Marinobacter Hydrocarbonoclasticus Research Articles

Effect of microbial growth rate on temperature and metabolic water recorded in 18O/16O ratios of PO4 in DNA

It has been recently demonstrated that both temperature and intracellular/metabolic water are recorded by the PO4 moieties comprising the backbone of DNA in microbial cells as well as in total microbial biomass PO4 (Blake et al., 2016; Li et al., 2016). Temperature and intracellular water composition are reflected in the 18O/16O ratio of PO4 (δ18OP) in DNA (Blake et al., 2016). To determine whether the reported temperature recording by microbial DNA-PO4 could be an artifact of variable microbial growth rate, which may also vary as a function of temperature, three strains of microorganisms having distinct and different growth rate patterns between 23 and 42 °C—Pseudomonas fluorescens, Acinetobacter ADP1 and Marinobacter aquaeolei were cultured over a range of temperatures and growth rate patterns. Growth curve patterns for the different strains were distinct and growth rates increased with temperature. However, as we show here, variations in δ18OP values of DNA-PO4 did not correlate with changes in bacterial growth rates at a given temperature, and O isotope fractionations (i.e., partitioning of O isotopes) between PO4 in DNA and O in water were not significantly different between strains (<1‰). Results suggest that for some microbial strains, strain-specific growth rates could cause minor variation in δ18OP values of microbial DNA independent of temperature effects. Thus, we interpret observed trends as strain-specific, intrinsic differences in growth patterns that do not significantly overprint the recording of temperature and intracellular water O isotopic composition by PO4 comprising the backbone of DNA.

Marinobacter nauticus (Baumann et al. 1972) comb. nov. arising from instances of synonymy and the incorrect interpretation of the International Code of Nomenclature of Prokaryotes.

Studies on Pseudomonas nautica Baumann et al. 1972 (Approved Lists 1980) and Marinobacter hydrocarbonoclasticus Gauthier et al. 1992 have shown that they should be treated as heterotypic synonyms. As a consequence, they have been treated as belonging to a single species, Marinobacter hydrocarbonoclasticus Gauthier et al. 1992. This interpretation of the International Code of Nomenclature of Bacteria/Prokaryotes is, however, based on a fundamental flaw in the interpretation of the wording of Rule 15 as documented in the 1975 and 1990 revisions where the wording has been partially corrected in the 2008 revision. A key aspect of the incorrect interpretation is that the nomenclatural type of a taxon, in this case Marinobacter hydrocarbonoclasticus Gauthier et al. 1992 (the nomenclatural type of the Marinobacter Gauthier et al. 1992) must be used instead of recognising the priority of the epithet in Pseudomonas nautica Baumann et al. 1972 (Approved Lists 1980), with the creation of a new combination Marinobacter nauticus (Baumann et al. 1972). It is now clear that there is no justification for that interpretation and it is necessary to create a new combination, Marinobacter nauticus (Baumann et al. 1972) in the situation where Marinobacter hydrocarbonoclasticus Gauthier et al. 1992 and Pseudomonas nautica Baumann et al. 1972 (Approved Lists 1980) are treated as heterotypic synonyms. Additional studies have shown that Marinobacter aquaeolei Nguyen et al. 1993 and Marinobacter hydrocarbonoclasticus Gauthier et al. 1992 should also be treated as heterotypic synonyms.

The Effective Emulsifying Property of Biosurfactant–Producing Marinobacter hydrocarbonoclasticus ST1 Obtained from Palm Oil Contaminated Sites

The Marinobacter hydrocarbonoclasticus ST1, isolated from soil contaminated with palm oil from palm oil mill factories in southern Thailand, was evaluated as a potential biosurfactant with effective emulsifying property. This strain was able to produce biosurfactant with the maximum emulsification activity of 81% and emulsification index of 60% after 60 h of cultivation under the optimized cultivation conditions. The yield of biosurfactant obtained by chloroform:methanol (2 : 1, vol/vol) extraction was 1.85 g/L. The stability of the biosurfactant was effective over a wide range of pH, temperature and salinity. The high thermostability of the biosurfactant was assessed by simultaneous thermal analyzer. In addition, a preliminary chemical characterization using FT-IR, 1H-NMR and 13C-NMR indicated that it is glycolipid biosurfactant. The features of this biosurfactant make it a promising product for many industrial applications involving to extreme conditions.

Structure and functional analysis of a bacterial adhesin sugar-binding domain.

Bacterial adhesins attach their hosts to surfaces through one or more ligand-binding domains. In RTX adhesins, which are localized to the outer membrane of many Gram-negative bacteria via the type I secretion system, we see several examples of a putative sugar-binding domain. Here we have recombinantly expressed one such ~20-kDa domain from the ~340-kDa adhesin found in Marinobacter hydrocarbonoclasticus, an oil-degrading bacterium. The sugar-binding domain was purified from E. coli with a yield of 100 mg/L of culture. Circular dichroism analysis showed that the protein was rich in beta-structure, was moderately heat resistant, and required Ca2+ for proper folding. A crystal structure was obtained in Ca2+ at 1.2-Å resolution, which showed the presence of three Ca2+ ions, two of which were needed for structural integrity and one for binding sugars. Glucose was soaked into the crystal, where it bound to the sugar’s two vicinal hydroxyl groups attached to the first and second (C1 and C2) carbons in the pyranose ring. This attraction to glucose caused the protein to bind certain polysaccharide-based column matrices and was used in a simple competitive binding assay to assess the relative affinity of sugars for the protein’s ligand-binding site. Fucose, glucose and N-acetylglucosamine bound most tightly, and N-acetylgalactosamine hardly bound at all. Isothermal titration calorimetry was used to determine specific binding affinities, which lie in the 100-μM range. Glycan arrays were tested to expand the range of ligand sugars assayed, and showed that MhPA14 bound preferentially to branched polymers containing terminal sugars highlighted as strong binders in the competitive binding assay. Some of these binders have vicinal hydroxyl groups attached to the C3 and C4 carbons that are sterically equivalent to those presented by the C1 and C2 carbons of glucose.

Understanding the cumulative effects of salinity, temperature and inoculation size for the design of optimal halothermotolerant bioanodes from hypersaline sediments

The main objective of this study was to understand the interaction between salinity, temperature and inoculum size and how it could lead to the formation of efficient halothermotolerant bioanodes from the Hypersaline Sediment of Chott El Djerid (HSCE). Sixteen experiments on bioanode formation were designed using a Box-Behnken matrix and response surface methodology to understand synchronous interactions. All bioanode formations were conducted on 6 cm2 carbon felt electrodes polarized at −0.1 V/SCE and fed with lactate (5 g/L) at pH 7.0. Optimum levels for salinity, temperature and inoculum size were predicted by NemrodW software as 165 g/L, 45 °C and 20%, respectively, under which conditions maximum current production of 6.98 ± 0.06 A/m2 was experimentally validated. Metagenomic analysis of selected biofilms indicated a relative abundance of the two phyla Proteobacteria (from 85.96 to 89.47%) and Firmicutes (from 61.90 to 68.27%). At species level, enrichment of Psychrobacter aquaticus, Halanaerobium praevalens, Psychrobacter alimentaris, and Marinobacter hydrocarbonoclasticus on carbon-based electrodes was correlated with high current production, high salinity and high temperature. Members of the halothermophilic bacteria pool from HSCE, individually or in consortia, are candidates for designing halothermotolerant bioanodes applicable in the bioelectrochemical treatment of industrial wastewater at high salinity and temperature.

Microremediation of tannery wastewater by siderophore producing marine bacteria

ABSTRACT The present study evaluated the microremediation potential of nine siderophore producing marine bacteria for hazardous raw tannery wastewater from common effluent treatment plant (CETP). Most of the pollutants detected in the wastewater were diminished after the bioremediation process. Further, among the three potent isolates selected for aerobic and anaerobic bioremediation study, Marinobacter hydrocarbonoclasticus demonstrated the highest bioremediation aerobically with a reduction in chromium (88%), sulphate (71%), phosphate (68%) and nitrate (57%). Notably, Nitratireductor kimnyeongensis could attack the effluent under both aerobic and anaerobic conditions as substantiated by statistically significant (p < .05) reduction in the pollutants [chromium (85%), sulphate (63%), Chemical Oxygen Demand (COD) (69%), phosphate (76%)]. From the study it is evident that the pollutant load reduction was achieved under both aerobic and anaerobic conditions, however, aerobic environment was more effective in reducing chromium, Biochemical Oxygen Demand (BOD), sulphate, nitrate and phosphate. The bioremediation efficiency was further confirmed by the bioassay experiments with plant and animal models where higher seed germination, greater plant length and biomass, as well as improved survival rate of Artemia nauplii for bioremediated wastewater was observed as compared to the untreated effluent indicating a significant reduction in toxicity. The results for simultaneous removal of multiple-toxicants thus signify effectiveness and ease of using the robust properties of these marine bacterial strains suggesting their potential application for bioremediation. Hence this could pave a promising way for an environment-friendly and economically feasible clean-up strategy for safer disposal of tannery wastewater.

Corrosion Inhibition of X80 Steel in Simulated Marine Environment with Marinobacter aquaeolei

In the present study, a novel bacterium (Marinobacter aquaeolei) was examined for its corrosion inhibiting behaviour against X80 pipeline steel. Electrochemical results showed that X80 steel immersed in the solution inoculated with M. aquaeolei possessed very high corrosion resistance compared to that of abiotic control. Besides, scanning electron microscopy, confocal laser scanning microscopy and energy-dispersive X-ray spectroscopy were employed to analyse the corrosion product and the biofilm formed on the metal surface. Fourier-transform infrared spectroscopy was also applied to determine the composition of extracellular polymeric substances (EPS). Above results indicated that the corrosion inhibition efficiency observed in biotic medium was very high (91%), proving that M. aquaeolei was an effective inhibitive agent for the corrosion of carbon steel. The inhibition was credited to the formation of bacterial biofilm and the compact protective layer of the secreted EPS. Thus, this study will introduce a natural, environmentally friendly and cost-effective system for the corrosion control of the carbon steel.

Increasing jojoba-like wax ester production in Saccharomyces cerevisiae by enhancing very long-chain, monounsaturated fatty acid synthesis

BackgroundFatty acids (FAs) with a chain length of more than 18 carbon atoms (> C18) are interesting for the production of specialty compounds derived from these FAs. These compounds include free FAs, like erucic acid (C22:1-Δ13), primary fatty alcohols (FOHs), like docosanol (C22:0-FOH), as well as jojoba-like wax esters (WEs) (C38-WE to C44-WE), which are esters of (very) long-chain FAs and (very) long-chain FOHs. In particular, FAs, FOHs and WEs are used in the production of chemicals, pharmaceuticals and cosmetic products. Jojoba seed oil is highly enriched in diunsaturated WEs with over 70 mol% being composed of C18:1–C24:1 monounsaturated FOH and monounsaturated FA moieties. In this study, we aim for the production of jojoba-like WEs in the yeast Saccharomyces cerevisiae by increasing the amount of very long-chain, monounsaturated FAs and simultaneously expressing enzymes required for WE synthesis.ResultsWe show that the combined expression of a plant-derived fatty acid elongase (FAE/KCS) from Crambe abyssinica (CaKCS) together with the yeast intrinsic fatty acid desaturase (FAD) Ole1p leads to an increase in C20:1 and C22:1 FAs in S. cerevisiae. We also demonstrate that the best enzyme candidate for C24:1 FA production in S. cerevisiae is a FAE derived from Lunaria annua (LaKCS). The combined overexpression of CaKCS and Ole1p together with a fatty acyl reductase (FAR/FAldhR) from Marinobacter aquaeolei VT8 (MaFAldhR) and a wax synthase (WS) from Simmondsia chinensis (SciWS) in a S. cerevisiae strain, overexpressing a range of other enzymes involved in FA synthesis and elongation, leads to a yeast strain capable of producing high amounts of monounsaturated FOHs (up to C22:1-FOH) as well as diunsaturated WEs (up to C46:2-WE).ConclusionsChanging the FA profile of the yeast S. cerevisiae towards very long-chain monounsaturated FAs is possible by combined overexpression of endogenous and heterologous enzymes derived from various sources (e.g. a marine copepod or plants). This strategy was used to produce jojoba-like WEs in S. cerevisiae and can potentially be extended towards other commercially interesting products derived from very long-chain FAs.

Intra-clade metabolomic profiling of MAR4 Streptomyces from the Macaronesia Atlantic region reveals a source of anti-biofilm metabolites.

The search for new and effective strategies to reduce bacterial biofilm formation is of utmost importance as bacterial resistance to antibiotics continues to emerge. The use of anti-biofilm agents that can disrupt recalcitrant bacterial communities can be an advantageous alternative to antimicrobials, as their use does not lead to the development of resistance mechanisms. Six MAR4 Streptomyces strains isolated from the Madeira Archipelago, at the unexplored Macaronesia Atlantic ecoregion, were used to study the chemical diversity of produced hybrid isoprenoids. These marine actinomycetes were investigated by analysing their crude extracts using LC-MS/MS and their metabolomic profiles were compared using multivariate statistical analysis (principal component analysis), showing a separation trend closely related to their phylogeny. Molecular networking unveiled the presence of a class of metabolites not previously described from MAR4 strains and new chemical derivatives belonging to the napyradiomycin and marinone classes. Furthermore, these MAR4 strains produce metabolites that inhibit biofilm formation of Staphylococcus aureus and Marinobacter hydrocarbonoclasticus. The anti-biofilm activity of napyradiomycin SF2415B3 (1) against S. aureus was confirmed.

Biosensor for direct bioelectrocatalysis detection of nitric oxide using nitric oxide reductase incorporated in carboxylated single-walled carbon nanotubes/lipidic 3 bilayer nanocomposite

An enzymatic biosensor based on nitric oxide reductase (NOR; purified from Marinobacter hydrocarbonoclasticus) was developed for nitric oxide (NO) detection. The biosensor was prepared by deposition onto a pyrolytic graphite electrode (PGE) of a nanocomposite constituted by carboxylated single-walled carbon nanotubes (SWCNTs), a lipidic bilayer [1,2-di-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-di-(9Z-octadecenoyl)-3-trimethylammonium-propane (DOTAP), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethylene glycol (DSPE-PEG)] and NOR. NOR direct electron transfer and NO bioelectrocatalysis were characterized by several electrochemical techniques. The biosensor development was also followed by scanning electron microscopy and Fourier transform infrared spectroscopy. Improved enzyme stability and electron transfer (1.96 × 10−4 cm.s−1 apparent rate constant) was obtained with the optimum SWCNTs/(DOPE:DOTAP:DSPE-PEG)/NOR) ratio of 4/2.5/4 (v/v/v), which biomimicked the NOR environment. The PGE/[SWCNTs/(DOPE:DOTAP:DSPE-PEG)/NOR] biosensor exhibited a low Michaelis-Menten constant (4.3 μM), wide linear range (0.44–9.09 μM), low detection limit (0.13 μM), high repeatability (4.1% RSD), reproducibility (7.0% RSD), and stability (ca. 5 weeks). Selectivity tests towards L-arginine, ascorbic acid, sodium nitrate, sodium nitrite and glucose showed that these compounds did not significantly interfere in NO biosensing (91.0 ± 9.3%–98.4 ± 5.3% recoveries). The proposed biosensor, by incorporating the benefits of biomimetic features of the phospholipid bilayer with SWCNT's inherent properties and NOR bioelectrocatalytic activity and selectivity, is a promising tool for NO.

Third-generation electrochemical biosensor based on nitric oxide reductase immobilized in a multiwalled carbon nanotubes/1-n-butyl-3-methylimidazolium tetrafluoroborate nanocomposite for nitric oxide detection

Nitric oxide (NO) has a crucial role in signaling and cellular physiology in humans. Herein, a novel third-generation biosensor based on the Marinobacter hydrocarbonoclasticus metalloenzyme (nitric oxide reductase (NOR)), responsible for the NO reduction in the denitrifying processes, was developed through the direct adsorption of a new nanocomposite (multiwalled carbon nanotubes (MWCNTs)/1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4)/NOR) onto a pyrolytic graphite electrode (PGE) surface. The NOR direct electron transfer behavior (formal potential of -0.255 ± 0.003 V vs. Ag/AgCl) and electrocatalysis towards NO reduction (−0.68 ± 0.03 V vs. Ag/AgCl) of the PGE/[MWCNTs/BMIMBF4/NOR] biosensor were investigated in phosphate buffer at pH 6.0. Large enzyme loading (2.04 × 10−10 mol/cm2), acceptable electron transfer rate between NOR and the PGE surface (ks = 0.35 s-1), and high affinity for NO (Km = 2.17 μmol L-1) were observed with this biosensor composition. A linear response to NO concentration (0.23–4.76 μmol L-1) was perceived with high sensitivity (0.429 μA/μmolL-1), a detection limit of 0.07 μmol L-1, appropriate repeatability (9.1% relative standard deviations (RSD)), reproducibility (6.0–11% RSD) and 80–102% recoveries. The biosensor was stable during 1 month retaining 79–116% of its initial response. These data confirmed that NOR incorporated in the MWCNTs/BMIMBF4 nanocomposite can efficiently maintain its bioactivity paving a new and effective way for NO biosensing.

Direct Evidence for Ferrous Ion Oxidation and Incorporation in the Absence of Oxidants by Dps from Marinobacter hydrocarbonoclasticus.

Dps proteins (DNA-binding protein from starved cells) are hollow-sphere-shaped, dodecameric enzymes found in bacteria and archaeal species. They can oxidize ferrous iron in a controlled manner using hydrogen peroxide or molecular oxygen as co-substrate, and most of them confer physical protection through DNA binding. Oxidized iron is stored, as a mineral core, in a central cavity. Direct evidence is now provided that, furthermore, Dps proteins containing small mineral cores can oxidize and mineralize toxic ferrous ions in anaerobic conditions and in the absence of any additional aqueous oxidant co-substrate. Dps proteins containing cores of 24 irons per dodecamer can oxidize about 5 ferrous irons per dodecamer, with that number approximately doubling for protein particles containing in average 96 irons per protein. This additional activity carries importance as it can be a detoxification mechanism present during anaerobic or oxygen-limited growth conditions.

Adhesion of Marinobacter hydrocarbonoclasticus to Surfactant-Decorated Dodecane Droplets.

We investigate the effect of interfacial properties on the adhesion of bacteria at oil/water interfaces using confocal microscopy. Surfactant-decorated dodecane droplets of diameter 20-60 μm are generated using a coflow microfluidic device, introduced into an aqueous saline suspension of Marinobacter hydrocarbonoclasticus bacteria, and imaged in 3-D over time. Using image analysis algorithms, we determine the number of bacteria adhering at oil/water interfaces over time in the presence of dioctyl sodium succinate (DOSS), a component of the dispersant used in oil-spill recovery. The adsorption of bacteria at the oil/water interface follows Langmuir first-order kinetics for all droplet sizes, with the greatest areal number density of bacteria adhered to the smallest droplets. We vary the surfactant type [DOSS, dicyclohexyl sodium sulfosuccinate, dibutyl sodium sulfosuccinate, cetyltrimethylammonium bromide, and Tween 20] and concentration and examine the effects on long-time adhesion of bacteria. For a fixed droplet size, the areal density of bacteria at the interface decreases with increasing surfactant concentration because of a reduction in oil/water interfacial tension that increases the free energy of adhesion of the bacterium.

Isolation and Characterization of Alkalophilic Xylanase Producing Bacteria MS-2-1 from Marine Water Sample

A novel marine bacterium was isolated from Pichavaram mangrove forest located near Chidambaram, Tamil Nadu and designated as MS-2-1. Morphological, cultural, physiological characteristics as well as 16S rRNA gene sequence based phylogenetic analysis confirmed taxonomic affiliation of MS 2 as Marinobacter aquaeolei. The optimum pH and temperature for maximum production of xylanase was observed at pH 8.0 and 30ºC.

Denitrification-Potential Evaluation and Nitrate-Removal-Pathway Analysis of Aerobic Denitrifier Strain Marinobacter hydrocarbonoclasticus RAD-2

An aerobic denitrifier was isolated from a long-term poly (3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV-supported denitrification reactor that operated under alternate aerobic/anoxic conditions. The strain was identified as Marinobacter hydrocarbonoclasticus RAD-2 based on 16S rRNA-sequence phylogenetic analysis. Morphology was observed by scanning electron microscopy (SEM), and phylogenetic characteristics were analyzed with the API 20NE test. Strain RAD-2 showed efficient aerobic denitrification ability when using NO3−-N or NO2−-N as its only nitrogen source, while heterotrophic nitrification was not detected. The average NO3−-N and NO2−-N removal rates were 6.47 mg/(L·h)and 6.32 mg/(L·h), respectively. Single-factor experiments indicated that a 5:10 C/N ratio, 25–40 °C temperature, and 100–150 rpm rotation speed were the optimal conditions for aerobic denitrification. Furthermore, the denitrifying gene napA had the highest expression on a transcriptional level, followed by the denitrifying genes nirS and nosZ. The norB gene was found to have significantly low expression during the experiment. Overall, great aerobic denitrification ability makes the RAD-2 strain a potential alternative in enhancing nitrate management for marine recirculating aquaculture system (RAS) practices.

Electroanalytical characterization of the direct Marinobacter hydrocarbonoclasticus nitric oxide reductase-catalysed nitric oxide and dioxygen reduction

Understanding the direct electron transfer processes between redox proteins and electrode surface is fundamental to understand the proteins mechanistic properties and for development of novel biosensors. In this study, nitric oxide reductase (NOR) extracted from Marinobacter hydrocarbonoclasticus bacteria was adsorbed onto a pyrolytic graphite electrode (PGE) to develop an unmediated enzymatic biosensor (PGE/NOR)) for characterization of NOR direct electrochemical behaviour and NOR electroanalytical features towards NO and O2. Square-wave voltammetry showed the reduction potential of all the four NOR redox centers: 0.095 ± 0.002, −0.108 ± 0.008, −0.328 ± 0.001 and −0.635 ± 0.004 V vs. SCE for heme c, heme b, heme b3 and non-heme FeB, respectively. The determined sensitivity (−4.00 × 10−8 ± 1.84 × 10−9 A/μM and - 2.71 × 10−8 ± 1.44 × 10−9 A/μM for NO and O2, respectively), limit of detection (0.5 μM for NO and 1.0 μM for O2) and the Michaelis Menten constant (2.1 and 7.0 μM for NO and O2, respectively) corroborated the higher affinity of NOR for its natural substrate (NO). No significant interference on sensitivity towards NO was perceived in the presence of O2, while the O2 reduction was markedly and negatively impacted (3.6 times lower sensitivity) by the presence of NO. These results clearly demonstrate the high potential of NOR for the design of innovative NO biosensors.

Marinobacter fuscus sp. nov., a marine bacterium of Gammaproteobacteria isolated from surface seawater.

A Gram-stain-negative bacterium, designated NH169-3T, was isolated from a surface seawater sample of the South China Sea and subjected to a taxonomic polyphasic investigation. Strain NH169-3T was strictly aerobic, non-motile, non-spore-forming and rod-shaped. The colony was 1.0-2.0 mm in diameter after the growth on marine agar at 30 °C for 72 h. The centre of the colony was smooth, circular, convex and brown with a transparent periphery. Strain NH169-3T was able to grow at temperatures between 4-40 °C (optimum, 37 °C), pH 5.5-9.0 (pH 7.5) and with 0-12.5 % (w/v) NaCl (3.0 %). Chemotaxonomic analysis showed that the sole respiratory quinone of strain NH169-3T was ubiquinone 9; major fatty acids were C16 : 0 and C18 : 1ω9c, and major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and one unidentified glycolipid. The DNA G+C content was 52.7 mol%. The comparison of 16S rRNA gene sequences showed that strain NH169-3T was closely related to Marinobacter shengliensis SL013A34A2T with a similarity of 98.0 %. Three phylogenetic trees reconstructed with neighbour-joining, maximum-parsimony and maximum-likelihood methods using 16S rRNA gene sequences showed that strain NH169-3T was grouped into a separated branch with M. shengliensis SL013A34A2T in a clade of the genus Marinobacter and closely related to Marinobacter halophilus JCM 30472T, Marinobacter vinifirmus DSM 17747T and Marinobacter hydrocarbonoclasticus DSM 8798T. Analyses of both phenotypic and phylogenetic properties have suggested that strain NH169-3T was distinctive from species with validly published names in genus Marinobacter. Thus, strain NH169-3T (=MCCC 1K03455T=KCTC 62226T) is proposed as a novel species in genus Marinobacter with the name Marinobacter fuscus sp. nov.

Growth and Toxin Production of Gambierdiscus spp. Can Be Regulated by Quorum-Sensing Bacteria.

Gambierdiscus spp. are the major culprit responsible for global ciguatera fish poisoning (CFP). At present, the effects of microbiological factors on algal proliferation and toxin production are poorly understood. To evaluate the regulatory roles of quorum-sensing (QS) bacteria in the physiology of Gambierdiscus, co-culture experiments with screened QS strains were conducted in this study. Except for the growth-inhibiting effect from the strain Marinobacter hydrocarbonoclasticus, the algal host generally displayed much higher growth potential and toxin production ability with the existence of QS strains. In addition, Bacillus anthracis particularly exhibited a broad-spectrum growth enhancement effect on various Gambierdiscus types, as well as a remarkable influence on algal toxicity. The variations of algal physiological status, including growth rate, chlorophyll content, and responsive behaviors, are potential reasons for the observed positive or negative affection. This study suggests that QS bacteria regulate the algal growth and toxin production. Based on the evidence, we further speculate that QS bacteria may contribute to the site-specific distribution of CFP risk through regulating the algal host biomass and toxicity.

AupA and AupB Are Outer and Inner Membrane Proteins Involved in Alkane Uptake in Marinobacter hydrocarbonoclasticus SP17.

ABSTRACTThis study describes the functional characterization of two proteins, AupA and AupB, which are required for growth on alkanes in the marine hydrocarbonoclastic bacterium Marinobacter hydrocarbonoclasticus. The aupA and aupB genes form an operon whose expression was increased upon adhesion to and biofilm formation on n-hexadecane. AupA and AupB are outer and inner membrane proteins, respectively, which are able to interact physically. Mutations in aupA or/and aupB reduced growth on solid paraffin and liquid n-hexadecane, while growth on nonalkane substrates was not affected. In contrast, growth of aup mutants on n-hexadecane solubilized in Brij 58 micelles was completely abolished. Mutant cells had also lost the ability to bind to n-hexadecane solubilized in Brij 58 micelles. These results support the involvement of AupA and AupB in the uptake of micelle-solubilized alkanes and provide the first evidence for a cellular process involved in the micellar uptake pathway. The phylogenetic distribution of the aupAB operon revealed that it is widespread in marine hydrocarbonoclastic bacteria of the orders Oceanospirillales and Alteromonadales and that it is present in high copy number (up to six) in some Alcanivorax strains. These features suggest that Aup proteins probably confer a selective advantage in alkane-contaminated seawater.

Overproduction of Fatty Acid Ethyl Esters by the Oleaginous Yeast Yarrowia lipolytica through Metabolic Engineering and Process Optimization.

Recent advances in the production of biofuels by microbes have attracted attention due to increasingly limited fossil fuels. Biodiesels, especially fatty acid ethyl esters (FAEEs), are considered a potentially fully sustainable fuel in the near future due to similarities with petrodiesels and compatibility with existing infrastructure. However, biosynthesis of FAEEs is limited by the supply of precursor lipids and acetyl-CoA. In the present study, we explored the production potential of an engineered biosynthetic pathway coupled to the addition of ethanol in the oleaginous yeast Yarrowia lipolytica. This type of yeast is able to supply a greater amount of precursor lipids than species typically used. To construct the FAEEs synthesis pathway, WS genes that encode wax ester synthases (WSs) from different species were codon-optimized and heterologously expressed in Y.lipolytica. The most productive engineered strain was found to express a WS gene from Marinobacter hydrocarbonoclasticus strain DSM 8798. To stepwisely increase FAEEs production, we optimized the promoter of WS overexpression, eliminated β-oxidation by deleting the PEX10 gene in our engineered strains, and redirected metabolic flux toward acetyl-CoA. The new engineered strain, coupled with an optimized ethanol concentration, led to an approximate 5.5-fold increase in extracellular FAEEs levels compared to the wild-type strain and a maximum FAEEs titer of 1.18 g/L in shake flask cultures. In summary, the present study demonstrated that an engineered Y.lipolytica strain possessed a high capacity for FAEEs production and may serve as a platform for more efficient biodiesel production in the future.