Delftia Lacustris Research Articles

Laundry Isolate Delftia sp. UBM14 Capable of Biodegrading Industrially Relevant Aminophosphonates.

Phosphonates such as ethylenediaminetetra (methylenephosphonic acid) (EDTMP) and aminotris (methylenephosphonic acid) (ATMP) are used every day in water treatment processes or in household products. Their consumption is still increasing, regardless of the debates on their environmental impact. Here, the microbial characterisation and determination of the biodegradation potential of selected industrially relevant phosphonates for the isolate Delftia sp. UMB14 is reported. The opportunistic strain was isolated from a biofilm that was derived from a conventional washing machine using conventional detergents containing phosphonates. In antimicrobial susceptibility testing, the strain was only susceptible to sulfonamide, tetracycline, and chloramphenicol. Physiological and biochemical characteristics were determined using the BIOLOG EcoPlate assay. Most importantly, the strain was shown to convert D-malic acid and D-mannitol, as confirmed for strains of Delftia lacustris, and thus the new isolate could be closely related. Biodegradation tests with different phosphonates showed that the strain preferentially degrades ATMP and EDTMP but does not degrade glyphosate (GS) and amino (methylphosphonic acid) (AMPA). A specific gene amplification confirmed the presence of phnX (phosphonoacetaldehyde hydrolase) and the absence of PhnJ (the gene for the core component of C-P lyase). The presence of PhnCDE is strongly suggested for the strain, as it is common in Delftia lacustris species.

Characterization and Genome Analysis of the Delftia lacustris Strain LzhVag01 Isolated from Vaginal Discharge

Delftia has been separated from freshwater, sludge, and soil and has emerged as a novel opportunistic pathogen in the female vagina. However, the genomic characteristics, pathogenicity, and biotechnological properties still need to be comprehensively investigated. In this study, a Delftia strain was isolated from the vaginal discharge of a 43-year-old female with histologically confirmed cervical intraepithelial neoplasm (CIN III), followed by whole-genome sequencing. Phylogenetic analysis and average nucleotide identity (ANI) analysis demonstrated that it belongs to Delftia lacustris, named D. lacustris strain LzhVag01. LzhVag01 was sensitive to β-lactams, macrolides, and tetracyclines but exhibited resistance to lincoamines, nitroimidazoles, aminoglycosides, and fluoroquinolones. Its genome is a single, circular chromosome of 6,740,460 bp with an average GC content of 66.59%. Whole-genome analysis identified 16 antibiotic resistance-related genes, which match the antimicrobial susceptibility profile of this strain, and 11 potential virulence genes. These pathogenic factors may contribute to its colonization in the vaginal environment and its adaptation and accelerate the progression of cervical cancer. This study sequenced and characterized the whole-genome of Delftia lacustris isolated from vaginal discharge, which provides investigators and clinicians with valuable insights into this uncommon species.

LCMS-Metabolomic Profiling and Genome Mining of Delftia lacustris DSM 21246 Revealed Lipophilic Delftibactin Metallophores.

Bacteria have evolved various strategies to combat heavy metal stress, including the secretion of small molecules, known as metallophores. These molecules hold a potential role in the mitigation of toxic metal contamination from the environment (bioremediation). Herein, we employed combined comparative metabolomic and genomic analyses to study the metallophores excreted by Delftia lacustris DSM 21246. LCMS-metabolomic analysis of this bacterium cultured under iron limitation led to a suite of lipophilic metallophores exclusively secreted in response to iron starvation. Additionally, we conducted genome sequencing of the DSM 21246 strain using nanopore sequencing technology and employed antiSMASH to mine the genome, leading to the identification of a biosynthetic gene cluster (BGC) matching the known BGC responsible for delftibactin A production. The isolated suite of amphiphilic metallophores, termed delftibactins C-F (1-4), was characterized using various chromatographic, spectroscopic, and bioinformatic techniques. The planar structure of these compounds was elucidated through 1D and 2D NMR analyses, as well as LCMS/MS-based fragmentation studies. Notably, their structures differed from previously known delftibactins due to the presence of a lipid tail. Marfey's and bioinformatic analyses were employed to determine the absolute configuration of the peptide scaffold. Delftibactin A, a previously identified metallophore, has exhibited a gold biomineralizing property; compound 1 was tested for and also demonstrated this property.

ADANA İLİNDE PERAKENDE SATILAN MEYVE VE SEBZELERDEN İZOLE EDİLEN GRAM-NEGATİF BAKTERİLERİN YAYGINLIĞI

In this study, 65 samples of fresh products (leafy vegetables, ready-to-eat mixed salads, and fruits) retailed in Adana province of Turkiye were investigated for presence of Gram-negative bacteria. Salmonella spp. was undetected in any samples. However, Klebsiella pneumoniae (22%), Stenotrophomonas maltophilia (15%), Citrobacter freundii (11%), E. coli (11%), Klebsiella oxytoca (11%), Acinetobacter spp. [A. baumannii, A. pittii, (7%)], Pseudomonas putida (7%), were the predominant microorganisms and were detected in (19/65) 29.2% of samples by MALDI-TOF system. Their bacterial counts were between 3.6 and 8.3 log CFU/g. Strains of Enterobacter ludwigii (4%), Delftia lacustris (4%), Burkholderia cenocepacia (4%), and Burkholderia vietnamiensis (4%) were less detected. Our results revealed the fruits and vegetables produced in Adana province generally comply with microbiological criteria of the Turkish Food Codex interms of Salmonella spp., but higher bacterial counst of E. coli (between 5.8 and 6.3 log CFU/g) was found. Besides, Escherichia coli, Acinetobacter spp., Klebsiella pneumoniae, Citrobacter freundii, and Stenotrophomonas maltophilia species could be risky to human health.

Screening of phyllospheric and endophytic bacteria as biocontrol agents of Xanthomonas oryzae pv. oryzae

Abstract. Widjayanti T, Kusuma RR, Aini LQ, Fitriani CDA, Sektiono AW, Hadi MS, Setiawan Y. 2023. Screening of phyllospheric and endophytic bacteria as biocontrol agents of Xanthomonas oryzae pv. oryzae. Biodiversitas 24: 2072-2079. The use of phyllospheric and endophytic bacteria as biocontrol agents may be an eco-friendly alternative strategy to control bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae (Xoo). This study aimed to evaluated the antagonistic potential of phyllospheric and endophytic bacteria against X. oryzae pv. oryzae. The phyllospheric and endophytic bacteria were isolated from organic rice fields in Tumpang Sub-district, Malang District, East Java, Indonesia. The pathogenicity of X. oryzae pv. oryzae was tested on rice plants by the leaf clipping inoculation method. In this study, eight combinations of phyllospheric bacteria (PB) and endophytic bacterial (EB) isolates were chosen based on the highest percentage of inhibition. Streptomycin (positive control) and distilled water (negative control) were also used as a treatment. Identification of selected phyllospheric and endophytic bacteria was carried out through morphological and molecular characteristics. In total, 181 of PB and 76 of EB were isolated from rice plants. Of these, 11 of PB and 13 of EB isolates had potential as antagonists, shown by inhibition zone. Among all treatments, P55+E15 combination showed the highest inhibition zone (83.49%), followed by P55+E27 (82.33%) and P55+E18 (80.98%). Based on morphological and molecular identification, P55, E15, E27, and E18 isolates were identified as Delftia lacustris, Bacillus cereus, Escherichia coli, and Lysinibacillus fusiformis, respectively. The combination of D. lacustris (P55) and B. cereus (E15) can be used as a biocontrol agent against X. oryzae pv. oryzae based on in vitro assay.

Abstract 5904: Intra-tumor microbes identified by RNAseq associated with response to immune checkpoint blockade in metastatic melanoma

Abstract The tumor microbiome has recently been shown to play a key role in the context of oncogenesis, cancer immune phenotype, cancer progression and treatment outcomes in a variety of cancers. We investigated the possible associations between tumor microbiome and successful treatment outcomes with immune checkpoint blockade (ICB) in patients with metastatic melanoma. We evaluated RNAseq from tumor samples, collected prior to the start of treatment with ICB, from 71 patients with metastatic melanoma. Samples were provided by eight members of the Oncology Research Information Exchange Network (ORIEN). Non-response was determined as change in treatment after less than 12 months. Patients maintaining the same treatment regimen for greater than 12 months were classified as responders. We applied our custom tool, {exotic} (Exogenous sequences in Tumor and Immune Cells), to carefully identify non-human sequences within the RNAseq data. After filtering reads aligning to the human reference genome, reads were further filtered of common laboratory contaminants, taxa inversely correlated with input RNA quantity, and taxa frequently found in the negative controls of microbiome experiments. A differential abundance analysis was performed on the response groups at every taxonomic level utilizing DESeq2. We calculated expression signatures using {tmesig}, and related them to ICB response using {IOSig}. We observed significantly enriched taxa (p-value < 0.05) with a high (>1.00) fold-difference in abundance between responders and non-responders found within the tumor RNAseq data, including Fusobacterium nucleatum and several viruses in responders, and Delftia lacustris and Fungi in non-responders. These microbes were associated with immune cell expression signatures, including Th17 cells and CD8+ T-cells. We calculated the gene expression scores of 30 signatures with literature precedence for the ability to predict ICB treatment outcomes in melanoma. The receiver operator characteristic (ROC) curve of the random forest classification model for prediction of response to ICB using the combined expression signature scores resulted in an AUC of 0.8750. Combining expression signature scores with microbe relative abundances at the genus level improved the ability to predict ICB response (AUC = 0.8958). Combining tumor expression signatures with curated tumor microbiome relative abundances improves the performance of predictive models for treatment outcomes with ICB in melanoma. Citation Format: Caroline E. Wheeler, Samuel Coleman, Rebecca Hoyd, Afaf Osman, Louis Denko, Aik Choon Tan, Daniel Spakowicz, Ahmad Tarhini. Intra-tumor microbes identified by RNAseq associated with response to immune checkpoint blockade in metastatic melanoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5904.

Indigenous Peat Cellulolytic Bacteria and Its Potential as A Liberica Coffee Growth Promoter

Among the main microbes in peat are cellulolytic bacteria. The research aimed to select peat cellulolytic bacteria and identified its potential as a plant growth promoter bacteria (PGPB). The cellulolytic bacteria were isolated by serial dilutions and cellulase activity by the carboxymethyl cellulose (CMC) method, species types recognized by the sequencing method and P solubilization and phytohormones productions by Pikovskaya, and the high-performance liquid chromatography method, respectively. Research results found the 1st identified peat cellulolytic bacteria, Comamonas testosteroni, dissolved fixed P, 1.908 μg PO43-/mL.day and released phytohormones of indole acetic acid (IAA) 0.385 mg/kg, gibberellin (Ga.3) 2.989 mg/kg, zeatin 0.348 mg/kg, and kinetin 0.115 mg/kg. The 2nd identified bacteria, Delftia lacustris, dissolved fixed P from 1.107 μg PO43-/mL.day to 1.329 μg PO43-/mL.day and produced IAA from 0.775 to 1.161 mg/kg, Ga.3 from 2.551 to 4.429 mg/kg, and zeatin from 0.228 to 1.127 mg/kg and no kinetin. Adding both cellulolytic bacterial colonies on peat improved Liberica coffee seedling growth significantly.

Metabolites produced by inoculated Vigna radiata during bacterial assisted phytoremediation of Pb, Ni and Cr polluted soil.

Phytoremediation assisted with plant growth promoting bacteria (PGPB) is a green technology to remediate metal contaminated soils. Plants usually produce secondary metabolites to tolerate metal toxicity. Present study was designed to explore the phytoremediation potential of Vigna radiata var. NM-II in the presence of metal resistant PGPB and comparison of metabolites produced under heavy metal stresses (Pb, Ni, Cr). Three PGPB selected for present study include Bacillus pumilus MB246, Serratia nematodiphila MB307 and Delftia Lacustris MB322. Pot experiments were conducted with inoculated V. radiata NM-II seeds grown in soil artificially contaminated with lead (Pb), Nickle (Ni) and chromium (Cr) at a concentration of 300, 200 and 100 mg/kg respectively. After harvesting various growth parameters were studied (root length, shoot length, fresh weight and dry weight). Bacterial colonization on root surfaces of harvested plants was observed through Scanning electron microscopy (SEM) and Elemental composition was recorded through Energy dispersive X-ray spectroscopy (EDX) attached with SEM. Metabolic response of harvested plants was studied through Gas chromatography Mass spectrophotometry (GC-MS) analysis. Metal accumulation in roots, shoots and soil was analysed by acid digestion method from which Bioaccumulation factor (BF) and Translocation factor (TF) of metal from soil to plant was calculated. Results revealed stimulatory effect of PGPB on growth and phytoextraction ability of V. radiata. Soil metal removal efficiency was in the order Pb>Ni>Cr, whereas metal distribution in each part of plant was root>stem>leaf. The BF and TF values suggested V. radiata as Pb and Ni excluder while moderate accumulator for Cr. Elemental analysis through Energy Dispersive X- ray spectroscopy (EDX) found potassium (K+)and calcium (Ca+)as highly abundant nutrients with least accumulation of sulphur (S). Metabolites study through GC-MS revealed variety of compounds (carbohydrates, amino acids, fatty acids, steroids etc) detected differentially under each metal treatment and their concentration was influenced by different bacterial inoculations. Overall 9-Octadecenamide was found as commonly present lipid compound in most of the treatments which is required for detoxification in plants. The study concluded beneficial role of PGPB for successful phytoremediation of heavy metals and differential response of metabolites towards each metal stress that is related to metal tolerance ability of V. radiata.

Roles of β-Indole Acetic Acid (IAA) Producing Endophytic Bacteria on the Recovery of Plant Growth and Survival Ability of Sugarcane Infected White Leaf Disease (SWLD).

β-Indole acetic acid is produced in the rhizosphere by endophytic bacteria and promotes plant growth. Effects of bacterial IAA producers (BIPs) on plant growth and recovery of sugarcane seedlings infected with phytoplasma causing white leaf disease (SWLD) were examined. Fifty-five endophytic bacteria isolated from rice roots were collected from the Mekong River Delta, Vietnam. Seven isolates showed β-Indole acetic acid production in culture medium supplemented with tryptophan. Interestingly, two of them (BC17 and BTII2) produced the highest β-Indole acetic acid after 4days of culture. Based on 16S rRNA sequences and phylogenetic analysis, the BC17 and BTII2 isolates were identified as Delftia lacustris and Rahnella aquatilis, respectively. Plant growth induced by the BC17 and BTII2 isolates showed statistically significant differences in height, root length and fresh weight of rice seedlings compared with non-treatment as the control. Treatment of two bacterial isolates in SWLD infected sugarcane plants also showed differences in height of sugarcane seedlings, while gradual symptoms of exposure decreased plant mortality compared to non-treatment as the control. BIPs were shown to be efficient biofertilizer inoculants that promoted plant growth and also ameliorated damage caused by phytoplasma-associated diseases at the sugarcane seedling stage.

Comparison of decomposition and adaptation capability of indigenous peat cellulolytic microorganisms

Cellulolytic microorganisms play an essential role in the weathering of lignocellulosic materials. An experiment conducted was to study the potential of indigenous peat cellulolytic microorganisms to decompose peat and adapt to life outside the peat ecosystem. Indigenous cellulolytic bacteria of peat, Comamonas testosteroni, and Delftia lacustris, and indigenous cellulolytic fungi of peat, Penicillium singorense, Aspergillus aculeatus, and Trichoderma sp. were tested their capability for that case. In a greenhouse, each cellulolytic bacteria and fungi colony inoculated to the peat were as treatments and peat without inoculation as control. The study also tested their adaptability to grow in media outside the peat, such as charcoal and zeolite mixed with processed coffee and cacao residue in Lab. The cellulolytic fungi were a little stronger than cellulolytic bacteria in peat decomposition. The fungi reduced the organic C of peat by 13.9%, while the bacteria were only 6.4%. The CO2 flux from peat inoculated by fungi colony, 0.68 mg CO2/kg peat, and by bacteria colony, 0.64 mg CO2/kg peat. Both microbes adapted to the environment outside of peat, especially charcoal and zeolite mixed with coffee and cacao residue. However, cellulolytic bacteria were more robust than cellulolytic fungi if living simultaneously in the same media.

Isolation and selection of nitrite metabolising bacteria from the bottom mud of lobster culture area in Xuan Dai bay, Phu Yen province

The study had isolated and selected groups of bacteria that metabolise nitrite from the bottom mud of lobster cages in Xuan Dai bay, Phu Yen province. Analysis results from 21 sludge samples taken from 11 cages of lobster farming area isolated 16 strains of bacteria capable of nitrite metabolism. After investigating biological characteristics and nitrite metabolism of bacteria strains, 10 strains of bacteria were collected with the ability to metabolise nitrite over 95% in 72 hours. In addition, 10 strains of bacteria with the highest NO2- treatment efficiency, identified by genetic analysis and looked up on BLAST, defined as Stenotrophomonas pavanii, Chryseobacterium gleum, Stenotrophomonas maltophilia, Delftia lacustris, Acinetobacter junii

Isolation and identification of Delftia lacustris Strain-MS3 as a novel and efficient adsorbent for lead biosorption: Kinetics and thermodynamic studies, optimization of operating variables

The development of industrial factories has led to increasing the entry rate of non-degradable compounds into the environment. Natural sorbents have been used extensively to remove heavy metals under optimal conditions. In the present research, the lead-resistant bacteria (Delftia lacustris Strain-MS3) were isolated and identified and the ability of this novel strain to tolerate different concentrations of Pb+2 were evaluated. Kinetics, thermodynamic study and the optimal conditions for lead uptake by isolated strain were statistically described. Factors affecting optimum operational conditions of lead biosorption were analyzed using response surface methodology (RSM), based on the Box-Behnken design (BBD) model. The maximum lead removal measured at pH value of 6.6, bacterial biomass to lead ratio of 22:3, and residence time of 180 min. There was a significant difference between the growth rates of Strain-MS3 in different treatments. Results illustrate the high accuracy of the selected model to determine the optimal experimental conditions in the metal biosorption process. The adsorption results match with the pseudo-second-order kinetics, suggesting that lead ions were uptake to the adsorbent in monolayers due to their chemical affinity. The thermodynamic parameters were also determined by the Gibbs free energy function, confirming that the adsorption process was spontaneous and accompanied by endothermic nature.

Cultivation and Genome Sequencing of Bacteria Isolated From the Coffee Berry Borer (Hypothenemus hampei), With Emphasis on the Role of Caffeine Degradation.

The coffee berry borer, the most economically important insect pest of coffee worldwide, is the only insect capable of feeding and reproducing solely on the coffee seed, a food source containing the purine alkaloid caffeine. Twenty-one bacterial species associated with coffee berry borers from Hawai’i, Mexico, or a laboratory colony in Maryland (Acinetobacter sp. S40, S54, S55, Bacillus aryabhattai, Delftia lacustris, Erwinia sp. S38, S43, S63, Klebsiella oxytoca, Ochrobactrum sp. S45, S46, Pantoea sp. S61, Pseudomonas aeruginosa, P. parafulva, and Pseudomonas sp. S30, S31, S32, S37, S44, S60, S75) were found to have at least one of five caffeine N-demethylation genes (ndmA, ndmB, ndmC, ndmD, ndmE), with Pseudomonas spp. S31, S32, S37, S60 and P. parafulva having the full complement of these genes. Some of the bacteria carrying the ndm genes were detected in eggs, suggesting possible vertical transmission, while presence of caffeine-degrading bacteria in frass, e.g., P. parafulva (ndmABCDE) and Bacillus aryabhattai (ndmA) could result in horizontal transmission to all insect life stages. Thirty-five bacterial species associated with the insect (Acinetobacter sp. S40, S54, S55, B. aryabhattai, B. cereus group, Bacillus sp. S29, S70, S71, S72, S73, D. lacustris, Erwinia sp. S38, S43, S59, S63, K. oxytoca, Kosakonia cowanii, Ochrobactrum sp. S45, S46, Paenibacillus sp. S28, Pantoea sp. S61, S62, P. aeruginosa, P. parafulva, Pseudomonas sp. S30, S31, S32, S37, S44, S60, S75, Stenotrophomonas sp. S39, S41, S48, S49) might contribute to caffeine breakdown using the C-8 oxidation pathway, based on presence of genes required for this pathway. It is possible that caffeine-degrading bacteria associated with the coffee berry borer originated as epiphytes and endophytes in the coffee plant microbiota.

Exploration of microbiome of medicinally important plants as biocontrol agents against Phytophthora parasitica.

In a preliminary plant-based microbiome study, diverse bacterial taxa were identified from different medicinal plants using 16S rRNA gene sequencing. Based on initial antimicrobial screening, eight (8) bacterial endophytes in six (6) different genera, Streptomyces, Pseudomonas, Enterobacter, Bacillus, Arthrobacter, and Delftia, from four important medicinal plants Dodonaea viscosa, Fagonia indica, Caralluma tuberculata, and Calendula arvensis were selected for further analyses. Antimicrobial assays revealed that Pseudomonas taiwanensis MOSEL-RD23 has strong anti-Phytophthora activity. Volatiles produced by P. taiwanensis MOSEL-RD23and Bacillus flexus MOSEL-MIC5 inhibited the growth of Phytophthora parasitica by more than 80%. Ethyl acetate extracts of Streptomyces alboniger MOSEL-RD3, P. taiwanensis MOSEL-RD23, Enterobacter hormaechei MOSEL-FLS1, and Bacillus tequilensis MOSEL-FLS3, and Delftia lacustris MB322 displayed high potency against P. parasitica. All these bacterial extracts showed strong inhibition of more than 80% inhibition in vitro against P. parasitica at different concentrations (4-400µg/mL). Bacterial extracts showing strong antimicrobial activity were selected for bioactivity-driven fractionation and showed anti-Phytophthoral activity in multiple fractions and different peaks observed in UV-Vis spectroscopy. In the detached-leaf assay against P. parasitica on tobacco, 1% ethyl acetate bacterial extract of S. alboniger MOSEL-RD3, P. taiwanensis MOSEL-RD23, E. hormaechei MOSEL-FLS1, B. tequilensis MOSEL-FLS3, and D. lacustris MB322 reduced lesion sizes and lesion frequencies caused by P. parasitica by 68 to 81%. Overall, P. taiwanensis MOSEL-RD23 showed positive activities for all the assays. Analyzing the potential of bacterial endophytes as biological control agents can potentially lead to the formulation of broad-spectrum biopesticides for the sustainable production of crops.

Bioremoval of graffiti using novel commercial strains of bacteria

Previous studies have provided evidence that bioremediation deals a novel approach to graffiti removal, thereby overcoming well-known limitations of current cleaning methods. In the present study eight bacteria aerobic, mesophilic and culturable from the American ATCC and the German DSMZ collections of microorganisms, some isolated from car paint waste, colored deposits in a pulp dryer and wastewater from dye works, were tested in the removal of silver and black graffiti spray paints using immersion strategies with glass slides. Absorbance at 600 nm and live/dead assays were performed to estimate bacterial density and activity in all samples. Also, pH and dissolved organic carbon (DOC) and inorganic carbon (DIC) measurements in the liquid media were made, as well as, thickness, colorimetric and infrared (FTIR) spectroscopy measurements in graffiti paint layers were used to evaluate the presence of the selected bacteria in the samples and the graffiti bioremoval capacity of bacteria. Data demonstrated that of the eight bacteria studied, Enterobacter aerogenes, Comamonas sp. and a mixture of Bacillus sp., Delftia lacustris, Sphingobacterium caeni, and Ochrobactrum anthropi were the most promising for bioremoval of graffiti. According to significant changes in FTIR spectra, indicating an alteration of the paint polymeric structure, coupled with the presence of a consistent quantity of live bacteria in the medium as well as a significant increase of DIC (a measure of metabolic activity) and a change in paint color.

Significant higher airborne antibiotic resistance genes and the associated inhalation risk in the indoor than the outdoor.

Inhalation of airborne antibiotic resistance genes (ARGs) can lead to antimicrobial resistance and potential health risk. In modern society, increasing individuals stay more indoors, however, studies regarding the exposure to airborne ARGs in indoor environments and the associated risks remain limited. Here, we compared the variance of aerosol-associated ARGs, bacterial microbiomes, and their daily intake (DI) burden in dormitory, office, and outdoor environments in a university in Tianjin. The results indicated that compared to outdoor aerosols, indoors exhibited significantly higher absolute abundance of both ARG subtypes and mobile genetic elements (MGEs) (1-7 orders of magnitude), 16S rRNA genes (2-3 orders), and total culturable bacteria (1-3 orders). Furthermore, we observed that significantly different airborne bacterial communities are the major drivers contributing to the variance of aerosol-associated ARGs in indoor and outdoor aerosols. Notably, the high abundances of total bacteria, potential pathogenic genera, and ARGs (particularly those harbored by pathogens) in indoor and outdoor aerosols, especially in indoors, may pose an increased exposure risk via inhalation. The successful isolation of human pathogens such as Elizabethkingia anopheles, Klebsiella pneumonia, and Delftia lacustris resistant to the "last-resort" antibiotics carbapenems and polymyxin B from indoor aerosols further indicated an increased exposure risk in indoors. Together, this study highlights the potential risks associated with ARGs and their inhalation to human health in indoor environments.

In vitro antagonistic potential, plant growth-promoting activity and indole-3-acetic acid producing trait of bacterial isolates from spent mushroom substrate of Agaricus bisporus

Spent mushroom substrate (SMS) is widely used as fertilizer and to control plant diseases. The microorganisms surviving in SMS play a crucial role in plant growth promotion and biocontrol properties of SMS. In this study, an effort was made to isolate and characterize the bacterial species present in the SMS of Agaricus bisporus and to study their antagonistic potential, plant growth-promoting ability and indole-3-acetic acid (IAA) producing trait. Six different bacterial isolates exhibiting morphological variabilities were obtained from the SMS by serial dilution technique. On the basis of 16S rRNA gene sequences, these isolates were identified as Staphylococcus epidermidis (Sh1 and Sh3), S. aureus (Sh2), Bacillus albus (Sh4), Delftia lacustris (Sh6) and Comamonas aquatica (Sh7). These bacterial strains were assayed for their antagonism against Pythium aphanidermatum, a phytopathogenic oomycete. The results of in vitro dual culture assay revealed that all the 6 bacterial isolates showed low levels of suppression of P. aphanidermatum and recorded less than 5 mm inhibition zone. Among the bacterial isolates, S. epidermidis Sh3 recorded the maximum inhibition zone of 4.2 mm. Plant growth promotion test using roll paper towel method revealed that C. aquatica Sh7, B. albus Sh4, D. lacustris Sh6 and S. epidermidis Sh3 caused a significant increase in seedling vigour of cucumber compared to control. The seeds treated with the bacterial isolate C. aquatica Sh7 showed the maximum seedling vigor. Assessment of in vitro production of IAA by the bacterial isolates revealed that the bacterial isolates highly varied (ranging from 0.28 to 9.25 mg L-1) in their potential for production of IAA. The maximum amount of IAA was produced by C. aquatica Sh7 (9.25 mg L-1), while the minimum was produced by S. epidermidis Sh1 (0.28 mg L-1).

Reduction of selenite to elemental Se(0) with simultaneous degradation of phenol by co-cultures of Phanerochaete chrysosporium and Delftia lacustris.

The simultaneous removal of phenol and selenite from synthetic wastewater was investigated by adopting two different co-culturing techniques using the fungus Phanerochaete chrysosporium and the bacterium Delftia lacustris. Separately grown biomass of the fungus and the bacterium (suspended co-culture) was incubated with different concentrations of phenol (0-1,200 mg/L) and selenite (10 mg/L). The selenite ions were biologically reduced to extracellular Se(0) nanoparticles (3.58 nm diameter) with the simultaneous degradation of up to 800 mg/L of phenol. Upon growing the fungus and the bacterium together using an attached growth co-culture, the bacterium grew as a biofilm onto the fungus. The extracellularly produced Se(0) in the attached growth co-culture had a minimum diameter of 58.5 nm. This co-culture was able to degrade completely 50 mg/L phenol, but was completely inhibited at a phenol concentration of 200 mg/L.

Microbial transformation of Se oxyanions in cultures of Delftia lacustris grown under aerobic conditions.

Delftia lacustris is reported for the first time as a selenate and selenite reducing bacterium, capable of tolerating and growing in the presence of ≥ 100 mM selenate and 25 mM selenite. The selenate reduction profiles of D. lacustris were investigated by varying selenate concentration, inoculum size, concentration and source of organic electron donor in minimal salt medium. Interestingly, the bacterium was able to reduce both selenate and selenite under aerobic conditions. Although considerable removal of selenate was observed at all concentrations investigated, D. lacustris was able to completely reduce 0.1 mM selenate within 96 h using lactate as the carbon source. Around 62.2% unaccounted selenium (unidentified organo-selenium compounds), 10.9% elemental selenium and 26.9% selenite were determined in the medium after complete reduction of selenate. Studies of the enzymatic activity of the cell fractions show that the selenite/selenate reducing enzymes were intracellular and independent of NADPH availability. D. lacustris shows an unique metabolism of selenium oxyanions to form elemental selenium and possibly also selenium ester compounds, thus a potential candidate for the remediation of selenium-contaminated wastewaters in aerobic environments. This novel finding will advance the field of bioremediation of selenium-contaminated sites and selenium bio-recovery and the production of potentially beneficial organic and inorganic reactive selenium species.

Effect of endosulfan tolerant bacterial isolates (Delftia lacustris IITISM30 and Klebsiella aerogenes IITISM42) with Helianthus annuus on remediation of endosulfan from contaminated soil

Endosulfan contaminated soil has become an important risk to the environment and human health worldwide. In the present study, endosulfan tolerant bacterial strain Delftia lacustris IITISM30 and Klebsiella aerogenes IITISM42 were isolated from pesticide stressed agricultural soil and tested for plant growth promoting activities. A pot experiment was performed using Helianthus annuus, grown in soil supplemented with endosulfan and inoculated with pure and consortium of bacterial strain IITISM30 and IITISM42. Inoculation increased plant biomass production and endosulfan degradation, maximum degradation (90% at 5 mg kg−1 of soil) was observed by inoculation with a consortium of bacterial strain IITISM30 and IITISM42. Moreover, there was significantly less endosulfan accumulation was observed in roots and shoots of bacterial inoculated plants as compared to uninoculated plants. Decrease in production of malonialdehyde (MDA) was noticed on inoculation of a bacterial strain. The study demonstrated that inoculation of a consortium of endosulfan tolerant plant growth promoting bacterial isolates could more effectively remediate endosulfan contaminated soils and decrease endosulfan residues in plants, than individual strains. Moreover, it revealed that combined use of H. annuus and endosulfan tolerant bacterial isolates IITISM30 and IITISM42 has great potential for remediating endosulfan contaminated soil.