Insights into effects of salt stress on the oil-degradation capacity, cell response, and key metabolic pathways of Bacillus sp. YM1 isolated from oily food waste compost

A novel bacterial strain, Bacillus sp. YM1, was isolated from compost for the efficient degradation of oily food waste under salt stress. The strain's lipase activity, oil degradation ability, and tolerance to salt stress were evaluated in a liquid medium. Additionally, the molecular mechanisms (including key genes and functional processes) underlying the strain's salt-resistant degradation of oil were investigated based on RNA-Seq technology. The results showed that after 24 h of microbial degradation, the degradation rate of triglycerides in soybean oil was 80.23% by Bacillus sp. YM1 at a 30 g L-1 NaCl concentration. The metabolizing mechanism of long-chain triglycerides (C50-C58) by the YM1 strain, especially the biodegradation rate of triglycerides (C18:3/C18:3/C18:3), could reach 98.65%. The most substantial activity of lipase was up to 325.77 U·L-1 at a salinity of 30 g L-1 NaCl. During salt-induced stress, triacylglycerol lipase was identified as the crucial enzyme involved in oil degradation in Bacillus sp. YM1, and its synthesis was regulated by the lip gene (M5E02_13495). Bacillus sp. YM1 underwent adaptation to salt stress through various mechanisms, including the accumulation of free amino acids, betaine synthesis, regulation of intracellular Na+/K+ balance, the antioxidative response, spore formation, and germination. The key genes involved in Bacillus sp. YM1's adaptation to salt stress were responsible for the synthesis of glutamate 5-kinase, superoxide dismutase, catalase, Na+/H+ antiporter, general stress protein, and sporogenic proteins belonging to the YjcZ family. Results indicated that the isolated strain of Bacillus sp. YM1 could significantly degrade oil in a short time under salt stress. This study would introduce new salt-tolerant strains for coping with the biodegradation of oily food waste and provide gene targets for use in genetic engineering.

Pleiotropic melatonin-mediated responses on growth and cadmium phytoextraction of Brassica napus: A bioecological trial for enhancing phytoremediation of soil cadmium

Melatonin (MT) has recently gained significant scientific interest, though its mechanism of action in enhancing plant vigor, cadmium (Cd) tolerance, and Cd phytoremediation processes are poorly understood. Therefore, here we investigated the beneficial role of MT in improving growth and Cd remediation potential of rapeseed (Brassica napus). Plants, with or without MT (200 µM L^-1), were subjected to Cd stress (30 mg kg¹). Without MT, higher Cd accumulation (up to 99%) negatively affected plant growth and developmental feature as well as altered expression of several key genes (DEGs) involved in different molecular pathways of B. napus. As compared to only Cd-stressed counterparts, MT-treated plants exhibited better physiological performance as indicated by improved leaf photosynthetic and gaseous exchange processes (3-48%) followed by plant growth (up to 50%), fresh plant biomass (up to 45%), dry plant biomass (up to 32%), and growth tolerance indices (up to 50%) under Cd exposure. MT application enhanced Cd tolerance and phytoremediation capacity of B. napus by augmenting (1) Cd accumulation in plant tissues and its translocation to above-ground parts (by up to 45.0%), (2) Cd distribution in the leaf cell wall (by up to 42%), and (3) Cd detoxification by elevating phytochelatins (by up to 8%) and metallothioneins (by upto 14%) biosynthesis, in comparison to Cd-treated plants. MT played a protective role in stabilizing hydrogen peroxide and malondialdehyde levels in the tissue of the Cd-treated plants by enhancing the content of osmolytes (proline and total soluble protein) and activities of antioxidant enzymes (SOD, CAT, APX and GR). Transcriptomic analysis revealed that MT regulated 1809 differentially expressed genes (828 up and 981 down) together with 297 commonly expressed DEGs (CK vs Cd and Cd vs CdMT groups) involved in plant-pathogen interaction pathway, protein processing in the endoplasmic reticulum pathway, mitogen-activated protein kinase signaling pathway, and plant hormone signal transduction pathway which ultimately promoted plant growth and Cd remediation potential in the Cd-stressed plants. These results provide insights into the unexplored pleiotropic beneficial action of MT in enhancing in the growth and Cd phytoextraction potential of B. napus, paving the way for developing Cd-tolerant oilseed crops with higher remediation capacity as a bioecological trial for enhancing phytoremediation of hazardous toxic metals in the environment.

Melatonin enhanced oilseed rape growth and mitigated Cd stress risk: A novel trial for reducing Cd accumulation by bioenergy crops

Melatonin (M) is a pleiotropic molecule that improves plant growth and increases heavy metal tolerance. The role of M for improving plant growth and tolerance under cadmium (Cd) stress, and mitigation of Cd-induced toxicity has not yet been sufficiently examined. Therefore, here we conducted a glasshouse experiment to explore the influence of various M dosages on Cd detoxification and stress-tolerance responses of Brassica napus under high Cd content (30 mg kg^-1). The effects of M on the modulation of Cd tolerance in B. napus plants have been investigated using various growth attributes, Cd accumulation and tolerance indices, and secondary metabolic parameters. We found that Cd stress inhibited root growth (by 11.9%) as well as triggered reactive oxygen species accumulation (by 31.2%) and MDA levels (by 18.7%); however, exogenous M substantially alleviated the adverse effect of oxidative stress by decreasing levels of H₂O₂ (by 38.7%), MDA (by 13.8%) and EL (by 1.8%) in the Cd-stressed plants, as compared to the M-untreated plants (control). Interestingly, exogenous M reduced Cd accumulation in roots (∼48.2-58.3-fold), stem (∼2.9-5.0-fold) and leaves (∼4.7-6.6-fold) compared to control plants, which might be due to an M-induced defense and/or detoxification response involving a battery of antioxidants. Overall, addition of the exogenous M to the Cd-stressed plants profoundly enhanced Cd tolerance in B. napus relative to control plants. These results suggested the biostimulatory role (at the physiological and molecular level) of M in improving growth, Cd tolerance, and Cd detoxification in B. napus, which indicate the potentiality of M for green remediation of Cd contaminated soils. This green trial would provide a reference for producing renewable bioenergy crops under Cd stress in contaminated soils. However, these recommendations should be verified under field conditions and the potential mechanisms for the interaction between Cd and M should be explicitly explored.

Targeting Cd coping mechanisms for stress tolerance in Brassica napus under spiked-substrate system: from physiology to remediation perspective

Cadmium (Cd) is a prevalent, non-essential, carcinogenic, and hazardous heavy metal that reduces plant productivity and capacity of arable land area around the globe. In the present substrate-based pot study, seedlings of Brassica napus 180015 were grown equidistantly in the spiked-substrate medium for 60 days under increasing concentrations of Cd (0, 10, 20, 30, 40, 50 mg kg^-1). Following harvest, the morpho-physio-biochemical, antioxidative, and Cd-induced tolerance responses were evaluated in B. napus under an increasing Cd stress regime. Additionally, these parameters were also investigated to select the plant's threshold tolerance limit for Cd under the spiked-substrate system. B. napus showed dynamic behavior regarding morpho-physio-biochemical attributes, including agronomic features, biomass, photosynthetic pigments, relative water content under increased Cd toxicity. Cd stress-induced hydrogen peroxide (H₂O₂) production with high MDA contents and passive EL, followed by the orchestration of both enzymatic (SOD, POD, APX, CAT, and GR) and non-enzymatic antioxidants (flavonoids, TPC, TPA, proline, and total soluble protein) up to a certain limit. In addition, Cd-induced stress upregulated transcriptional levels of antioxidative enzyme SOD, POD, APX, GR, and MT encoded genes in B. napus. The increasing trend of Cd accumulation in different tissues at the highest Cd concentration was as follows: root > leaf > stem. In spiked substrate system, B. napus demonstrated improved metal extractability performance and a high potential for phyto-management of low to moderate Cd contamination, implying that this study could be used for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.Novelty statementThis study provides an insight into Cd-coping mechanisms of oilseed rape involved in alleviating toxicity and simultaneous phyto-management of increasing Cd concentration under spiked substrate system. The current study is the first scientific evidence of using a Cd-spiked soilless substrate medium. The present study will further strengthen our understanding of Cd-instigated positive responses in B. napus. Furthermore, it will provide a useful basis for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.

Microbe-EDTA mediated approach in the phytoremediation of lead-contaminated soils using maize (Zea mays L.) plants

In the current study, we investigated the potential of Cronobacter sakazakii- ethylenediaminetetraacetic acid (EDTA) assisted phytoremediation potential of Zea mays L. to remediate lead (Pb)-contaminated soils. The C. sakazakii exhibited various stress tolerance mechanisms via plant growth promoting (PGP) traits, intrinsic extracellular enzyme production and antibiotic resistance. A greenhouse experiment was conducted to examine the dual effects of plant growth promoting endophytic bacteria (PGPEB)-chelator synergy in maize plants under different Pb contaminated soil regimes. C. sakazaii-EDTA (5 mM EDTA kg^-1) complex significantly (p < 0.05) enhanced plant growth and biomass (48.91%); chlorophyll a, b and carotenoid contents (27.26%, 25.02% and 42.09%); relative water content (61.33%); proline content (63.60%); root and shoot Pb accumulation capacity (52.31% and 44.71%) in Pb contaminated soils. This may suggest the efficacy of current approach in enhancing plant tolerance capability toward Pb-uptake and phytoremediation capacity. Moreover, maize plants showed differential response to Pb availability in soil-1 (S1; Pb spiked soil, 500 mg kg^-1) and soil-2 (S2; aged-contaminated soil) under various treatments. We describe the intriguing role of C. sakazakii-EDTA-maize system for Pb decontamination which can be used as a base line to explore the proposed combinatorial approach for long-term trails under field conditions for reclamation of Pb-contaminated soils.HighlightsThe PGPEB-EDTA mediated potential of Z. mays against Pb spiked and industrial contaminated soils is noticed.Increased tolerance of Z. mays against Pb in association with C. sakazakii, and EDTA is reported first time.Enhanced accumulation of metals by Z. mays is reported under combined treatment of C. sakazakii, and EDTA.Inoculation of plants with C. sakazakii, and EDTA has positive effects on growth and accumulation of Pb by Z. mays.

Pennisetum giganteum: An emerging salt accumulating/tolerant non-conventional crop for sustainable saline agriculture and simultaneous phytoremediation

Soil salinity is a global threat to the environmental sustainability, in particular to the developing countries due to their limited resources for soil reclamation. In a greenhouse pot experiment, Pennisetum giganteum, was investigated for its tolerance to salt stress and simultaneous phytoremediation capability. 4 weeks post-germination, NaCl (10, 50, 150, 250, 350, 450 and 550 mM) and tap water (control) was applied after every 2 consecutive days for two weeks in a completely randomized design and their effects were established in the growth and physico-chemical aspects of these plants. Our results indicated that P. giganteum withstood high salt stress (with 550 mM NaCl tolerance threshold level). Interestingly, the plants grown under saline conditions had higher biomass yield when compared to the control. Furthermore, the antioxidant activity and proline content of plants under saline conditions were significantly (p < 0.05) higher than those of control plants, indicating their adaptability to high salt stress. Biochemical analysis such as chlorophyll contents, total soluble sugar, total phenol and protein contents revealed considerable differences between plants grown under higher NaCl stress compared to the control conditions. Additionally, significantly different ionic flux along with high K⁺/Na⁺ ratio was observed in plants grown under a range of saline conditions. The results obtained are therefore of value to indicate P. giganteum an eco-friendly alternate source for the phytoremediation of saline soils and may be used as base for future research on this plant. Effective strategies need to be adopted with this plant to reclaim saline-degraded as well as marginal soils.

Plant growth promotion and enhanced uptake of Cd by combinatorial application of Bacillus pumilus and EDTA on Zea mays L

In developing countries, Cd contamination is ubiquitous which limits agriculture productivity. The current study was designed to investigate the efficacy of plant-Bacillus pumilus-ethylene diamine tetraacetic acid (EDTA) and plant-microbe-chelator (PMC) synergy for enhanced plant growth and Cd-uptake potential of Zea mays in industrially contaminated and cadmium (Cd) spiked soil. A pot experiment was conducted by growing Z. mays seedlings either inoculated with B. pumilus or un-inoculated along with the application of 5 mM EDTA. Plants were exposed to two levels of Cd contamination for 45 days. An increase in Cd uptake was observed in Z. mays inoculated with B. pumilus followed by EDTA treatment as compared to non-inoculated and un-treated ones. Zea mays showed improved values with PMC approach for different growth parameters including root length (41%), shoot length (40%), fresh weight (59%), dry weight (49%), chlorophyll contents (49%), and relative water contents (30%). Higher tolerance index (117%) was observed for plants grown in soil spiked with 300 mg kg^-1 Cd (S2). PMC application markedly enhanced Cd uptake potential of Z. mays up to 12% and 68.8%, respectively, in S1 and S2 soil. While the PMC application increased Cd accumulation capacity of Z. mays by 71.2% and 52.5% in S1 and S2 soil. The calculated bioaccumulation and translocation factor revealed that Z. mays possess Cd uptake potential, and this ability can be significantly enhanced with PMC application.