Detection, expression and quantitation of the biodegradative genes in Antarctic microorganisms using PCR

The bioremediation of the typical persistent organic pollutants (POPs) by microalgae-bacteria consortia: A systematic review

With industrialisation and the rapidly growing agricultural demand, many organic compounds have been leaked into the environment, causing serious damage to the biosphere. Persistent organic pollutants (POPs) are a type of toxic chemicals that are resistant to degradation through normal chemical, biological or photolytic approaches. With their stable chemical structures, POPs can be accumulated in the environment, and transported through wind and water, causing global environmental issues. Many researches have been conducted to remediate POPs contamination using various kinds of biological methods, and significant results have been seen. Microalgae-bacteria consortium is a newly developed concept for biological technology in contamination treatment, with the synergetic effects between microalgae and bacteria, their potential for pollutants degradation can be further released. In this review, two types of POPs (polychlorinated biphenyls and polycyclic aromatic hydrocarbons) are selected as the targeted pollutants to give a systematic analysis of the biodegradation through microalgae and bacteria, including the species selection, the identification of dominant enzymes, as well as the real application performance of the consortia. In the end, some outlooks and suggestions are given to further guide the development of applying microalgae-bacteria consortia in remediating POPs contamination. In general, the coculturing of microalgae and bacteria is a novel and efficient way to fulfil the advanced treatment of POPs in soil or liquid phase, and both monooxygenase and dioxygenase belonging to oxygenase play a vital role in the biodegradation of PCBs and PAHs. This review provides a general guide in the future investigation of biological treatment of POPs.

Role of Microbes in the degradation of organic semivolatile compounds in polar ecosystems: A review

The Arctic and the Antarctic Continent correspond to two eco-regions with extreme climatic conditions. These regions are exposed to the presence of contaminants resulting from human activity (local and global), which, in turn, represent a challenge for life forms in these environments. Anthropogenic pollution by semi-volatile organic compounds (SVOCs) in polar ecosystems has been documented since the 1960s. Currently, various studies have shown the presence of SVOCs and their bioaccumulation and biomagnification in the polar regions with negative effects on biodiversity and the ecosystem. Although the production and use of these compounds has been regulated, their persistence continues to threaten biodiversity and the ecosystem. Here, we summarize the current literature regarding microbes and SVOCs in polar regions and pose that bioremediation by native microorganisms is a feasible strategy to mitigate the presence of SVOCs. Our systematic review revealed that microbial communities in polar environments represent a wide reservoir of biodiversity adapted to extreme conditions, found both in terrestrial and aquatic environments, freely or in association with vegetation. Microorganisms adapted to these environments have the potential for biodegradation of SVOCs through a variety of genes encoding enzymes with the capacity to metabolize SVOCs. We suggest that a comprehensive approach at the molecular and ecological level is required to mitigate SVOCs presence in these regions. This is especially patent when considering that SVOCs degrade at slow rates and possess the ability to accumulate in polar ecosystems. The implications of SVOC degradation are relevant for the preservation of polar ecosystems with consequences at a global level.

Bacterial Isolates from Greek Sites and Their Efficacy in Degrading Petroleum

Polycyclic aromatic hydrocarbons (PAHs) are a major organic pollutant, not only because they do not self-degenerate but also because they accumulate in the food chain and give rise to serious repercussions in terms of biodiversity sustainability. Petroleum-degrading bacteria have long been used as a promising solution in the effort to biodegrade crude oil. In this study, new isolates from specific Greek environments displaying various levels of crude oil contamination, as well as isolates belonging to the ATHUBA collection, were thoroughly investigated for their capacity to degrade crude oil. Furthermore, the presence of nahH and alkJ genes in the above bacterial isolates, as well as their ability to form agglomerates or release surfactants, was investigated. Two consortia were formed, and their ability to degrade crude oil was tested, achieving similar degrading capacities as those observed with the individual strains. A Pseudomonas plecoglossicida isolate demonstrated the highest percentage (76.7%) ability to degrade crude oil. The biodegradation rate of this isolate was further evaluated by measuring the alkanes/hopanes ratio over a period of ten days, exhibiting a higher degradation rate in short-chain (C11–C21) alkanes, whereas a decrease in the ratio was observed when the number of carbons in petroleum increased. This is the first detailed report on bacterial communities in oil-polluted areas of Greece that contain a variety of bacteria with the ability to degrade PAHs in contaminated sites and may provide a novel alternative to various bioremediation processes or be used as inocula in autochthonous bioaugmentation procedures for crude oil biodegradation.

Enhanced biodegradation and valorization of drilling wastewater via simultaneous production of biosurfactants and polyhydroxyalkanoates by Pseudomonas citronellolis SJTE-3

Pseudomonas citronellolis SJTE-3 was isolated as a highly efficient microorganism for biodegradation and valorization of drilling fluids (DF) wastewater. The strain metabolised DF and oily mud exhibiting up to 93%, 86%, 85% and 88% of chemical oxygen demand (COD), n-dodecane, n-tetradecane and naphthalene removal efficiency respectively. Enhanced bioconversion was enabled through production of biosurfactants that reduced the surface tension of water by 53% and resulted in 43.3% emulsification index (E24), while synthesizing 24% of dry cell weight (DCW) as medium-chain-length polyhydroxyalkanoates (PHA). Expression from the main pathways for alkanes and naphthalene biodegradation as well as biosurfactants and PHA biosynthesis revealed that although the alkanes and naphthalene biodegradation routes were actively expressed even at stationary phase, PHA production was stimulated at late stationary phase and putisolvin could comprise the biosurfactant synthesized. The bioconversion of toxic petrochemical residues to added-value thermoelastomers and biosurfactants indicate the high industrial significance of P. citronellolis SJTE-3.

Bacterial bioaugmentation enhances hydrocarbon degradation, plant colonization and gene expression in diesel-contaminated soil

Environmental contamination by hydrocarbons is a major problem, and hydrocarbon accumulation in soil poses hazardous threat to ecosystems. Phytoremediation, which involves plants, is an encouraging technique for the removal of hydrocarbons from polluted soil and water. The purpose of this investigation was to examine whether bacterial inoculation enhanced the phytoremediation of hydrocarbons in diesel-contaminated soil vegetated with maize (Zea mays L.). The two cultivars of maize, MMRI Yellow and Pearl White, were planted in diesel-polluted soil (0, 1.5, 2.5, and 3.5 g diesel kg^-1 soil), and inoculated with the consortium of three alkane-degrading bacterial strains, Arthrobacter oxydans ITRH49, Pseudomonas sp. ITRI73 and Pseudomonas sp. MixRI75. Bacterial inoculation enhanced plant growth and hydrocarbon degradation. Between two cultivars, MMRI Yellow showed better growth and hydrocarbon degradation in the presence and absence of bacterial inoculation. Maximum hydrocarbon degradation (80%) was observed in the soil having minimum concentration of diesel (1.5 g kg^-1 soil), and vegetated with bacterial inoculated MMRI Yellow maize cultivar. Furthermore, more bacterial colonization, and abundance and expression of the alkane hydroxylase gene (alkB) were observed in the root interior than in the rhizosphere and shoot interior of the plants. The bacteria-mediated phytoremediation of soil contaminated with hydrocarbons suggested that the collective use of plants and bacteria was the most beneficial approach for the reclamation of diesel-contaminated soil in comparison with vegetation alone.

Metagenomic Analysis of Soil Bacterial Community and Level of Genes Responsible for Biodegradation of Aromatic Hydrocarbons

The aim of the studies was to compare the composition of soil bacterial metabiomes originating from urbanized areas and areas con¬taminated with hydrocarbons with those from agricultural soil and forest soil obtained from a protected wild-life park area. It should be noted that hydrocarbons are everywhere therefore bacteria capable of their utilization are present in every soil type. In the hydrocarbon-contaminated soil and in the soil of anthropogenic origin, the bacteria belonging to Gammaproteobacteria were dominant (28.4-36.6%), whereas in the case of agricultural soil and protected wild-life park soil their ratios decreased (22.8-23.0%) and were similar to that of Alphaproteobacteria. No statistically significant changes were observed in terms of the Operational Taxonomic Unit identified in the studies soils, however, based on the determined alpha-diversity it can be established that contaminated soils were characterized by lower biodiversity indices compared to agricultural and forest soils. Furthermore, the dioxygenase level was also evaluated in the studied soils, which are genes encoding crucial enzymes for the decomposition of mono- and polycyclic aromatic hydrocarbons during the biodegradation of diesel oil (PAHRHDαGN, PAHRHDαGP, xylE, Cat 2,3, ndoB). It was concluded that both the population structure of the soil metabiome and the number of genes crucial for biodegradation processes differed significantly between the soils. The level of analysed genes showed a similar trend, as their highest number in relations to genes encoding 16S RNA was determined in urban and hydrocarbon-contaminated soil.

Microbial diversity and bioremediation of rhizospheric soils from Trindade Island - Brazil

Pristine environments may harbor complex microbial communities with metabolic potential for use in bioremediation of organic pollutants. This study aimed to evaluate crude oil biodegradation by microbial communities present in rhizospheric soils of Bulbostylis nesiotis and Cyperus atlanticus on Trindade Island and the compositional structure of these communities. After 60 days under aerobic conditions, Total Petroleum Hydrocarbon biodegradation ranged from 66 to 75%, depending on the plant species and the origin of the soil samples. There was no response of petroleum biodegradation to fertilization with N:P:K (80:160:80 mg dm^-3). Soil contamination with crude oil did not necessarily reduce microbial diversity. The richness and diversity increased in contaminated soils in some specific situations. We conclude that microbial communities from pristine soils have the ability to remove hydrocarbons through biodegradation and that Bulbostylis nesiotis and Cyperus atlanticus inhabiting Trindade Island harbor rhizospheric microbial communities with potential for application in rhizoremediation.

Advanced Rhodococcus Biocatalysts for Environmental Biotechnologies

The review is devoted to biocatalysts based on actinobacteria of the genus Rhodococcus, which are promising for environmental biotechnologies. In the review, biotechnological advantages of Rhodococcus bacteria are evaluated, approaches used to develop robust and efficient biocatalysts are discussed, and their relevant applications are given. We focus on Rhodococcus cell immobilization in detail (methods of immobilization, criteria for strains and carriers, and optimization of process parameters) as the most efficient approach for stabilizing biocatalysts. It is shown that advanced Rhodococcus biocatalysts with improved working characteristics, enhanced stress tolerance, high catalytic activities, human and environment friendly, and commercially viable are developed, which are suitable for wastewater treatment, bioremediation, and biofuel production.

Diversity of crude oil-degrading bacteria and alkane hydroxylase (alkB) genes from the Qinghai-Tibet Plateau

The aim of this study was to survey the response of the microbial community to crude oil and the diversity of alkane hydroxylase (alkB) genes in soil samples from the Qinghai-Tibet Plateau (QTP). The enrichment cultures and clone libraries were used. Finally, 53 isolates and 94 alkB sequences were obtained from 10 pristine soil samples after enrichment at 10 °C with crude oil as sole carbon source. The isolates fell into the phyla Proteobacteria, Actinobacteria, and Bacteroidetes, with the dominance of Pseudomonas and Acinetobacter. The composition of degraders was different from polar habitats where Acinetobacter sp. is not a predominant responder of alkane degradative microbial communities. Phylogenetic analysis showed that the alkB genes from isolates and enrichment communities formed eight clusters and mainly related with alkB genes of Pseudomonas, Rhodococcus, and Acinetobacter. The alkB gene diversity in the QTP was lower than marine environments and polar soil samples. In particular, a total of 10 isolates exhibiting vigorous growth with crude oil could detect no crude oil degradation-related gene sequences, such as alkB, P450, almA, ndoB, and xylE genes. The Shannon-Wiener index of the alkB clone libraries from the QTP ranged from 1.00 to 2.24 which is similar with polar pristine soil samples but lower than that of contaminated soils. These results indicated that the Pseudomonas, Acinetobacter, and Rhodococcus genera are the candidate for in situ bioremediation, and the environment of QTP may be still relatively uncontaminated by crude oil.

Isolation, identification, and crude oil degradation characteristics of a high-temperature, hydrocarbon-degrading strain

In this work, a hydrocarbon-degrading bacterium Y-1 isolated from petroleum contaminated soil in the Dagang Oilfield was investigated for its potential effect in biodegradation of crude oil. According to the analysis of 16S rRNA sequences, strain Y-1 was identified as Bacillus licheniformis. The growth parameters such as pH, temperature, and salinity were optimised and 60.2% degradation of crude oil removal was observed in 5days. The strain Y-1 showed strong tolerance to high salinity, alkalinity, and temperature. Emplastic produced by strain Y-1 at high temperatures could be applied as biosurfactant. Gas chromatography analysis demonstrated that the strain Y-1 efficiently degraded different alkanes from crude oil, and the emplastic produced by strain Y-1 promoted the degradation rates of long-chain alkanes when the temperature increased to 55°C. Therefore, strain Y-1 would play an important role in the area of crude oil contaminant bioremediation even in some extreme conditions.

Bacterial community shift in the coastal Gulf of Mexico salt-marsh sediment microcosm in vitro following exposure to the Mississippi Canyon Block 252 oil (MC252)

In this study, we examined the responses by the indigenous bacterial communities in salt-marsh sediment microcosms in vitro following treatment with Mississippi Canyon Block 252 oil (MC252). Microcosms were constructed of sediment and seawater collected from Bayou La Batre located in coastal Alabama on the Gulf of Mexico. We used an amplicon pyrosequencing approach on microcosm sediment metagenome targeting the V3–V5 region of the 16S rRNA gene. Overall, we identified a shift in the bacterial community in three distinct groups. The first group was the early responders (orders Pseudomonadales and Oceanospirillales within class Gammaproteobacteria), which increased their relative abundance within 2 weeks and were maintained 3 weeks after oil treatment. The second group was identified as early, but transient responders (order Rhodobacterales within class Alphaproteobacteria; class Epsilonproteobacteria), which increased their population by 2 weeks, but returned to the basal level 3 weeks after oil treatment. The third group was the late responders (order Clostridiales within phylum Firmicutes; order Methylococcales within class Gammaproteobacteria; and phylum Tenericutes), which only increased 3 weeks after oil treatment. Furthermore, we identified oil-sensitive bacterial taxa (order Chromatiales within class Gammaproteobacteria; order Syntrophobacterales within class Deltaproteobacteria), which decreased in their population after 2 weeks of oil treatment. Detection of alkane (alkB), catechol (C2,3DO) and biphenyl (bph) biodegradation genes by PCR, particularly in oil-treated sediment metacommunity DNA, delineates proliferation of  the hydrocarbon degrading bacterial community. Overall, the indigenous bacterial communities in our salt-marsh sediment in vitro microcosm study responded rapidly and shifted towards members of the taxonomic groups that are capable of surviving in an MC252 oil-contaminated environment.

Distribution of petroleum degrading genes and factor analysis of petroleum contaminated soil from the Dagang Oilfield, China

Genes that encode for enzymes that can degrade petroleum hydrocarbons (PHs) are critical for the ability of microorganisms to bioremediate soils contaminated with PHs. Distributions of two petroleum-degrading genes AlkB and Nah in soils collected from three zones of the Dagang Oilfield, Tianjin, China were investigated. Numbers of copies of AlkB ranged between 9.1 × 10(5) and 1.9 × 10(7) copies/g dry mass (dm) soil, and were positively correlated with total concentrations of PHs (TPH) (R(2) = 0.573, p = 0.032) and alkanes (C33 ~ C40) (R(2) = 0.914, p < 0.01). The Nah gene was distributed relatively evenly among sampling zones, ranging between 1.9 × 10(7) and 1.1 × 10(8) copies/g dm soil, and was negatively correlated with concentrations of total aromatic hydrocarbons (TAH) (R(2) = -0.567, p = 0.035) and ∑16 PAHs (R(2) = -0.599, p = 0.023). Results of a factor analysis showed that individual samples of soils were not ordinated as a function of the zones.

Abundance and diversity of functional genes involved in the degradation of aromatic hydrocarbons in Antarctic soils and sediments around Syowa Station

Hydrocarbon catabolic genes were investigated in soils and sediments in nine different locations around Syowa Station, Antarctica, using conventional PCR, real-time PCR, cloning, and sequencing analysis. Polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenase (PAH-RHD)-coding genes from both Gram-positive and Gram-negative bacteria were observed. Clone libraries of Gram-positive RHD genes were related to (i) nidA3 of Mycobacterium sp. py146, (ii) pdoA of Terrabacter sp. HH4, (iii) nidA of Diaphorobacter sp. KOTLB, and (iv) pdoA2 of Mycobacterium sp. CH-2, with 95-99% similarity. Clone libraries of Gram-negative RHD genes were related to the following: (i) naphthalene dioxygenase of Burkholderia glathei, (ii) phnAc of Burkholderia sartisoli, and (iii) RHD alpha subunit of uncultured bacterium, with 41-46% similarity. Interestingly, the diversity of the Gram-positive RHD genes found around this area was higher than those of the Gram-negative RHD genes. Real-time PCR showed different abundance of dioxygenase genes between locations. Moreover, the PCR-denaturing gradient gel electrophoresis (DGGE) profile demonstrated diverse bacterial populations, according to their location. Forty dominant fragments in the DGGE profiles were excised and sequenced. All of the sequences belonged to ten bacterial phyla: Proteobacteria, Actinobacteria, Verrucomicrobia, Bacteroidetes, Firmicutes, Chloroflexi, Gemmatimonadetes, Cyanobacteria, Chlorobium, and Acidobacteria. In addition, the bacterial genus Sphingomonas, which has been suggested to be one of the major PAH degraders in the environment, was observed in some locations. The results demonstrated that indigenous bacteria have the potential ability to degrade PAHs and provided information to support the conclusion that bioremediation processes can occur in the Antarctic soils and sediments studied here.

Draft Genome Sequence of Pseudomonas sp. Strain Ant30-3, a Psychrotolerant Bacterium with Biodegradative Attribute Isolated from Antarctica

Pseudomonas sp. strain Ant30-3, isolated from fuel-contaminated Antarctic soil, exhibited distinctive psychrotolerant attributes and the potential for degrading aromatic hydrocarbon compounds at cold temperatures. We report here the 6.14-Mb draft genome of Ant30-3, which will provide insights into the genomic basis for the psychrotolerant and biodegradative properties of this bacterium.

The Use of a Combination of alkB Primers to Better Characterize the Distribution of Alkane-Degrading Bacteria

The alkane monooxygenase AlkB, which is encoded by the alkB gene, is a key enzyme involved in bacterial alkane degradation. To study the alkB gene within bacterial communities, researchers need to be aware of the variations in alkB nucleotide sequences; a failure to consider the sequence variations results in the low representation of the diversity and richness of alkane-degrading bacteria. To minimize this shortcoming, the use of a combination of three alkB-targeting primers to enhance the detection of the alkB gene in previously isolated alkane-degrading bacteria was proposed. Using this approach, alkB-related PCR products were detected in 79% of the strains tested. Furthermore, the chosen set of primers was used to study alkB richness and diversity in different soils sampled in Carmópolis, Brazil and King George Island, Antarctica. The DNA extracted from the different soils was PCR amplified with each set of alkB-targeting primers, and clone libraries were constructed, sequenced and analyzed. A total of 255 alkB phylotypes were detected. Venn diagram analyses revealed that only low numbers of alkB phylotypes were shared among the different libraries derived from each primer pair. Therefore, the combination of three alkB-targeting primers enhanced the richness of alkB phylotypes detected in the different soils by 45% to 139%, when compared to the use of a single alkB-targeting primer. In addition, a dendrogram analysis and beta diversity comparison of the alkB composition showed that each of the sampling sites studied had a particular set of alkane-degrading bacteria. The use of a combination of alkB primers was an efficient strategy for enhancing the detection of the alkB gene in cultivable bacteria and for better characterizing the distribution of alkane-degrading bacteria in different soil environments.

Plant-bacteria partnerships for the remediation of hydrocarbon contaminated soils

Plant-bacteria partnerships have been extensively studied and applied to improve crop yield. In addition to their application in agriculture, a promising field to exploit plant-bacteria partnerships is the remediation of soil and water polluted with hydrocarbons. Application of effective plant-bacteria partnerships for the remediation of hydrocarbons depend mainly on the presence and metabolic activities of plant associated rhizo- and endophytic bacteria possessing specific genes required for the degradation of hydrocarbon pollutants. Plants and their associated bacteria interact with each other whereby plant supplies the bacteria with a special carbon source that stimulates the bacteria to degrade organic contaminants in the soil. In return, plant associated-bacteria can support their host plant to overcome contaminated-induced stress responses, and improve plant growth and development. In addition, plants further get benefits from their associated-bacteria possessing hydrocarbon-degradation potential, leading to enhanced hydrocarbon mineralization and lowering of both phytotoxicity and evapotranspiration of volatile hydrocarbons. A better understanding of plant-bacteria partnerships could be exploited to enhance the remediation of hydrocarbon contaminated soils in conjunction with sustainable production of non-food crops for biomass and biofuel production.

Soil type affects plant colonization, activity and catabolic gene expression of inoculated bacterial strains during phytoremediation of diesel

The combined use of plants and associated microorganisms has great potential for cleaning up soils contaminated with petroleum hydrocarbons. Apart from environmental conditions the physicochemical properties of the soil are the main factors influencing the survival and activity of an inoculated strain as well as the growth of plants. This study examined the effect of different soil types (sandy, loamy sand and loam) on the survival, gene abundance and catabolic gene expression of two inoculated strains (Pseudomonas sp. strain ITRI53 and Pantoea sp. strain BTRH79) in the rhizosphere and shoot interior of Italian ryegrass vegetated in diesel contaminated soils. High colonization, gene abundance and expression in loamy soils were observed. By contrast, low colonization, gene abundance and absence of gene expression in sandy soil were found. The highest levels of genes expression and hydrocarbon degradation were seen in loamy soil that had been inoculated with BTRH79 and were significantly higher compared to those in other soils. A positive correlation was observed between gene expression and hydrocarbon degradation indicating that catabolic gene expression is necessary for contaminant degradation. These results suggest that soil type influences the bacterial colonization and microbial activities and subsequently the efficiency of contaminant degradation.