenylalanine, L-tyrosine and L-3,4-dihydroxyphenylalanine/L-dopa). In all studied systems amino acids preferentially migrate to the IL-rich phase, and with AGB-ILs, the amino acid extraction efficiencies to the IL-rich phase range between 65% and 100%, obtained in a single-step. Furthermore, the studied AGB-ILs display a higher ability to form ABS and to extract amino acids than ABS composed of more traditional and commercial ILs. In summary, novel ABS composed of AGB-ILs can be formed and used as separation routes of value-added compounds of biotechnological interest. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 2018 © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1205-1212, 2018.

1H-NMR-Based Endometabolome Profiles of Burkholderia cenocepacia Clonal Variants Retrieved from a Cystic Fibrosis Patient during Chronic Infection

During cystic fibrosis (CF) chronic lung infections, bacteria of the Burkholderia cepacia complex (Bcc) are exposed for several years to a stressful and changing environment. These environmental challenges results in genetic changes of the initial infecting strain with the consequent diversification of genotypes and phenotypes. The exploitation of functional and comparative genomic approaches has suggested that such diversification is associated with massive metabolic remodeling but these alterations are poorly understood. In the present work, we have explored a high resolution ¹H-NMR-based metabolomic approach coupled to multivariate analysis to compare the endometabolome of three B. cenocepacia clonal variants retrieved from a CF patient from the onset of infection (IST439) until death with cepacia syndrome after 3.5 years (IST4113 and IST4134), to complement former proteomic and transcriptomic analyses. A fourth clonal variant (IST4129) retrieved from the same CF patient when the clinical condition worsened during the last months of life, was also examined since it was found to lack the third replicon. The metabolomic profiles obtained, based on the complete ¹H-NMR spectra, highlight the separation of the four clonal variants examined, the most distinct profile corresponding to IST4129. Results indicate a variable content of several amino acids in the different isolates examined and suggest that glycolysis and the glyoxylate shunt are favored in late variants. Moreover, the concentration of two metabolites with demonstrated cellular protective functions against stress, glycine-betaine and trehalose, is different in the different isolates examined. However, no clear correlation could be established between their content and stress tolerance. For example, IST4113, previously found to be the most resistant variant to antimicrobials of different classes, exhibits low levels of trehalose and glycine-betaine but the highest resistance to heat and oxidative stress. Also, IST4129, with a high level of glycine-betaine but lacking the third replicon, previously associated with stress resistance and virulence, exhibits the highest susceptibility to all the stresses tested. Taken together, results from this study provide insights into the metabolic diversification of B. cenocepacia clonal variants during long-term infection of the CF airways.