Removal of gaseous n-valeric acid in the air by Rhodococcus sp. B261 immobilized onto ceramic beads

n-Valeric acid, one of the main malodorous pollutants from livestock houses was eliminated with a biofilter prepared with Rhodococcus sp. B261 immobilized onto ceramic beads. The strain was isolated from composted pig faeces and grown in an artificial medium containing volatile fatty acids as a carbon source. The cells were immobilized onto ceramic beads in vacuo. The beads were aseptically incubated at 37 °C, pH 8.0, for 24h for activation of the cells. The beads with immobilized cells (3.36×10⁹ c.f.u./g ceramic beads) and moisture content of 35% (w/w) were packed into a glass column equipped with a water jacket to keep the temperature constant. One hundred-seventy ppm of gaseous n-valeric acid were removed for 11 days at 30h ^-1 (space velocity) and 37 °C.     

Degradation of benzene by a Rhodococcus sp. using immobilized cell systems

The continuous degradation of benzene by a Rhodococcus sp. using free and immobilized cell systems was compared. Cell entrapment in calcium and strontium alginate beads and adhesion on support materials such as glass beads were found to be unsatisfactory. Degradation of benzene by cells immobilized in either ceramic or cellulose carriers proved to be more efficient than its non-immobilized counterpart. A retention time of 36 h was required to effect a 97% degradation of benzene using suspended free cells while cells immobilized on cellulose or ceramic carriers effected 97% degradation at 24 and 18 h, respectively. Recycling of the ceramic carriers was also possible and resulted in an even shorter retention time of 12h to effect a 97% degradation of benzene. Cell adhesion on the support materials was confirmed by scanning electron microscopy.     

Application of chitosan beads immobilized Rhodococcus sp. NCIM 2891 cholesterol oxidase for cholestenone production

The cell-bound cholesterol oxidase from the Rhodococcus sp. NCIM 2891 was purified three fold by diethylaminoethyl–sepharose chromatography. The estimated molecular mass (SDS-PAGE) and K_m of the enzyme were ∼55.0 kDa and 151 μM, respectively. The purified cholesterol oxidase was immobilized on chitosan beads by glutaraldehyde cross-linking reaction and immobilization was confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. The optimum temperature (45 °C, 5 min) for activity of the enzyme was increased by 5 °C after immobilization. Both the free and immobilized cholesterol oxidases were found to be stable in many organic solvents except for acetone. Fe²⁺ and Pb²⁺ at 0.1 mM of each acted as inhibitors, while Ag⁺, Ca²⁺, Ni²⁺ and Zn²⁺ activated the enzyme at similar concentration. The biotransformation of cholesterol (3.75 mM) with the cholesterol oxidase immobilized beads (3.50 U) leads to ∼88% millimolar yield of cholestenone in a reaction time of 9 h at 25 °C. The immobilized enzyme retains ∼67% activity even after 12 successive batches of operation. The biotransformation method thus, shows a great promise for the production of pharmaceutically important cholestenone.     

Production of branched-chain volatile fatty acids by certain anaerobic bacteria.

Net production of isobutyric acid, isovaleric acid, and 2-methylbutyric acid by cultures of Bacteroides ruminicola and Megasphaera elsdenii on media that contained Trypticase or casein hydrolysate continued (up to 5 days) after growth had ceased. Only trace quantities of these acids were produced in a medium that contained a mixture of amino acids that did not include the branched-chain amino acids. M. elsdenii produced increased quantities of the branched-chain fatty acids in a medium that contained Trypticase when glucose was reduced or eliminated from the culture medium. However, B. ruminicola produced increased quantities of branched-chain fatty acids and of phenylacetic acid from Trypticase when glucose was supplied at 3 mg/ml rather than at 1 mg/ml. Single strains of Streptococcus bovis, Selenomonas ruminantium, Bacteroides amylophilus, and Butyrivibrio fibrisolvens did not produce branched-chain fatty acids.     

Fermentation of Chlorella sp. for anaerobic bio-hydrogen production: influences of inoculum-substrate ratio, volatile fatty acids and NADH

This study evaluated the influences of inoculum-substrate ratio (ISR), volatile fatty acids (VFAs) and nicotinamide adenine dinucleotide, the reduced form (NADH) on hydrogen production during the anaerobic fermentation of Chlorella sp. in batch tests at 35 °C. The results indicated that the hydrogen concentration and lag time increased when ISR decreased, and the maximum hydrogen production and hydrogen content, 7.13 mL/g VS and 45.3%, respectively, were obtained when ISR was equal to 0.3. On the other hand, VFAs concentrations increased with the increase of hydrogen. The NADH increased while the daily output of hydrogen decreased as the fermentation carried on. The results suggested that ISR, VFAs, and NADH were important parameters for effective anaerobic hydrogen production using Chlorella sp. as substrate.     

Rhodococcus sp. F92 immobilized on polyurethane foam shows ability to degrade various petroleum products

This work reports on the immobilization and performance of a hydrocarbon-degrading microorganism on polyurethane foam (PUF) in the bioremediation of petroleum hydrocarbons. The ability of four different microorganisms to immobilize on PUF and to degrade various petroleum products (Arabian light crude (ALC), Al-Shaheen crude (ASC), diesel and oil slops) was assessed by measuring the n-alkane fraction remaining in the petroleum products over time. A Rhodococcus sp. (designated as F92) had the highest number of immobilized viable cells (10(9) cells per cm3 PUF) and a maximum attachment efficiency of 90% on PUF of a density of 14 kg/m3. Scanning electron microscopy showed the presence of extracellular structures that could play an important role in the immobilization of F92 on PUF. Analysis by GC-MS revealed that both free and immobilized F92 cells were able to degrade approximately 90% of the total n-alkanes in the petroleum products tested within 1 week at 30 degrees C. Rhodococcus sp. F92 was efficiently immobilized onto PUF and the immobilized cells were able to degrade a variety of petroleum products such as ALC, ASC, diesel and oil slops. The results suggest the potential of using PUF-immobilized Rhodococcus sp. F92 to bioremediate petroleum hydrocarbons in an open marine environment.     

Influence of selected physical parameters on the biodegradation of acrylamide by immobilized cells of Rhodococcus sp.

The influences of concentration of acrylamide, pH, temperature, duration of storage of encapsulated cells and presence of different metals and chelators on the ability of immobilized cells of a Rhodococcus sp. to degrade acrylamide were evaluated. Immobilized cells (3 g) rapidly degraded 64 and 128 mM acrylamide in 3 and 5 h, espectively, whereas free cells took more than 24 h to degrade 64 mM acrylamide. An acrylamide concentration of 128 mM inhibited the growth of the free cells. Immobilized bacteria were slow to degrade acrylamide at 10 °C. Less than 60% of acrylamide was degraded in 4 h. However, 100% of the compound was degraded in less than 3 h at 28 °C and 45 °C. The optimum pH for the degradation of acrylamide by encapsulated cells was pH 7.0. Less than 10% of acrylamide was degraded at pH 6.0, while ca. 60% of acrylamide was degraded at pH 8.0 and 8.5. Copper and nickel inhibited the degradation, suggesting the presence of sulfhydryl (-SH) groups in the active sites of the acrylamide degrading amidase. Iron enhanced the rates of degradation and chelators (EDTA and 1,10 phenanthroline) reduced the rates of degradation suggesting the involvement of iron in its active site(s) of the acrylamide-degrading-amidase. Immobilized cells could be stored up to 10 days without any detectable loss of acrylamide-degrading activity.     

Naphthalene degradation via salicylate and gentisate by Rhodococcus sp. strain B4.

Rhodococcus sp. strain B4, isolated from a soil sample contaminated with polycyclic aromatic hydrocarbons, grows with naphthalene as the sole source of carbon and energy. Salicylate and gentisate were identified as intermediates in the catabolism of naphthalene. In contrast to the well-studied catabolic pathway encoded by the NAH7 plasmid of Pseudomonas putida, salicylate does not induce the genes of the naphthalene-degradative pathway in Rhodococcus sp. strain B4. The key enzymes of naphthalene degradation in Rhodococcus sp. strain B4 have unusual cofactor requirements. The 1,2-dihydroxynaphthalene oxygenase activity depends on NADH and the salicylate 5-hydroxylase requires NADPH, ATP, and coenzyme A.     

Asymmetric oxidation of 1,3-propanediols to chiral hydroxyalkanoic acids by Rhodococcus sp. 2N

Rhodococcus sp. 2N was found as a 1,3-propanediols-oxidizing strain from soil samples through enrichment culture using 2,2-diethyl-1,3-propanediol (DEPD) as the sole carbon source. The culture condition of the strain 2N was optimized, and the highest activity was observed when 0.3% (w/v) DEPD was added in the culture medium as an inducer. Chiral HPLC analysis of the hydroxyalkanoic acid converted from 2-ethyl-2-methyl-1,3-propanediol (EMPD) revealed that the strain 2N catalyzed the (R)-selective oxidation of EMPD. The reaction products and intermediates from DEPD and EMPD were identified by nuclear magnetic resonance analyses, and the results suggested that only one hydroxymethyl group of the propanediols was converted to carboxy group via two oxidation steps. Under optimized conditions and after a 72-h reaction time, the strain 2N produced 28 mM (4.1 g/L) of 2-(hydroxymethyl)-2-methylbutanoic acid from EMPD with a molar conversion yield of 47% and 65% ee (R).     

Performance of microbial fuel cell with volatile fatty acids from food wastes

Food wastes were used as feedstock for the direct production of electricity in a microbial fuel cell (MFC). MFC operations with volatile fatty acids (VFA) produced 533 mV with a maximum power density of 240 mW/m². Short-chain VFAs, such as acetate, were degraded more rapidly and thus supported higher power generation than longer chain ones. In general, the co-existence of other, different VFAs slowed the removal of each VFA, which indicated that anodic microbes were competing for different substrates. 16S rRNA gene analysis using PCR-DGGE indicated that the MFC operation with VFAs had enriched unique microbial species.     

Growth and biochemical composition with emphasis on the fatty acids of Tetraselmis sp.

Summary The influence of temperature (15–32°C) and the ratio of nitrogen to phosphorus (N/P) in the culture medium (0.5–80) on the growth kinetics and protein, chlorophyll, lipid and fatty acid content of the marine microalga Tetraselmis sp. have been studied. Below an N/P of 20, growth was determined by N limitation and above 20 by P limitation. Protein increased with a rise in N content at any test temperature. The chlorophyll content increased with temperature, with maximum values at 25°C. The lipid content decreased with increasing N/P ratio above 20°C. The polyunsaturated fatty acid content tends to be inversely proportional to the growth rate within the N/P range 20–80. The quotient of the n ₃ and n ₆ polyunsaturated-fatty-acid fractions, an indicator of the nutritive value of microalgae, was found to be within the range 2–3. These values were obtained either between 25 and 28°C independent of the N/P ratio used at 20°C for N/P ratios higher than 40.0. Offsprint requests to: Emilio Molina     

Growth-mediated variations in fatty acids of Xenorhabdus sp

The bacterium Xenorhabdus sp. is symbiotically associated with the entomopathogenic nematode Steinernema riobravis. This nematode is produced in monoxenic culture with Xenorhabdus sp. and is sold as a biological insecticide. Acceptable yields in fermentors can only be achieved in the presence of vigorous growth of the bacterium. We investigated the fatty acid composition of Xenorhabdus species when grown at 15, 20, 25 or 30 degrees C on media containing one of two primary carbon sources: glucose or lipids from the insect host, Galleria mellonella. Both temperature and primary carbon source significantly affected lipid quantity and quality in Xenorhabdus sp. Bacteria grown with insect lipids as a primary carbon source accumulated more lipids with greater proportion of longer chain fatty acids than bacteria grown with glucose as a primary carbon source. Cells grown with insect lipids at 15 degrees C had a lower lipid content than cells grown on the same media at 20, 25 or 30 degrees C. Increasing growth temperature increased saturated fatty acids and decreased unsaturated fatty acids, irrespective of carbon source. We recommend addition of complex fatty acid sources that resemble natural host lipids to growth medium for mass producing entomopathogenic nematodes. This could provide nematode quality similar to in vivo-produced nematodes.