Vitreoscilla Hemoglobin Improves Sophorolipid Production in Starmerella Bombicola O-13-1 Under Oxygen Limited Conditions.

Sophorolipids (SLs) are homologous microbial secondary metabolites produced by Starmerella bombicola and have been widely applied in many industrial fields. The biosynthesis of SLs is a highly aerobic process and is often limited by low dissolved oxygen (DO) levels. In this study, the Vitreoscilla hemoglobin (VHb) gene was transformed into S. bombicola O-13-1 by homologous recombination to alleviate oxygen limitation. VHb expression improved the intracellular oxygen utilization efficiency under either oxygen-rich or oxygen-limited conditions. In shake flask culture, the production of SLs was higher in the recombinant (VHb+) strain than in the wild-type (VHb-) strain, while the oxygen uptake rate of the recombinant (VHb+) strain was significantly lower than that of the wild-type (VHb-) strain. In a 5 L bioreactor, the production of SLs did not increase significantly, but the DO level in the fermentation broth of the VHb+ strain was 21.8% higher than that of VHb- strain under oxygen-rich conditions. Compared to wide-type strains (VHb-), VHb expression enhanced SLs production by 25.1% in the recombinants (VHb+) under oxygen-limited conditions. In addition, VHb expression raised the transcription levels of key genes involved in the electron transfer chain (NDH, SDH, COX), TCA cycle (CS, ICD, KDG1) and SL synthesis (CYP52M1 and UGTA1) in the recombinant (VHb+) strains. VHb expression in S. bombicola could enhance SLs biosynthesis and intracellular oxygen utilization efficiency by increasing ATP production and cellular respiration. Our findings highlight the potential use of VHb to improve the oxygen utilization efficiency of S. bombicola in the industrial-scale production of SLs using industrial and agricultural by-products like molasses and waste oil as fermentation feedstock.

Bioavailability of dissolved organic nitrogen and its uptake by Ulva prolifera: Implications in the outbreak of a green bloom off the coast of Qingdao, China.

To investigate bioavailability of dissolved organic nitrogen (DON) and its contribution to nitrogen demand for Ulva prolifera, a cruise was conducted during a bloom of U. prolifera in Qingdao coastal waters, China, dissolved inorganic nitrogen (DIN) and DON components were investigated. Uptakes of both DIN and DON by U. prolifera were synchronously measured onboard using stable isotope techniques. The contribution of DON to total dissolved N (TDN) was >50% and that of labile components (urea and to amino acids, AA) to DON exceeded 30%. Both DIN and DON were utilized by U. prolifera, which uptake NH4-N preferentially, then urea, NO3-N and AA in turn; whereas the ranking of turnover times from short to long was AA, NH4-N, urea and NO3-N. The high uptake rates and short turnover time of AA and urea indicated that DON may play an important role in the nutrition of U. prolifera.

[Potential Bioavailability of Dissolved Organic Nitrogen in the Discharge Outlets of Sewage Treatment Plants Around the Jiaozhou Bay].

Dissolved organic nitrogen (DON) is an important portion of total dissolved nitrogen (TDN) transported to the coastal from land-based sources and its bioavailable moieties of DON are regarded as potentially important nitrogen sources for eutrophication in coastal environments. Based on the four field observations conducted in July, November 2012 and in March, May 2013 at the four sewage treatment plants (STPs) around the Jiaozhou Bay (JZB), the concentrations and compositions of total dissolved nitrogen (TDN) as well as total dissolved amino acids (TDAA) were analyzed, and the ratio of dissolved organic carbon (DOC) to DON and the composition and abundance of amino acids were regarded as indexes to evaluate the bioavailability of DON in STPs around JZB. The concentrations of TDN ranged from 413.10 µmol L⁻¹ to 3,580.65 µmol · L⁻¹ and showed a seasonal variation tendency, which were higher in March and November and lower in May and July, and the percentages of DON to TDN varied from 2.14% to 88.75%. In the discharge outlets of STPs around JZB, the values of DOC/DON were low and ranged from 0.2 mol · mol⁻¹ to 26.2 mol · mol⁻¹ with an average of (5.05 ± 6.39) mol · mol⁻¹, while the values of TDAA/DOC were high and ranged from 0.33% to 3.02% with an average of 1.54% ± 0.78%. Based on TDAA/DOC, the bioavailable proportion of the dissolved organic matter was estimated, which accounted for 0.44% to 46.97%. In conclusion, DON in the discharge outlets of STPs around JZB possessed high bioavailability and might contribute to the eutrophication of coastal water in JZB.

[Effects of Oil Pollutants on the Performance of Marine Benthonic Microbial Fuel Cells and Its Acceleration of Degradation].

Degradation of oil pollutants under the sea is slow for its oxygen-free environment which has caused long-term harm to ocean environment. This paper attempts to accelerate the degradation of the sea oil pollutants through electro catalysis by using the principle of marine benthonic microbial fuel cells (BMFCs). The influence of oil pollutants on the battery performance is innovatively explored by comparing the marine benthonic microbial fuel cells ( BMFCs-A) containing oil and oil-free microbial fuel cells (BMFCs-B). The acceleration effect of BMFCs is investigated by the comparison between the oil-degrading rate and the number of heterotrophic bacteria of the BMFCs-A and BMFCs-B on their anodes. The results show that the exchange current densities in the anode of the BMFCs-A and BMFCs-B are 1. 37 x 10(-2) A x m(-2) and 1.50 x 10(-3) A x m(-2) respectively and the maximum output power densities are 105.79 mW x m(-2) and 83.60 mW x m(-2) respectively. The exchange current densities have increased 9 times and the maximum output power density increased 1. 27 times. The anti-polarization ability of BMFCs-A is improved. The heterotrophic bacteria numbers of BMFCs-A and BMFCs-C on their anodes are (66 +/- 3.61) x 10(7) CFU x g(-1) and (7.3 +/- 2.08) x 10(7) CFU x g(-1) respectively and the former total number has increased 8 times, which accelerates the oil-degrading rate. The degrading rate of the oil in the BMFCs-A is 18.7 times higher than that in its natural conditions. The BMFCs can improve its electrochemical performance, meanwhile, the degradation of oil pollutants can also be accelerated. A new model of the marine benthonic microbial fuel cells on its acceleration of oil degradation is proposed in this article.

[Studies on micelle behaviors of sophorolipid biosurfactant by steady-state fluorescence probe method].

The critical micelle concentration (CMC) of sophorolipid was determined by steady-state fluorescence probe method in which pyrene was used as fluorescence probe. Meanwhile, the changes in the sophorolipid CMC were examined in the addition of NaCl and aliphatic alcohol, respectively. The results showed that the CMC of sophorolipid was 1.3 x 10(-4) mol x L(-1) and had a slight decrease as NaCl concentration increased. However, the CMC of sophorolipid appeared to increase in the presence of aliphatic alcohol. The aggregation numbers and the micelle size of sophorolipid solution were investigated by fluorescence quenching and laser light scattering method. The aggregation numbers were 4-8 with the concentrations of sophorolipid in the range of 4 -8 CMC and the micelle mean diameter for sophorolipid with the concentration of 6 CMC was about 90 nm. These experimental results indicated that the micelle should be incompact.

[Evaluation on biodegradability of hydrocarbon biomarkers in two crude oils under laboratory conditions].

Biodegradabilities of several hydrocarbon biomarker groups, including isoprene, hopanes and steranes in a medium-crude oil BZ34-1 and a heavy-crude oil SZ36-1 from offshore, were determined under laboratory conditions. The results of GC-MS analysis showed that isoprene biomarkers such as pristane and phytane in both crude oils degraded obviously in 60-day experiment period. The degradation ratios of pristane and phytane in the medium-crude oil BZ34-1 reached 20.2% and 15.0%, respectively; while those in the heavy-crude oil SZ36-1 reached 95.6% and 75.4%, respectively. Pristane and phytane in the heavy-crude oil SZ36-1 were degraded in the early period of biodegradation, but these two biomarkers in the medium-crude oil BZ34-1 were degraded in middle and late biodegradation phases. However, hopanes and steranes in the both oils were not biodegraded obviously during the whole period. These results indicated that pristane and phytane could be used to evaluate bioremediation efficiency in the early biodegradation phase for light or medium oils, while hopanes and steranes could be used to evaluate bioremediation efficiency within the whole given experiment process.

[Role of irradiance on the seasonality of Skeletonema costatum Cleve blooms in the coastal area in East China Sea].

With field culture experiments and model calculations, the role of light on why in both spring and summer Skeletonema costatum Cleve blooms can occur in the coastal area in East China Sea were studied. The results show that the growth optimal light intensity (I(opt)) of S. costatum increases gradually to a maximum of 121.6 W x m(-2) with temperature (t) up to 25 degrees C, and a rapid decline in I(opt) accompanies further increases in t beyond 25 degrees C. Such an asymmetric inverse V-shape I(opt)-t curve can be well described by Blanchard's equation. By this equation, I(opt) of each month was calculated based on monthly sea surface temperature, and though changes about 2 months later than light intensity above sea surface (I(0)), I(opt) is closely correlated with seasonal I(0) and transparency of sea water (R2 = 0.907 +/- 0.115, p < 0.001), which indicates that S. costatum adapts to the seasonality of light in sea water in the coastal area by varying I(opt) seasonally. Such an adaptive strategy leads to thick (about 6 m) light-optimal water layers for growth from early spring to late summer. The high adaptability to light and light optimum characteristics in sea water is one of the important reasons for S. costatum blooms in the both seasons in the coastal area in ECS.

[Effects of irradiance on blooms of the dinoflagellate Prorocentrum donghaiense Lu in the coastal area in East China Sea].

With field culture experiments and model calculations, the natural-light-dependent growth and the optimal light layers in sea water for growth of red tide dinoflagellate Prorocentrum donghaiense Lu were studied in order to analyze the role of light on algal blooms in the coastal area in East China Sea in spring. The results show that the relationship of growth and light can be well described by Steele's equation, and the optimal light intensity (Iopt) of P. donghaiense is (38.2 +/- 3.8) W x m(-2), which is lower than Iopt for several other red tide algae (40-133 W x m(-2)), meaning that P. donghaiense may have an advantage when developing blooms in turbid environments where solar irradiance is easily attenuated. The optimal light layers for P. donghaiense growth are thicker offshore than inshore, and the thickness of optimal light layers in the subsurface water usually in 3-15 m in depth is about 5-10 m in the red tide area. The trade-off of light and nutrient fitness results in blooms in the so-called red tide area, and the light-optimum characteristic of the subsurface water is an important factor for the subsurface bloom development in spring.