Biological breakdown of denitrifying sulfide removal process in high-rate expanded granular bed reactor

This work conducted a denitrifying sulfide removal (DSR) test in an expanded granular sludge bed (EGSB) reactor at sustainable loadings of 6.09 kg m⁻³ day⁻¹ for sulfide, 3.11 kg m⁻³ day⁻¹ for nitrate–nitrogen, and 3.27 kg m⁻¹ day⁻¹ for acetate–carbon with >93% efficiency, which is significantly higher than those reported in literature. Strains Pseudomonas sp., Nitrincola sp., and Azoarcus sp. very likely yield heterotrophs. Strains Thermothrix sp. and Sulfurovum sp. are the autotrophs required for the proposed high-rate EGSB-DSR system. The EGSB-DSR reactor experienced two biological breakdowns, one at loadings of 4.87, 2.13, and 1.82 kg m⁻³ day⁻¹; reactor function was restored by increasing nitrate and acetate loadings. Another breakdown occurred at loadings of up to 8.00, 4.08, and 4.50 kg m⁻¹ day⁻¹; the heterotrophic denitrification pathway declined faster than the autotrophic pathway. The mechanism of DSR breakdown is as follows. High sulfide concentration inhibits heterotrophic denitrifiers, and the system therefore accumulates nitrite. Autotrophic denitrifiers are then inhibited by the accumulated nitrite, thereby leading to breakdown of the DSR process.     

Atrazine biodegradation by a bacterial community immobilized in two types of packed-bed biofilm reactors

Through selective enrichment of atrazine-metabolizing microorganisms, a microbial community was selected from agricultural soil. Bacterial isolates, identified by their closest similarity with 16S rDNA sequences stored in NCBI GeneBank, belonged to the genera: Massilia, Stenotrophomonas, Klebsiella, Sphingomonas, Ochrobactrum, Arthrobacter, Microbacterium, Xanthomonas and Ornithinimicrobium. From these strains, only the first six used atrazine as nitrogen and carbon source. The microbial community attached to a non-porous support was evaluated for its atrazine biodegradation rate and removal efficiency under aerobic conditions in two types of packed-bed biofilm reactors fed with a mineral salt medium containing glucose plus atrazine, or atrazine as the sole carbon and nitrogen source. Removal efficiencies near 100% were obtained at loading rates up to 10 mg l⁻¹ h⁻¹. After long periods of continuous operation, the richness of microbial species in biofilm reactors diminished to only three bacterial strains; Stenotrophomonas sp., Ochrobactrum sp. and Arthrobacter sp. By PCR analysis of their DNA, the presence of atzABC genes codifying for the enzymes of the upper catabolic pathway of atrazine, was confirmed in the three strains. The gene atzD that encodes for the cyanuric acid amidohydrolase enzyme was detected only in Stenotrophomonas sp.     

Cultivable Bacterial Diversity of Alkaline Lonar Lake, India

Aerobic, alkaliphilic bacteria were isolated and characterized from water and sediment samples collected in the winter season, January 2002 from alkaline Lonar lake, India, having pH 10.5. The total number of microorganisms in the sediment and water samples was found to be 10²–10⁶ cfu g⁻¹ and 10²–10⁴ cfu ml⁻¹, respectively. One hundred and ninety-six strains were isolated using different enrichment media. To study the bacterial diversity of Lonar lake and to select the bacterial strains for further characterization, screening was done on the basis of pH and salt tolerance of the isolates. Sixty-four isolates were subjected to phenotypic, biochemical characterization and 16S rRNA sequencing. Out of 64, 31 bacterial isolates were selected on the basis of their enzyme profile and further subjected to phylogenetic analysis. Phylogenetic analysis indicated that most of the Lonar lake isolates were related to the phylum Firmicutes, containing Low G+C, Gram-positive bacteria, with different genera: Bacillus, Paenibacillus, Alkalibacillus, Exiguobacterium, Planococcus, Enterococcus and Vagococcus. Seven strains constituted a Gram-negative bacterial group, with different genera: Halomonas, Stenotrophomonas and Providencia affiliated to γ-Proteobacteria, Alcaligenes to β-Proteobacteria and Paracoccus to α-Proteobacteria. Only five isolates were High G+C, Gram-positive bacteria associated with phylum Actinobacteria, with various genera: Cellulosimicrobium, Dietzia, Arthrobacter and Micrococcus. Despite the alkaline pH of the Lonar lake, most of the strains were alkalitolerant and only two strains were obligate alkaliphilic. Most of the isolates produced biotechnologically important enzymes at alkaline pH, while only two isolates (ARI 351 and ARI 341) showed the presence of polyhydroxyalkcanoate (PHA) and exopolysaccharide (EPS), respectively.     

Efficacy of bacterial consortium-AIE2 for contemporaneous Cr(VI) and azo dye bioremediation in batch and continuous bioreactor systems, monitoring steady-state bacterial dynamics using qPCR assays

Bacterial consortium-AIE2 with a capability of contemporaneous Cr(VI) reduction and azo dye RV5 decolourization was developed from industrial wastewaters by enrichment culture technique. The 16S rRNA gene based molecular analyses revealed that the consortium bacterial community structure consisted of four bacterial strains namely, Alcaligenes sp. DMA, Bacillus sp. DMB, Stenotrophomonas sp. DMS and Enterococcus sp. DME. Cumulative mechanism of Cr(VI) reduction by the consortium was determined using in vitro Cr(VI) reduction assays. Similarly, the complete degradation of Reactive Violet 5 (RV5) dye was confirmed by FTIR spectroscopic analysis. Consortium-AIE2 exhibited simultaneous bioremediation efficiencies of (97.8 ± 1.4) % and (74.1 ± 1.2) % in treatment of both 50 mg l⁻¹ Cr(VI) and RV5 dye concentrations within 48 h of incubation at pH 7 and 37°C in batch systems. Continuous bioreactor systems achieved simultaneous bioremediation efficiencies of (98.4 ± 1.5) % and (97.5 ± 1.4) % after the onset of steady-state at 50 mg l⁻¹ input Cr(VI) and 25 mg l⁻¹ input RV5 concentrations, respectively, at medium dilution rate (D) of 0.014 h⁻¹. The 16S rRNA gene copy numbers in the continuous bioreactor as determined by real-time PCR assay indicated that Alcaligenes sp. DMA and Bacillus sp. DMB dominated consortium bacterial community during the active continuous bioremediation process.     

Enhancing denitrifying sulfide removal with functional strains under micro-aerobic condition

The biological denitrifying sulfide reaction (DSR) frequently proceeds in anaerobic environments since excess oxygen inhibits the activity of the denitrifiers. This study isolated a consortium H7, comprising two strains, Penibacillus sp. and Aneurinibacillus aneurinilyticus. It indicated that the DSR performance with the H7 in a mixotrophic medium is significantly enhanced at high sulfide concentrations. The H7 was inhibited by adding >200 mg l⁻¹ of S²⁻ under anaerobic conditions. However, when 280 mg ⁻¹ of S²⁻ was added, H7 could still degrade some of the sulfide, nitrate and acetate under micro-aerobic conditions. Micro-aerobic conditions stimulated the activity of sulfide oxidase and increased the removal rate of highly concentrated sulfide, reducing the inhibition of sulfide on denitrifiers and improving DSR performance.     

Identification of novel denitrifying bacteria Stenotrophomonas sp. ZZ15 and Oceanimonas sp. YC13 and application for removal of nitrate from industrial wastewater

Two novel denitrifying bacteria were successfully isolated from industrial wastewater and soil samples. Using morphological, biochemical/biophysical and 16S rRNA gene analyses, these two bacteria were identified as Stenotrophomonas sp. ZZ15 and Oceanimonas sp. YC13, respectively. Both of these two bacteria showed efficient NO₃ ⁻-N removing abilities under a semi-anaerobic condition without obvious accumulation of NO₂ ⁻-N, N₂O-N and NH₄ ⁺-N. NO₃ ⁻-N removal from paper mill wastewater was also successful by treatments with either a denitrifier or an immobilization method. Therefore, this study provides valuable denitrifying bacteria in biotreatment of industrial wastewater and other environmental pollution caused by NO₃ ⁻/NO₂ ⁻.     

Simultaneous biological removal of sulfur, nitrogen and carbon using EGSB reactor

High-rate biological conversion of sulfide and nitrate in synthetic wastewater to, respectively, elemental sulfur (S⁰) and nitrogen-containing gas (such as N₂) was achieved in an expanded granular sludge bed (EGSB) reactor. A novel strategy was adopted to first cultivate mature granules using anaerobic sludge as seed sludge in sulfate-laden medium. The cultivated granules were then incubated in sulfide-laden medium to acclimate autotrophic denitrifiers. The incubated granules converted sulfide, nitrate, and acetate simultaneously in the same EGSB reactor to S⁰, N-containing gases and CO₂ at loading rates of 3.0 kg S m⁻³ d⁻¹, 1.45 kg N m⁻³ d⁻¹, and 2.77 kg Ac m⁻¹ d⁻¹, respectively, and was not inhibited by sulfide concentrations up to 800 mg l⁻¹. Effects of the C/N ratio on granule performance were identified. The granules cultivated in the sulfide-laden medium have Pseudomonas spp. and Azoarcus sp. presenting the heterotrophs and autotrophs that co-work in the high-rate EGSB-SDD (simultaneous desulfurization and denitrification) reactor.     

Structural and Functional Responses of a Sewage Microbial Community to Dilution-Induced Reductions in Diversity

The relationship between functional redundancy and microbial community structure–diversity was examined using laboratory incubations to ensure constant environmental conditions. Serial dilutions of a sewage microbial community were prepared, used to inoculate sterile sewage, and maintained in batch culture. Probability suggests that dilution of the initial community should remove rare organism types, creating mixtures of cells differing in diversity. Regrowth of the diluted mixtures generated communities similar in abundance but differing in community structure and relative diversity (as determined using two DNA fingerprinting techniques and dilution-to-extinction analysis of community-level physiological profiles). The in situ function of each regrown community was examined by monitoring the short-term uptake of five different ¹⁴C-labeled compounds (glucose, acetate, citrate, palmitic acid, and an amino acid mixture). No significant differences were detected between treatments in either the rate of uptake of a substrate or the efficiency with which each community assimilated each compound. The fact that the activity of the original community was the same as that of a community regrown from an inoculum containing fewer that 100 cells (10⁻⁶ dilution) indicates that functional redundancy was quite high in this system. For each organism type eliminated during the dilution process, at least one of the remaining types was able to provide the same function at the same level as the lost one. Further research is necessary to determine what impact this functional redundancy may have on overall ecosystem function and stability.     

Amino Acid Deamination by Ruminal <Emphasis Type="Italic">Megasphaera elsdenii</Emphasis> Strains

When ruminal fluid from a cow fed timothy hay was serially diluted (10-fold increments into anaerobic broth containing 15 mg ml⁻¹ Trypticase), the low dilutions (≤10⁻⁶) had optical densities greater than 2.0 and ammonia concentrations greater than 100 mM. The optical densities and ammonia concentrations of the 10⁻⁸ and 10⁻⁹ dilutions were very low, but large cocci were observed in the 10⁻⁸ dilution. The large cocci were isolated and identified by 16S rDNA sequencing as Megasphaera elsdenii. The freshly isolated strain (JL1) grew well on Trypticase, but less than 4% of the amino acid nitrogen in Trypticase was converted to ammonia. Optical density and ammonia production were twice as great if Casamino acids were provided, and similar results were obtained with seven other strains (B159, AW106, YT91, LC1, T81, J1, and YZ70). Specific activities of deamination (based on Casamino acids) of the eight strains ranged from 100 (strain JL1) to 325 (strain B159) nmol mg protein⁻¹ min⁻¹. None of the strains could utilize branched-chain amino acids as an energy source for growth, but specific activities of branched-chain amino acid deamination ranged from 15 to 65 nmol mg protein⁻¹ min⁻¹. All eight of the M. elsdenii strains grew well in the presence of 5 μM monensin, and only two of the strains were strongly inhibited by 20 μM monensin. On the basis of these results, it appears that M. elsdenii is deficient in peptidase activity and can utilize only a few amino acids. Some M. elsdenii strains produced ammonia and branched-chain volatile fatty acids nearly as fast as obligate amino acid-fermenting ruminal bacteria, but the extent of this production was at least fourfold lower. Because all of the strains could tolerate 5 μM monensin, it is unlikely that this feed additive would significantly inhibit M. elsdenii in vivo. Received: 12 December 2001 / Accepted: 5 February 2002     

Physiology and kinetics of trimethylamine conversion by two methylotrophic strains in continuous cultivation systems

The change of dilution rate (D) on both Methylophilus methylotrophus NCIMB11348 and Methylobacterium sp. RXM CCMI908 growing in trimethylamine (TMA) chemostat cultures was studied in order to assess their ability to remove odours in fish processing plants. M. methylotrophus NCIMB11348 was grown at dilution rates of 0.012–0.084 h⁻¹ and the biomass level slightly increased up to values of D around 0.07 h⁻¹. The maximum cell production rate was obtained at 0.07 h⁻¹ corresponding to a maximum conversion of carbon into cell mass (35%). The highest rate of TMA consumption was 3.04 mM h⁻¹ occurring at D=0.076 h⁻¹. Methylobacterium sp. RXM CCMI908 was grown under similar conditions. The biomass increased in a more steep manner up to values of D around 0.06 h⁻¹. The maximum cell production rate (0.058 g l⁻¹h⁻¹) was obtained in the region close to 0.06 h⁻¹ where a maximum conversion of the carbon into cell mass (40%) was observed. The maximum TMA consumption was 2.33 mM h⁻¹ at D=0.075 h⁻¹. The flux of carbon from TMA towards cell synthesis and carbon dioxide in both strains indicates that the cell is not excreting products but directing most of the carbon source to growth. Carbon recovery levels of approximately 100% show that the cultures are carbon-limited. Values for theoretical maximum yields and maintenance coefficients are presented along with a kinetic assessment based on the determination of the substrate saturation constant and maximum growth rate for each organism. Received: 25 February 1999 / Received revision: 14 May 1999 / Accepted: 17 May 1999     

Chromium Reduction,Plant Growth–Promoting Potentials,and Metal Solubilizatrion by <Emphasis Type="Italic">Bacillus sp</Emphasis>. Isolated from Alluvial Soil

The plant growth–promoting potentials, production of siderophore and solubilization of insoluble phosphorus (P) and zinc and lead by the chromium (vi) -reducing Bacillus species, PSB 1, PSB 7, and PSB 10, was assessed both in the presence and absence of chromium under in vitro conditions. The Bacillus strains tolerated chromium up to the concentration of 500 (PSB1), 400 (PSB7), and 550 μg ml⁻¹ (PSB10), respectively, on nutrient agar plates. Bacillus sp. PSB 10 reduced Cr (vi) by 87% at pH 7, which was followed by Bacillus sp. PSB 1 (83%) and PSB 7 (74%) in nutrient broth after 120 h of incubation. A concentration of 50 μg ml⁻¹ of Cr (vi) was completely reduced by Bacillus sp. PSB 1 and PSB 10 (after 100 h) and PSB 7 (after 120 h). The Bacillus strains PSB 1, PSB 7, and PSB 10 produced 19.3, 17.7, and 17.4 μg ml⁻¹ of indole acetic acid, respectively, in luria bertani broth at 100 μg ml⁻¹ of tryptophan, which consistently decreased with an increase in chromium concentration. The Bacillus strains were positive for siderophore, HCN, and ammonia both in the absence and presence of chromium. The Bacillus strains solubilized 375 (PSB 1), 340 (PSB 7), and 379 (PSB 10) μg ml⁻¹ P, respectively, in Pikovskaya broth devoid of chromium. In contrast, chromium at 150 μg ml⁻¹ reduced the amount of P solubilized by 17 (PSB 1), 15 (PSB 7), and 9% (PSB 10) compared to control. The tested bacterial strains solubilized a considerable amount of zinc and lead in nutrient broth both in the absence and presence of chromium. Generally, the chromium reduction and the plant growth–promoting potentials of chromium-reducing Bacillus were strongly correlated at the tested concentration of chromium. The present observations demonstrated that the chromium-reducing, metal-solubilizing, and plant growth–promoting potentials of the Bacillus strains PSB1, PSB 7, and PSB10 were not adversely affected by the chromium application and, hence, may be applied for raising the productivity of crops under metal-contaminated soils.     

Chemical composition and antibacterial potential of Artemisia arborescens L. essential oil

This study was undertaken to characterize the essential oil (EO) of Artemisia arborescens growing wild in Sicily. EO, extracted by steam distillation, was examined for its chemical composition and for its capability to inhibit some food-borne pathogen bacteria. A total of 43 compounds (13 monoterpene hydrocarbons, 14 oxygenated monoterpenes, 10 sesquiterpene hydrocarbons, three oxygenated sesquiterpenes and less amount of other three compounds), which account 93.73% of the total oil, were identified by gas chromatography and gas chromatography–mass spectrometry. Oxygenated monoterpenes (57.32%) constituted the main fraction, with β-thujone as the main compound (45.04%), followed by the sesquiterpene hydrocarbon chamazulene (22.71%). Undiluted EO showed a large inhibition spectrum against strains of Listeria monocytogenes (34 out of 44), whilst it was ineffective against enterobacteria and salmonellas. The minimum inhibition concentration (MIC) was evaluated for the two most sensitive strains (L. monocytogenes 186 and 7BO) at two cellular concentrations (10⁶ and 10⁷ CFU ml⁻¹). The lowest MIC (0.625 μl ml⁻¹, dilution of oil with acetone) was found for strain L. monocytogenes 186 at 10⁶ CFU ml⁻¹.     

Insecticide-tolerant and plant growth promoting <Emphasis Type="Italic">Bradyrhizobium</Emphasis> sp. (<Emphasis Type="Italic">vigna</Emphasis>) improves the growth and yield of greengram [<Emphasis Type="Italic">Vigna radiata</Emphasis> (L.) Wilczek] in insecticide-stressed soils

This study was designed to identify rhizobial strains specific to greengram expressing higher tolerance against insecticides, fipronil and pyriproxyfen, and synthesizing plant growth regulators even amid insecticide-stress. Of the 50 bradyrhizobial isolates, the Bradyrhizobium sp. strain MRM6 showed tolerance up to 1,600 μg mL⁻¹ against each of fipronil and pyriproxyfen. The tolerant Bradyrhizobium sp. (vigna) produced plant growth promoting substances in substantial amounts, both in the presence and absence of insecticides. The strain MRM6 was further used to investigate its impact on greengram grown in soils treated with 200 (the recommended dose), 400 and 600 μg kg⁻¹ soil of fipronil and 1,300 (the recommended dose), 2,600 and 3,900 μg kg⁻¹ soil of pyriproxyfen. Fipronil at 600 μg kg⁻¹ soils and pyriproxyfen at 3,900 μg kg⁻¹ soils had greatest toxic effects and decreased plant biomass, symbiotic efficiency, nutrient uptake and seed yield of greengram plants. The Bradyrhizobium sp. (vigna) inoculant when used with fipronil and pyriproxyfen significantly increased the measured parameters compared to the plants grown in soils treated solely with the same concentration of each insecticide. This study inferred that the Bradyrhizobium sp. (vigna) strain MRM6 may be exploited as bio-inoculant to increase the productivity of greengram exposed to insecticide-stressed soils.     

Inability of Some <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis> Strains to Act as Recipients of Plasmid pRAS1 in Conjugal Transfer Experiments

Plasmids belonging to the IncU incompatibility group are mobile genetic elements isolated frequently from Aeromonas spp. These plasmids share structural and functional characteristics and often carry Class-1 integrons bearing antibiotic resistance genes. In this work the ability of two IncU plasmids, pAr-32 and pRAS1 to establish in different A. hydrophila strains after conjugal transfer was studied. In vitro transfer frequencies on solid surface ranged from 10⁻¹ to 10⁻⁶ for pAr-32 and from 10⁻³ to 10⁻⁵ for pRAS1. While carrying out these experiments we detected four strains unable to acquire plasmid pRAS1, indicating that the genetic background of recipients affects the establishment of the plasmid. We explored the possible reasons why these strains failed to yield transconjugants after mating experiments using A. salmonicida 718 as a donor. Factors included donor cell recognition, incompatibility, surface exclusion and restriction of incoming DNA. We found that none of these factors could explain the refractivity of non-receptive A. hydrophila strains to yield transconjugants. Although we do not know the reasons of this refractivity, we may speculate that these isolates lack a product necessary to replicate or stabilize plasmid pRAS1. Alternatively, these strains could contain a product that impedes plasmid establishment.     

Development of a phosphate-removal system using a marine photosynthetic bacterium Chromatium sp.

The marine photosynthetic bacterium Chromatium sp. successfully removed orthophosphate when grown phototrophically. The phosphate-uptake rate was almost constant at more than 5.0 mg- PO₄ ³⁻/l in synthetic medium. Addition of seawater causes flocculation of this strain. The successful use of seawater as an inexpensive source of magnesium could prove to be effective in the removal of photosynthetic bacterial cells from a medium. A semicontinuous culture system was used for the removal of low concentrations of phosphate and the phosphate-uptake activity of Chromatium sp. was maintained under 0.1 day⁻¹ dilution rate. This strain was also able to remove high concentrations of phosphate from domestic sewage. Received 24 May 1996 / Received revision: 5 August 1996 / Accepted: 6 September 1996     

Morphometry and growth of three <Emphasis Type="Italic">Synechococcus</Emphasis>-like picoplanktic cyanobacteria at different culture conditions

Three phycocyanin-rich strains of Synechococcus-like picoplanktic cyanobacteria, isolated from the plankton of Czech oligotrophic to eutrophic freshwater reservoirs, were investigated in crossed gradients of light and temperature and in combination with two different culture media (BG-11 and WC). The strains exhibited similar growth and reproduction patterns and displayed overlapping ranges of cell size (1.5 × 0.8 μm) under standardized laboratory conditions (18 μmol m⁻² s⁻¹; 20°C). However, strains behavior differed in the crossed gradients. All strains preferred BG-11 medium, where also remarkable size changes could be observed. Length, width, cell abundance and growth rate of two strains were positively correlated with temperature and nutrients, whereas the impact of light intensity was insignificant. Maximum cell elongation (involution cells up to 19 μm) occurred in two strains only in BG-11 medium at highest temperature (28°C) and highest irradiance (53 μmol m⁻² s⁻¹). Cell dimensions in WC medium were constant under most conditions given. The third strain was influenced by all three factors, from which light and nutrients played pivotal role. The length of the lag-phase for all strains appeared to be temperature dependent (negative correlation). Despite the fact that the cell volume in all strains increased more than five times under the lowest light and low temperature (6 μmol m⁻² s⁻¹, <15°C) in both media, the length/width ratio remained unchanged. The strains differed in the degree of cell enlargement and cell division symmetry as well as in optimum temperature and light dependence. Based on this experimental work two strains could be identified as Synechococcus sp. and one as Cyanobium sp., which can be used as a support for the following genetical analyses.     

Influence of co-inoculation of bacteria-cyanobacteria on crop yield and C–N sequestration in soil under rice crop

The performance of three selected bacterial strains—PR3, PR7 and PR10 (Providencia sp., Brevundimonas sp., Ochrobacterium sp.) and three cyanobacterial strains CR1, CR2 and CR3 (Anabaena sp., Calothrix sp., Anabaena sp.), and their combinations was evaluated in a pot experiment with rice variety Pusa-1460, comprising 51 treatments along with recommended fertilizer controls. Highest yield enhancement of 19.02% was recorded in T12 (CR2), over control, while significant enhancement in nitrogen fixing potential was recorded in treatments involving combination of bacterial-cyanobacterial strains—T37 (PR3 + CR1 + CR3) and T21 (PR7 + CR1). Organic carbon was significantly increased in all microbe-inoculated treatments, which could be correlated with microbial biomass carbon values and activities of all the enzymes tested in our study. Also, panicle weight and plant biomass were highly correlated with soil microbial carbon. Comparative evaluation revealed the superior performance of strains CR2, CR1 (both Anabaena sp.) and PR10 (Ochrobacterium sp.) in increasing the growth and grain yield of rice and improving soil health, besides N (nitrogen) savings of 40–80 kg ha⁻¹. The study for the first time illustrated the positive effects of co-inoculation of bacterial and cyanobacterial strains for integrated nutrient management of rice crop.     

Anomalies in the growth kinetics of Saccharomyces cerevisiae strains in aerobic chemostat cultures

Aerobic glucose-limited chemostat cultivations were conducted with Saccharomyces cerevisiae strains NRRL Y132, ATCC 4126 and CBS 8066, using a complex medium. At low dilution rates all three strains utilised glucose oxidatively with high biomass yield coefficients, no ethanol production and very low steady-state residual glucose concentrations in the culture. Above a threshold dilution rate, respiro-fermentative (oxido-reductive) metabolism commenced, with simultaneous respiration and fermentation occurring, which is typical of Crabtree-positive yeasts. However, at high dilution rates the three strains responded differently. At high dilution rates S. cerevisiae CBS 8066 produced 7–8 g ethanol L⁻¹ from 20 g glucose L⁻¹ with concomitant low levels of residual glucose, which increased markedly only close to the wash-out dilution rate. By contrast, in the respiro-fermentative region both S. cerevisiae ATCC 4126 and NRRL Y132 produced much lower levels of ethanol (3–4 g L⁻¹) than S. cerevisiae CBS 8066, concomitant with very high residual sugar concentrations, which was a significant deviation from Monod kinetics and appeared to be associated either with high growth rates or with a fermentative (or respiro-fermentative) metabolism. Supplementation of the cultures with inorganic or organic nutrients failed to improve ethanol production or glucose assimilation. Journal of Industrial Microbiology & Biotechnology (2000) 24, 231–236. Received 09 August 1999/ Accepted in revised form 18 December 1999     

Performance assessment of malolactic fermenting bacteria Oenococcus oeni and Lactobacillus brevis in continuous culture

The growth performance of malolactic fermenting bacteria Oenococcus oeni NCIMB 11648 and Lactobacillus brevis X₂ was assessed in continuous culture. O. oeni grew at a dilution rate range of 0.007 to 0.052 h⁻¹ in a mixture of 5:6 (g l⁻¹) of glucose/fructose at an optimal pH of 4.5, and L. brevis X₂ grew at 0.010 to 0.089 h⁻¹ in 10 g l⁻¹ glucose at an optimal pH of 5.5 in a simple and safe medium. The cell dry weight, substrate uptake and product formation were monitored, as well as growth kinetics, yield parameters and fermentation balances were also evaluated under pH control conditions. A comparison of growth characteristics of two strains was made, and this showed significantly different performance. O. oeni has lower maximum specific growth rate (μ_max=0.073 h⁻¹), lower maximum cell productivity (Q _x ^max=17.6 mg cell l⁻¹ h⁻¹), lower maximum biomass yield (Y _x/s ^max=7.93 g cell mol⁻¹ sugar) and higher maintenance coefficient (m _s=0.45 mmol⁻¹ sugar g⁻¹ cell h⁻¹) as compared with L. brevis X₂ (μ_max=0.110 h⁻¹; Q _x ^max=93.2 g⁻¹ cell mol⁻¹ glucose; Y _x/s ^max=22.3 g cell mol⁻¹ glucose; m _s=0.21 mmol⁻¹ glucose g⁻¹ cell h⁻¹). These data suggest a possible more productive strategy for their combined use in maturation of cider and wine.     

Reduction of produced elementary sulfur in denitrifying sulfide removal process

Denitrifying sulfide removal (DSR) processes simultaneously convert sulfide, nitrate, and chemical oxygen demand from industrial wastewater into elemental sulfur, dinitrogen gas, and carbon dioxide, respectively. The failure of a DSR process is signaled by high concentrations of sulfide in reactor effluent. Conventionally, DSR reactor failure is blamed for overcompetition for heterotroph to autotroph communities. This study indicates that the elementary sulfur produced by oxidizing sulfide that is a recoverable resource from sulfide-laden wastewaters can be reduced back to sulfide by sulfur-reducing Methanobacterium sp. The Methanobacterium sp. was stimulated with excess organic carbon (acetate) when nitrite was completely consumed by heterotrophic denitrifiers. Adjusting hydraulic retention time of a DSR reactor when nitrite is completely consumed provides an additional control variable for maximizing DSR performance.