Evaluation of the cytotoxicity and interaction of lead with lead resistant bacterium Acinetobacter junii Pb1

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

Flow Cytometric Investigation of Salinicola halophilus S28 Physiological Response Provides Solid Evidence for Its Uncommon and High Ability to Face Salt-Stress Conditions

In a previous work, some bacterial strains isolated from the Saline di Tarquinia marine salterns (Viterbo, Italy) showed very unusual growth profiles in relation to temperature and salinity variations when grown in solid media. In particular, Salinicola halophilus S28 showed optimal or suboptimal growth in a very wide range of NaCl concentrations, suggesting a great coping ability with salinity variations. These intriguing outcomes did not fit with the general Salinicola halophilus description as a moderately halophilic species. Therefore, this study profiles the actual physiological status of S28 cells subjected to different NaCl concentrations to provide evidence for the actual coping ability of strain S28 with broad salinity variations. Flow cytometry was selected as the evaluation method to study the physiological status of bacterial cells subjected to different salinity levels, monitoring the strain response at different growth phases over 72 h. Strain S28 showed maximal growth at 8% NaCl; however, it grew very well with no statistically significant differences at all salinity conditions (4–24% NaCl). Flow cytometric results provided clear evidence of its actual and strong ability to face increasing salinity, revealing a good physiological response up to 24% of NaCl. In addition, strain S28 showed very similar cell physiological status at all salinity levels, as also indicated by the flat growth profile revealed in the range of 4–24% NaCl. This is the first study regarding the physiological response during the growth of halophilic bacteria under different conditions of salinity via flow cytometry. This technique represents an effective tool for the investigation of the physiological status of each cell, even if it is somehow underrated and underused by microbiologists for this purpose.

Uncovering the phytochemicals of root exudates and extracts of lead (Pb) tolerant Chrysopogon zizanioides (L.) Roberty in response to lead contamination and their effect on the chemotactic behavior of rhizospheric bacteria

The chemical composition of root exudates and root extracts from Chrysopogon zizanioides (L.) Roberty cv KS-1 was determined in the presence of lead [Pb(II)]. Hitherto, no information is available in the literature concerning the phytochemical components of root exudates of C. zizanioides. Significantly higher concentrations of total carbohydrates (26.75 and 42.62% in root exudates and root extract, respectively), reducing sugars (21.46 and 56.11% in root exudates and root extract, respectively), total proteins (9.22 and 23.70% in root exudates and root extract, respectively), total phenolic acids (14.69 and 8.33% in root exudates and root extract, respectively), total flavonoids (14.30 and 12.28% in root exudates and root extract, respectively), and total alkaloids (12.48 and 7.96% in root exudates and root extract, respectively) were observed in samples from plants growing under Pb(II) stress in comparison to the respective controls. GC-MS profiling showed the presence of a diverse group of compounds in root exudates and extracts, including terpenes, alkaloids, flavonoids, carotenoids, plant hormones, carboxylic/organic acids, and fatty acids. Among the detected compounds, many have an important role in plant development, regulating rhizosphere microbiota and allelopathy. Furthermore, the results indicated that C. zizanioides exudates possess a chemotactic response for rhizospheric bacterial strains Bacillus licheniformis, Bacillus subtilis, and Acinetobacter junii Pb1.

Quorum Quenching Strains Isolated from the Microbiota of Sea Anemones and Holothurians Attenuate Vibriocorallilyticus Virulence Factors and Reduce Mortality in Artemiasalina

Interference with quorum-sensing (QS) intercellular communication systems by the enzymatic disruption of N-acylhomoserine lactones (AHLs) in Gram-negative bacteria has become a promising strategy to fight bacterial infections. In this study, seven strains previously isolated from marine invertebrates and selected for their ability to degrade C6 and C10-HSL, were identified as Acinetobacter junii, Ruegeria atlantica, Microbulbifer echini, Reinheimera aquimaris, and Pseudomonas sihuiensis. AHL-degrading activity against a wide range of synthetic AHLs were identified by using an agar well diffusion assay and Agrobacterium tumefaciens NTL4 and Chromobacterium violaceum CV026 and VIR07 as biosensors. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis indicated that this activity was not due to an AHL lactonase. All the strains degraded Vibrio coralliilyticus AHLs in coculture experiments, while some strains reduced or abolished the production of virulence factors. In vivo assays showed that strains M3-111 and M3-127 reduced this pathogen’s virulence and increased the survival rate of Artemia salina up to 3-fold, indicating its potential use for biotechnological purposes. To our knowledge, this is the first study to describe AHL-degrading activities in some of these marine species. These findings highlight that the microbiota associated with marine invertebrates constitute an important underexplored source of biological valuable compounds.

Reduction of Hexavalent Chromium [Cr(VI)] by Heavy Metal Tolerant Bacterium Alkalihalobacillus clausii CRA1 and Its Toxicity Assessment Through Flow Cytometry

A chromate-resistant bacterial strain was isolated from tannery effluent; based on morphological, biochemical, and 16S rRNA gene sequencing, it was identified as Alkalihalobacillus clausii and designated A. clausii CRA1. It was found to be halophilic, alkaliphilic, and resistant to multiple heavy metals like Cr(VI), Cd(II), As(II), Pb(II), Ni(II), Hg(II), Cu(II), Zn(II), and Fe(II). The strain was found to reduce 72% of chromate in 6 days in Cr(VI) spiked Luria Bertani medium with unaffected bacterial growth at an initial C(VI) concentration of 50 mg L^-1. Chromate reductase activity of culture supernatant (cultivated in LB broth) and cell lysate of the bacterium was found to be 23 and 43U, where 1U is µmol of Cr(VI) reduced/min/mg protein. Flow cytometry studies revealed that no significant effect of Cr(VI) on cell viability was observed till 12 h of exposure at 100, 200, 400 mg L^-1 concentrations, indicated by non-significant cell death (propidium iodide positive cells). However, at 800 and 1000 mg L^-1 Cr(VI) concentration, toxicity (cell death) was observed after 12 h of exposure. FACs studies also indicated that exposure to Cr(VI) increases cell size and cell granularity, which was also confirmed in SEM and TEM images of Cr(VI) treated cells. The presence of Cr(III) species in EDX spectra of Cr(VI) treated cells confirms that reduction of Cr(VI) to Cr(III) is the primary mechanism of Cr(VI) removal by the bacterium. Therefore, the bacterium A. clausii has potential for application in chromate removal from industrial waste effluents.

Identification of lead-resistant rhizobacteria of Carthamus tinctorius and their effects on lead absorption of Sunflower

AIMS

Using rhizobacteria as plant growth-promoting agents for improving heavy-metal phytoremediation processes in contaminated soil has attracted a lot of attention mainly because of their eco-friendliness. The aim of this study was the evaluation of lead phytoremediation by Carthamus tinctorius improved with the isolated and molecularly identified lead-resistant rhizobacteria.

METHODS AND RESULTS

Rhizobacteria were isolated from C. tinctorius root and was identified using macroscopic and microscopic characteristics, biochemical testing and PCR. Then, the indole acetic acid production and phosphate-solubilizing activity were determined. Finally, the amount of lead in the plant was measured by atomic absorption method. Five strains of Bacillus cereus, Bacillus muralis, Bacillus sp., Pseudomonas fluorescens and Brevibacterium frigoritolerans with the ability of mineral phosphate solubilizing, high levels of indole acetic acid production and resistance to lead were isolated from the rhizosphere of C. tinctorius. The amount of produced indole acetic acid and the level of phosphate solubilizing by the isolates were 7.1-69.54 µg ml^-1 and 91-147.3 µg ml^-1 respectively. Lead assimilation in aerial part of safflower ranged from 925 to 2175 ppm. P. fluorescens and B. cereus strains had the highest effect on Lead assimilation with 2175 and 1862 ppm respectively.

CONCLUSIONS

The results showed that different bacterial treatments influenced the rate of lead absorption by C. tinctorius exposed to lead stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

Use of rhizosphere isolates of C. tinctorius can improve phytoremediation capability and lead absorption in lead-contaminated soil.

Functional consequences of lead and mercury exposomes in the heart

Lead and mercury are heavy metals that are highly toxic to life forms. There are no known physiological processes that require them, and they do not have a particular threshold concentration to produce biologic damage. They are non-biodegradable, and they slowly accumulate in the environment in a dynamic equilibrium between air, water, soil, food, and living organisms. Their accumulation in the environment has been increasing over time, because they were not banned from use in anthropogenic industrial production. In their +2 cationic state they are powerful oxidizing agents with the ability to interfere significantly with processes that require specific divalent cations. Acute or chronic exposure to lead and mercury can produce multisystemic damage, especially in the developing nervous systems of children and fetuses, resulting in variety of neurological consequences. They can also affect the cardiovascular system and especially the heart, either directly through their action on cardiomyocytes or indirectly through their effects on innervation, humoral responses or blood vessel alterations. For example, heart function modified by these heavy metals are heart rate, contraction, excitability, and rhythm. Some cardiac molecular targets have been identified and characterized. The direct mechanisms of damage of these heavy metals on heart function are discussed. We conclude that exposome to these heavy metals, should be considered as a major relevant risk factor for cardiac diseases.

Antiviral activity of sulfated polysaccharides from marine algae and its application in combating COVID-19: Mini review

Marine-derived sulfated polysaccharides possess various antiviral activities against a broad range of enveloped and non-enveloped viruses. It has become the potential source of antiviral drugs for pharmaceutical development. In this review, we will discuss the different types of sulfated polysaccharides and their structural classification. Some of the major sulfated polysaccharides with potent antiviral activity, including carrageenan, agar, ulvan, fucoidan, and alginates, are considered in this review. The mechanism of these sulfated polysaccharides in inhibiting the different stages of the viral infection process inside the host cell is also demonstrated. It involves blocking the initial entry of the virus or inhibiting its transcription and translation by modulating the immune response of the host cell. In addition, we explore the potential of sulfated polysaccharides as antiviral agents in preventing recent Corona Virus Disease-2019 (COVID-19).

Cyanobacterial Extracellular Polymeric Substances for Heavy Metal Removal: A Mini Review

Heavy metals from various natural and anthropogenic sources are becoming a chief threat to the aquatic system owing to their toxic and lethal effect. The treatment of such contaminated wastewater is one of the prime concerns in this field. For decades, a huge array of innovative biosorbents is used for heavy metal removal. Though extensive microbes and their biomolecules have been experimented and have showed great potential but most of them have failed to have the substantial breakthrough for the practical application. The present review emphasis on the potential utilization of the cyanobacteria for the heavy metal removal along with the toxic effect imposed by the pollutant. Furthermore, the effect of significant parameters, plausible mechanistic insights of the heavy metal toxicity imposed onto the cyanobacteria is also discussed in detail. The role of extrapolymeric substances and metallothionein secreted by the microbes are also elaborated. The review was evident that the cyanobacterial species have a huge potential towards the heavy metal removal from the aqueous system ranging from very low to very high concentrations.

Biodegradation of Total Petroleum Hydrocarbons in Soil: Isolation and Characterization of Bacterial Strains from Oil Contaminated Soil

In this study, we isolated seven strains (termed BY1–7) from polluted soil at an oil station and evaluated their abilities to degrade total petroleum hydrocarbons (TPHs). Following 16 rRNA sequence analysis, the strains were identified as belonging to the genera Bacillus, Acinetobacter, Sphingobium, Rhodococcus, and Pseudomonas, respectively. Growth characterization studies indicated that the optimal growth conditions for the majority of the strains was at 30 °C, with a pH value of approximately 7. Under these conditions, the strains showed a high TPH removal efficiency (50%) after incubation in beef extract peptone medium for seven days. Additionally, we investigated the effect of different growth media on growth impact factors that could potentially affect the strains’ biodegradation rates. Our results suggest a potential application for these strains to facilitate the biodegradation of TPH-contaminated soil.

Phosphate microbial mineralization consolidation of waste incineration fly ash and removal of lead ions

This paper proposes a green environment-friendly Bacillus subtilis to mineralize and consolidate waste incineration fly ash and heavy metal cations, and there is no harmful by-product in the mineralization process. Different phosphate products can be prepared, and are more stable than the microbially-induced carbonate precipitation (MICP) in nature. Typical heavy metal oxides were mainly PbO, ZnO, CdO, NiO, CuO and Cr₂O₃ in the chemical composition of waste incineration fly ash. Microstructure and chemical composition of waste incineration fly ash before and after treatment were characterized by powder X-ray diffraction (XRD) analysis and scanning electron microscopy. Scanning electron microscopy (SEM) images showed that the morphology of the Bacillus subtilis was mainly a rod-like structure. The optimal hydrolysis dosage of the organic phosphate monoester sodium salt was 0.2mol in the bacterial solution (1L, 20 g/L). The optimum required mass of the bacterial powder was 15 g/kg in treatment process of the waste incineration fly ash. The initial concentration of lead ions was 40.28 mg/L in waste incineration fly ash solution. After the optimum dosage treatment, the removal efficiency of lead ions was 78.15%, 79.64%, 77.70% and 80.14% when curing time was 1, 2, 4 and 6d, respectively. The waste incineration fly ash had a Shore hardness of 22 after the optimum amount of bacterial liquid treatment. Results of wind erosion test showed that the wind erosion rate of waste incineration fly ash was 2.6, 0, 0, 0, 0 and 0 g/h when blank group, deionized water, 100, 200, 300 and 400 mL of bacterial solutions treated, respectively. The bio-mineralization method provides an approach for the safe disposal of heavy metals in the contaminated areas of tailings, electroplating sewage, waste incineration plants, and so on.

Novel waste-derived biochar from biomass gasification effluent: preparation, characterization, cost estimation, and application in polycyclic aromatic hydrocarbon biodegradation and lipid accumulation by Rhodococcus opacus

This study evaluated an enhancement of simultaneous polycyclic aromatic hydrocarbon (PAH) biodegradation and lipid accumulation by Rhodococcus opacus using biochar derived cheaply from biomass gasification effluent. The chemical, physical, morphological, thermal, and magnetic properties of the cheaply derived biochar were initially characterized employing different techniques, which indicated that the material is easy to separate, recover, and reuse for further application. Batch experiments were carried out to study biochar-aided PAH biodegradation by R. opacus clearly demonstrating its positive effect on PAH biodegradation and lipid accumulation by the bacterium utilizing the synthetic media containing 2-, 3- or 4-ring PAH compounds, at an initial concentration in the range 50-200 mg L^-1, along with 10% (w/v) inoculum. An enhancement in PAH biodegradation from 79.6 to 92.3%, 76.1 to 90.5%, 74.1 to 88.2%, and 71.6 to 82.3% for naphthalene, anthracene, phenanthrene, and fluoranthene, respectively, were attained with a corresponding lipid accumulation of 68.1%, 74.2%, 72.4%, and 63% (w/w) of cell dry weight (CDW). From contact angle measurements carried out in the study, enhancement in PAH biodegradation and lipid accumulation due to the biochar was attributed to an improved bioavailability of PAH to the degrading bacterium.