Production of 1,3-propanediol by Klebsiella pneumoniae from glycerol broth

Broth containing 152 g glycerol l⁻¹ from Candida krusei culture was converted to 1,3-propanediol by Klebsiella pneumoniae. Residual glucose in the broth promoted growth of K. pneumoniae while acetate was inhibitory. After desalination treatment of glycerol broth by electrodialysis, the acetate in the broth was removed. A fed-batch culture with electrodialytically pretreated broth as␣substrate was developed giving 53 g 1,3- propanediol l⁻¹ with a yield of 0.41 g g⁻¹ glycerol and a productivity of 0.94 g l⁻¹ h⁻¹.     

Isolation and Partial Characterization of Het− Fix− Mutant Strain of the Diazotrophic Cyanobacterium Anabaena variabilis Showing Chromatic Adaptation

We propose a model to describe the changes taking place in biochemical processes/events to explain the development of heterocyst and nitrogenase in a diazotrophic cyanobacterium Anabaena variabilis. For this purpose, a mutant strain of A. variabilis lacking heterocyst differentiation and incapable of growth with dinitrogen as the sole source of nitrogen has been isolated after nitrosoguanidine (NTG) mutagenesis and selection by penicillin enrichment. The mutant strain (Het⁻ Fix⁻) thus isolated has morphological variation and was incapable of reducing acetylene under anaerobic conditions, indicating its mutational loss of the process of nitrogen fixation. The Het⁻ Fix⁻ mutant strain had reduced glutamine synthetase (transferase) activity compared with its wild-type counterpart, suggesting a link between nif gene expression and the expression of gln A, the structural gene of GS. The Het⁻ Fix⁻ mutant strain compared with its wild-type strain also had an extremely high level of phycobiliprotein and a low level of carotenoids. Furthermore, the coiling of vegetative filaments in the Het⁻ Fix⁻ mutant strain, which reduced the surface area to be exposed to light, was a direct indication of the chromatic adaptation, because the mutant strain was found to be photosensitive, showing bleaching of the cells under high light intensity. Received: 13 December 2000 / Accepted: 9 February 2001     

Lipid accumulation in <Emphasis Type="Italic">Schizochytrium</Emphasis> G13/2S produced in continuous culture

Lipid and docosahexaenoic acid (DHA) accumulation into Schizochytrium G13/2S was studied under batch and continuous culture. Different glucose and glutamate concentrations were supplemented in a defined medium. During batch cultivation, lipid accumulation, 35% total fatty acids (TFA) occurred at the arithmetic growth phase but ceased when cell growth stopped. When continuous culture was performed under different glutamate concentrations, nitrogen-growth-limiting conditions induced the accumulation of 30–28% TFA in Schizochytrium. As the dilution rate decreased from 0.08 to 0.02 h⁻¹, both cell dry weight and TFA content of the cell increased. Under a constant dilution rate of 0.04 h⁻¹, carbon-limiting conditions decreased the TFA to 22%. Fatty acid profile was not affected by the different nutrient concentrations provided during continuous culture. Consequently, lipid accumulation can be induced through the carbon and nitrogen source concentration in the medium to maximise the TFA and subsequently DHA productivity by this microorganism.     

Consequences of cps mutation of Klebsiella pneumoniae on 1,3-propanediol fermentation

The filtration in 1,3-propanediol (1,3-PD) downstream process is influenced by the large amounts of capsular polysaccharides (CPS) produced by Klebsiella pneumoniae CGMCC 1.6366. The morphological and fermentation properties were investigated with the CPS-deficient mutant K. pneumoniae CGMCC 1.6366 CPS. Similar biomass was obtained with CGMCC 1.6366, and the mutant strain in batch cultures indicating the cell growth was slightly inhibited by CPS defection. The viscosity of fermentation broth by mutant strain decreased by 27.45%. The flux with ceramic membrane filter was enhanced from 168.12 to 303.6 l h⁻¹ m⁻², exhibiting the great importance for downstream processing of 1,3-PD fermentation. The products spectrum of mutant isolate changed remarkably regarding to the concentration of fermentation products. The synthesis of important 1,3-PD and 2,3-butanediol was enhanced from 9.73 and 4.06 g l⁻¹ to 10.37 and 4.77 g l⁻¹ in batch cultures. The noncapsuled K. pneumoniae provided higher 1,3-PD yield of 0.54 mol mol⁻¹ than that of encapsuled wild parent in batch cultures. The fed-batch fermentation of mutant strain resulted in 1,3-PD concentration, yield, and productivity of 78.13 g l⁻¹, 0.53 mol mol⁻¹, and 1.95 g l⁻¹ h⁻¹, respectively.     

Expression of a ferredoxin-dependent glutamate synthase gene in mesophyll and vascular cells and functions of the enzyme in ammonium assimilation in Nicotiana tabacum (L.)

GLU1 encodes the major ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) in Arabidopsis thaliana (ecotype Columbia). With the aim of providing clues on the role of Fd-GOGAT, we analyzed the expression of Fd-GOGAT in tobacco (Nicotiana tabacum L. cv. Xanthi). The 5′ flanking element of GLU1 directed the expression of the uidA reporter gene in the palisade and spongy parenchyma of mesophyll, in the phloem cells of vascular tissue and in the roots of tobacco. White light, red light or sucrose induced GUS expression in the dark-grown seedlings in a pattern similar to the GLU1 mRNA accumulation in Arabidopsis. The levels of GLU2 mRNA encoding the second Fd-GOGAT and NADH-glutamate synthase (NADH-GOGAT, EC 1.4.1.14) were not affected by light. Both in the light and in darkness, ¹⁵NH₄⁺ was incorporated into [5−¹⁵N]glutamine and [2−¹⁵N]glutamate by glutamine synthetase (GS, EC 6.3.1.2) and Fd-GOGAT in leaf disks of transgenic tobacco expressing antisense Fd-GOGAT mRNA and in wild-type tobacco. In the light, low level of Fd-glutamate synthase limited the [2−¹⁵N]glutamate synthesis in transgenic leaf disks. The efficient dark labeling of [2−¹⁵N]glutamate in the antisense transgenic tobacco leaves indicates that the remaining Fd-GOGAT (15–20% of the wild-type activity) was not the main limiting factor in the dark ammonium assimilation. The antisense tobacco under high CO₂ contained glutamine, glutamate, asparagine and aspartate as the bulk of the nitrogen carriers in leaves (62.5%), roots (69.9%) and phloem exudates (53.2%). The levels of glutamate, asparagine and aspartate in the transgenic phloem exudates were similar to the wild-type levels while the glutamine level increased. The proportion of these amino acids remained unchanged in the roots of the transgenic plants. Expression of GLU1 in mesophyll cells implies that Fd-GOGAT assimilates photorespiratory and primary ammonium. GLU1 expression in vascular cells indicates that Fd-GOGAT provides amino acids for nitrogen translocation. The nucleotide sequence data of the GLU1 gene reported in the present study is available from GenBank with the following accession number: AY189525     

Carbon-limited fed-batch production of medium-chain-length polyhydroxyalkanoates from nonanoic acid by <Emphasis Type="Italic">Pseudomonas putida</Emphasis> KT2440

Pseudomonas putida KT2440 grew on glucose at a specific rate of 0.48 h⁻¹ but accumulated almost no poly-3-hydroxyalkanoates (PHA). Subsequent nitrogen limitation on nonanoic acid resulted in the accumulation of only 27% medium-chain-length PHA (MCL-PHA). In contrast, exponential nonanoic acid-limited growth (μ = 0.15 h⁻¹) produced 70 g l⁻¹ biomass containing 75% PHA. At a higher exponential feed rate (μ = 0.25 h⁻¹), the overall productivity was increased but less biomass (56 g l⁻¹) was produced due to higher oxygen demand, and the biomass contained less PHA (67%). It was concluded that carbon-limited exponential feeding of nonanoic acid or related substrates to cultures of P. putida KT2440 is a simple and highly effective method of producing MCL-PHA. Nitrogen limitation is unnecessary.     

Microbial production of 1,3-propanediol from glycerol by Klebsiella pneumoniae under micro-aerobic conditions up to a pilot scale

1,3-Propanediol (1,3-PD) can be produced from glycerol by Klebsiella pneumoniae under micro-aerobic conditions. Recently, this fed-batch fermentation process has been successfully scaled up to 1 m³. The final 1,3-PD concentration, molar yield and volumetric productivity of 72 g l⁻¹, 57% and 2.1 g l⁻¹ h⁻¹, respectively, are close to those of 75 g l⁻¹, 61%, and 2.2 g l⁻¹ h⁻¹ under anaerobic conditions. This process would be suitable for the production of 1,3-PD on a large scale.     

The role fo glutamine synthetase and glutamine metabolism in nitrogen metabolite repression, a regulatory phenomenon in the lower eukaryote Neurospora crassa

Summary Growth of Neurospora crassa on media containing NH ₄ ⁺ leads to the repression of a variety of permeases and alternative pathways which would generate NH ₄ ⁺ , so called ammonium repression. The mutant am ₂ which lacks NADP-GDH is not subject to ammonium repression of nitrate reductase or urea permease, but like the wild type has repressed levels of these systems when grown in the presence of proline, glutamate or glutamine. The glutamine synthetase (GS) mutant gln-la has derepressed levels of the aforementioned systems unless grown with glutamine.The oligomeric state of GS depends upon the nitrogen sufficiency of the cell, a tetrameric form predominates under conditions of nitrogen limitation and an octameric form under conditions of nitrogen sufficiency. We have found that the tetrameric form GS predominates in the mutants am ₂ and gln-la when they are ammonium derepressed.The mechanism of NH ₄ ⁺ repression in N. crassa is thought to entail a cessation of positive gene action by the product of the nit-2 regulatory gene. We propose that under conditions of NH ₄ ⁺ sufficiency, and hence glutamine sufficiency, the octameric form of GS represses nit-2 gene expression and thereby achieves ammonium repression.     

Regulation of expression of nif and hut operons in Klebsiella pneumoniae by glnA linked genes of Escherichia coli

Summary Recombinant DNA plasmids containing inserts from the glnA region of Escherichia coli were used to study the expression of gln, hut, and nif operons in a regulation defective mutant (Gln^–Hut^–Nif^–) of Klebsiella pneumoniae, KP5060. Genes adjacent to the C-terminal end of glnA on the E. coli chromosome were able to derepress hut and nif operons in K. pneumoniae in the absence of glnA product. However, complete derepression of nif operons required inclusion of the segment adjacent to the N-terminal end of the glnA region of the E. coli chromosome along with the C-terminal end segment. In the absence of functional glnA, such a fully derepressed strain expressed nif and hut constitutively indicating a role for the catalytic activity of glutamine synthetase in repression of the genes under nitrogen control.     

Effects of temperature, and availability of nitrogen and phosphorus on the abundance of Anabaena and Microcystis in Lake Biwa, Japan: an experimental approach

Under optimal nutrient conditions, both Microcystis sp. and Anabaena sp. isolated from Lake Biwa grew optimally at 28–32°C but differed in maximal growth rates, phosphate uptake kinetics, maximal phosphorus quotas, and growth responses to nitrogen and phosphorus limitation. The maximal growth rates of Microcystis and Anabaena were 1.6 and 1.25 divisions day⁻¹, respectively. With phosphate and nitrate in the growth-limiting range, the growth of Microcystis was optimal at an N : P ratio of 100 : 1 (by weight) and declined at lower (nitrogen limitation) and higher (phosphorus limitation) ratios. In contrast, Anabaena growth rates did not change at N : P ratios from 1000 : 1 to 10 : 1. Starting with cells containing the maximal phosphorus quota, Microcystis growth in minus-phosphorus medium ceased in 7–9 days, compared with 12–13 days for Anabaena. The phosphate turnover time in cultures starved to their minimum cell quotas was 7.9 min for Microcystis and 0.6 min for Anabaena. Microcystis had a higher K _s (0.12 μg P l⁻¹ 10⁻⁶ cells) and lower V _max (9.63 μg P l⁻¹ h⁻¹ 10⁻⁶ cells), than Anabaena (K _s 0.02 μg P l⁻¹ h⁻¹ 10⁻⁶ cells; V _max 46.25 63 μg P l⁻¹ h⁻¹ 10⁻⁶ cells), suggesting that Microcystis would not be able to grow well in phosphorus-limited waters. We conclude that in spite of the higher growth rate under ideal conditions, Microcystis does not usually bloom in the North Basin because of low availability of phosphorus and nitrogen. Although Anabaena has an efficient phosphorus-uptake system, its main strategy for growth in low-phosphorus environments may depend on storage of phosphorus during periods of abundant phosphorus supply, which are rare in the North Basin. Received: July 31, 2000 / Accepted: October 18, 2000     

Complementation analysis of glnA-linked mutations which affect nitrogen fixation in Klebsiella pneumoniae

Summary A number of mutants have been isolated which affect regulation of the nitrogen fixation (nif) gene cluster in Klebsiella pneumoniae and all of which are linked to glnA, the structural gene for glutamine synthetase (G.S.). These mutants were classified on the basis of their G.S. and nitrogenase activities in conditions of nitrogen limitation and excess. The plasmid R68.45 was then used to generate a number of R-primes carrying the glnA region of the K. pneumoniae chromosome. One of these R-primes (pGE10) was subsequently used in complementation analysis and by isolation of transposon-induced insertion mutations in pGE10 we have demonstrated the existence of a gene, glnG, closely linked to glnA. Mutations in glnG have a similar phenotype to glnG mutants described in Escherichia coli (Pahel and Tyler 1979) and Salmonella typhimurium (Kustu et al. 1979) in that they substantially reduce G.S. activity but are not glutamine auxotrophs. GlnG mutants have very low nitrogenase activity indicating that the glnG product may be involved in regulation of the nif gene cluster in K. pneumoniae.     

The relative importance of tryptophan-dependent and tryptophan-independent biosynthesis of indole-3-acetic acid in tobacco during vegetative growth

A quantitative study of indole-3-acetic acid (IAA) turnover, and the contribution of tryptophan-dependent and tryptophan-independent IAA-biosynthesis pathways, was carried out using protoplast preparations and shoot apices obtained from wild-type and transgenic, IAA-overproducing tobacco (Nicotiana tabacum L.) plants, during a phase of growth when the level of endogenous IAA was stable. Based on the rate of disappearance of [¹³C₆]IAA, the half-life of the IAA pool was calculated to be 1.1 h in wild-type protoplasts and 0.8 h in protoplasts from the IAA-overproducing line, corresponding to metabolic rates of 59 and 160 pg IAA (μg Chl)⁻¹ h⁻¹, respectively. The rate of conversion of tryptophan to IAA was 15 pg IAA (μg Chl)⁻¹ h⁻¹ in wild-type protoplasts and 101 pg IAA (μg Chl)⁻¹ h⁻¹ in protoplasts from IAA-overproducing plants. In both instances, IAA was metabolised more rapidly than it was synthesised from tryptophan. As the endogenous IAA pools were in a steady state, these findings indicate that IAA biosynthesis via the tryptophan-independent pathway was 44 pg IAA (μg Chl)⁻¹ h⁻¹ and 59 pg IAA (μg Chl)⁻¹ h⁻¹, respectively, in the wild-type and transformed protoplast preparations. In a parallel study with apical shoot tissue, the presumed site of IAA biosynthesis, the rate of tryptophan-dependent IAA biosynthesis exceeded the rate of metabolism of [¹³C₆]IAA despite the steady state of the endogenous IAA pool. The most likely explanation for this anomaly is that, unlike the protoplast system, injection of substrates into the apical tissues did not result in uniform distribution of label, and that at least some of the [²H₅]tryptophan was metabolised in compartments not normally active in IAA biosynthesis. This demonstrates the importance of using experimental systems where labelling of the precursor pool can be strictly controlled. Received: 18 January 2000 / Accepted 24 February 2000     

Production of high-density Chlorella culture grown in fermenters

The freshwater microalga Chlorella vulgaris was grown heterotrophically in fed-batch 50–600-L fermenters at 36°C, on aerated and mixed nutrient solution with urea as a nitrogen and glucose as a carbon and energy source. Cell density increased from the initial value 6.25 to 117.18 g DW L⁻¹ in 32 h in the fermenter 50 L at a mean growth rate 3.52 g DW L⁻¹ h⁻¹. The DW increase in the fermenter 200 L was from 7.25 to 94.82 g DW L⁻¹ in 26.5 h at a mean growth rate 3.37 g DW L⁻¹ h⁻¹. Mean specific growth rate μ was about 0.1 h⁻¹ in the both fermenters, if nutrients and oxygen were adequately supplied. The DW increase in the fermenter 600 L was from 0.8 to 81.6 g DW L⁻¹ in 66.5 h at a mean growth rate 1.22 g DW L⁻¹ h⁻¹ and μ = 0.07 h⁻¹. A limitation of the cell growth rate in 600 L fermenter caused by a low dissolved oxygen concentration above cell densities higher than 10 g DW L⁻¹) occurred. Specific growth rate decreased approximately linearly with increasing glucose concentration (25–80 g glucose L⁻¹) at the beginning of cultivation and decreased with the time of cultivation. The cell yield was 0.55–0.69 g DW (g glucose)⁻¹. The content of proteins, β-carotene, and chlorophylls in the cells steadily increased and starch content decreased, by keeping aerated and mixed culture another 12 h in fermenter after the cell growth was stopped due to glucose deficiency.     

Regulation by ammonium and glucose of Arthrobacter fluorescens alanine dehydrogenase

Alanine dehydrogenase in Arthrobacter fluorescens exhibited an allosteric behaviour and two K _m values for ammonium were estimated. In batch cultures at different ammonium concentrations and in continuous culture following an NH₄ ⁺ pulse, the level of ADH activity seems to be regulated by the ammonium concentration, high activities being observed when extracellular ammonium was in excess. The response to the growth rate of an ammonium-limited chemostat culture of A. fluorescens seems to indicate that alanine dehydrogenase and glutamine synthetase activities were inversely related. High activities of glutamate oxaloacetate transaminase and glutamate pyruvate transaminase have been found in crude extract of ammonium-limited cultures. From the results obtained in batch cultures grown at different glucose concentrations and in carbon-limited chemostat culture it appeared that the limitation by glucose influenced alanine dehydrogenase activity negatively. No glutamate dehydrogenase activity and no glutamate synthase activity could be detected with either NADH or NADPH as coenzymes.Abbreviations ADH alanine dehydrogenase - GS glutamine synthetase - GDH glutamate dehydrogenase - GOGAT glutamine oxoglutarate aminotransferase - GOT glutamate oxaloacetate transaminase - GPT glutamate pyruvate transaminase     

Bacterial and phytoplankton dynamics in a sub-tropical estuary

Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates and growth efficiencies were studied in July 2001 and January 2002 during both spring and neap tides, along a tidal cycle, at three sites in a subtropical estuary. Major freshwater inputs located in the Northern region led to differences in both phytoplankton and bacterioplankton biomass and activity along the estuary. While in the Northern region phytoplankton is light-limited, with mean phytoplankton production (PP) between 1.1 and 1.9 μg C l⁻¹ h⁻¹ and mean specific growth rates (PSG) between 0.14 and 0.16 d⁻¹, the Southern region registered values as high as 24.7 μg C l⁻¹ h⁻¹ for PP and 2.45 d⁻¹ (mean PP between 3.4 and 7.3 μg C l⁻¹ h⁻¹; mean PSG between 0.28 and 0.57 d⁻¹). On the other hand, maximum bacterial production (BP: 63.8 μg C l⁻¹ h⁻¹) and specific growth rate (BSG: 32.26 d⁻¹) were observed in the Northern region (mean BP between 3.4 and 12.8 μg C l⁻¹ h⁻¹; mean BSG between 1.98 and 6.67 day⁻¹). These bacterial activity rates are among the highest recorded rates in estuarine and coastal waters, indicating that this system can be highly heterotrophic, due to high loads of allochthonous carbon (mainly derived from mangrove forest). Our results also showed that, despite that BP rates usually exceeded PP, in the Southern region BP may be partially supported (∼45%) by PP, since a significant regression was observed between BP and PP (r = 0.455, P < 0.001). Handling editor: P. Viaroli     

Microbial fed-batch production of 1,3-propanediol by Klebsiella pneumoniae under micro-aerobic conditions

The microbial production of 1,3-propanediol (1,3-PD) by Klebsiella pneumoniae under micro-aerobic conditions was investigated in this study. The experimental results of batch fermentation showed that the final concentration and yield of 1,3-PD on glycerol under micro-aerobic conditions approached values achieved under anaerobic conditions. However, less ethanol was produced under microaerobic than anaerobic conditions at the end of fermentation. The batch micro-aerobic fermentation time was markedly shorter than that of anaerobic fermentation. This led to an increment of productivity of 1,3-PD. For instance, the concentration, molar yield, and productivity of 1,3-PD of batch micro-aerobic fermentation by K. pneumoniae DSM 2026 were 17.65 g/l, 56.13%, and 2.94 g l^–1 h^–1, respectively, with a fermentation time of 6 h and an initial glycerol concentration of 40 g/l. Compared with DSM 2026, the microbial growth of K. pneumoniae AS 1.1736 was slow and the concentration of 1,3-PD was low under the same conditions. Furthermore, the microbial growth in fed-batch fermentation by K. pneumoniae DSM 2026 was faster under micro-aerobic than anaerobic conditions. The concentration, molar yield, and productivity of 1,3-PD in fed-batch fermentation under micro-aerobic conditions were 59.50 g/l, 51.75%, and 1.57 g l^–1 h^–1, respectively. The volumetric productivity of 1,3-PD under microaerobic conditions was almost twice that of anaerobic fed-batch fermentation, at 1.57 and 0.80 g l^–1 h^–1, respectively.     

Growth rate and nutrient limitation affect the transport of Rhodococcus sp. strain DN22 through sand

Rhodococcus strain DN22 grows on the nitramine explosive RDX as a sole nitrogen source, and is potentially useful for bioremediation of explosives-contaminated soil. In order for strain DN22 to be effectively applied in situ, inoculum cells must reach zones of RDX contamination via passive transport, a process that is difficult to predict at field-scale. We examined the effect of growth conditions on the transport of DN22 cells through sand columns, using chemostat-grown cultures. Strain DN22 formed smaller coccoid cells at low dilution rate (0.02 h⁻¹) and larger rods at high dilution rate (0.1 h⁻¹). Under all nutrient limitation conditions studied, smaller cells grown at low dilution rate were retained more strongly by sand columns than larger cells grown at high dilution rate. At a dilution rate of 0.05, cells from nitrate-limited cultures were retained more strongly than cells from RDX-limited or succinate-limited cultures. Breakthrough concentrations (C/C ₀) from sand columns ranged from 0.04 (nitrate-limited, D=0.02 h⁻¹) to 0.98 (succinate-limited, D=0.1 h⁻¹). The observed strong effect of culture conditions on transport of DN22 cells emphasizes the importance of physiology studies in guiding the development of bioremediation technologies.     

Production of curdlan using sucrose or sugar cane molasses by two-step fed-batch cultivation of Agrobacterium species

Maltose and sucrose were efficient carbon sources for the production of curdlan by a strain of Agrobacterium sp. A two-step, fed-batch operation was designed in which biomass was first produced, followed by curdlan production which was stimulated by nitrogen limitation. There exists an optimal timing for nitrogen limitation for curdlan production in the two-step, fed-batch operation. Maximum curdlan production (60 g L⁻¹) was obtained from sucrose with a productivity of 0.2 g L⁻¹ h⁻¹ when nitrogen was limited at a cell concentration of 16.0 g L⁻¹. It was also noted that the curdlan yield from sucrose was as high as 0.45 g curdlan g⁻¹ sucrose, and the highest specific production rate was 1.0 g curdlan g⁻¹ cells h⁻¹ right after nitrogen limitation. Of particular importance was the use of molasses as a cheap carbon source to produce curdlan in the two-step, fed-batch cultivation. As high as 42 g L⁻¹ of curdlan with a yield of 0.35 g curdlan g⁻¹ total sugar was obtained after 120 h of fed-batch cultivation. Received 20 August 1996/ Accepted in revised form 26 November 1996     

Enhanced 1,3-propanediol production by supply of organic acids and repeated fed-batch culture

In fed-batch culture of Klebsiella pneumoniae, 1,3-propanediol production was growth associated, while the by-products, including lactic acid and ethanol, increased sharply as the cells grew slowly. When the fed-batch culture was supplied with a mixture of organic acids including citrate, fumarate and succinate, cell growth and 1,3-propanediol production increased significantly, whereas the by-products, especially lactic acid and ethanol, decreased sharply. High concentrations of PDO and acetate inhibited cell growth and PDO production. To improve the PDO production, repeated fed-batch culture with addition of the organic acid mixture was performed in a 5-l reactor. The fed-batch culture was repeated five times, and the 1,3-propanediol yield and concentration reached above 0.61 mol mol⁻¹ and 66 g l⁻¹, respectively, in 20 h for each cycle. Furthermore, the PDO productivity reached above 3.30 g l⁻¹ h⁻¹ in each cycle, which was much higher than that of the original fed-batch culture.     

Biokinetic parameters and behavior of <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis> during anaerobic growth

The biokinetics of glucose metabolism were evaluated in Aeromonas hydrophila during growth in an anaerobic biosystem. After approx 34 h growth, A. hydrophila metabolized 5,000 mg glucose l⁻¹ into the end-products ethanol, acetate, succinate and formate. The maximum growth rate, μ _m, half saturation coefficients, K _s, microbial yield coefficient, Y, cell mass decay rate coefficient, k _d, and substrate inhibition coefficient, K _si were 0.25 ± 0.03 h⁻¹, 118 ± 31 mg glucose l⁻¹, 0.12 μg DNA mg glucose⁻¹, 0.01 h⁻¹, and 3,108 ± 1,152 mg glucose l⁻¹, respectively. These data were used to predict the performance of a continuous growth system with an influent glucose concentration of 5,000 mg l⁻¹. Results of the analysis suggest that A. hydrophila will metabolize glucose at greater than 95% efficiency when hydraulic retention times (HRTs) exceed 7 h, whereas the culture is at risk of washing out at an HRT of 6.7 h.