Anh LeDuy

Analysis of the relative abundance of different types of bacteria capable of toluene degradation in a compost biofilter.

Abstract A microbial community of a compost biofilter treating toluene vapors was investigated using serum-bottle assays and mineral-agar plates. Toluene was not consumed in the absence of oxygen. However, filter-bed extracts exposed to toluene vapor as the only carbon source produced distinct colony types (phenotypic groups) that were counted separately. Strains from each group were isolated and checked for toluene-degradation activity in serum bottles. Only 15% of colonies were true toluene degraders. This population was divided into 11 genotypic groups based on DNA fingerprints. Identification of a member of each group using 16S rRNA gene-sequence comparison showed that they belonged to seven genera: Acinetobacter, Azoarcus, Mycobacterium, Nevskia, Pseudomonas, Pseudonocardia and Rhodococcus. Together, members of the genera Pseudonocardia and Rhodococcus were 34 times more numerous than all the others. We hypothesized that these two organisms are K-strategists (adapted to a resource-restricted and crowded environment) and that the compost biofilter is a K-environment. This would explain why they are not outnumbered by faster growers like Pseudomonas or Acinetobacter species, which would be r-strategists (adapted to a resource-abundant and uncrowded environment).

Batch fermentation of whey ultrafiltrate by Lactobacillus helveticus for lactic acid production

SummaryCheese whey ultrafiltrate (WU) was used as the carbon source for the production of lactic acid by batch fermentation with Lactobacillus helveticus strain milano. The fermentation was conducted in a 400 ml fermentor at an agitation rate of 200 rpm and under conditions of controlled temperature (42° C) and pH. In the whey ultrafiltrate-corn steep liquor (WU-CSL) medium, the optimal pH for fermentation was 5.9. Inoculum propagated in skim milk (SM) medium or in lactose synthetic (LS) medium resulted in the best performance in fermentation (in terms of growth, lactic acid production, lactic acid yield and maximum productivity of lactic acid), as compared to that propagated in glucose synthetic (GS) medium. The yeast extract ultrafiltrate (YEU) used as the nitrogen/growth factor source in the WU medium at 1.5% (w/v) gave the highest maximum productivity of lactic acid of 2.70 g/l-h, as compared to the CSL and the tryptone ultrafiltrate (TU). L. helveticus is more advantageous than Streptococcus thermophilus and Lactobacillus delbrueckii for the production of lactic acid from WU. The L. helveticus process will provide an alternative solution to the phage contamination in dairy industries using Lactobacillus bulgaricus.

Improved performance of anaerobic digestion ofSpirulinamaxima algal biomass by addition of carbon-rich wastes

Mixtures of carbon-rich wastes andS. maxima algal biomass increase markedly the performance of anaerobic digestion. A mixture of 507 sewage sludge and algae increases the methane yield and the productivity over twofold. Peat hydrolyzate and sewage sludge, when added to algae, have shown a synergistic effect and spent sulfite liquor added at concentrations over 307 V/V has inhibited methanogenic activity.

Influence of mechanical and thermochemical pretreatments on anaerobic digestion ofSpirulinamaxima algal biomass

The algaSpirulinamaxima was subjected to mechanical (ultrasonic + mechanical disintegration) and thermochemical pretreatments and used as a substrate in anaerobic digestion. Results indicate that the pretreatments increased the solubility of biomass and had a positive effect on acid forming bacteria. Thermochemical treatments produced compounds toxic to methanogenic bacteria especially when treatment conditions became more severe.

Oxygen requirement in pullulan fermentation

SummaryOxygen was essential for the biosynthesis of pullulan by Aureobasidium pullulans. In a growth medium, pullulan yield and synthesis rate were proportional to the oxygen availability. However, under controlled oxygen environment in a non-growth medium, the synthesis rate and the yield of pullulan were inversely proportional to the oxygen tension. A relationship between melanin production and oxygen transfer conditions was also observed. The elapsed time prior to the appearance of the pigment was dependent upon the degree of oxygen availability.

Kinetics of biopolymer synthesis: A revisit

Abstract This review focuses on the development of simple unstructured kinetic models for quantitative description of biopolymer conversion processes. Together with the Luedeking-Piret model, several growth kinetic equations have been attempted for representing the literature data on several exopolysaccharides and one endobiopolymer, poly-β-hydroxybutyric acid. Critique on the applicability and pitfalls of such models is discussed in detail.

Assay of xylanase and xylosidase activities in bacterial and fungal cultures

The factors causing variation in the determination of xylanase (1,4-β-D-xylan xylanohydrolase, EC 3.2.1.8) and xylosidase (β-D-xyloside xylohydrolase, EC 3.2.1.37) have been studied. The results showed that the reported activities in international units (U) varied by a factor of 3 to 107, depending on the dilution of enzyme made prior to assay. Determination of xylanase was also affected by the type of substrate used, and it varied from 1.5 to 104 U ml−1 among three different xylan preparations from larchwood. The measured units of enzymatic activity appear to vary with the availability of easily degradable xylooligosaccharides in the substrate. The defining of composition and the use of a standard method for the preparation of xylan would help in minimizing variation due to substrate. The use of enzyme dilution to give 0.9 to 1.0 mg of reducing sugars for the calculation of xylanase units and an absorbance between 0.8 and 1.2 for the calculation of xylosidase units would help in minimizing the variation in the results obtained by different laboratories using the same substrate.

Testing of an ammonia ion selective electrode for ammonia nitrogen measurement in the methanogenic sludge

SummaryThe ammonia ion selective electrode method was the most practical and the most convenient one for measuring the ammonia nitrogen in methanogenic sludge. This is because of its simplicity, rapidity, high precision and accuracy, freedom from interference, small sample size, and possibility for continuous monitoring.

Enhanced production of pullulan from lactose by adaptation and by mixed culture techniques

SummaryBy multiple transfer technique, an adapted strain of Aureobasidium pullulans yielded a polysaccharide concentration of 10,5 g/L. By mixed culturing with Ceratocystis ulmi, the polysaccharide concentration was increased to 15,5 g/L in lactose medium.

The effects of pressure on the growth of Aureobasidium pullulans and the synthesis of pullulan

SummaryThe feasibility of pressurized culture was explored for the growth of Aureobasidium pullulans and the synthesis of pullulan. For all volumetric flow rates of air, the production of biomass increased with pressure up to a critical value ranging from 0.50 to 0.75 MPa, at which point a drastic decrease in biomass production and a change in cellular morphology was observed. For pullulan synthesis, the same dramatic decrease was observed at approximately the same critical pressure. In the pressure range 0.1–0.65 MPa, the synthesis of pullulan was subject to what is believed to be the competing effects of oxygen availability and pressure inhibition.