Hydrodynamic Treadmill Reveals Reduced Rising Speeds of Oil Droplets Deformed by Marine Bacteria.

In marine environments, microscopic droplets of oil can be transported over large distances in the water column. Bacterial growth on the droplets' surface can deform the oil-water interface to generate complex shapes and significantly enlarge droplets. Understanding the fate of spilled oil droplets requires bridging these length scales and determining how microscale processes affect the large-scale transport of oil. Here, we describe an experimental setup, the hydrodynamic treadmill, developed to keep rising oil droplets stationary in the lab frame for continuous and direct observation. Oil droplets with radii 10 < R < 100 µm were colonized and deformed by bacteria over several days before their effective rising speeds were measured. The rising speeds of deformed droplets were significantly slower than those of droplets without bacteria. This decrease in rising speed is understood by an increase in drag force and a decrease in buoyancy as a result of bio-aggregate formation at the droplet surface. Additionally, we found sinking bio-aggregate particles of oil and bacterial biofilms and quantified their composition using fluorescence microscopy. Our experiments can be adapted to further study the interactions between oil droplets and marine organisms and could significantly improve our understanding of the transport of hydrocarbons and complex aggregates.

Phytoremediation of crude oil-contaminated sediment using Suaeda heteroptera enhanced by Nereis succinea and oil-degrading bacteria.

A 150-day experiment was performed to investigate the stimulatory effect of a promising phytoremediation strategy consisting of Suaeda heteroptera (S. heteroptera), Nereis succinea (N. succinea), and oil-degrading bacteria for cleaning up total petroleum hydrocarbons (TPHs) in spiked sediment. Inoculation with oil-degrading bacteria and/or N. succinea increased plant yield and TPH accumulation in S. heteroptera plants. The highest TPH dissipation (40.5%) was obtained in the combination treatment, i.e., S. heteroptera + oil-degrading bacteria + N. succinea, in which the sediment TPH concentration decreased from an initial value of 3955 to 2355 mg/kg in 150 days. BAF, BCF, and TF confirmed the role of N. succinea and oil-degrading bacteria in the amelioration and translocation of TPHs. In addition, TPH toxicity of S. heteroptera was alleviated by N. succinea and oil-degrading bacteria addition through the reduction of oxidative stress. Therefore, S. heteroptera could be used for cleaning up oil-contaminated sediment, particularly in the presence of oil-degrading bacteria + N. succinea. Field studies on oil-degrading bacteria + N. succinea may provide new insights on the rehabilitation and restoration of sediments contaminated by TPHs.

Our study attempted to investigate the stimulatory effect of a promising phytoremediation strategy consisting of Suaeda heteroptera (S. heteroptera), Nereis succinea (N. succinea), and oil-degrading bacteria for cleaning up TPH in spiked sediment. Planting S. heteroptera can greatly increase sediment TPH removal, and its removal was enhanced greater after inoculation with oil-degrading bacteria and/or N. succinea. Moreover, the promising phytoremediation strategy developed in the current work can serve as an efficient, novel approach to removal TPH in sediment/soil. In our opinions, these findings provide insights into the assessment of their ecological risks in the environments that are of interest to broad readership of International Journal of Phytoremediation.

Isolation, characterization and determination of biotechnological potential of oil-degrading bacteria from Algerian centre coast.

AIMS: The Algerian coastline is exposed to several types of pollution, including hydrocarbons. The aim of this work was to isolate oil-degrading bacteria and to explore the intrinsic bioremediation potential of part of its contaminated harbour. METHODS AND RESULTS: A collection of 119 strains, capable to grow on mineral medium supplemented with hydrocarbons, were obtained from polluted sediment and seawater collected from Sidi Fredj harbour (Algiers). Twenty-three strains were selected for further studies. Sequencing of the 16S rRNA gene showed that most isolates belong to genera of hydrocarbonoclastic bacteria (Alcanivorax), generalist hydrocarbons degraders (Marinobacter, Pseudomonas, Gordonia, Halomonas, Erythrobacter and Brevibacterium) and other bacteria not known as hydrocarbon degraders (Xanthomarina) but were able to degrade hydrocarbons. Strains related to Marinobacter and Alcanivorax were frequently isolated from our samples and resulted the most effective in degrading crude oil. Screening of catabolic genes alkB and xylA revealed the presence of alkB gene in several bacterial strains; one isolate harboured both catabolic genes while other isolates carried none of the studied genes. However, they grew in the presence of crude oil implying the existence of other biodegradation pathways. CONCLUSIONS: The samples of seawater and sediment from the Algerian coast contain high level of hydrocarbon-degrading bacteria that could be interesting and useful for future bioremediation purposes. SIGNIFICANCE AND IMPACT OF THE STUDY: This investigation demonstrates the diversity of hydrocarbon-degrading bacteria from a marine-contaminated area in Algeria, and their variable biodegradation abilities.

Production of Biosurfactant Produced from Used Cooking Oil by Bacillus sp. HIP3 for Heavy Metals Removal.

Heavy metals from industrial effluents and sewage contribute to serious water pollution in most developing countries. The constant penetration and contamination of heavy metals into natural water sources may substantially raise the chances of human exposure to these metals through ingestion, inhalation, or skin contact, which could lead to liver damage, cancer, and other severe conditions in the long term. Biosurfactant as an efficient biological surface-active agent may provide an alternative solution for the removal of heavy metals from industrial wastes. Biosurfactants exhibit the properties of reducing surface and interfacial tension, stabilizing emulsions, promoting foaming, high selectivity, and specific activity at extreme temperatures, pH, and salinity, and the ability to be synthesized from renewable resources. This study aimed to produce biosurfactant from renewable feedstock, which is used cooking oil (UCO), by a local isolate, namely Bacillus sp. HIP3 for heavy metals removal. Bacillus sp. HIP3 is a Gram-positive isolate that gave the highest oil displacement area with the lowest surface tension, of 38 mN/m, after 7 days of culturing in mineral salt medium and 2% (v/v) UCO at a temperature of 30 °C and under agitation at 200 rpm. An extraction method, using chloroform:methanol (2:1) as the solvents, gave the highest biosurfactant yield, which was 9.5 g/L. High performance liquid chromatography (HPLC) analysis confirmed that the biosurfactant produced by Bacillus sp. HIP3 consists of a lipopeptide similar to standard surfactin. The biosurfactant was capable of removing 13.57%, 12.71%, 2.91%, 1.68%, and 0.7% of copper, lead, zinc, chromium, and cadmium, respectively, from artificially contaminated water, highlighting its potential for bioremediation.

Sphingopyxis nepalensis sp. nov., isolated from oil-contaminated soil.

During a study of oil-degrading bacteria, three yellow-coloured, Gram-stain-negative, non-motile and rod-shaped bacteria, designated strains Ktm-14T, Ktm-17 and Ktm-18, were isolated from oil-contaminated soil of Biratnagar, Morang, Nepal. The strains were able to grow at 15-37 °C, pH 4.5-10.0 and 0-2 % (w/v) NaCl concentration. Strains Ktm-14T, Ktm-17 and Ktm-18 were characterized by multiple taxonomic approaches. Based on 16S rRNA gene sequence analysis, strains Ktm-14T, Ktm-17 and Ktm-18 belonged to the genus Sphingopyxis and shared highest sequence similarity with Sphingopyxis ginsengisoliGsoil 250T (98.94 %). The only respiratory quinone was ubiquinone-10 and the predominant polyamine was spermidine. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine, phosphatidylmonomethylethanolamine and sphingoglycolipids. The predominant fatty acids were C17 : 1ω6c, summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and C16 : 0. The DNA G+C content values of strains Ktm-14T, Ktm-17 and Ktm-18 were 65.8, 65.9 and 65.6 mol%, respectively. The DNA-DNA relatedness between Ktm-14T and Ktm-17 and Ktm-18 were higher than 70 % but with closely related reference strains were less than 40 %. The morphological, physiological, chemotaxonomic and phylogenetic analyses clearly distinguished strain Ktm-14T from its closest phylogenetic neighbours. Thus, strain Ktm-14T represents a novel species of the genus Sphingopyxis, for which the name Sphingopyxisnepalensis sp. nov. is proposed. The type strain is Ktm-14T (=KEMB 9005-694T=KACC 19389T=JCM 32250T), and strains Ktm-17 and Ktm-18 represent two additional strains.

Study on immobilization of marine oil-degrading bacteria by carrier of algae materials.

This study investigated the immobilizations with of bacteria two kinds of algal materials, Enteromorpha residue and kelp residue. The lipophilicity of them were compared by diesel absorption rates. The immobilization efficiency of Bacillus sp. E3 was measured to evaluate whether these carriers would satisfy the requirement for biodegradation of oil spills. The bacteria were immobilized through adsorption with the sterilized and non-sterilized carriers to compare the differences between the two treatments. Oil degradation rates were determined using gravimetric and GC-MS methods. Results showed the absorption rates of Enteromorpha residue and kelp residue for diesel were 411 and 273% respectively and remained approximately 105 and 120% after 2 h of erosion in simulated seawater system. After immobilized of Bacillus sp. E3, the oil degradation rates of them were higher than 65% after 21 days biodegradations. GC-MS analysis showed that two immobilizations degraded higher than 70% of the total alkane and the total PAHs, whereas the free bacteria degraded 63% of the total alkane and 66% the total PAHs. And the bacteria immobilized with the carriers degraded more HMW-alkanes and HMW-PAHs than the free bacteria. The bacteria immobilized by non-sterilized kelp residue showed a considerably higher degradation rate than that using sterilized kelp residue. A considerably higher cells absorption rate of immobilization was obtained when using kelp residue, and the preparation of immobilization was low cost and highly efficient. The experiments show the two algae materials, especially the kelp residue, present potential application in bioremediation of marine oil spills.

Inhibitory Effect of Taurine on Biofilm Formation During Alkane Degradation in Acinetobacter oleivorans DR1.

Taurine, 2-aminoethanesulfonate, is known to function as an antioxidant or membrane stabilizer in eukaryotic cells, but its role in bacteria has been poorly characterized. Biofilm formation of Acinetobacter oleivorans DR1 was significantly reduced by taurine only during alkane degradation, suggesting that taurine affects alkane-induced cell surface. Structurally similar compounds harboring an amine group such as hypotaurine or ethylenediamine have a similar effect, which was not observed with sulfonate-containing chemicals such as ethanesulfonic acid, hexanesulfonic acid. Our biochemical assays and physiological tests demonstrate that taurine reduced cell surface hydrophobicity, which resulted in interruption of the interactions between cells and oily substrate surfaces, such that cells utilized alkanes less effectively. Interestingly, taurine-mediated reduction of quorum sensing (QS) signal production and QS-control sapA gene expression indicated that membrane permeability of quorum signals was also interfered by taurine. Composition and biomass of extracellular polymeric saccharides were changed in taurine-amended conditions. Taken together, our data provide evidence that amine-containing taurine can inhibit biofilm formation of DR1 cells during alkane degradation by (i) changing cell surface charge and (ii) reducing membrane hydrophobicity and QS sensing.

Profiling microbial community structures across six large oilfields in China and the potential role of dominant microorganisms in bioremediation.

Successful bioremediation of oil pollution is based on a comprehensive understanding of the in situ physicochemical conditions and indigenous microbial communities as well as the interaction between microorganisms and geochemical variables. Nineteen oil-contaminated soil samples and five uncontaminated controls were taken from six major oilfields across different geoclimatic regions in China to investigate the spatial distribution of the microbial ecosystem. Microbial community analysis revealed remarkable variation in microbial diversity between oil-contaminated soils taken from different oilfields. Canonical correspondence analysis (CCA) further demonstrated that a suite of in situ geochemical parameters, including soil moisture and sulfate concentrations, were among the factors that influenced the overall microbial community structure and composition. Phylogenetic analysis indicated that the vast majority of sequences were related to the genera Arthrobacter, Dietzia, Pseudomonas, Rhodococcus, and Marinobacter, many of which contain known oil-degrading or oil-emulsifying species. Remarkably, a number of archaeal genera including Halalkalicoccus, Natronomonas, Haloterrigena, and Natrinema were found in relatively high abundance in some of the oil-contaminated soil samples, indicating that these Euryarchaeota may play an important ecological role in some oil-contaminated soils. This study offers a direct and reliable reference of the diversity of the microbial community in various oil-contaminated soils and may influence strategies for in situ bioremediation of oil pollution.

Transcriptome analysis of Acinetobacter calcoaceticus HX09 strain with outstanding crude-oil-degrading ability.

Microbial remediation plays a pivotal role in the elimination of petroleum pollutants, making it imperative to investigate the capabilities of microorganisms in degrading petroleum. The present study describes the isolation of a promising strain, Acinetobacter sp. HX09, from petroleum-contaminated water. GC-MS analysis revealed a remarkable removal efficiency for short and medium-chain alkanes, with a rate of approximately 64% after a 7-days incubation at 30 °C. Transcriptome analysis of HX09 exhibited a predominant upregulation in gene expression levels by the induce of crude oil. Notably, genes such as alkane 1-monooxygenase, dehydrogenases and fatty acid metabolic enzymes exhibited fold changes range from 3.16 to 1.3. Based on the alkB gene sequences in HX09, the Phyre2 algorithm generated a three-dimensional structure that exhibited similarity to segments of acyl coenzyme desaturases and acyl lipid desaturases. Furthermore, three biodegradation-related gene clusters were predicted in HX09 based on the reference genome sequence. These findings contribute to our understanding of the hydrocarbon-degrading mechanisms employed by Acinetobacter species and facilitate the development of effective remediation strategies for crude oil- polluted environments.

Long-term patterns of hydrocarbon biodegradation and bacterial community composition in epipelagic and mesopelagic zones of an Arctic fjord.

Oil spill attenuation in Arctic marine environments depends on oil-degrading bacteria. However, the seasonally harsh conditions in the Arctic such as nutrient limitations and sub-zero temperatures limit the activity even for bacteria capable of hydrocarbon metabolism at low temperatures. Here, we investigated whether the variance between epipelagic (seasonal temperature and inorganic nutrient variations) and mesopelagic zone (stable environmental conditions) could limit the growth of oil-degrading bacteria and lead to lower oil biodegradation rates in the epipelagic than in the mesopelagic zone. Therefore, we deployed absorbents coated with three oil types in a SW-Greenland fjord system at 10-20 m (epipelagic) and 615-650 m (mesopelagic) water depth for one year. During this period we monitored the development and succession of the bacterial biofilms colonizing the oil films by 16S rRNA gene amplicon quantification and sequencing, and the progression of oil biodegradation by gas chromatography - mass spectrometry oil fingerprinting analysis. The removal of hydrocarbons was significantly different, with several polycyclic aromatic hydrocarbons showing longer half-life times in the epipelagic than in the mesopelagic zone. Bacterial community composition and density (16S rRNA genes/ cm2) significantly differed between the two zones, with total bacteria reaching to log-fold higher densities (16S rRNA genes/cm2) in the mesopelagic than epipelagic oil-coated absorbents. Consequently, the environmental conditions in the epipelagic zone limited oil biodegradation performance by limiting bacterial growth.

Distribution and abundance of oil-degrading bacteria in seawater of the Yellow Sea and Bohai Sea, China.

Petroleum hydrocarbons are widespread in seawater. As an important sea area in northern China, the content and distribution of petroleum hydrocarbons in seawater need our attention because of the high toxicity and lasting polluting effects on the ecological environment of the Yellow Sea and Bohai Sea. In addition, there are few reports comparing the diversity of oil-degrading bacteria before and after enrichment. Therefore, we collected surface seawater from 10 sites in the Yellow Sea and Bohai Sea in the autumn of 2020 to study the distribution characteristics of total petroleum hydrocarbons (TPH) and the diversity of oil-degrading bacteria. The concentration of TPH was 81.65 µg/L-139.55 µg/L at ten sites in the Bohai Sea and the Yellow Sea, which conformed to the China Grade II water quality standard (GB3097-1997). Moreover, the pristine/phytane (PR/PH) value of most sites was close to 1, indicating that the area was obviously polluted by exogenous petroleum hydrocarbons. We found that oil-degrading bacteria in the seawater of the Yellow Sea and the Bohai Sea had a good degradation effect on C11-C14 short chain alkanes (degradation rate of 59.19-73.22 %) and C1-C4 phenanthrene (degradation rate of 48.19-60.74 %). In terms of the diversity of oil-degrading bacteria, Gammaproteobacteria and Alphaproteobacteria dominated the enriched bacterial communities. Notably, the relative abundance of Alcanivorax changed significantly before and after enrichment. We proposed that surface seawater in the Bohai Sea and Yellow Sea could form oil-degrading bacteria mainly composed of Alcanivorax, which had great potential for oil pollution remediation.

Construction and application of highly efficient waste cooking oil degrading bacteria consortium in oily wastewater.

The treatment of cooking oil wastewater is an urgent issue need to be solved. We aimed to screen for efficient oil-degrading bacteria and develop a new microbial agent for degrading waste cooking oil in oily wastewater. Three extremely effective oil-degrading bacteria, known as YZQ-1, YZQ-3, and YZQ-4, were found by the enrichment and acclimation of samples from various sources and separation using oil degradation plates. The 16S rRNA sequencing analysis and phylogenetic tree construction showed that the three strains were Bacillus tropicus, Pseudomonas multiresinivorans, and Raoultella terrigena. Under optimal degradation conditions, the maximal degradation rates were 67.30 ± 3.69%, 89.65 ± 1.08%, and 79.60 ± 5.30%, respectively, for YZQ-1, YZQ-3, and YZQ-4. Lipase activity was highest for YZQ-3, reaching 94.82 ± 12.89 U/L. The best bacterial alliance was obtained by adding equal numbers of microbial cells from the three strains. Moreover, when this bacterial alliance was applied to oily wastewater, the degradation rate of waste cooking oil was 61.13 ± 7.30% (3.67% ± 2.13% in the control group), and COD removal was 62.4% ± 5.65% (55.60% ± 0.71% in the control group) in 72 h. Microbial community analysis results showed YZQ-1 and YZQ-3 were adaptable to wastewater and could coexist with local bacteria, whereas YZQ-4 could not survive in wastewater. Therefore, the combination of YZQ-1 and YZQ-3 can efficiently degrade oil and shows great potential for oily wastewater treatment.

Biodegradation of water-accommodated aromatic oil compounds in Arctic seawater at 0 °C.

Oil spills in Arctic marine environments are expected to increase concurrently with the expansion of shipping routes and petroleum exploitation into previously inaccessible ice-dominated regions. Most research on oil biodegradation focusses on the bulk oil, but the fate of the water-accommodated fraction (WAF), mainly composed of toxic aromatic compounds, is largely underexplored. To evaluate the bacterial degradation capacity of such dissolved aromatics in Greenlandic seawater, microcosms consisting of 0 °C seawater polluted with WAF were investigated over a 3-month period. With a half-life (t1/2) of 26 days, m-xylene was the fastest degraded compound, as measured by gas chromatography - mass spectrometry. Substantial slower degradation was observed for ethylbenzene, naphthalenes, phenanthrene, acenaphthylene, acenaphthene and fluorenes with t1/2 of 40-105 days. Colwellia, identified by 16S rRNA gene sequencing, was the main potential degrader of m-xylene. This genus occupied up to 47 % of the bacterial community until day 10 in the microcosms. Cycloclasticus and Zhongshania aliphaticivorans, potentially utilizing one-to three-ringed aromatics, replaced Colwellia between day 10 and 96 and occupied up to 6 % and 23 % of the community, respectively. Although most of the WAF can ultimately be eliminated in microcosms, our results suggest that the restoration of an oil-impacted Arctic environment may be slow as most analysed compounds had t1/2 of over 2-3 months and the detrimental effects of a spill towards the marine ecosystem likely persist during this time.

Access-dispersion-recovery strategy for enhanced mitigation of heavy crude oil pollution using magnetic nanoparticles decorated bacteria.

Heavy crude oil (HCO) pollution has gained global attention, but traditional bioremediating practices demonstrate limited effectiveness. This study developed magnetic nanoparticles decorated bacteria (MNPB) using an oil-degrading and biosurfactant-producing Rhodococcus erythropolis species and identified a novel access-dispersion-recovery strategy for enhanced HCO pollution mitigation. The strategy entails (1) magnetic navigation of the MNPB towards HCO layer, (2) enhanced oil dispersion and formation of suspended oil-bacteria aggregates, and (3) magnetic recovery of these aggregates. The UV-spectrophotometer analysis showed that this strategy can enable up to 62% removal of HCO. The GC-MS analysis demonstrated that the MNPB enhanced the degradation of low-molecular-weight aromatics comparing with the pure bacteria, and the recovery process further removed oil-bacteria aggregates and entrained high-molecular-weight aromatics. The feasibility of using MNPB to mitigate HCO pollution could shed light on the emerging bioremediation applications.

Worms eat oil: Alcanivorax borkumensis hydrocarbonoclastic bacteria colonise Caenorhabditis elegans nematodes intestines as a first step towards oil spills zooremediation.

The environmental hazards of oil spills cannot be underestimated. Bioremediation holds promise among various approaches to tackle oil spills in soils and sediments. In particular, using oil-degrading bacteria is an efficient and self-regulating way to remove oil spills. Using animals for oil spills remediation is in its infancy, mostly due to the lack of efficient oil-degrading capabilities in eukaryotes. Here we show that Caenorhabditis elegans nematodes survive for extended periods (up to 22 days) on pure crude oil diet. Moreover, we report for the first time the use of Alcanivorax borkumensis hydrocarbonoclastic bacteria for colonisation of C. elegans intestines, which allows for effective digestion of crude oil by the nematodes. The worms fed and colonised by A. borkumensis demonstrated the similar or even better longevity, resistance against oxidative and thermal stress and reproductivity as those animals fed with Escherichia coli bacteria (normal food). Importantly, A. borkumensis-carrying nematodes were able to accumulate oil droplet from oil-contaminated soils. Artificial colonisation of soil invertebrates with oil-degrading bacteria will be an efficient way to distribute microorganisms in polluted soil, thus opening new avenues for oil spills zooremediation.

Biodegradation of weathered crude oil by microbial communities in solid and melted sea ice.

Oil spilled in the Arctic may drift into ice-covered areas and become trapped until the ice melts. To determine if exposure to oil during freezing may have a priming effect on degradation of the oil, weathered dispersed oil (2-3 mg/L) was frozen into solid ice for 200 days at -10 °C, then melted and incubated for 64 days at 4 °C. No degradation was measured in oil frozen into ice prior to melting. Both total amount of oil and target compounds were biotransformed by the microbial community from the melted ice. However, oil released from melted ice was degraded at a slower rate than oil incubated in fresh seawater at the same temperature (4 °C), and by a different microbial community. These data suggest negligible biodegradation of oil frozen in sea ice, while oil-degrading bacteria surviving in the ice may contribute to biodegradation when the ice melts.

Biodiversity and oil degradation capacity of oil-degrading bacteria isolated from deep-sea hydrothermal sediments of the South Mid-Atlantic Ridge.

Studies have reported that various hydrocarbons and hydrocarbon-degrading bacteria are found in global deep-sea hydrothermal regions. However, little is known about degradation characteristics of culturable hydrocarbon-degrading bacteria from these regions. We speculate that these bacteria can be used as resources for the bioremediation of oil pollution. In this study, six oil-degrading consortia were obtained from the hydrothermal region of the Southern Mid-Atlantic Ridge through room-temperature enrichment experiments. The dominant oil-degrading bacteria belonged to Nitratireductor, Pseudonocardia, Brevundimonas and Acinetobacter. More varieties of hydrocarbon-degrading bacteria were obtained from sediments (preserved at 4 °C) near hydrothermal vents. Most strains had the ability to degrade high molecular weight petroleum components. In addition, Pseudonocardia was shown to exhibit a high degradation ability for phytane and pristine for the first time. This study may provide new insights into the community structure and biodiversity of culturable oil-degrading bacteria in deep-sea hydrothermal regions.

Time- and compound-dependent microbial community compositions and oil hydrocarbon degrading activities in seawater near the Chinese Zhoushan Archipelago.

Marine microorganisms play an irreplaceable role in removing spilled oil. Zhoushan archipelago has one of the busiest ports and oil stockpiles in China. However, little is known about which and how fast oil-degrading microorganisms could biodegrade spilled oil here. By combining 14C-/3H-based radiotracer assays and MiSeq sequencing, we report the successive pattern of microbial oil-degrading activities and community compositions. The biodegradation rates of alkanes and PAHs (Polycyclic Aromatic Hydrocarbons) were significantly stimulated by oil addition, and reached their maximum after incubation for 3 and 7 days, respectively. Meanwhile, the abundances of alkB and phnAc genes increased and the bacterial communities continuously shifted. Potential oil-degrading bacteria Alcanivorax, Erythrobacter were the dominant degraders by day 3, whereas the dominant degraders shifted to C1-B045, Alteromonas, Pseudohongiella in the later period. These results provide valuable insights into the cooperative system of the versatile oil-degrading bacteria in successively biodegrading complex oil hydrocarbons in oil spills.

Hydrocarbon-Degrading Bacteria Alcanivorax and Marinobacter Associated With Microalgae Pavlova lutheri and Nannochloropsis oculata.

Marine hydrocarbon-degrading bacteria play an important role in natural petroleum biodegradation processes and were initially associated with man-made oil spills or natural seeps. There is no full clarity though on what, in the absence of petroleum, their natural niches are. Few studies pointed at some marine microalgae that produce oleophilic compounds (alkanes, long-chain fatty acids, and alcohols) as potential natural hosts of these bacteria. We established Dansk crude oil-based enrichment cultures with photobioreactor-grown marine microalgae cultures Pavlova lutheri and Nannochloropsis oculata and analyzed the microbial succession using cultivation and SSU (16S) rRNA amplicon sequencing. We found that petroleum enforced a strong selection for members of Alpha- and Gamma-proteobacteria in both enrichment cultures with the prevalence of Alcanivorax and Marinobacter spp., well-known hydrocarbonoclastic bacteria. In total, 48 non-redundant bacterial strains were isolated and identified to represent genera Alcanivorax, Marinobacter, Thalassospira, Hyphomonas, Halomonas, Marinovum, Roseovarius, and Oleibacter, which were abundant in sequencing reads in both crude oil enrichments. Our assessment of public databases demonstrated some overlaps of geographical sites of isolation of Nannochloropsis and Pavlova with places of molecular detection and isolation of Alcanivorax and Marinobacter spp. Our study suggests that these globally important hydrocarbon-degrading bacteria are associated with P. lutheri and N. oculata.

Potential effects of bacterial communities on the formation of blooms of the harmful dinoflagellate Prorocentrum after the 2014 Texas City "Y" oil spill (USA).

The association between phytoplankton blooms and oil spills is still controversial despite numerous studies. Surprisingly, to date, there have been no studies on the effect of bacterial communities (BCs) exposed to crude oil on phytoplankton growth, even though crude oil changes BCs, which can then affect phytoplankton growth and species composition. Co-culture with crude oil-exposed BCs significantly stimulated the growth of Prorocentrum texanum in the laboratory. To gain more direct evidence, oil-degrading bacteria from oil-contaminated sediment collected after the Texas City "Y" oil spill were isolated, and changes in dinoflagellate growth when co-cultured with single bacterial isolates was investigated. The oil-degrading bacterial isolates significantly stimulated the growth of dinoflagellates (axenic and xenic cultures) through releasing growth-promoting substances. This study provides new evidence for the potential role of oil-degrading bacteria in the formation of phytoplankton blooms after an oil spill.