G. Goma

Production of citrinin by various species ofMonascus

SummaryThe production of citrinin by variousMonascus species was determinated using various culture mediums and conditions. The maximal production was obtained in fermentor usingM. ruber with concentrations of 380 mg/l. Since citrinin is a toxic product, it is essential that the production of red pigments as food additives fromMonascus sp. avoid the occurrence of citrinin; so, we argue that some nitrogen sources are unfavorable to the production of citrinin.

Kinetic analysis of red pigment and citrinin production by Monascus ruber as a function of organic acid accumulation.

In submerged cultures performed in synthetic medium containing glucose and glutamate, the filamentous fungus Monascus ruber produced a red pigment and a mycotoxin, citrinin. In oxygen-limiting conditions, the production of these two metabolites was growth-associated, as was the production of primary metabolites. In oxygen-excess conditions, the profile of citrinin production was typical of a secondary metabolite, since it was produced mostly during the stationary phase. In contrast, the production of the pigment decreased rapidly throughout the culture, showing a profile characteristic of an inhibitory mechanism. The organic acids produced during the culture, L-malate and succinate, were shown to be slightly inhibitory against pigment production, while citrinin production was unaffected. However, this inhibition could not account for the observed profile of pigment production in batch cultures. Other dicarboxylic acids such as fumarate or tartrate showed a similar effect to that provoked by malate and succinate as regards pigment production. It was concluded that the decrease in red pigment production during the culture was due to the inhibitory effect of an unknown product whose accumulation was favored in aerobic conditions.

Towards a reduction in excess sludge production in activated sludge processes: biomass physicochemical treatment and biodegradation.

Abstract To decrease activated sludge production, microbial cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline, acid) were studied to generate Alcaligenes eutrophus and sludge lysates and to evaluate their biodegradability. Gentle treatment conditions produced the best results. Complete cell deactivation was obtained for temperatures higher than 55 °C. The release kinetics were similar for temperatures varying from 60 °C to 100 °C. A 20-min incubation was suitable for reaching 80% of the maximum releasable carbon. In thermal-chemical hydrolysis, NaOH was the most efficient for inducing cell lysis. Carbon release was a two-step process. First an immediate release occurred, which was of the same order of magnitude for A. eutrophus and sludge [100–200 mg dissolved organic C (DOC) g total suspended solids (TSS)−1], followed by a post-treatment release. The second step was virtually equivalent to the first for sludge, and weaker for A. eutrophus (<50 mg DOC g TSS−1). The biodegradability of the soluble fraction, both the immediate and the post-treatment carbon release, was investigated. The optimal degradation yield, obtained with sludge cells, reached 55% after 48 h of incubation and 80% after 350 h. The most consistent lysis and biodegradation results occurred at pH 10 and 60 °C after a 20-min incubation.

Influence of nitrogen and iron limitations on lipid production by Cryptococcus curvatus grown in batch and fed-batch culture

Abstract Cryptococcus curvatus , an oleaginous yeast, was grown under iron (Fe) and nitrogen (N)-limited conditions to produce lipid with a high stearic acid (C18:0) content in batch and fed-batch culture. In batch culture, lack of ferrous ions had no evident effect on growth, lipid production or lipid composition. The highest stearic acid content in the total lipid was 14% in N-limited medium in batch culture. The combined effect of Fe and N-limitation in fed-batch culture was to increase the stearic acid content to 19% of the total lipids and the consumed carbon to nitrogen (C:N) ratio to 20 g/g. The highest biomass concentration achieved was 70 g/litre and 53% (w/w) lipid accumulated when grown for about 172 h in fed-batch culture. A C:N ratio between 20 and 50 was optimal for intracellular lipid accumulation and a ratio > 50 g/g became crucial for both growth and lipid production in fed-batch culture. The maximal C:N ratio achieved at the end of the culture was 75 g/g. Lipid yield from glucose (g lipid/g glucose) was 0·14 and the fatty acids of lipids obtained were mainly oleic (C18:1), palmitic (C16:0) and stearic (C18:0).

High production of 1,3-propanediol from glycerol by Clostridium butyricum VPI 3266 in a simply controlled fed-batch system

SummaryA simple fed-batch system which controls substrate feeding by measuring the CO2 produced during the fermentation, was developped. This Fed-batch approach allowed high production of 1,3-propanediol from glycerol by Clostridium butyricum by avoiding substrate inhibition phenomena. 65 g/l of 1,3-propanediol was produced with a productivity of 1.21 g/l.h and a yield of 0.56. The concentration of 1,3-propanediol obtained and the productivity were significantly higher than those reached in batch culture.

Medium-Chain Fatty Acids Affect Citrinin Production in the Filamentous Fungus Monascus ruber

ABSTRACT During submerged culture in the presence of glucose and glutamate, the filamentous fungus Monascus ruber produces water-soluble red pigments together with citrinin, a mycotoxin with nephrotoxic and hepatoxic effects on animals. Analysis of the13C-pigment molecules from mycelia cultivated with [1-13C]-, [2-13C]-, or [1,2-13C]acetate by 13C nuclear magnetic resonance indicated that the biosynthesis of the red pigments used both the polyketide pathway, to generate the chromophore structure, and the fatty acid synthesis pathway, to produce a medium-chain fatty acid (octanoic acid) which was then bound to the chromophore by atrans-esterification reaction. Hence, to enhance pigment production, we tried to short-circuit the de novo synthesis of medium-chain fatty acids by adding them to the culture broth. Of fatty acids with carbon chains ranging from 6 to 18 carbon atoms, only octanoic acid showed a 30 to 50% stimulation of red pigment production, by a mechanism which, in contrast to expectation, did not involve its direct trans-esterification on the chromophore backbone. However, the medium- and long-chain fatty acids tested were readily assimilated by the fungus, and in the case of fatty acids ranging from 8 to 12 carbon atoms, 30 to 40% of their initial amount transiently accumulated in the growth medium in the form of the corresponding methylketone 1 carbon unit shorter. Very interestingly, these fatty acids or their corresponding methylketones caused a strong reduction in, or even a complete inhibition of, citrinin production byM. ruber when they were added to the medium. Several data indicated that this effect could be due to the degradation of the newly synthesized citrinin (or an intermediate in the citrinin pathway) by hydrogen peroxide resulting from peroxisome proliferation induced by medium-chain fatty acids or methylketones.

Production of 2-Phenylethyl Alcohol by Kluyveromyces marxianus

Among the numerous yeasts able to produce flavor compounds, several strains of Kluyveromyces species are known for the synthesis of large amounts of aromatic compounds. In particular, the accumulation of 2‐phenylethyl alcohol in liquid cultures of Kluyveromyces marxianus was observed after incubation on a semisynthetic medium at 30 °C, 125 rpm. Changes in the carbon sources led to a significant modification of the amount of this aromatic compound; moreover, the variations in the level of dl‐phenylalanine and the exclusive use of a precursor isomer (l) also affected the synthesis of 2−phenylethyl alcohol. Finally, this study revealed the growth inhibition of K. marxianus when the concentration of 2‐phenylethyl alcohol reached a critical value near 1.4 g/L; the use of an exponential model allowed the inhibition constant ki to be determined (ki = 0.35 g/L) .

Lipid production by an unsaturated fatty acid auxotroph of the oleaginous yeast Apiotrichum curvatum grown in single-stage continuous culture

An unsaturated fatty acid auxotroph of the oleaginous yeast Apiotrichum curvatum, named UfaM3, blocked in the conversion of stearic to oleic acid was cultivated in single-stage continuous culture. The influence of consumed carbon to nitrogen ratios (C/N ratios, g g−1) obtained at various dilution rates (D) on fatty acid (FA) accumulation and its profiles were studied. In continuous culture in N-limited medium a maximum FA accumulation of 45.6% (g g−1 of dry biomass) was obtained at an optimal D of 0.049 h−1, recording an efficiency of substrate conversion of 0.48 g g−1 and 0.22 g g−1 for biomass and lipids, respectively. The quality of lipid approached cocoa butter at an optimal C/N ratio of between 20 and 30. The C/N ratio in the incoming medium was 38.5 g g−1 with 30 g l−1 of glucose and both C and N sources were completely consumed at a critical D of ≤ 0.07 h−1. The stability of the mutant was demonstrated in the steady-state conditions of the chemostat with regard to the FA composition of its lipids.

Butanol tolerance and autobacteriocin production byClostridium acetobutylicum

Serial enrichment was used to obtain a strain ofClostridium acetobutylicum demonstrating a 40% increase in tolerance to added butanol and a further 17% improvement in the ability to produce butanol. The glucose and the butyrate consumption were higher for the G1 variant than for the wild-type strain. In consideration of the higher butanol tolerance, a disappointly low titer of butanol was produced by the new strain. This can be explained by the higher level of autobacteriocin produced by G1. Control of autobacteriocin production appears to be one of the key factors limiting the potential of the acetone butanol fermentation.

Effect of various nutrient limitations on fatty acid production by Rhodotorula glutinis

The effects of nitrogen (N), phosphorus (P), zinc (Zn) or iron (Fe) limitations on lipid and especially α-linolenic acid (ALA) synthesis in the oleaginous yeast Rhodotorula glutinis have been investigated. Exhaustion of the limiting element in the medium resulted in an enhancement of both the fatty acid cell content (FA/X) and the corresponding productivity. Except for Fe-limited media, lipid accumulation was always coupled with an increase in the yield of ALA synthesis, whereas in all the limiting conditions the productivity of ALA declined. Kinetic investigations showed that this decline resulted from a sharp decrease in the specific rates of ALA synthesis associated with slowing down of growth. A comparative study showed that the highest yields and specific rates of fatty acid and ALA synthesis were induced by P-limitation early in the lipid accumulation phase. However, above a FA/X of 15%, N-limiting conditions become more attractive for producing lipids. During P-limited growth a down-shift of temperature from 30° C to 25° C was shown ao reduce the range of FA/X values at which the specific rate of fatty acid synthesis was maximal but without any other effect on fatty acid formation. In contrast, the decreased temperature resulted in enhanced ALA production by maintaining the specific rate of synthesis near to the maximal value of 3.6 mg gX−1h−1, where X* is free fatty acid biomass, and increased the corresponding yield by a factor of up to three.