To assess the potential of duckweeds as agents for nitrogen removal and biofuel feedstocks, Spirodela polyrhiza, Lemna minor, Lemna gibba, and Landoltia punctata were cultured in effluents of municipal wastewater, swine wastewater, or anaerobic digestion for 4 days. Total dissolved inorganic nitrogen (T-DIN) of 20-50 mg/L in effluents was effectively removed by inoculating with 0.3-1.0 g/L duckweeds. S. polyrhiza showed the highest nitrogen removal (2.0-10.8 mg T-DIN/L/day) and biomass production (52.6-70.3 mg d.w./L/day) rates in all the three effluents. Ethanol and methane were produced from duckweed biomass grown in each effluent. S. polyrhiza and L. punctata biomass showed higher ethanol (0.168-0.191, 0.166-0.172 and 0.174-0.191 g-ethanol/g-biomass, respectively) and methane (340-413 and 343-408 NL CH4/kg VS, respectively) production potentials than the others, which is related to their higher carbon and starch contents and calorific values.

Microalgae are a promising biomass feedstock for biofuels production. The use of wastewater effluent as a nutrient medium would improve the economics of microalgal biofuels production. Bacterial communities in aquatic environments may either stimulate or inhibit microalgal growth. Microalgal productivity could be enhanced if the positive effects of indigenous bacteria could be exploited. However, much is unknown about the effects of indigenous bacteria on microalgal growth and the characteristics of bacterial communities associated with microalgae in microalgae–effluent culture. To assess the effects of the indigenous bacteria in wastewater effluent on microalgal growth, three microalgae, Chlamydomonas reinhardtii, Chlorella vulgaris, and Euglena gracilis, were cultured in two municipal wastewater effluents and one swine wastewater effluent with and without indigenous bacteria for 7 days. All microalgae grew better in all effluents with indigenous bacteria than without bacteria. Biomass production of C. reinhardtii, C. vulgaris, and E. gracilis increased > 1.5, 1.8–2.8, and > 2.1-fold, respectively, compared to the axenic cultures of each microalga. The in situ indigenous bacterial communities in the effluents therefore promoted the growth of the three microalgae during 7-day cultures. Furthermore, the total numbers of bacterial 16S rRNA genes in the 7-day microalgae–effluent cultures were 109‒793 times the initial numbers. These results suggest that the three microalgae produced and supplied organic carbon that supported bacterial growth in the effluent. At the phylum and class levels, Proteobacteria (Alphaproteobacteria and Betaproteobacteria) and Bacteroidetes (Sphingobacteriia and Saprospirae) were selectively enriched in all microalgae–effluent cultures. The enriched core bacterial families and genera were functions of the microalgal species and effluents. These results suggest that certain members of the bacterial community promote the growth of their “host” microalgal species. To enhance their own growth, microalgae may be able to selectively stimulate specific bacterial groups from among the in situ indigenous bacterial community found in wastewater effluent (i.e., microalgae growth-promoting bacteria: MGPB). The MGPB from effluent cultures could be used as “probiotics” to enhance microalgal growth in effluent culture. Wastewater effluent may therefore be a valuable resource, not only of nutrients, but also of MGPB to enable more efficient microalgal biomass production.

We isolated three Sphingobium fuliginis strains from Phragmites australis rhizosphere sediment that were capable of utilizing 4- tert -butylphenol as a sole carbon and energy source. These strains are the first 4- tert -butylphenol-utilizing bacteria. The strain designated TIK-1 completely degraded 1.0 mM 4- tert -butylphenol in basal salts medium within 12 h, with concomitant cell growth. We identified 4- tert -butylcatechol and 3,3-dimethyl-2-butanone as internal metabolites by gas chromatography-mass spectrometry. When 3-fluorocatechol was used as an inactivator of meta -cleavage enzymes, strain TIK-1 could not degrade 4- tert -butylcatechol and 3,3-dimethyl-2-butanone was not detected. We concluded that metabolism of 4- tert -butylphenol by strain TIK-1 is initiated by hydroxylation to 4- tert -butylcatechol, followed by a meta -cleavage pathway. Growth experiments with 20 other alkylphenols showed that 4-isopropylphenol, 4- sec -butylphenol, and 4- tert -pentylphenol, which have alkyl side chains of three to five carbon atoms with α-quaternary or α-tertiary carbons, supported cell growth but that 4- n -alkylphenols, 4- tert -octylphenol, technical nonylphenol, 2-alkylphenols, and 3-alkylphenols did not. The rate of growth on 4- tert -butylphenol was much higher than that of growth on the other alkylphenols. Degradation experiments with various alkylphenols showed that strain TIK-1 cells grown on 4- tert -butylphenol could degrade 4-alkylphenols with variously sized and branched side chains (ethyl, n -propyl, isopropyl, n -butyl, sec -butyl, tert -butyl, n -pentyl, tert -pentyl, n -hexyl, n -heptyl, n -octyl, tert -octyl, n -nonyl, and branched nonyl) via a meta -cleavage pathway but not 2- or 3-alkylphenols. Along with the degradation of these alkylphenols, we detected methyl alkyl ketones that retained the structure of the original alkyl side chains. Strain TIK-1 may be useful in the bioremediation of environments polluted by 4- tert -butylphenol and various other 4-alkylphenols.

Background: Euglena gracilis, a unicellular flagellated microalga, is regarded as one of the most promising species as microalgal feedstock for biofuels. Its lipids (mainly wax esters) are suitable for biodiesel and jet fuel. Culture ofE. gracilisusing wastewater effluent will improve the economics ofE. gracilisbiofuel production. Enhancement of the productivity ofE. gracilisbiomass is critical to creating a highly efficient biofuels production system. Certain bacteria have been found to promote microalgal growth by creating a favorable microenvironment. These bacteria have been characterized as microalgae growth-promoting bacteria (MGPB). Co-culture of microalgae with MGPB might offer an effective strategy to enhance microalgal biomass production in wastewater effluent culture systems. However, no MGPB has been identified to enhance the growth ofE. gracilis. The objectives of this study were, therefore, to isolate and characterize the MGPB effective forE. gracilisand to demonstrate that the isolated MGPB indeed enhances the production of biomass and lipids byE. gracilisin wastewater effluent culture system.Results: A bacterium,Emticiciasp. EG3, which is capable of promoting the growth of microalgaE. gracilis, was isolated from anE. gracilis-municipal wastewater effluent culture. Biomass production rate ofE. graciliswas enhanced 3.5-fold and 3.1-fold by EG3 in the co-culture system using a medium of heat-sterilized and non-sterilized wastewater effluent, respectively, compared to growth in the same effluent culture but without EG3. Two-step culture system was examined as follows:E. graciliswas cultured with or without EG3 in wastewater effluent in the first step and was further grown in wastewater effluent in the second step. Production yields of biomass and lipids byE. graciliswere enhanced 3.2-fold and 2.9-fold, respectively, in the second step of the system in whichE. graciliswas co-cultured with EG3 in the first step.Conclusion: Emticiciasp. EG3 is the first MGPB forE. gracilis. Growth-promoting bacteria such as EG3 will be promising agents for enhancingE. gracilisbiomass/biofuel productivities.