Application of cuminaldehyde and ciprofloxacin for the effective control of biofilm assembly of Pseudomonas aeruginosa: A combinatorial study

Pseudomonas aeruginosa is widely associated with biofilm-mediated antibiotic resistant chronic and acute infections which constitute a persistent healthcare challenges. Addressing this threat requires exploration of novel therapeutic strategies involving the combination of natural compounds and conventional antibiotics. Hence, our study has focused on two compounds; cuminaldehyde and ciprofloxacin, which were strategically combined to target the biofilm challenge of P. aeruginosa. The minimum inhibitory concentration (MIC) of cuminaldehyde and ciprofloxacin was found to be 400 μg/mL and 0.4 μg/mL, respectively. Moreover, the fractional inhibitory concentration index (FICI = 0.62) indicated an additive interaction prevailed between cuminaldehyde and ciprofloxacin. Subsequently, sub-MIC doses of cuminaldehyde (25 μg/mL) and ciprofloxacin (0.05 μg/mL) were selected for an array of antibiofilm assays which confirmed their biofilm inhibitory potential without exhibiting any antimicrobial activity. Furthermore, selected doses of the mentioned compounds could manage biofilm on catheter surface by inhibiting and disintegrating existing biofilm. Additionally, the test combination of the mentioned compounds reduced virulence factors secretion, accumulated reactive oxygen species and increased cell-membrane permeability. Thus, the combination of cuminaldehyde and ciprofloxacin demonstrates potential in combating biofilm-associated Pseudomonal threats.

Piperine, a phytochemical prevents the biofilm city of methicillin-resistant Staphylococcus aureus: A biochemical approach to understand the underlying mechanism

Methicillin-resistant Staphylococcus aureus (MRSA), a drug-resistant human pathogen causes several nosocomial as well as community-acquired infections involving biofilm machinery. Hence, it has gained a wide interest within the scientific community to impede biofilm-induced MRSA-associated health complications. The current study focuses on the utilization of a natural bioactive compound called piperine to control the biofilm development of MRSA. Quantitative assessments like crystal violet, total protein recovery, and fluorescein-di-acetate (FDA) hydrolysis assays, demonstrated that piperine (8 and 16 μg/mL) could effectively compromise the biofilm formation of MRSA. Light and scanning electron microscopic image analysis confirmed the same. Further investigation revealed that piperine could reduce extracellular polysaccharide production by down-regulating the expression of icaA gene. Besides, piperine could reduce the cell-surface hydrophobicity of MRSA, a crucial factor of biofilm formation. Moreover, the introduction of piperine could interfere with microbial motility indicating the interaction of piperine with the quorum-sensing components. A molecular dynamics study showed a stable binding between piperine and AgrA protein (regulator of quorum sensing) suggesting the possible meddling of piperine in quorum-sensing of MRSA. Additionally, the exposure to piperine led to the accumulation of intracellular reactive oxygen species (ROS) and potentially heightened cell membrane permeability in inhibiting microbial biofilm formation. Besides, piperine could reduce the secretion of diverse virulence factors from MRSA. Further exploration revealed that piperine interacted with extracellular DNA (e-DNA), causing disintegration by weakening the biofilm architecture. Conclusively, this study suggests that piperine could be a potential antibiofilm molecule against MRSA-associated biofilm infections.

Cuminaldehyde and Tobramycin Forestall the Biofilm Threats of Staphylococcus aureus: A Combinatorial Strategy to Evade the Biofilm Challenges

Staphylococcus aureus, an opportunistic Gram-positive pathogen, is known for causing various infections in humans, primarily by forming biofilms. The biofilm-induced antibiotic resistance has been considered a significant medical threat. Combinatorial therapy has been considered a reliable approach to combat antibiotic resistance by using multiple antimicrobial agents simultaneously, targeting bacteria through different mechanisms of action. To this end, we examined the effects of two molecules, cuminaldehyde (a natural compound) and tobramycin (an antibiotic), individually and in combination, against staphylococcal biofilm. Our experimental observations demonstrated that cuminaldehyde (20 μg/mL) in combination with tobramycin (0.05 μg/mL) exhibited efficient reduction in biofilm formation compared to their individual treatments (p < 0.01). Additionally, the combination showed an additive interaction (fractional inhibitory concentration value 0.66) against S. aureus. Further analysis revealed that the effective combination accelerated the buildup of reactive oxygen species (ROS) and increased the membrane permeability of the bacteria. Our findings also specified that the cuminaldehyde in combination with tobramycin efficiently reduced biofilm-associated pathogenicity factors of S. aureus, including fibrinogen clumping ability, hemolysis property, and staphyloxanthin production. The selected concentrations of tobramycin and cuminaldehyde demonstrated promising activity against the biofilm development of S. aureus on catheter models without exerting antimicrobial effects. In conclusion, the combination of tobramycin and cuminaldehyde presented a successful strategy for combating staphylococcal biofilm-related healthcare threats. This combinatorial approach holds the potential for controlling biofilm-associated infections caused by S. aureus.

Piperine, a Plant Alkaloid, Exhibits Efficient Disintegration of the Pre-existing Biofilm of Staphylococcus aureus: a Step Towards Effective Management of Biofilm Threats

Staphylococcus aureus causes a range of chronic infections in humans by exploiting its biofilm machinery and drug-tolerance property. Although several strategies have been proposed to eradicate biofilm-linked issues, here, we have explored whether piperine, a bioactive plant alkaloid, can disintegrate an already existing Staphylococcal biofilm. Towards this direction, the cells of S. aureus were allowed to develop biofilm first followed by treatment with the test concentrations (8 and 16 µg/mL) of piperine. In this connection, several assays such as total protein recovery assay, crystal violet assay, extracellular polymeric substances (EPS) measurement assay, fluorescein diacetate hydrolysis assay, and fluorescence microscopic image analysis confirmed the biofilm-disintegrating property of piperine against S. aureus. Piperine reduced the cellular auto-aggregation by decreasing the cell surface hydrophobicity. On further investigation, we observed that piperine could down regulate the dltA gene expression that might reduce the cell surface hydrophobicity of S. aureus. It was also observed that the piperine-induced accumulation of reactive oxygen species (ROS) could enhance biofilm disintegration by decreasing the cell surface hydrophobicity of the test organism. Together, all the observations suggested that piperine could be used as a potential molecule for the effective management of the pre-existing biofilm of S. aureus.

Combinatorial application of cuminaldehyde and gentamicin shows enhanced antimicrobial and antibiofilm action on Pseudomonas aeruginosa

The emergence of biofilm-induced drug tolerance poses a critical challenge to public healthcare management. Pseudomonas aeruginosa, a gram-negative opportunistic bacterium, is involved in various biofilm-associated infections in human hosts. Towards this direction, in the present study, a combinatorial approach has been explored as it is a demonstrably effective strategy for managing microbial infections. Thus, P. aeruginosa has been treated with cuminaldehyde (a naturally occurring phytochemical) and gentamicin (an aminoglycoside antibiotic) in connection to the effective management of the biofilm challenges. It was also observed that the test molecules could show increased antimicrobial activity against P. aeruginosa. A fractional inhibitory concentration index (FICI) of 0.65 suggested an additive interaction between cuminaldehyde and gentamicin. Besides, a series of experiments such as crystal violet assay, estimation of extracellular polymeric substance (EPS), and microscopic images indicated that an enhanced antibiofilm activity was obtained when the selected compounds were applied together on P. aeruginosa. Furthermore, the combination of the selected compounds was found to reduce the secretion of virulence factors from P. aeruginosa. Taken together, this study suggested that the combinatorial application of cuminaldehyde and gentamicin could be considered an effective approach towards the control of biofilm-linked infections caused by P. aeruginosa.

1, 4-naphthoquinone efficiently facilitates the disintegration of pre-existing biofilm of Staphylococcus aureus through eDNA intercalation

1, 4-naphthoquinone, a plant-based quinone derivative, has gained much attention for its effectiveness against several biofilm-linked diseases. The biofilm inhibitory effect of 1, 4-naphthoquinone against Staphylococcus aureus has already been reported in our previous study. We observed that the extracellular DNA (eDNA) could play an important role in holding the structural integrity of the biofilm. Hence, in this study, efforts have been directed to examine the possible interactions between 1, 4-naphthoquinone and DNA. An in silico analysis indicated that 1, 4-naphthoquinone could interact with DNA through intercalation. To validate the same, UV-Vis spectrophotometric analysis was performed in which a hypochromic shift was observed when the said molecule was titrated with calf-thymus DNA (CT-DNA). Thermal denaturation studies revealed a change of 8℃ in the melting temperature (Tm) of CT-DNA when complexed with 1, 4-naphthoquinone. The isothermal calorimetric titration (ITC) assay revealed a spontaneous intercalation between CT-DNA and 1, 4-naphthoquinone with a binding constant of 0.95 ± 0.12 × 108. Furthermore, DNA was run through an agarose gel electrophoresis with a fixed concentration of ethidium bromide and increasing concentrations of 1, 4-naphthoquinone. The result showed that the intensity of ethidium bromide-stained DNA got reduced concomitantly with the gradual increase of 1, 4-naphthoquinone suggesting its intercalating nature. To gain further confidence, the pre-existing biofilm was challenged with ethidium bromide wherein we observed that it could also show biofilm disintegration. Therefore, the results suggested that 1, 4-naphthoquinone could exhibit disintegration of the pre-existing biofilm of Staphylococcus aureus through eDNA intercalation.

The combinatorial applications of 1,4-naphthoquinone and tryptophan inhibit the biofilm formation of Staphylococcus aureus

Microorganisms embedded within an extracellular polymeric matrix are known as biofilm. The extensive use of antibiotics to overcome the biofilm-linked challenges has led to the emergence of multidrug-resistant strains. Staphylococcus aureus is one such nosocomial pathogen that is known to cause biofilm-linked infections. Thus, novel strategies have been adopted in this study to inhibit the biofilm formation of S. aureus. Two natural compounds, namely, 1,4-naphthoquinone (a quinone derivative) and tryptophan (aromatic amino acid), have been chosen as they could independently show efficient antibiofilm activity. To enhance the antibiofilm potential, the two compounds were combined and tested against the same organism. Several experiments like crystal violet (CV) assay, protein estimation, extracellular polymeric substance (EPS) extraction, and estimation of metabolic activity confirmed that the combination of the two compounds could significantly inhibit the biofilm formation of S. aureus. To comprehend the underlying mechanism, efforts were further directed to understand whether the two compounds could inhibit biofilm formation by compromising the cell surface hydrophobicity of the bacteria. The results revealed that the cell surface hydrophobicity got reduced by ~ 49% when the compounds were applied together. Thus, the combinations could show enhanced antibiofilm activity by attenuating cell surface hydrophobicity. Further studies revealed that the selected concentrations of the compounds could disintegrate (~ 70%) the pre-existing biofilm of the test bacteria without showing any antimicrobial activity. Hence, the combined application of tryptophan and 1,4-naphthoquinone could be used to inhibit the biofilm threats of S. aureus.

Synergistic interaction of cuminaldehyde and tobramycin: a potential strategy for the efficient management of biofilm caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic pathogen, has been found to cause several chronic and acute infections in human. Moreover, it often shows drug-tolerance and poses a severe threat to public healthcare through biofilm formation. In this scenario, two molecules, namely, cuminaldehyde and tobramycin, were used separately and in combination for the efficient management of biofilm challenge. The minimum inhibitory concentration (MIC) of cuminaldehyde and tobramycin was found to be 150 µg/mL and 1 µg/mL, respectively, against Pseudomonas aeruginosa. The checkerboard assay revealed that the fractional inhibitory concentration (FIC) index of cuminaldehyde and tobramycin was 0.36 suggesting a synergistic association between them. The sub-MIC dose of cuminaldehyde (60 µg/mL) or tobramycin (0.06 µg/mL) individually did not show any effect on the microbial growth curve. However, the same combinations could affect microbial growth curve of Pseudomonas aeruginosa efficiently. In connection to biofilm management, it was observed that the synergistic interaction between cuminaldehyde and tobramycin could inhibit biofilm formation more efficiently than their single use (p < 0.01). Further investigation revealed that the combinations of cuminaldehyde and tobramycin could generate reactive oxygen species (ROS) that resulted in the increase of membrane permeability of bacterial cells leading to the efficient inhibition of microbial biofilm formation. Besides, the synergistic interaction between cuminaldehyde (20 µg/mL) and tobramycin (0.03 µg/mL) also showed significant biofilm dispersal of the test microorganism (p < 0.01). Hence, the results suggested that synergistic action of cuminaldehyde and tobramycin could be applied for the efficient management of microbial biofilm.

Piperine Exhibits Potential Antibiofilm Activity Against Pseudomonas aeruginosa by Accumulating Reactive Oxygen Species, Affecting Cell Surface Hydrophobicity and Quorum Sensing

Gram-positive and Gram-negative bacteria often develop biofilm through different mechanisms in promoting pathogenicity. Hence, the antibiofilm molecule needs to be examined separately on both organisms to manage the biofilm threat. Since the antibiofilm activity of piperine against Staphylococcus aureus was already reported; here, we aimed to examine the antibiofilm activity of it against Pseudomonas aeruginosa. P. aeruginosa is an opportunistic Gram-negative pathogen that can cause several healthcare-associated infections by exploiting biofilm. Several experiments like crystal violet assay, estimation of total protein, measurement of extracellular polymeric substance, and microscopic analysis confirmed that lower concentrations (8 and 16 µg/mL) of piperine could inhibit the microbial biofilm formation considerably. Besides, it could also reduce the secretion of virulence factors from P. aeruginosa. Further investigation showed that the cell surface hydrophobicity and microbial motility of the test organism got reduced under the influence of piperine. Piperine exposure was found to increase the accumulation of reactive oxygen species (ROS) that resulted in the inhibition of biofilm formation. Furthermore, the molecular simulation studies suggested that piperine could affect the quorum sensing network of P. aeruginosa. Towards this direction, we noticed that piperine treatment could decrease the expression of the quorum sensing gene (lasI) that resulted in the inhibition of biofilm formation. Besides biofilm inhibition, piperine was also found to disintegrate the pre-existing biofilm of P. aeruginosa without showing any antimicrobial property to the test organism. Thus, piperine could be used for the sustainable protection of public-healthcare by compromising the biofilm assembly of P. aeruginosa.

Serratia sp. scl1: isolation of a novel thermostable lipase producing microorganism which holds industrial importance

Lipase being a hydrolysable enzyme plays a major role in serving various purposes of the industries. Thus, it is very important to have a sustainable and efficient source of this enzyme. In this present study, several microorganisms were isolated from medicinal effluent of a pharmaceutical industry that could produce efficient lipase activity. Among these isolates, a designated strain scl1 was isolated and based on the molecular and biochemical characterisation was tentatively assigned to the genus Serratia. Preliminary studies confirmed the strain scl1 was found to exhibit the highest production of lipase at a temperature and pH of 35 °C and 7, respectively under the incubation for 48 h. Further, the lipase activity was measured by following spectrophotometric method using pNPP as the substrate in which the Km and Vmax of the crude enzyme was found to be 3.349 × 10^-3 M and 5.68 × 10^-1 unit/mL, respectively. The extracellular crude lipase was found to show a temperature and pH optima of 75 °C and 8, respectively which gave a strong indication that the enzyme appeared to be highly thermostable. This study revealed the strain scl1 is able to produce a thermostable lipase which can meet the needs of the modern-day industrialization techniques. However, more work is required to purify the enzyme and get it ready for commercial applications.

Identification of a novel quinoline-based UV-protective pigment from a psychrotrophic Arctic bacterium

AIMS

Psychrotrophs are extremophilic microorganisms that grow optimally in low temperature having many unique bioactive molecules of biotechnological applications. In this study we characterized a pigment from an arctic bacterium with protective activity towards UV exposure.

METHODS AND RESULTS

The present research reports isolation and characterization of a psychrotrophic bacteria, RSAP2, from the soil sample of NyAlesund (78°56"N, 11°54"E), Svalbard, Norway. The strain showed closest 16S rRNA gene sequence similarity (99.9%) with Kocuria indica NIO-1021. RSAP2 is a Gram-positive, coccoid aerobe which produces a yellow pigment. The optimal parameters for pigment production while grown in LB medium were 3% (w/v) NaCl and 4 days of incubation of the culture at 20°C and pH 9 with shaking (180 rpm). The pigment was extracted in methanol and acetone (2:1) and further purified through column chromatography. It was characterized by mass spectrometry, UV-Visible, fluorescence, IR, ¹ H NMR, ¹³ C NMR spectroscopy and CHNS/O -analysis. The pigment has a molecular weight of about 258 daltons and the molecular formula was determined as C₁₅ H₁₈ N₂ O₂ and is a quinoline derivative. We show that the pigment can protect E. coli against UV-mediated mutagenesis. We further demonstrate that the pigment displays a significant antimicrobial effect and in sublethal concentrations it impairs biofilm formation ability of the model organism Staphylococcus aureus.

CONCLUSIONS

The pigment of a psychrotrophic Arctic bacterium, most likely a strain of K. indica, was purified and its chemical structure was determined. The quinoline-based pigment has the ability to protect live cells from UV induced damage.

SIGNIFICANCE AND IMPACT OF STUDY

Analysis and characterization of this newly isolated quinoline-based pigment is a potential candidate for future application in skin care products.

Mechanistic insight into the synergism of IL-27 and IL-28B in regulation of benzo(a)pyrene-induced lung carcinogenesis associated ROS/NF-κB/NLRP3 crosstalk

AIM

Our previous work depicted that benzo(a)pyrene (BaP)-induced lung cancer associated pulmonary redox imbalance and inflammation were effectively regulated by the combinatorial treatment of IL-27 and IL-28B. So in continuation of that finding the present study was designed to reveal the inflammation regulating signaling network modulated by IL-27 and IL-28B treatment related to BaP-induced lung cancer.

METHODS

Male Swiss albino mice were treated with BaP to induce lung tumor. Then they received individual as well as combinatorial treatment of IL-27 and IL-28B. At the end of the experimental schedule, the expression of NF-κB signaling proteins, the formation of NLRP3 inflammasome complex and IL-18; IL-17A expression in the lung were observed using Western blot and RT-PCR. The tissue and serum levels of some proinflammatory cytokines were also studied using ELISA. Mast cell density was also studied using toluidine blue staining procedure.

RESULTS

Treatment with IL-27 or IL-28B alone was successful to regulate the expression of NF-κB signaling proteins and NLRP3 complex in some cases but best attenuation was observed in animals who received both IL-27 and IL-28B in combination. In combination, it was successful in down-regulating the expression of p-ERK1/2 and in reducing the accumulation of mast cells in the lung tissue associated with BaP-induced lung carcinogenesis. The impaired PPARγ expression was also reinstated upon combination treatment.

CONCLUSION

Altogether, the treatment in combination with IL-27 and IL-28B is an effective regimen to attenuate the ROS/NF-κB/NLRP3 axis associated with BaP-induced lung carcinogenesis.

Bromelain and Olea europaea (L.) leaf extract mediated alleviation of benzo(a)pyrene induced lung cancer through Nrf2 and NFκB pathway

Lung cancer is the most aggressive as well as deadly form of cancer and most of the lung cancer cases are involved in direct smoking or passive smoking. Oxidative stress and pulmonary inflammation regulated by some transcription factors like Nrf2, NF-κB etc. play important roles in lung cancer. Various combinations of therapies are currently attributed to lung cancer treatment. A plethora of evidence supports that the consumption of plant-derived foods can prevent chronic diseases like cancer. Leaves of olive (Olea europaea L.) are rich in phenolic compounds which are having antioxidant and anti-inflammatory property. Also, bromelain from pineapple juice and from pineapple stem is a potent anti-inflammatory agent. We took a pragmatic approach to prevent carcinogenesis by supplementing the combination of these two extracts. In this study, we have tried to evaluate the amelioration of various hallmarks associated with benzo(a)pyrene-induced lung carcinogenesis upon the combinatorial treatment of ethanolic olive leaf extract (EOLE) and bromelain. We have studied the role of EOLE in amelioration of BaP-induced oxidative stress in the lung. As several reports of anticancer activity of bromelain are available, we have combined EOLE with bromelain to study their protective role against BaP-mediated lung damage. Changes in DNA integrity, LPO level in lung after EOLE-treated animal were examined. Then, we have evaluated the synergistic role of EOLE and bromelain. We have found that EOLE in combination with bromelain was able to increase the translocation of Nrf2 from cytoplasm to nucleus and decrease the translocation of NF-κB from cytoplasm to nucleus. Combination of treatment also reduced the expression of TNFα, IL-6, and some matrix metalloproteinases in lung tissue. Our findings suggest that EOLE and bromelain can synergistically reduce the BaP-induced lung carcinogenesis associated with inflammation and oxidative stress via regulating the expression of various inflammatory markers and also modulating the activity of pulmonary antioxidant armories.

Tryptophan interferes with the quorum sensing and cell surface hydrophobicity of Staphylococcus aureus: a promising approach to inhibit the biofilm development

Staphylococcus aureus, a Gram-positive bacterium has been implicated in a plethora of human infections by virtue of its biofilm-forming ability. Inhibition in microbial biofilm formation has been found to be a promising approach towards compromising microbial pathogenesis. In this regard, various natural and synthetic molecules have been explored to attenuate microbial biofilm. In this study, the role of an amino acid, L-tryptophan was examined against the biofilm-forming ability of S. aureus. The compound did not execute any antimicrobial characteristics, instead, showed strong antibiofilm activity with the highest biofilm inhibition at a concentration of 50 µg/mL. Towards understanding the underlying mechanism of the same, efforts were given to examine whether tryptophan could inhibit biofilm formation by interfering with the quorum-sensing property of S. aureus. A molecular docking analysis revealed an efficient binding between the quorum-sensing protein, AgrA, and tryptophan. Moreover, the expression of the quorum-sensing gene (agrA) got significantly reduced under the influence of the test compound. These results indicated that tryptophan could interfere with the quorum-sensing property of the organism thereby inhibiting its biofilm formation. Further study revealed that tryptophan could also reduce the cell surface hydrophobicity of S. aureus by downregulating the expression of dltA. Moreover, the tested concentrations of tryptophan did not show any significant cytotoxicity. Hence, tryptophan could be recommended as a potential antibiofilm agent to manage the biofilm-associated infections caused by S. aureus.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02924-3.

1,4-Naphthoquinone disintegrates the pre-existing biofilm of Staphylococcus aureus by accumulating reactive oxygen species

Staphylococcus aureus causes several nosocomial and community-acquired infections in human host involving biofilm. Thus, strategies need to be explored to curb biofilm threats by either inhibiting the formation of biofilm or disintegrating the pre-existing biofilm. Towards this direction, we had already revealed the biofilm inhibiting properties of 1,4-naphthoquinone against S. aureus. In this study, we have investigated whether this compound can act on pre-existing biofilm. Hence, biofilm of S. aureus was developed first and challenged further with 1,4-naphthoquinone. Experiments such as crystal violet assay, fluorescence microscopy, and estimation of total biofilm protein were performed to confirm the biofilm disintegration properties of 1,4-naphthoquinone. The disintegration of pre-existing biofilm could be attributed to the generation of reactive oxygen species (ROS). To investigate further, we observed that extracellular DNA (eDNA) was found to play an important role in holding the biofilm network as DNaseI treatment could cause an efficient disintegration of the same. To examine the effect of ROS on the eDNA, we exposed pre-existing biofilm to either 1,4-naphthoquinone or a combination of both 1,4-naphthoquinone and ascorbic acid for different length of time. Post-incubation, ROS generation and the amount of eDNA associated with the biofilm were determined wherein an inversely proportional relationship was observed between them. The result indicated that with the increase of ROS generation, the amount of eDNA associated with biofilm got decreased substantially. Thus, the results indicated that the generation of ROS could degrade the eDNA thereby compromising the integrity of biofilm which lead to the disintegration of pre-existing biofilm.

Structure-activity insights of harmine targeting DNA, ROS inducing cytotoxicity with PARP mediated apoptosis against cervical cancer, anti-biofilm formation and in vivo therapeutic study

Harmine exhibits pH dependent structural equilibrium and possesses numerous biological and pharmacological activities. Mode and mechanism of DNA binding and its cytotoxicity were studied by multiple spectroscopic, calorimetric, molecular docking and in vitro apoptotic as well as in vivo biochemical and histological studies. It exists as cationic (structure I) and decationic form (structure II) in the pH range 3.0-7.8 and 8.5-12.4, respectively, with a pK_a of 8.0. Structure I at pH 6.8 binds strongly to DNA with a cooperative mode of binding of K_iω 1.03 × 10⁶ M^-1and stoichiometry of 5.0 nucleotide phosphates. Structure I stabilized DNA by 10 °C, showed85%quenching of fluorescence intensity, perturbation in circular dichroism, partial intercalation and enthalpy driven exothermic binding. While, structure II at pH 8.5 has very weak interaction with CT DNA. Cytotoxic potencies of structure I was tested on four different cancer cell lines along with normal embryonic cell. It showed maximum cytotoxicity with GI₅₀of 20 µM, against HeLa causing several apoptotic induction abilities. Harmine exhibited G2M arrest with ROS induced effective role in PARP mediated apoptosis as well as anti-inflammatory action on HeLa cells. Harmine further presented MIC and antibiofilm activity against Staphylococcus aureus in presence of <160 and 30 µg/ml, respectively. Mice with post harmine treatment (30 mg/kg b.w., I.P.) showed maximum recovery from damaged to near normal architecture of cervical epithelial cells. This study may be of prospective use in a framework to design novel beta carboline compounds for improved therapeutic applications in future against cervical cancer. HighlightsHarmine exists in structure I and structure II forms in the pH 6.8 and 8.5with a pK_a of 8.0.Structure I at pH 6.8 binds strongly to DNA compared to structure II.Structure I showed maximum cytotoxicity with GI₅₀ of 20 µM against HeLa.ROS mediated cytotoxicitywithG2M arrest with PARP mediated apoptosis was studied.Harmine (30µg/ml) exhibited antibiofilm activity against Staphylococcus aureus.Post harmine dose (30 mg/kg b.w., I.P.) in mice showed recovery of cervical epithelial cells.Communicated by Ramaswamy H. Sarma.

Attenuation of Pseudomonas aeruginosa biofilm by thymoquinone: an individual and combinatorial study with tetrazine-capped silver nanoparticles and tryptophan

Microbial biofilm indicates a cluster of microorganisms having the capability to display drug resistance property, thereby increasing its proficiency in spreading diseases. In the present study, the antibiofilm potential of thymoquinone, a black seed-producing natural molecule, was contemplated against the biofilm formation by Pseudomonas aeruginosa. Substantial antimicrobial activity was exhibited by thymoquinone against the test organism wherein the minimum inhibitory concentration of the compound was found to be 20 μg/mL. Thereafter, an array of experiments (crystal violet staining, protein count, and microscopic observation, etc.) were carried out by considering the sub-MIC doses of thymoquinone (5 and 10 μg/mL), each of which confirmed the biofilm attenuating capacity of thymoquinone. However, these concentrations did not show any antimicrobial activity. Further explorations on understanding the underlying mechanism of the same revealed that thymoquinone accumulated reactive oxygen species (ROS) and also inhibited the expression of the quorum sensing gene (lasI) in Pseudomonas aeruginosa. Furthermore, by taking up a combinatorial approach with two other reported antibiofilm agents (tetrazine-capped silver nanoparticles and tryptophan), the antibiofilm efficiency of thymoquinone was expanded. In this regard, the highest antibiofilm activity was observed when thymoquinone, tryptophan, and tetrazine-capped silver nanoparticles were applied together against Pseudomonas aeruginosa. These combinatorial applications of antibiofilm molecules were found to accumulate ROS in cells that resulted in the inhibition of biofilm formation. Thus, the combinatorial study of these antibiofilm molecules could be applied to control biofilm threats as the tested antibiofilm molecules alone or in combinations showed negligible or very little cytotoxicity.

Isolation of a soil bacterium for remediation of polyurethane and low-density polyethylene: a promising tool towards sustainable cleanup of the environment

A soil bacterium, designated strain AKS31, was isolated on the plastic polyurethane (PUR) and based on the molecular and biochemical analysis was tentatively assigned to the genus Pseudomonas. Preliminary studies suggested that strain AKS31 had the capability of biodegrading polyurethane (PUR) and low-density polyethylene (LDPE). This observation was confirmed by the analysis of the biodegradation products. The hydrolyzed products of PUR analyzed sequentially by High-Performance Liquid Chromatography (HPLC) and Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) showed the presence of diethylene glycol suggesting the presence of an esterase. A gene that could be involved in producing an esterase-like activity (PURase gene) was identified after the amplification and sequencing of a PCR product. Fourier Transformed Infrared (FTIR) spectrophotometric analysis of AKS31-treated LDPE film revealed the incorporation of hydroxyl groups suggesting the involvement of a hydroxylase in the degradation of LDPE. It is established that plastics form microplastics and microbeads in soils which negatively impact the health of living organisms and there have been concentrated research efforts to remediate this problem. Microcosm studies revealed that when strain AKS31 was bioaugmented with soil both the polymers were degraded during which time the heterotrophic plate counts, soil respiration and soil organic carbon content increased but this was not the case with the control nonbioaugmented microcosm. The results demonstrate that the strain AKS31 may have the potential in biodegradation of PUR and LPDE present as plastic microbeads and thereby improving soil health. Further studies in this direction are warranted.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02592-9.

1,4-Naphthoquinone accumulates reactive oxygen species in Staphylococcus aureus: a promising approach towards effective management of biofilm threat

Staphylococcus aureus, a Gram-positive opportunistic microorganism, promotes pathogenicity in the human host through biofilm formation. Microorganisms associated with biofilm often exhibit drug-resistance property that poses a major threat to public healthcare. Thus, the exploration of new therapeutic approaches is the need of the hour to manage biofilm-borne infections. In the present study, efforts are put together to test the antimicrobial as well as antibiofilm activity of 1,4-naphthoquinone against Staphylococcus aureus. The result showed that the minimum bactericidal concentration (MBC) of this compound was found to be 100 µg/mL against Staphylococcus aureus. In this regard, an array of experiments (crystal violet, biofilm protein measurement, and microscopic analysis) related to biofilm assay were conducted with the sub-MBC concentrations (1/20 and 1/10 MBC) of 1,4-naphthoquinone. All the results of biofilm assay demonstrated that these tested concentrations (1/20 and 1/10 MBC) of the compound (1,4-naphthoquinone) showed a significant reduction in biofilm development by Staphylococcus aureus. Moreover, the tested concentrations (1/20 and 1/10 MBC) of the compound (1,4-naphthoquinone) were able to reduce the microbial motility of Staphylococcus aureus that might affect the development of biofilm. Further studies revealed that the treatment of 1,4-naphthoquinone to the organism was found to increase the cellular accumulation of reactive oxygen species (ROS) that resulted in the inhibition of biofilm formation by Staphylococcus aureus. Hence, it can be concluded that 1,4-naphthoquinone might be considered as a promising compound towards biofilm inhibition caused by Staphylococcus aureus.

Exploration of strategies to increase the nitrogen and phosphate content of solid waste landfill soil

Several strategies were undertaken to increase the fertility of landfill soil as rapid urbanization remarkably decreases the agricultural land, posing challenges to the fast-growing human population. Towards this direction, soil microcosms were prepared wherein the addition of nutrient or biofertilizer or the combination of both increased the soil nitrogen and phosphate content considerably. The maximum amount of nitrogen fixation and phosphate solubilization occurred in microcosm treated with biofertilizer and nutrient. To investigate the underlying cause, we observed that separate application of nutrient or biofertilizer or combined application of both increased the abundance of nitrogen-fixing and phosphate-solubilizing bacteria in the microcosms. However, the highest abundance of nitrogen-fixing and phosphate-solubilizing bacteria was spotted in a microcosm challenged with nutrient and biofertilizer together. It was detected that with increasing population of nitrogen-fixing and phosphate-solubilizing bacteria, the soil nitrogen and phosphate level also got enhanced, respectively, thus establishing a strong positive correlation between them. The microcosm treated with biofertilizer and nutrient manifested the highest degree of heterotrophic microbial growth and microbial activity than the microcosms either treated with nutrient or biofertilizer. The microcosm treated with nutrient and biofertilizer was found to exhibit the highest functional diversity compared to others. A surface plot was constructed to demonstrate the association among microbial activity, functional diversity, and the availability of soil nitrogen and phosphate content of soil. The result indicates that the combined application of nutrient and biofertilizer increases the microbial activity leading to the formation of a heterogeneous ecosystem that enhances the nitrogen and phosphate content of landfill soil considerably.

Functional diversity performs a key role in the isolation of nitrogen-fixing and phosphate-solubilizing bacteria from soil

Functional diversity covers diverse functional traits of microorganisms in an ecosystem. Thus, we hypothesized that it could play an important role in the isolation of nitrogen-fixing and phosphate-solubilizing bacteria. These bacteria have been considered as biofertilizer for sustainable agriculture development. Soils were collected from different sites of agricultural field and performed several microbiological tests in which we observed considerable differences in heterotrophic microbial abundance and microbial activities among the microcosms. Functional diversity depends on both microbial richness and evenness. Based on the results of metabolic fingerprinting of the carbon sources of BiOLOG-ECO plates, richness and evenness was measured by determining Shannon diversity index and Gini coefficient, respectively. The results showed significant differences in both microbial richness and evenness, suggesting considerable variation of functional diversity among the microcosms. Thereafter, nitrogen-fixing and phosphate-solubilizing bacteria were isolated on Burk's and Pikovskaya media, respectively. The results revealed considerable variation of both types of bacterial abundance among the microcosms. Microcosm (T2) showing the highest functional diversity houses the maximum numbers of nitrogen-fixing and phosphate-solubilizing bacteria. Similarly, the microcosm (T5) exhibiting the lowest functional diversity houses the minimum numbers of nitrogen-fixing and phosphate-solubilizing bacteria. Thus, a strong positive correlation was observed between functional diversity and both types of bacterial abundance among the soil samples. Higher richness and evenness lead to the development of increased functional diversity that facilitates to accommodate substantial numbers of nitrogen-fixing and phosphate-solubilizing bacteria in soil. Taken together, the results demonstrated that functional diversity plays an important role in the isolation of nitrogen-fixing and phosphate-solubilizing bacteria from soil.

Pre-oxidation of low-density polyethylene (LDPE) by ultraviolet light (UV) promotes enhanced degradation of LDPE in soil

Polyethylene represents nearly 64% of all the synthetic plastics produced and are mainly used for domestic and industrial applications. Their extensive use poses a serious environmental threat because of their non-biodegradable nature. Among all the polyethylene remediation strategies, in situ bioremediation happens to be the safest and efficient one. In the current study, efforts had been given to compare the extent of LDPE degradation under UV-treated and UV-untreated conditions by soil microcosm. Landfill soil was collected and UV-treated and UV-untreated LDPE were added separately to the soil following incubation under similar conditions. Electron microscopic images as well as the weight loss and the tensile strength results clearly revealed that UV-treated LDPE showed better degradation than the non-treated ones in soil. To elucidate the mechanism of this enhanced biodegradation, the bond spectra of differentially treated LDPE were analyzed by FTIR. The results obtained from bond spectra studies revealed that UV treatment increases both carbonyl and terminal double-bond index of the LDPE, thereby making it highly susceptible for microbial degradation. Moreover, incubation of UV-treated LDPE with soil favors better adherence of metabolically active and significantly higher number of microorganisms on it. Taken together, all these results demonstrate the higher microbial association and their better metabolic potential to the UV-treated LDPE that lead to enhanced degradation of the LDPE by the soil microorganisms.

Zinc oxide nanoparticle inhibits the biofilm formation of Streptococcus pneumoniae

Biofilms are structured consortia of microbial cells that grow on living and non living surfaces and surround themselves with secreted polymers. Infections with bacterial biofilms have emerged as a foremost public health concern because biofilm growing cells can be highly resistant to both antibiotics and host immune defenses. Zinc oxide nanoparticles have been reported as a potential antimicrobial agent, thus, in the current study, we have evaluated the antimicrobial as well as antibiofilm activity of zinc oxide nanoparticles against the bacterium Streptococcus pneumoniae which is a significant cause of disease. Zinc oxide nanoparticles showed strong antimicrobial activity against S. pneumoniae, with an MIC value of 40 μg/ml. Biofilm inhibition of S. pneumoniae was also evaluated by performing a series of experiments such as crystal violet assay, microscopic observation, protein count, EPS secretion etc. using sub-MIC concentrations (3, 6 and 12 µg/ml) of zinc oxide nanoparticles. The results showed that the sub-MIC doses of zinc oxide nanoparticles exhibited significant anti-biofilm activity against S. pneumoniae, with maximum biofilm attenuation found at 12 μg/ml. Taken together, the results indicate that zinc oxide nanoparticles can be considered as a potential agent for the inhibition of microbial biofilms.

Addition of Rubber to soil damages the functional diversity of soil

Rubber is a polymer of isoprene, consisting mainly of cis-1,4-polyisoprene units. The unmanageable production and its irresponsible disposal pose severe threats to environmental ecology. Therefore, the current study focuses extensively on the ill-effects of Rubber disposal on soil microbial functional diversity as it reflects the health of ecosystem by acting as a key component in ecosystem productivity. To investigate the effect of Rubber on soil microbial functional diversity, soil samples were collected from landfill sites and three different soil microcosms (Rubber treated, untreated, and sterile soil) were prepared. The soil enzymatic activity was determined by fluorescein diacetate hydrolysis followed by the determination of the microbial metabolic potential and functional diversity by average well color development and Shannon-Weaver index (H), respectively. BiOLOG ECO plates were used for determining the microbial functional diversity of the soil microcosms. Higher heterotrophic microbial count as well as higher soil microbial activity was observed in Rubber untreated soil than Rubber treated soil microcosm. The result indicated that the addition of Rubber to soil reduced soil heterotrophic microbial count and soil microbial activity considerably. Similarly, soil microbial metabolic potential as well as microbial functional diversity of soil had been decreased by the addition of Rubber gloves in it. Variation in soil microbial metabolic spectrum between Rubber treated and untreated microcosm was confirmed by multivariate analysis. Collectively, all the results demonstrated that the addition of Rubber to soil reduced the soil microbial functional diversity considerably. Therefore, it is necessary for the commission of serious steps regarding Rubber disposal and protection of the environment from serious environmental issues.

Biofertilizers: a potential approach for sustainable agriculture development

The worldwide increase in human population raises a big threat to the food security of each people as the land for agriculture is limited and even getting reduced with time. Therefore, it is essential that agricultural productivity should be enhanced significantly within the next few decades to meet the large demand of food by emerging population. Not to mention, too much dependence on chemical fertilizers for more crop productions inevitably damages both environmental ecology and human health with great severity. Exploitation of microbes as biofertilizers is considered to some extent an alternative to chemical fertilizers in agricultural sector due to their extensive potentiality in enhancing crop production and food safety. It has been observed that some microorganisms including plant growth promoting bacteria, fungi, Cyanobacteria, etc. have showed biofertilizer-like activities in the agricultural sector. Extensive works on biofertilizers have revealed their capability of providing required nutrients to the crop in sufficient amounts that resulted in the enhancement of crop yield. The present review elucidates various mechanisms that have been exerted by biofertilizers in order to promote plant growth and also provides protection against different plant pathogens. The aim of this review is to discuss the important roles and applications of biofertilizers in different sectors including agriculture, bioremediation, and ecology.

Antibiofilm activity of Parkia javanica against Pseudomonas aeruginosa: a study with fruit extract

Parkia javanicais a well-known ethno-botanical plant of the north-east region of India.

3-Amino-4-aminoximidofurazan derivatives: small molecules possessing antimicrobial and antibiofilm activity against Staphylococcus aureus and Pseudomonas aeruginosa

AIM

The therapeutic treatment of microbial infections involving biofilm becomes quite challenging because of its increasing antibiotic resistance capacities. Towards this direction, in the present study we have evaluated the antibiofilm property of synthesized 3-amino-4-aminoximidofurazan compounds having polyamine skeleton. These derivatives were synthesized by incorporating furazan and biguanide moieties.

METHODS AND RESULTS

Different 3-amino-4-aminoximidofurazan derivatives (PI1-4) were synthesized via protic acid catalysis and subsequently characterized by (1) H NMR and (13) C NMR spectra, recorded at 400 and 100 MHz respectively. We have tested the antimicrobial and antibiofilm activities of these synthetic derivatives (PI1-4) against both Staphylococcus aureus and Pseudomonas aeruginosa. The compounds so tested were also compared with standard antibiotics namely Tobramycin (Ps. aeruginosa) and Azithromycin (Staph. aureus) which were used as a positive control in all experimental sets. All these compounds (PI1-4) exhibited moderate to significant antimicrobial activities against both micro-organisms wherein compound PI3 showed maximum activity. Biofilm inhibition of both micro-organisms was then evaluated by crystal violet and safranin staining, estimation of biofilm total protein and microscopy methods using sub-MIC dose of these compounds. Results showed that all compounds executed anti biofilm activity against both Staph. aureus and Ps. aeruginosa wherein compound PI3 exhibited maximum activity. In relation with microbial biofilm inhibition, we have observed reduction in bacterial motility, proteolytic activity and secreted exo-polysaccharide (EPS) from both Staph. aureus and Ps. aeruginosa when they were grown in presence of these compounds. While addressing the issue of toxicity on host, we have observed that these molecules exhibited minimum level of R.B.C degradation.

CONCLUSION

These findings establish the antibacterial and anti biofilm properties of 3-amino-4-aminoximidofurazan derivatives (PI1-4).

SIGNIFICANCE AND IMPACT OF THE STUDY

Therefore, our current findings demonstrate that 3-amino-4-aminoximidofurazan derivatives (PI1-4) may hold promise to be effective biofilm and microbial inhibitors that may be clinically significant.

Attenuation of Pseudomonas aeruginosa biofilm formation by Vitexin: A combinatorial study with azithromycin and gentamicin

Microbial biofilm are communities of surface-adhered cells enclosed in a matrix of extracellular polymeric substances. Extensive use of antibiotics to treat biofilm associated infections has led to the emergence of multiple drug resistant strains. Pseudomonas aeruginosa is recognised as a model biofilm forming pathogenic bacterium. Vitexin, a polyphenolic group of phytochemical with antimicrobial property, has been studied for its antibiofilm potential against Pseudomonas aeruginosa in combination with azithromycin and gentamicin. Vitexin shows minimum inhibitory concentration (MIC) at 260 μg/ml. It’s antibiofilm activity was evaluated by safranin staining, protein extraction, microscopy methods, quantification of EPS and in vivo models using several sub-MIC doses. Various quorum sensing (QS) mediated phenomenon such as swarming motility, azocasein degrading protease activity, pyoverdin and pyocyanin production, LasA and LasB activity of the bacteria were also evaluated. Results showed marked attenuation in biofilm formation and QS mediated phenotype of Pseudomonas aeruginosa in presence of 110 μg/ml vitexin in combination with azithromycin and gentamicin separately. Molecular docking of vitexin with QS associated LuxR, LasA, LasI and motility related proteins showed high and reasonable binding affinity respectively. The study explores the antibiofilm potential of vitexin against P. aeruginosa which can be used as a new antibiofilm agent against microbial biofilm associated pathogenesis.

Microbial siderophores and their potential applications: a review

Siderophores are small organic molecules produced by microorganisms under iron-limiting conditions which enhance the uptake of iron to the microorganisms. In environment, the ferric form of iron is insoluble and inaccessible at physiological pH (7.35-7.40). Under this condition, microorganisms synthesize siderophores which have high affinity for ferric iron. These ferric iron-siderophore complexes are then transported to cytosol. In cytosol, the ferric iron gets reduced into ferrous iron and becomes accessible to microorganism. In recent times, siderophores have drawn much attention due to its potential roles in different fields. Siderophores have application in microbial ecology to enhance the growth of several unculturable microorganisms and can alter the microbial communities. In the field of agriculture, different types of siderophores promote the growth of several plant species and increase their yield by enhancing the Fe uptake to plants. Siderophores acts as a potential biocontrol agent against harmful phyto-pathogens and holds the ability to substitute hazardous pesticides. Heavy-metal-contaminated samples can be detoxified by applying siderophores, which explicate its role in bioremediation. Siderophores can detect the iron content in different environments, exhibiting its role as a biosensor. In the medical field, siderophore uses the "Trojan horse strategy" to form complexes with antibiotics and helps in the selective delivery of antibiotics to the antibiotic-resistant bacteria. Certain iron overload diseases for example sickle cell anemia can be treated with the help of siderophores. Other medical applications of siderophores include antimalarial activity, removal of transuranic elements from the body, and anticancer activity. The aim of this review is to discuss the important roles and applications of siderophores in different sectors including ecology, agriculture, bioremediation, biosensor, and medicine.

Selenium Nanoparticles for Stress-Resilient Fish and Livestock

The fisheries and livestock sectors capture the highest share of protein-rich animal food and demonstrate accelerated growth as an agriculture subsidiary. Environmental pollution, climate change, as well as pathogenic invasions exert increasing stress impacts that lead the productivity momentum at a crossroads. Oxidative stress is the most common form of stress phenomenon responsible for the retardation of productivity in fisheries and livestock. Essential micronutrients play a determinant role in combating oxidative stress. Selenium, one of the essential micronutrients, appears as a potent antioxidant with reduced toxicity in its nanoscale form. In the present review, different methods of synthesis and characterization of nanoscale selenium have been discussed. The functional characterization of nano-selenium in terms of its effect on growth patterns, feed digestibility, and reproductive system has been discussed to elucidate the mechanism of action. Moreover, its anti-carcinogenic and antioxidant potentiality, antimicrobial and immunomodulatory efficacy, and fatty acid reduction in liver have been deciphered as the new phenomena of nano-selenium application. Biologically synthesized nano-selenium raises hope for pharmacologically enriched, naturally stable nanoscale selenium with high ecological viability. Hence, nano-selenium can be administered with commercial feeds for improvising stress resilience and productivity of fish and livestock.

Biofilm, pathogenesis and prevention--a journey to break the wall: a review

Biofilms contain group(s) of microorganisms that are found to be associated with the biotic and abiotic surfaces. Biofilms contain either homogenous or heterogeneous populations of bacteria which remain in the matrix made up of extracellular polymeric substances secreted by constituent population of the biofilm. Biofilms can be either single or multilayered. Biofilms are an increasing issue of concern that is gaining importance with each passing day. Due to the ubiquitous nature of biofilms, it is difficult to eradicate them. It has been seen that many infectious diseases harbour biofilms of bacterial pathogens as the reservoir of persisting infections which can prove fatal at times. The presence of biofilms can be seen in diseases like endocarditis, cystic fibrosis, periodontitis, rhinosinusitis and osteomyelitis. The presence of biofilms has been mostly seen in medical implants and urinary catheters. Various signalling events including two-component signalling, extra cytoplasmic function and quorum sensing are involved in the formation of biofilms. The presence of an extracellular polymeric matrix in biofilms makes it difficult for the antimicrobials to act on them and make the bacteria tolerant to antibiotics and other drugs. The aim of this review was to discuss about the basic formation of a biofilm, various signalling cascades involved in biofilm formation, possible mechanisms of drug resistance in biofilms and recent therapeutic approaches involved in successful eradication of biofilms.

Adaptation of Pseudomonas sp. AKS2 in biofilm on low-density polyethylene surface: an effective strategy for efficient survival and polymer degradation

Background

Pseudomonas sp. AKS2 can efficiently degrade low-density polyethylene (LDPE). It has been shown that this degradation of LDPE by AKS2 is correlated to its ability to form biofilm on the polymer surface. However, the underlying mechanism of this biofilm-mediated degradation remains unclear. Since bioremediation potential of an organism is related to its adaptability in a given environment, we hypothesized that AKS2 cells undergo successful adaptation in biofilm on LDPE, which leads to higher level of LDPE degradation. To verify this, the current study investigated a number of parameters of AKS2 cells in biofilm that are known to be involved in adaptation process.

Results

Successful adaptation always develops a viable microbial population. So we examined the viability of AKS2 cells in biofilm. We observed the presence of viable population in the biofilm. To gain an insight, the growth of AKS2 cells in biofilm on LDPE at different time points was examined. Results showed a better reproductive competence and more colonization for AKS2 biofilm cells than planktonic cells, indicating the increased fitness of AKS2 biofilm cells than their planktonic counterpart. Towards understanding fitness, we determined the hydrolytic activity, different carbon source utilization potentials, functional diversity and homogeneity of AKS2 biofilm cells. Results showed increased hydrolytic activity (approximately 31%), higher metabolic potential, higher functional diversity (approximately 27%) and homogeneity for biofilm-harvested cells than planktonic cells. We also examined cellular surface hydrophobicity, which is important for cellular attachment to LDPE surface. Consistent with the above results, the cell surface hydrophobicity of biofilm-harvested AKS2 cells was found to be higher (approximately 26%) compared to that of their planktonic counterpart. All these results demonstrated the occurrence of physiological as well as structural adaptations of AKS2 cells in biofilm on LDPE surface that resulted in better attachment, better utilization of polymer and better growth of AKS2 cells, leading to the development of a stable colony on LDPE surface.

Conclusions

The present study shows that AKS2 cells in biofilm on LDPE surface undergo successful adaptation that leads to enhanced LDPE degradation, and thus, it helps us to understand the underlying mechanism of biofilm-mediated polymer degradation process by AKS2 cells.

Cell surface hydrophobicity: a key component in the degradation of polyethylene succinate by Pseudomonas sp. AKS2

AIM

Polyethylene succinate (PES) contains hydrolysable ester bonds that make it a potential substitute for polyethylene (PE) and polypropylene (PP). Towards bioremediation of PES, we have already reported that a new strain of Pseudomonas, Pseudomonas sp. AKS2, can efficiently degrade PES and hypothesized that cell surface hydrophobicity plays an important role in this degradation process. In this study, our efforts were targeted towards establishing a correlation between cell surface hydrophobicity and PES degradation.

METHODS AND RESULTS

We have manipulated cell surface hydrophobicity of AKS2 by varying concentrations of glucose and ammonium sulphate in the growth medium and subsequently examined the extent of PES degradation. We observed an increase in PES degradation by AKS2 with an increase in cell surface hydrophobicity. The increased surface hydrophobicity caused an enhanced biofilm formation on PES surface that resulted in better polymer degradation.

CONCLUSION

The current study establishes a direct correlation between cell surface hydrophobicity of an organism and its potential to degrade a nonpolar polymer like PES.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cell surface hydrophobicity manipulation can be used as an important strategy to increase bioremediation of nonpolar polymer like PES.

Low-density polyethylene degradation by Pseudomonas sp. AKS2 biofilm

Polyethylene materials are a serious environmental concern as their nondegradable nature allows them to persist in the environment. Recent studies have shown that polyethylene can be degraded by microbes at a very slow rate, whereby detectable changes are evident after several years. In the present study, we report the degradation of low-density polyethylene by Pseudomonas sp. AKS2. Unlike the previous reports, degradation by Pseudomonas sp. AKS2 is relatively fast as it can degrade 5 ± 1 % of the starting material in 45 days without prior oxidation. This degradation can be altered by agents that modulate hydrophobic interaction between polythene and the microbe. As mineral oil promotes hydrophobic interactions, it enhances bacterial attachment to the polymer surface. This enhanced attachment results in increased biofilm formation and enhanced polymer degradation. In contrast, Tween 80 reduces bacterial attachment to the polymer surface by lowering hydrophobic interactions and thereby reduces polymer degradation. Thus, this study establishes a correlation between hydrophobic interaction and polymer degradation and also relates the biofilm formation ability of bacteria to polymer degrading potential.

Bioaugmentation of polyethylene succinate-contaminated soil with Pseudomonas sp. AKS2 results in increased microbial activity and better polymer degradation

Pseudomonas sp. AKS2 isolated from soil degrades polyethylene succinate (PES) efficiently in the laboratory. However, this organism may not be able to degrade PES with similar efficiency in a natural habitat. Since in situ remediation is preferred for the effective removal of recalcitrant materials like plastic, in the current study, bioaugmentation potential of this organism was investigated. To investigate the potential of the AKS2 strain to bioaugment the PES-contaminated soil, a microcosm-based study was carried out wherein naturally attenuated, biostimulated, and AKS2-inoculated (bioaugmented) soil samples were examined for their ability to degrade PES. The results showed better degradation of PES by bioaugmented soil than other microcosms. Consistent with it, a higher number of PES-degrading organisms were found in the bioaugmented microcosm. The bioaugmented microcosm also exhibited a higher level of average well color development in BiOLOG ECO plate assay than the other two. The corresponding Shannon-Weaver index and Gini coefficient revealed a higher soil microbial diversity of bioaugmented microcosm than the others. This was further supported by community-level physiological profile of three different microcosms wherein we have observed better utilization of different carbon sources by bioaugmented microcosms. Collectively, these results demonstrate that bioaugmentation of PES-contaminated soil with AKS2 not only enhances polymer degradation but also increases microbial diversity. Bioaugmentation of soil with AKS2 enhances PES degradation without causing damage to soil ecology. Thus, Pseudomonas sp. AKS2 has the potential to be implemented as a useful tool for in situ bioremediation of PES.

Antibacterial activity of long-chain fatty alcohols against mycobacteria

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis and results in innumerable deaths across the world. The emergence of multidrug-resistant and extremely drug-resistant tuberculosis strains and its coinfection with HIV has made tuberculosis more difficult to treat. Therefore, new antimycobacterial agent(s) for both therapy and disinfection are urgently required. In this context the present study describes the antibacterial property of long-chain fatty alcohols against mycobacteria. The antimycobacterial activities of alcohols with chain length ranging from C(5) to C(13) were examined against Mycobacterium smegmatis mc(2) 155 and M. tuberculosis H(37)R(v). The best activity was found with one with a C(10) chain length. This bactericidal activity can partly be attributed to its ability to damage the robust and complex cell envelope of Mycobacteria. Moreover, our study reveals the ability of decanol to attenuate biofilm formation by M. smegmatis. This knowledge can be used to develop new therapeutics and disinfectants against mycobacteria.

Isolation of a novel Pseudomonas sp from soil that can efficiently degrade polyethylene succinate

PURPOSE

Polyethylene succinate (PES) is a biodegradable synthetic polymer and therefore widely used as a base material in plastic industry to circumvent the environmental problems related with the non-biodegradability of other polymers like polyethylene. Till date only few organisms have been reported to have the ability to degrade PES. Therefore for better management of PES-related environmental waste, the present study is targeted towards isolating mesophilic organism(s) capable of more efficient degradation of PES.

RESULTS

Strain AKS2 was isolated from soil based on survival on a selection plate wherein PES was used as sole carbon source. Ribotyping and biochemical tests revealed that AKS2 is a new strain of Pseudomonas. Scanning electron and atomic force microscopic analysis of the PES films obtained after incubation with AKS2 confirmed PES-degradation ability of AKS2, wherein an alteration in surface topology was observed. The kinetics of PES weight loss showed that AKS2 degrades PES maximally during its logarithmic growth phase at a rate of 1.65 mg/day. This degradation is mediated by esterase activity and may also involve cell-surface hydrophobicity. It has also been observed that AKS2 is able to degrade PES considerably even in the presence of glucose, which is likely to increase the bioremediation potential of this isolate.

CONCLUSION

A new strain of Pseudomonas has been isolated from soil that is able to adhere to PES and degrade this polymer efficiently. This organism has the potential to be implemented as a useful tool for bioremediation of PES-derived materials.

Isolation of a Pseudomonas aeruginosa strain from soil that can degrade polyurethane diol

Polyurethane diol (PUR-diol), a synthetic polymer, is widely used as a modifier for water-soluble resins and emulsions in wood appliances and auto coatings. Non-biodegradability of polyurethanes (PUR) and PUR-based materials poses a threat to environment that has led scientists to isolate microbes capable of degrading PUR. However, the bio-degradation of PUR-diol has not yet been reported. In this study, we report isolation of a soil bacterium that can survive using PUR-diol as sole carbon source. PUR-diol degradation by the organism was confirmed by thin layer chromatographic analysis of the conditioned medium obtained after the growth wherein a significant reduction of PUR-diol was observed compared to non-inoculated medium. To quantify the PUR-diol degradation, a sensitive assay based on High Performance Thin Layer Chromatography has been developed that showed 32% degradation of PUR-diol by the organism in 10 days. Degradation kinetics showed the maximal depletion of PUR-diol during logarithmic growth of the organism indicating a direct relation between the growth and PUR-diol degradation. Mutagenic study and GC-MS analysis revealed that esterase activity is involved in this degradation event. The ribotyping and metabolic fingerprinting analysis showed that this organism is a strain of Pseudomonous aeruginosa (P. aeruginosa). It has also been observed that this strain is able to degrade Impranil DLN™, a variety of commercially available PUR. Therefore this study identifies a new bacterium from soil that has the potential to reduce PUR-related waste burden and adds a new facet to diverse functional activities of P. aeruginosa.