Sphingobium sp. HV3 degrades both herbicides and polyaromatic hydrocarbons using ortho- and meta-pathways with differential expression shown by RT-PCR

Unveiling the Characteristics of Microbiota in Different Mucosal Layers of Leopard Coral Grouper (Plectropomus leopardus)

Mucosal microbiomes play an important role in digestion, nutrition, and resistance to pathogens and toxins in fish; thus, characterizing the mucosal microbiomes of economically important fish species is paramount. In this study, mucosal microbiomes of healthy leopard coral grouper (Plectropomus leopardus), which is of economic importance worldwide, were systematically analyzed and compared by using 16S rRNA amplicon sequencing. The analysis of alpha-diversity and beta-diversity revealed significant differences in the structure and composition of the microbial community between different mucosal layers of P. leopardus. The skin microbiota showed the lowest microbial diversity among the three tissues, and the highest interindividual variability within gill groups was observed. Proteobacteria is the dominant phylum of the gut, skin, and gill microbiomes. Microbial biomarkers of the three mucosal tissues were identified, with the genera Parvibaculum, Aminobacter, Sphingobium, and Ralstonia for skin; Mesoflavibacter, Winogradskyella, Malaciobacter, Nautella, and Marinobacterium for gills; and Cetobacterium, Photobacterium, and Vibrio for gut. These genera were also the core microorganisms in each tissue. A large number of identical pathways of the three mucosal surfaces microbiome (e.g., pathways related to metabolism, human diseases, genetic/environmental information processing) and some specifically enriched pathways in each tissue were identified. Co-occurrence network analysis revealed that there were more ecological communities and higher functional diversity in the gill microbiota, and the interactions between gut microbiota are closer and more stable. Our study provides a new perspective for a comprehensive understanding of the mucosal microbiota of P. leopardus, contributing to an in-depth exploration of the interaction between fish and microorganisms, and may help to predict potential disease outbreaks, thus promoting the development of the fish farming industry.

Microbial community structure and metabolic profile of anthropized freshwater tributary channels from La Plata River, Argentina, to develop sustainable remediation strategies

Microbial communities from freshwater sediments are involved in biogeochemical cycles and they can be modified by physical and chemical changes in the environment. Linking the microbial community structure (MCS) with physicochemistry of freshwater courses allows a better understanding of its ecology and can be useful to assess the ecological impact generated by human activity. The MCS of tributary channels from La Plata River affected by oil refinery (C, D, and E) and one also by urban discharges (C) was studied. For this purpose, 16S rRNA metabarcoding analysis, in silico metagenome functional prediction, and the hydrocarbon degradation potential (in silico predictions of hydrocarbon-degrading genes and their quantification by qPCR) of the MCS were studied. Principal coordinate analysis revealed that the MCS was different between sites, and it was not structured by the hydrocarbon content. Site C showed physicochemical characteristics, bacterial taxa, and an in silico functional prediction related to fermentative/heterotrophic metabolism. Site D, despite having higher concentration of hydrocarbon, presented autotrophic, syntrophic, and methanogenic pathways commonly involved in natural processes in anoxic sediments. Site E showed and intermediate autotrophic/heterotrophic behavior. The hydrocarbon degradation potential showed no positive correlation between the hydrocarbon-degrading genes quantified and predicted. The results suggest that the hydrocarbon concentration in the sites was not enough selection pressure to structure the bacterial community composition. Understanding which is the variable that structures the bacterial community composition is essential for monitoring and designing of sustainable management strategies for contaminated freshwater ecosystems.

Bioremediation of contaminated soil and groundwater by in situ biostimulation

Bioremediation by in situ biostimulation is an attractive alternative to excavation of contaminated soil. Many in situ remediation methods have been tested with some success; however, due to highly variable results in realistic field conditions, they have not been implemented as widely as they might deserve. To ensure success, methods should be validated under site-analogous conditions before full scale use, which requires expertise and local knowledge by the implementers. The focus here is on indigenous microbial degraders and evaluation of their performance. Identifying and removing biodegradation bottlenecks for degradation of organic pollutants is essential. Limiting factors commonly include: lack of oxygen or alternative electron acceptors, low temperature, and lack of essential nutrients. Additional factors: the bioavailability of the contaminating compound, pH, distribution of the contaminant, and soil structure and moisture, and in some cases, lack of degradation potential which may be amended with bioaugmentation. Methods to remove these bottlenecks are discussed. Implementers should also be prepared to combine methods or use them in sequence. Chemical/physical means may be used to enhance biostimulation. The review also suggests tools for assessing sustainability, life cycle assessment, and risk assessment. To help entrepreneurs, decision makers, and methods developers in the future, we suggest founding a database for otherwise seldom reported unsuccessful interventions, as well as the potential for artificial intelligence (AI) to assist in site evaluation and decision-making.

Plasmid-mediated catabolism for the removal of xenobiotics from the environment

The large-scale application of xenobiotics adversely affects the environment. The genes that are present in the chromosome of the bacteria are considered nonmobile, whereas the genes present on the plasmids are considered mobile genetic elements. Plasmids are considered indispensable for xenobiotic degradation into the contaminated environment. In the contaminated sites, bacteria with plasmids can transfer the mobile genetic element into another strain. This mechanism helps in spreading the catabolic genes into the bacterial population at the contaminated sites. The indigenous microbial strains with such degradative plasmids are important for the bioremediation of xenobiotics. Environmental factors play a critical role in the conjugation efficiency, which is involved in the bioremediation of the xenobiotics at the contaminated sites. However, there is still a need for more research to fill in the gaps regarding plasmids and their impact on bioremediation. This review explores the role of bacterial plasmids in the bioremediation of xenobiotics from contaminated environments.

Truffle Microbiome Is Driven by Fruit Body Compartmentalization Rather than Soils Conditioned by Different Host Trees

Truffles are among the most expensive edible mushrooms; their value is worth billions of U.S. dollars annually in international markets. They establish ectomycorrhizal symbiotic relationships with diverse host tree roots and produce hypogeous ascomata. Their whole life cycle is closely related to their associated microbiome. However, whether truffle-associated compartments or host tree rhizospheres are the vital driver for truffle ascomata microbiome is unclear. To identify and compare fungal and bacterial communities in four truffle-associated compartments (Tuber indicum: bulk soil, adhering soil to peridium, peridium, and gleba) from three host trees, we sequenced their ITS (fungal) and 16S (bacterial) ribosomal DNA using the Illumina MiSeq high-throughput platform. We further applied the amplicon data to analyze the core microbiome and microbial ecological networks. Tuber indicum microbiome composition was strongly driven by its associated compartments rather than by their symbiotic host trees. Truffle microbiome was bacteria dominated, and its bacterial community formed a substantially more complex interacting network compared to that of the fungal community. The core fungal community changed from Basidiomycota dominated (bulk soil) to Rozellomycota dominated (interphase soil); the core bacterial community shifted from Bacteroidetes to Proteobacteria dominance from truffle peridium to gleba tissue. Especially, at the truffle and soil interphase, the niche-based selection of truffle microbiome was verified by (i) a clear exclusion of four bacterial phyla (Rokubacteria, Nitrospirae, Chloroflexi, and Planctomycetes) in gleba; (ii) a significant decrease in alpha-diversity (as revealed by Chao 1, Shannon, and Simpson indices); and (iii) the complexity of the network substantially decreased from bulk soil to soil-truffle interphase and further to the peridium and gleba. The network analysis of microbiome showed that the microbial positive interactions were higher in truffle tissues than in both bulk soil and peridium-adhering soil and that Cupriavidus, Bradyrhizobium, Aminobacter, and Mesorhizobium spp. were the keystone network hubs in the truffle gleba. This study provides insights into the factors that drive the truffle microbiome dynamics and the recruitment and function of the microbiome components. IMPORTANCE Currently, the factors that drive the microbiome associated with truffles, the most highly prized fungi in the world, are largely unknown. We demonstrate for the first time here that truffle microbiome composition is strongly driven by associated compartments rather than by symbiotic host trees. The truffle microbiome was bacteria dominated, and its bacterial community formed a substantially more complex (with the higher numbers of nodes, links, and modules) interacting network compared to that of the fungal community. Network analysis showed a higher number of positive microbial interactions with each other in truffle tissues than in both bulk soil and peridium-adhering soil. For the first time, the fungal community structure associated with truffles using high-throughput sequencing, microbial networks, and keystone species analyses is presented. This study provides novel insights into the factors that drive the truffle microbiome dynamics and the recruitment and function of the microbiome components, showing that they are more complex than previously thought.

Co-biodegradation of pyrene and other PAHs by the bacterium Acinetobacter johnsonii

Polycyclic aromatic hydrocarbons (PAHs) usually co-exist in environment with interactional effects. Currently, Acinetobacter johnsonii was employed to degrade 400 mg L^-1 of pyrene (PYR) and kinetic modeling indicated substrate inhibition over 76 mg L^-1 by introducing an inhibition constant parameter. In PAHs co-biodegradation, naphthalene (NAP) dominated biodegradation processes through the preferential utilization as growth substrate. The peak biodegradation of PYR increased to 415 mg L^-1 with 65 mg L^-1 of NAP. Furthermore, phenanthrene (PHE), PYR and anthracene (ANT) were degraded in turn and ended in reverse order. When the concentrations reached their respective limiting concentration of 22%, ANT could not be degraded and PHE and PYR biodegradations also respectively terminated at 66 and 45 h later with a removal rate of 40% and 26% due to very low specific activities of salicylate hydroxylase and catechol 2,3-dioxygenase. However, by introducing 125-133 mg L^-1 of NAP, the bacterial potential was effectively enhanced to 29% after cell underwent a re-stimulation stage with the exhaustion of NAP. NAP prominently contributed to cell growth to stimulate secretion of key enzymes, but the advantage would gradually get lost with the decline of its titer. To research the interplay of PAHs is conducive to targeted decontamination.

Sphingobium aquiterrae sp. nov., a toluene, meta- and para-xylene-degrading bacterium isolated from petroleum hydrocarbon-contaminated groundwater

A Gram-negative, aerobic, slightly yellow-pigmented bacterium, designated as SKLS-A10^T, was isolated from groundwater sample of the 'Siklós' petroleum hydrocarbon contaminated site (Hungary). Phylogenetic analysis based on 16S rRNA gene sequence revealed that strain SKLS-A10^T formed a distinct phyletic lineage within the genus Sphingobium. It shared the highest 16S rRNA gene homology with Sphingobium abikonense DSM 23268^T (97.29 %), followed by Sphingobium lactosutens DSM 23389^T (97.23 %), Sphingobium phenoxybenzoativorans KCTC 42448^T (97.16 %) and Sphingobium subterraneum NBRC 109814^T (96.74 %). The predominant fatty acids (>5 % of the total) are C18 : 1ω7c, C14 : 0 2-OH, C16 : 1ω7c/iso C15 : 0 2-OH, C17 : 1ω6c and C16 : 0. The major ubiquinone is Q-10. The predominant polyamine is spermidine. The major polar lipids are sphingoglycolipid and diphosphatidylglycerol. The DNA G+C content of strain SKLS-A10^T is 65.9 mol%. On the basis of evidence from this taxonomic study using a polyphasic approach, strain SKLS-A10^T represents a novel species of the genus Sphingobium for which the name Sphingobiumaquiterrae sp. nov. is proposed. The type strain is SKLS-A10^T (=DSM 106441^T=NCAIM B. 02634^T).

Co-biodegradation of anthracene and naphthalene by the bacterium Acinetobacter johnsonii

NAP (Naphthalene) and ANT (anthracene) usually co-exist in environment and possessed interactional effects on their biodegradation in environment. Presently, a strain of Acinetobacter johnsonii was employed to degrade NAP and ANT in single- and dual-substrate systems. NAP was utilized as prefer substrate by cells to accelerate ANT biodegradation. As much as 200 mg L^-1 ANT could be entirely degraded with 1,500 mg L^-1 NAP, which was beyond bacterial potential in single substrate system. Especially, the shortest biodegradation period (103 h) for ANT was observed with the presence of 50 mg L^-1 NAP. By contrast, ANT showed strong inhibition on NAP degradation, while the peak biodegradation of 1,950 mg L^-1 NAP with 50 mg L^-1 ANT could still proceed. By introducing an inhibition constant parameter to fit the inhibition on cells, modeling indicated the substrate inhibition for NAP and ANT over the concentrations of 174 and 49 mg L^-1, respectively. Furthermore, enzyme assay revealed the pathway of meta fission in NAP biodegradation due to the appearance of catechol 2,3-dioxygenase activity, and low-level lipase excretion was also found in both NAP and ANT biodegradation, but hardly affect NAP and ANT biodegradation in the present study. To research the interplay of NAP and ANT is conducive to targeted decontamination.

Abilities and genes for PAH biodegradation of bacteria isolated from mangrove sediments from the central of Thailand

PAH-degrading bacteria, including Novosphingobium sp. PCY, Microbacterium sp. BPW, Ralstonia sp. BPH, Alcaligenes sp. SSK1B, and Achromobacter sp. SSK4, were isolated from mangrove sediments. These isolates degraded 50-76% of 100 mg/l phenanthrene within 2 weeks. Strains PCY and BPW also degraded pyrene at 98% and 71%, respectively. Furthermore, all of them probably produced biosurfactants in the presence of hydrocarbons. Interestingly, PCY has a versatility to degrade various PAHs. Molecular techniques and plasmid curing remarkably revealed the presence of the alpha subunit of pyrene dioxygenase gene (nidA), involving in its pyrene/phenanthrene degrading ability, located on megaplasmid of PCY which has never before been reported in sphingomonads. Moreover, genes encoding ferredoxin, reductase, extradiol dioxygenase (bphA3A4C) and exopolysaccharide biosynthetase, which may be involved in PAH degradation and biosurfactant production, were also found in PCY. Therefore, we conclude that these isolates, especially PCY, can be the candidates for use as inoculums in the bioremediation.

Metagenomic analysis of the bioremediation of diesel-contaminated Canadian high arctic soils

As human activity in the Arctic increases, so does the risk of hydrocarbon pollution events. On site bioremediation of contaminated soil is the only feasible clean up solution in these remote areas, but degradation rates vary widely between bioremediation treatments. Most previous studies have focused on the feasibility of on site clean-up and very little attention has been given to the microbial and functional communities involved and their ecology. Here, we ask the question: which microorganisms and functional genes are abundant and active during hydrocarbon degradation at cold temperature? To answer this question, we sequenced the soil metagenome of an ongoing bioremediation project in Alert, Canada through a time course. We also used reverse-transcriptase real-time PCR (RT-qPCR) to quantify the expression of several hydrocarbon-degrading genes. Pseudomonas species appeared as the most abundant organisms in Alert soils right after contamination with diesel and excavation (t = 0) and one month after the start of the bioremediation treatment (t = 1m), when degradation rates were at their highest, but decreased after one year (t = 1y), when residual soil hydrocarbons were almost depleted. This trend was also reflected in hydrocarbon degrading genes, which were mainly affiliated with Gammaproteobacteria at t = 0 and t = 1m and with Alphaproteobacteria and Actinobacteria at t = 1y. RT-qPCR assays confirmed that Pseudomonas and Rhodococcus species actively expressed hydrocarbon degradation genes in Arctic biopile soils. Taken together, these results indicated that biopile treatment leads to major shifts in soil microbial communities, favoring aerobic bacteria that can degrade hydrocarbons.

Effects of gene-augmentation on the formation, characteristics and microbial community of 2,4-dichlorophenoxyacetic acid degrading aerobic microbial granules

Development of 2,4-dichlorophenoxyacetic acid (2,4-D) degrading aerobic granular sludge was conducted in two sequencing batch reactors (SBR) with one bioaugmented with a plasmid pJP4 donor strain Pseudomonas putida SM1443 and the other as a control. Half-matured aerobic granules pre-grown on glucose were used as the starting seeds and a two-stage operation strategy was applied. Granules capable of utilizing 2,4-D (about 500 mg/L) as the sole carbon source was successfully cultivated in both reactors. Gene-augmentation resulted in the enhancement of 2,4-D degradation rates by the percentage of 65-135% for the granules on Day 18, and 6-24% for the granules on Day 105. Transconjugants receiving plasmid pJP4 were established in the granule microbial community after bioaugmentation and persisted till the end of operation. Compared with the control granules, the granules in the bioaugmented reactor demonstrated a better settling ability, larger size, more abundant microbial diversity and stronger tolerance to 2,4-D. The finally obtained granules in the bioaugmented and control reactor had a granule size of around 600 μm and 500 μm, a Shannon-Weaver diversity index (H) of 0.96 and 0.55, respectively. A shift in microbial community was found during the granulation process.