Potential of Variovorax paradoxus isolate BFB1_13 for bioremediation of BTEX contaminated sites

Variovorax sp. strain P1R9 applied individually or as part of bacterial consortia enhances wheat germination under salt stress conditions

Endophytes isolated from extremophile plants are interesting microbes for improving the stress tolerance of agricultural plants. Here, we isolated and characterized endophytic bacteria showing plant growth-promoting (PGP) traits from plants in two extreme Chilean biomes (Atacama Desert and Chilean Patagonia). Forty-two isolates were characterized as both halotolerant auxin producers (2-51 mg L-1) and 1-aminocyclopropane-1-carboxylate (ACC)-degrading bacteria (15-28 µmol αKB mg protein-1 h-1). The most efficient isolates were tested as single strains, in dual and triple consortia, or in combination with previously reported PGP rhizobacteria (Klebsiella sp. 27IJA and 8LJA) for their impact on the germination of salt-exposed (0.15 M and 0.25 M NaCl) wheat seeds. Interestingly, strain P1R9, identified as Variovorax sp., enhanced wheat germination under salt stress conditions when applied individually or as part of bacterial consortia. Under salt stress, plants inoculated with dual consortia containing the strain Variovorax sp. P1R9 showed higher biomass (41%) and reduced lipid peroxidation (33-56%) than uninoculated plants. Although the underlying mechanisms remain elusive, our data suggest that the application of Variovorax sp. P1R9, alone or as a member of PGP consortia, may improve the salt stress tolerance of wheat plants.

Current trends in bioremediation and bio-integrated treatment of petroleum hydrocarbons

Petroleum hydrocarbons and their derivatives constitute the leading group of environmental pollutants worldwide. In the present global scenario, petroleum and natural gas production, exploration, petroleum refining, and other anthropogenic activities produce huge amounts of hazardous petroleum wastes that accumulate in the terrestrial and marine environment. Due to their carcinogenic, neurotoxic, and mutagenic characteristics, petroleum pollutants pose severe risks to human health and exert ecotoxicological effects on the ecosystems. To mitigate petroleum hydrocarbons (PHs) contamination, implementing "green technologies" for effective cleanup and restoration of an affected environment is considered as a pragmatic approach. This review provides a comprehensive outline of newly emerging bioremediation technologies, for instance; nanobioremediation, electrokinetic bioremediation, vermiremediation, multifunctional and sustainably implemented on-site applied biotechnologies such as; natural attenuation, biostimulation, bioaugmentation, bioventing, phytoremediation and multi-process hybrid technologies. Additionally, the scope of the effectiveness and limitations of individual technologies in treating the petroleum hydrocarbon polluted sites are also evaluated.

Novel BTEX-degrading strains from subsurface soil: Isolation, identification and growth evaluation

Monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene, and o, m, and p-xylenes (BTEX) are high-risk pollutants because of their mutagenic and carcinogenic nature. These pollutants are found with elevated levels in groundwater and soil in Canada at several contaminated sites. The intrinsic microbes present in the subsurface have the potential to degrade pollutants by their metabolic pathways and convert them to non-toxic products. However, the low subsurface temperature (5-10 °C) limits their growth and degradation ability. This study examined the feasibility of subsurface heat augmentation using geothermal heating for BTEX bioremediation. Novel potent BTEX-degrading bacterial strains were isolated from soil at 3.0, 42.6, and 73.2 m depths collected from a geothermal borehole during installation and screened using an enrichment technique. The selected strains were identified with Sanger sequencing and phylogenetic tree analysis, revealing that all the strains except Bacillus subtilis are novel with respective to BTEX degradation. The isolates, Microbacterium esteraromaticum and Bacillus infantis showed the highest degradation with 67.98 and 65.2% for benzene, 72.8 and 71.02% for toluene, 77.52 and 76.44% for ethylbenzene, and 74.58 and 74.04% for xylenes respectively. Further, temperature influence at 15 ± 1 °C, 28 ± 1 °C and 40 ± 1 °C was observed, which showed increased growth by two-fold and on average 35-49% more biodegradation at higher temperatures. Results showed that temperature is a positive stimulant for bioremediation, hence geothermal heating could also be a stimulant for in-situ bioremediation.

Influence of growth substrate and contaminant mixtures on the degradation of BTEX and MTBE by Rhodococcus rhodochrous ATCC strain 21198

The degradation of the prevalent environmental contaminants benzene, toluene, ethylbenzene, and xylenes (BTEX) along with a common co-contaminant methyl tert-butyl ether (MTBE) by Rhodococcus rhodochrous ATCC Strain 21198 was investigated. The ability of 21198 to degrade these contaminants individually and in mixtures was evaluated with resting cells grown on isobutane, 1-butanol, and 2-butanol. Growth of 21198 in the presence of BTEX and MTBE was also studied to determine the growth substrate that best supports simultaneous microbial growth and contaminants degradation. Cells grown on isobutane, 1-butanol, and 2-butanol were all capable of degrading the contaminants, with isobutane grown cells exhibiting the most rapid degradation rates and 1-butanol grown cells exhibiting the slowest. However, in conditions where BTEX and MTBE were present during microbial growth, 1-butanol was determined to be an effective substrate for supporting concurrent growth and contaminant degradation. Contaminant degradation was found to be a combination of metabolic and cometabolic processes. Evidence for growth of 21198 on benzene and toluene is presented along with a possible transformation pathway. MTBE was cometabolically transformed to tertiary butyl alcohol, which was also observed to be transformed by 21198. This work demonstrates the possible utility of primary and secondary alcohols to support biodegradation of monoaromatic hydrocarbons and MTBE. Furthermore, the utility of 21198 for bioremediation applications has been expanded to include BTEX and MTBE.

Metagenomic analysis reveals specific BTEX degrading microorganisms of a bacterial consortium

Petroleum hydrocarbon contamination is of environmental and public health concerns due to its toxic components. Bioremediation utilizes microbial organisms to metabolism and remove these contaminants. The aim of this study was to enrich a microbial community and examine its potential to degrade petroleum hydrocarbon. Through successive enrichment, we obtained a bacterial consortium using crude oil as sole carbon source. The 16 S rRNA gene analysis illustrated the structural characteristics of this community. Metagenomic analysis revealed the specific microbial organisms involved in the degradation of cyclohexane and all the six BTEX components, with a demonstration of the versatile metabolic pathways involved in these reactions. Results showed that our consortium contained the full range of CDSs that could potentially degrade cyclohexane, benzene, toluene, and (o-, m-, p-) xylene completely. Interestingly, a single taxon that possessed all the genes involved in either the activation or the central intermediates degrading pathway was not detected, except for the Novosphingobium which contained all the genes involved in the upper degradation pathway of benzene, indicating the synergistic interactions between different bacterial genera during the hydrocarbon degradation.

Metagenome analyses of microbial population in geotextile fabrics used in permeable reactor barriers for toluene biodegradation

Toluene is one of the hydrocarbons that contaminate soil and groundwater, and has a high cost to remediate, which makes it an environmental pollutant of concern. This study aimed to find bacterial distribution from nonwoven geotextile (GT) fabric specimens in a pilot-scale permeable reactive barrier (PRB). Upon 167 days of incubation with the addition of toluene, the microbial community on the GT surfaces (n = 12) was investigated by the 16S rRNA metagenome sequencing approach. According to taxonomic classification, the Proteobacteria phylum dominated the metagenomes of all the geotextile samples (80-90%). Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway database search of the toluene degradation mechanism revealed the susceptible toluene-degrading species. For the toluene-to-benzoate degradation, the Cupriavidus genus, particularly C. gilardii, C. metallidurans, and C. taiwanensis, are likely to be functional. In addition to these species, the Novosphingobium genus was abundantly localized in the GTs, in particular Novosphingobium sp. ABRDHK2. The results suggested the biodegradation potential of these species in toluene remediation. Overall, this work sheds light on the variety of microorganisms found in the geotextile fabrics used in PRBs and the species involved in the biodegradation of toluene from several sources, including soil, sediment, and groundwater.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03460-y.

Reviewing and renewing the use of beneficial root and soil bacteria for plant growth and sustainability in nutrient-poor, arid soils

A rapidly increasing human population coupled with climate change and several decades of over-reliance on synthetic fertilizers has led to two pressing global challenges: food insecurity and land degradation. Therefore, it is crucial that practices enabling both soil and plant health as well as sustainability be even more actively pursued. Sustainability and soil fertility encompass practices such as improving plant productivity in poor and arid soils, maintaining soil health, and minimizing harmful impacts on ecosystems brought about by poor soil management, including run-off of agricultural chemicals and other contaminants into waterways. Plant growth promoting bacteria (PGPB) can improve food production in numerous ways: by facilitating resource acquisition of macro- and micronutrients (especially N and P), modulating phytohormone levels, antagonizing pathogenic agents and maintaining soil fertility. The PGPB comprise different functional and taxonomic groups of bacteria belonging to multiple phyla, including Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria, among others. This review summarizes many of the mechanisms and methods these beneficial soil bacteria use to promote plant health and asks whether they can be further developed into effective, potentially commercially available plant stimulants that substantially reduce or replace various harmful practices involved in food production and ecosystem stability. Our goal is to describe the various mechanisms involved in beneficial plant-microbe interactions and how they can help us attain sustainability.

Characteristics and Comparative Genomic Analysis of a Novel Virus, VarioGold, the First Bacteriophage of Variovorax

Variovorax represents a widespread and ecologically significant genus of soil bacteria. Despite the ecological importance of these bacteria, our knowledge about the viruses infecting Variovorax spp. is quite poor. This study describes the isolation and characterization of the mitomycin-induced phage, named VarioGold. To the best of our knowledge, VarioGold represents the first characterized virus for this genus. Comparative genomic analyses suggested that VarioGold is distinct from currently known bacteriophages at both the nucleotide and protein levels; thus, it could be considered a new virus genus. In addition, another 37 prophages were distinguished in silico within the complete genomic sequences of Variovorax spp. that are available in public databases. The similarity networking analysis highlighted their general high diversity, which, despite clustering with previously described phages, shows their unique genetic load. Therefore, the novelty of Variovorax phages warrants the great enrichment of databases, which could, in turn, improve bioinformatic strategies for finding (pro)phages.

Natural Biodegradation of Vinyl Chloride and cis-Dichloroethene in Aerobic and Suboxic Conditions

Chlorinated ethene (CE) groundwater contamination is commonly treated through anaerobic biodegradation (i.e., reductive dechlorination) either as part of an engineered system or through natural attenuation. Aerobic biodegradation has also been recognized as a potentially significant pathway for the removal of the lower CEs cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). However, the role of aerobic biodegradation under low oxygen conditions typical of contaminated groundwater is unclear. Bacteria capable of aerobic VC biodegradation appear to be common in the environment, while aerobic biodegradation of cDCE is less common and little is known regarding the organisms responsible. In this study, we investigate the role of aerobic cDCE and VC biodegradation in a mixed contaminant plume (including CEs, BTEX, and ketones) at Naval Air Station North Island, Installation Restoration Site 9. Sediment and groundwater collected from the plume source area, mid-plume, and shoreline were used to prepare microcosms under fully aerobic (8 mg/L dissolved oxygen (DO)) and suboxic (< 1 mg/L DO) conditions. In the shoreline microcosms, VC and cDCE were rapidly degraded under suboxic conditions (100% and 77% removal in < 62 days). In the suboxic VC microcosms, biodegradation was associated with a > 5 order of magnitude increase in the abundance of functional gene etnE, part of the aerobic VC utilization pathway. VC and cDCE were degraded more slowly under fully aerobic conditions (74% and 30% removal) in 110 days. High-throughput 16S rRNA and etnE sequencing suggest the presence of novel VC- and cDCE-degrading bacteria. These results suggest that natural aerobic biodegradation of cDCE and VC is occurring at the site and provide new evidence that low (< 1 mg/L) DO levels play a significant role in natural attenuation of cDCE and VC.

A review on biofiltration techniques: Recent advancements in the removal of volatile organic compounds and heavy metals in the treatment of polluted water

Good quality of water determines the healthy life of living beings on this earth. The cleanliness of water was interrupted by the pollutants emerging out of several human activities. Industrialization, urbanization, heavy population, and improper disposal of wastes are found to be the major reasons for the contamination of water. Globally, the inclusion of volatile organic compounds (VOCs) and heavy metals released by manufacturing industries, pharmaceuticals, and petrochemical processes have created environmental issues. The toxic nature of these pollutants has led researchers, scientists, and industries to exhibit concern towards the complete eradication of them. In this scenario, the development of wastewater treatment methodologies at low cost and in an eco-friendly way had gained importance at the international level. Recently, bio-based technologies were considered for environmental remedies. Biofiltration based works have shown a significant result for the removal of volatile organic compounds and heavy metals in the treatment of wastewater. This was done with several biological sources such as bacteria, fungi, algae, plants, yeasts, etc. The biofiltration technique is cost-effective, simple, biocompatible, sustainable, and eco-friendly compared to conventional techniques. This review article provides deep insight into biofiltration technologies engaged in the removal of volatile organic compounds and heavy metals in the wastewater treatment process.

Development of a bacterial consortium from Variovorax paradoxus and Pseudomonas veronii isolates applicable in the removal of BTEX

In this study, we report on the development of a novel bacterial consortium, consisting of Variovorax paradoxus and Pseudomonas veronii isolates, applicable in the biodegradation of all six BTEX compounds (benzene, toluene, ethylbenzene, o-, m- and p-xylene) and the bioremediation of contaminated sites. The co-cultivability of the selected bacterial isolates was determined in nutrient-rich medium, as well as in BTEX amended mineral salts solution using Terminal Restriction Fragment Length Polymorphism (T-RFLP) and CFU determinations. BTEX biodegradation capacity of the two-strain consortium was assessed in mineral salts solution, where a series of BTEX depletions and supplementations occurred, as well as in a real, BTEX polluted environmental sample (contaminated groundwater) in the presence of the autochthonous bacterial community. The obtained results indicated that the developed bacterial consortium is very efficient in BTEX biodegradation. Under laboratory conditions, the acclimatized bacterial consortium completely degraded the BTEX mixture with a concentration as high as 20 mg l^-1 in a mineral salt medium within a short span of 6 h. Close to in situ groundwater conditions (incubated at 15 °C under static conditions in the absence of light), groundwater microcosms containing the autochthonous bacterial community inoculated with the developed bacterial consortium showed more efficient toluene, o-, m-and p-xylene biodegradation capacity than microcosms containing solely the native microbial population originally found in the groundwater. In the inoculated microcosms, after 115 h of incubation the concentration (~ 1.7 mg l^-1 each) of o-, m- and p-xylene decreased to zero, whereas in the non-inoculated microcosms the concentration of xylene isomers was still 0.2, 0.3 and 0.3 mg l^-1, respectively. The allochthonous bioaugmentation of the contaminated groundwater with the obtained inoculant was successful and manifested in a better BTEX degradation rate. Our results suggest that the obtained bacterial consortium can be a new, stable and efficient bioremediation agent applicable in the synergistic elimination of BTEX compounds from contaminated sites.