The volatile organic compound acetoin enhances the colonization of Azorhizobium caulinodans ORS571 on Sesbania rostrata

Chemoreceptors play a crucial role in assisting bacterial sensing and response to environmental stimuli. Genome analysis of Azorhizobium caulinodans ORS571 revealed the presence of 43 putative chemoreceptors, but their biological functions remain largely unknown. In this study, we identified the chemoreceptor AmaP (methyl-accepting protein of A. caulinodans), characterized by the presence of the CHASE3 domain and exhibited a notable response to acetoin. Thus, we investigated the effect of acetoin sensing on its symbiotic association with the host. Our findings uncovered a compelling role for acetoin as a key player in enhancing various facets of A. caulinodans ORS571's performance including biofilm formation, colonization, and nodulation abilities. Notably, acetoin bolstered A. caulinodans ORS571's efficacy in promoting the growth of S. rostrata, even under moderate salt stress conditions. This study not only broadens our understanding of the AmaP protein with its distinctive CHASE3 domain but also highlights the promising potential of acetoin in fortifying the symbiotic relationship between A. caulinodans and Sesbania rostrata.

Untargeted metabolomics unveiled the role of butanoate metabolism in the development of Pseudomonas aeruginosa hypoxic biofilm

Pseudomonas aeruginosa is a versatile opportunistic pathogen which causes a variety of acute and chronic human infections, some of which are associated with the biofilm phenotype of the pathogen. We hypothesize that defining the intracellular metabolome of biofilm cells, compared to that of planktonic cells, will elucidate the metabolic pathways and biomarkers indicative of biofilm inception. Disc-shaped stainless-steel coupons (12.7 mm diameter) were employed as a surface for static biofilm establishment. Each disc was immersed in a well, of a 24-well microtiter plate, containing a 1-mL Lysogeny broth (LB) suspension of P. aeruginosa ATCC 9027, a strain known for its biofilm prolificacy. This setup underwent oxygen-depleted incubation at 37°C for 24 hours to yield hypoxic biofilms and the co-existing static planktonic cells. In parallel, another planktonic phenotype of ATCC 9027 was produced in LB under shaking (200 rpm) incubation at 37°C for 24 hours. Planktonic and biofilm cells were harvested, and the intracellular metabolites were subjected to global untargeted metabolomic analysis using LC-MS technology, where small metabolites (below 1.5 kDa) were selected. Data analysis showed the presence of 324 metabolites that differed (p < 0.05) in abundance between planktonic and biofilm cells, whereas 70 metabolites did not vary between these phenotypes (p > 0.05). Correlation, principal components, and partial least square discriminant analyses proved that the biofilm metabolome is distinctly clustered away from that of the two planktonic phenotypes. Based on the functional enrichment analysis, arginine and proline metabolism were enriched in planktonic cells, but butanoate metabolism was enriched in biofilm cells. Key differential metabolites within the butanoate pathway included acetoacetate, 2,3-butandiol, diacetyl, and acetoin, which were highly upregulated in the biofilm compared to the planktonic cells. Exogenous supplementation of acetoin (2 mM), a critical metabolite in butanoate metabolism, augmented biofilm mass, increased the structural integrity and thickness of the biofilm, and maintained the intracellular redox potential by balancing NADH/NAD+ ratio. In conclusion, P. aeruginosa hypoxic biofilm has a specialized metabolic landscape, and butanoate pathway is a metabolic preference and possibly required for promoting planktonic cells to the biofilm state. The butanoate pathway metabolites, particularly acetoin, could serve as markers for biofilm development.

Limiting acetoin generation during 2,3-butanediol fermentation with Paenibacillus polymyxa using lignocellulosic hydrolysates

Recent decarbonization efforts have led to interests in producing more bio-based chemicals. One attractive compound produced biochemically is the platform chemical known as 2,3-butanediol (2,3-BDO). In this work a mild alkaline pretreatment using sodium carbonate was performed on corn stover (CS) and switchgrass (SG) to generate hydrolysates for fermentation with the 2,3-BDO producer bacteria strain Paenibacillius polymyxa. Enzymatic hydrolysis performed on the pretreated CS and SG produced theoretical sugar yields of 80 % and 95 % for glucose and xylose, respectively. Fermentations with P. polymxya conducted in anaerobic bottles produced 2,3-BDO reaching concentrations ranging from 14 to 18 g/L with negligible conversion into acetoin. Bioreactor fermentations using the hydrolysate media generated up to 43 g/L and 34 g/L of 2,3-BDO from pretreated CS and SG, respectively, within 24 h of fermentation. However, 2,3-BDO product output was reduced by 40-50 % over the remainder of the fermentation due to conversion into acetoin caused by glucose depletion.

Metabolic engineering of Caldicellulosiruptor bescii for 2,3-butanediol production from unpretreated lignocellulosic biomass and metabolic strategies for improving yields and titers

The platform chemical 2,3-butanediol (2,3-BDO) is used to derive products, such as 1,3-butadiene and methyl ethyl ketone, for the chemical and fuel production industries. Efficient microbial 2,3-BDO production at industrial scales has not been achieved yet for various reasons, including product inhibition to host organisms, mixed stereospecificity in product formation, and dependence on expensive substrates (i.e., glucose). In this study, we explore engineering of a 2,3-BDO pathway in Caldicellulosiruptor bescii, an extremely thermophilic (optimal growth temperature = 78°C) and anaerobic bacterium that can break down crystalline cellulose and hemicellulose into fermentable C5 and C6 sugars. In addition, C. bescii grows on unpretreated plant biomass, such as switchgrass. Biosynthesis of 2,3-BDO involves three steps: two molecules of pyruvate are condensed into acetolactate; acetolactate is decarboxylated to acetoin, and finally, acetoin is reduced to 2,3-BDO. C. bescii natively produces acetoin; therefore, in order to complete the 2,3-BDO biosynthetic pathway, C. bescii was engineered to produce a secondary alcohol dehydrogenase (sADH) to catalyze the final step. Two previously characterized, thermostable sADH enzymes with high affinity for acetoin, one from a bacterium and one from an archaeon, were tested independently. When either sADH was present in C. bescii, the recombinant strains were able to produce up to 2.5-mM 2,3-BDO from crystalline cellulose and xylan and 0.2-mM 2,3-BDO directly from unpretreated switchgrass. This serves as the basis for higher yields and productivities, and to this end, limiting factors and potential genetic targets for further optimization were assessed using the genome-scale metabolic model of C. bescii.IMPORTANCELignocellulosic plant biomass as the substrate for microbial synthesis of 2,3-butanediol is one of the major keys toward cost-effective bio-based production of this chemical at an industrial scale. However, deconstruction of biomass to release the sugars for microbial growth currently requires expensive thermochemical and enzymatic pretreatments. In this study, the thermo-cellulolytic bacterium Caldicellulosiruptor bescii was successfully engineered to produce 2,3-butanediol from cellulose, xylan, and directly from unpretreated switchgrass. Genome-scale metabolic modeling of C. bescii was applied to adjust carbon and redox fluxes to maximize productivity of 2,3-butanediol, thereby revealing bottlenecks that require genetic modifications.

Adaptation to pollination by fungus gnats underlies the evolution of pollination syndrome in the genus Euonymus

BACKGROUND AND AIMS

Dipteran insects are known pollinators of many angiosperms, but knowledge on how flies affect floral evolution is relatively scarce. Some plants pollinated by fungus gnats share a unique set of floral characters (dark red display, flat shape and short stamens), which differs from any known pollination syndromes. We tested whether this set of floral characters is a pollination syndrome associated with pollination by fungus gnats, using the genus Euonymus as a model.

METHODS

The pollinator and floral colour, morphology and scent profile were investigated for ten Euonymus species and Tripterygium regelii as an outgroup. The flower colour was evaluated using bee and fly colour vision models. The evolutionary association between fungus gnat pollination and each plant character was tested using a phylogenetically independent contrast. The ancestral state reconstruction was performed on flower colour, which is associated with fungus gnat pollination, to infer the evolution of pollination in the genus Euonymus.

KEY RESULTS

The red-flowered Euonymus species were pollinated predominantly by fungus gnats, whereas the white-flowered species were pollinated by bees, beetles and brachyceran flies. The colour vision analysis suggested that red and white flowers are perceived as different colours by both bees and flies. The floral scents of the fungus gnat-pollinated species were characterized by acetoin, which made up >90 % of the total scent in three species. Phylogenetically independent contrast showed that the evolution of fungus gnat pollination is associated with acquisition of red flowers, short stamens and acetoin emission.

CONCLUSIONS

Our results suggest that the observed combination of floral characters is a pollination syndrome associated with the parallel evolution of pollination by fungus gnats. Although the role of the red floral display and acetoin in pollinator attraction remains to be elucidated, our finding underscores the importance of fungus gnats as potential contributors to floral diversification.

Mechanism of microbial production of acetoin and 2,3-butanediol optical isomers and substrate specificity of butanediol dehydrogenase

3-Hydroxybutanone (Acetoin, AC) and 2,3-butanediol (BD) are two essential four-carbon platform compounds with numerous pharmaceutical and chemical synthesis applications. AC and BD have two and three stereoisomers, respectively, while the application of the single isomer product in chemical synthesis is superior. AC and BD are glucose overflow metabolites produced by biological fermentation from a variety of microorganisms. However, the AC or BD produced by microorganisms using glucose is typically a mixture of various stereoisomers. This was discovered to be due to the simultaneous presence of multiple butanediol dehydrogenases (BDHs) in microorganisms, and AC and BD can be interconverted under BDH catalysis. In this paper, beginning with the synthesis pathways of microbial AC and BD, we review in detail the studies on the formation mechanisms of different stereoisomers of AC and BD, summarize the properties of different types of BDH that have been tabulated, and analyze the structural characteristics and affinities of different types of BDH by comparing them using literature and biological database data. Using microorganisms, recent research on the production of optically pure AC or BD was also reviewed. Limiting factors and possible solutions for chiral AC and BD production are discussed.

Glyoxylate Shunt and Pyruvate-to-Acetoin Shift Are Specific Stress Responses Induced by Colistin and Ceragenin CSA-13 in Enterobacter hormaechei ST89

Ceragenins, including CSA-13, are cationic antimicrobials that target the bacterial cell envelope differently than colistin. However, the molecular basis of their action is not fully understood. Here, we examined the genomic and transcriptome responses by Enterobacter hormaechei after prolonged exposure to either CSA-13 or colistin. Resistance of the E. hormaechei 4236 strain (sequence type 89 [ST89]) to colistin and CSA-13 was induced in vitro during serial passages with sublethal doses of tested agents. The genomic and metabolic profiles of the tested isolates were characterized using a combination of whole-genome sequencing (WGS) and transcriptome sequencing (RNA-seq), followed by metabolic mapping of differentially expressed genes using Pathway Tools software. The exposure of E. hormaechei to colistin resulted in the deletion of the mgrB gene, whereas CSA-13 disrupted the genes encoding an outer membrane protein C and transcriptional regulator SmvR. Both compounds upregulated several colistin-resistant genes, such as the arnABCDEF operon and pagE, including genes coding for DedA proteins. The latter proteins, along with beta-barrel protein YfaZ and VirK/YbjX family proteins, were the top overexpressed cell envelope proteins. Furthermore, the l-arginine biosynthesis pathway and putrescine-ornithine antiporter PotE were downregulated in both transcriptomes. In contrast, the expression of two pyruvate transporters (YhjX and YjiY) and genes involved in pyruvate metabolism, as well as genes involved in generating proton motive force (PMF), was antimicrobial specific. Despite the similarity of the cell envelope transcriptomes, distinctly remodeled carbon metabolism (i.e., toward fermentation of pyruvate to acetoin [colistin] and to the glyoxylate pathway [CSA-13]) distinguished both antimicrobials, which possibly reflects the intensity of the stress exerted by both agents. IMPORTANCE Colistin and ceragenins, like CSA-13, are cationic antimicrobials that disrupt the bacterial cell envelope through different mechanisms. Here, we examined the genomic and transcriptome changes in Enterobacter hormaechei ST89, an emerging hospital pathogen, after prolonged exposure to these agents to identify potential resistance mechanisms. Interestingly, we observed downregulation of genes associated with acid stress response as well as distinct dysregulation of genes involved in carbon metabolism, resulting in a switch from pyruvate fermentation to acetoin (colistin) and the glyoxylate pathway (CSA-13). Therefore, we hypothesize that repression of the acid stress response, which alkalinizes cytoplasmic pH and, in turn, suppresses resistance to cationic antimicrobials, could be interpreted as an adaptation that prevents alkalinization of cytoplasmic pH in emergencies induced by colistin and CSA-13. Consequently, this alteration critical for cell physiology must be compensated via remodeling carbon and/or amino acid metabolism to limit acidic by-product production.

Radial ZnO nanorods decorating Co3O4 nanoparticles for highly selective and sensitive detection of the 3-hydroxy-2-butanone biomarker

Indirect monitoring of Listeria monocytogenes (LM) via a gas sensor that can detect the bacterial metabolite 3-hydroxy-2-butanone (3H-2B) is a newly emerged strategy. However, such sensors are required simultaneously endow with outstanding selectivity, high sensitivity, and ppb-level detection limit, which remains technologically challenging. Herein, we have developed highly selective and sensitive 3H-2B sensors that consist of zinc oxide nanorods decorated with cobaltosic oxide nanoparticles (ZnO NRs/Co₃O₄ NPs), which have been synthesized by combined optimized hydrothermal and annealing process. Specifically, the ZnO NRs/Co₃O₄ NPs exhibit ultrahigh sensitivity to 5 ppm 3H-2B (R_a/R_g = 550 at 260 °C). The sensor prototypes enable detection as low as 10 ppb 3H-2B, show excellent long-term stability, and present remarkable selectivity through interfering selectivity survey and principal component analysis (PCA). Such outstanding sensing performance is attributed to the modulated electron depletion layer by n-p heterojunctions and abundant gas diffusion pathways via the radial architecture, which was verified via electrochemical impedance spectroscopy test, Mott-Schottky measurement, and ultraviolet-visible absorption analysis. Our highly selective and sensitive ZnO NRs/Co₃O₄ NPs have the potential in the real-time detection of 3H-2B biomarker.

Volumetric oxygen transfer coefficient as fermentation control parameter to manipulate the production of either acetoin or D-2,3-butanediol using bakery waste

The formation of either acetoin or D-2,3-butanediol (D-BDO) by Bacillus amyloliquefaciens cultivated on bakery waste hydrolysates has been evaluated in bioreactor cultures by varying the volumetric oxygen transfer coefficient (k_La). The highest D-BDO production (55.2 g L^-1) was attained in batch fermentations with k_La value of 64 h^-1. Batch fermentations performed at 203 h^-1 led to the highest productivity (2.16 g L^-1h^-1) and acetoin production (47.4 g L^-1). The utilization of bakery waste hydrolysate in fed-batch cultures conducted at k_La of 110 h^-1 led to combined production of acetoin, meso-BDO and D-BDO (103.9 g L^-1). Higher k_La value (200 h^-1) resulted to 65.9 g L^-1 acetoin with 1.57 g L^-1h^-1 productivity. It has been demonstrated that the k_La value may divert the bacterial metabolism towards high acetoin or D-BDO production during fermentation carried out in crude bakery waste hydrolysates.

Production of acetoin from renewable resources under heterotrophic and mixotrophic conditions

This study aimed to reveal whether Cupriavidus necator H16 is suited for the production of acetoin based on the carboxylic acids acetate, butyrate and propionate under heterotrophic and mixotrophic conditions. The chosen production strain, lacking the polyhydroxybutyrate synthases phaC1 and phaC2, was revealed to be beneficiary for autotrophic acetoin production. Proteomic analysis of the strain determined that the deletions do indeed have a significant impact on pyruvate formation and its subsequent direction towards the introduced acetoin-synthesis pathway. Moreover, the strain was tested for its ability to use typical dark fermentation products under hetero- and mixotrophic conditions. Growth with butyrate and acetate led to low efficiencies, while 46.54% ±0.78 of the added propionate was converted into acetoin. Interestingly, mixotrophic conditions led to simultaneous consumption of acetate and butyrate with the gaseous substrates and lowered efficiency. In contrast, mixotrophic propionate consumption led to diauxic behavior and high carbon efficiency of 71.2% ±0.64.

Acetoin modulates conformational change of surfactin: Interfacial assembly and crude oil-washing performance

Due to its special structure, the cyclic lipopeptide surfactin showed remarkable responsiveness to stimuli such as pH, temperature and metal ions. However, few studies investigated the effect of fermented by-products on the conformational change and interfacial assembly of surfactin. Here, the effect of acetoin, a primary metabolite of Bacillus subtilis, on the conformational change and interfacial assembly of surfactin was studied in detail. Surface tension measurements showed that the critical micelle concentration (CMC) of surfactin increased from 1.14 × 10^-5 to 4.32 × 10^-5 M in the presence of acetoin. Moreover, acetoin has increased the interfacial tension of surfactin aqueous solution-crude oil from 1.08 mN/m to 3.01 mN/m. Circular dichroism (CD) spectra and dynamic light-scattering (DLS) further demonstrated that acetoin had induced the conformational transition of surfactin from β-sheet to β-turn structure, and caused surfactin forming some larger micelle aggregations. Afterwards, it was further found that acetoin decreased the oil sand cleaning efficiency of surfactin from 59.7% to 6.6%, and deteriorated the O/W emulsion stability and altered the silicate wettability toward less water wet state. Based on the experimental results, a possible mechanism of the interaction between surfactin and acetoin was proposed.

Protecting tobacco plants from O3 injury by Bacillus velezensis with production of acetoin

Plant growth-promoting rhizobacteria (PGPRs) confer benefits to crops by producing volatile organic compounds (VOCs) to trigger induced systemic tolerance (IST). Here we show that Bacillus velezensis GJ11, a kind of PGPRs, produce VOCs such as 2,3-butanediol and acetoin to trigger IST and cause stomatal closure against O3 injury in tobacco plants. Compared to 2,3-butanediol, acetoin was more effective on triggering IST against O3 injury. The bdh-knockout strain GJ11Δbdh with a blocked metabolic pathway from acetoin to 2,3-butanediol produced more acetoin triggering stronger IST against O3 injury than GJ11. Both acetoin and GJ11Δbdh effectively enhance the antioxidant enzymes activity (e.g. superoxide dismutase and catalases) that is favorable for scavenging the reactive oxygen species like H2 O2 in leaves after exposure to O3 . Consequently, less H2 O2 accumulation was observed, and reasonably less chlorophylls and proteins were damaged by H2 O2 in the tobacco leaves treated with acetoin or GJ11Δbdh. The field experiment also showed that both acetoin and GJ11Δbdh could protect tobacco plants from O3 injury after application by root-drench. This study provides new insights into the role of rhizobacterial B. velezensis and its volatile component of acetoin in triggering defense responses against stresses such as O3 in plants.

Metabolic engineering of carbon overflow metabolism of Bacillus subtilis for improved N-acetyl-glucosamine production

Bacillus subtilis is widely used as cell factories for the production of important industrial biochemicals. Although many studies have demonstrated the effects of organic acidic byproducts, such as acetate, on microbial fermentation, little is known about the effects of blocking the neutral byproduct overflow, such as acetoin, on bioproduction. In this study, we focused on the influences of modulating overflow metabolism on the production of N-acetyl-d-glucosamine (GlcNAc) in engineered B. subtilis. We found that acetoin overflow competes with GlcNAc production, and blocking acetoin overflow increased GlcNAc titer and yield by 1.38- and 1.39-fold, reaching 48.9 g/L and 0.32 g GlcNAc/g glucose, respectively. Further blocking acetate overflow inhibited cell growth and GlcNAc production may be induced by inhibiting glucose uptake. Taken together, our results show that blocking acetoin overflow is a promising strategy for enhancing GlcNAc production. The strategies developed in this work may be useful for engineering strains of B. subtilis for producing other important biochemicals.

Deacidification of grass silage press juice by continuous production of acetoin from its lactate via an immobilized enzymatic reaction cascade

An immobilized enzymatic reaction cascade was designed and optimized for the deacidification of grass silage press juice (SPJ), thus facilitating the production of bio-based chemicals. The cascade involves a three-step process using four enzymes immobilized in a Ca-alginate gel and uses lactic acid to form acetoin, a value-added product. The reaction is performed with a continuous, pH-dependent substrate feed under oxygenation. With titrated lactic acid yields of up to 91% and reaction times of ca. 6h was achieved. Using SPJ as titrant yields of 49% were obtained within 6h. In this deacidification process, with acetoin one value-added bio-based chemical is produced while simultaneously the remaining press juice can be used in applications that require a higher pH. Such, this system can be applied in a multi-product biorefinery concept to take full advantage of nutrient-rich SPJ, which is a widely available and easily storable renewable resource.

Production of acetoin from hydrothermally pretreated oil mesocarp fiber using metabolically engineered Escherichia coli in a bioreactor system

Acetoin is used in the biochemical, chemical and pharmaceutical industries. Several effective methods for acetoin production from petroleum-based substrates have been developed, but they all have an environmental impact and do not meet sustainability criteria. Here we describe a simple and efficient method for acetoin production from oil palm mesocarp fiber hydrolysate using engineered Escherichia coli. An optimization of culture conditions for acetoin production was carried out using reagent-grade chemicals. The final concentration reached 29.9gL^-1 with a theoretical yield of 79%. The optimal pretreatment conditions for preparing hydrolysate with higher sugar yields were then determined. When acetoin was produced using hydrolysate fortified with yeast extract, the theoretical yield reached 97% with an acetoin concentration of 15.5gL^-1. The acetoin productivity was 10-fold higher than that obtained using reagent-grade sugars. This approach makes use of a compromise strategy for effective utilization of oil palm biomass towards industrial application.

3-Hydroxy-2-butanone and the first encounter fight in the male lobster cockroach, Nauphoeta cinerea

Although agonistic behavior in the male lobster cockroach, Nauphoeta cinerea, has been known for more than 40 years, this is the first study to directly collect and quantify the emitted pheromones. In the present study, emitted volatile pheromones were collected from each male pair for 60 min during the first encounter fight and identified and quantified by gas chromatography-mass spectrometry. The major compound collected was 3-hydroxy-2-butanone (3H-2B). The strength of the attack by the dominant male was classified into three categories from weakest (C) to strongest (A). Of the 92 pairs, eight (8.7%) showed no agonistic interactions, and the amount of 3H-2B collected was 121.8+/-37.7 ng/male pair. In the five pairs (5.4%) displaying attack strength C, the amount of 3H-2B collected was 689.6+/-273.7 ng/male pair, and the attack duration was 9.6+/-2.4 min. In the 53 pairs (57.6%) showing attack strength B, the corresponding values were 5396.2+/-449.0 ng/male pair and 22.7+/-1.6 min, while those for the 26 pairs (28.3%) showing attack strength A were 7910.4+/-1120.6 ng/male pair and 24.9+/-2.9 min. For both attack strengths A and B, a linear relationship was found between the amount of 3H-2B collected and attack duration, suggesting that the longer the duration of the attack, the more 3H-2B was emitted. In addition, the rate of 3H-2B emission for attack strength A was significantly higher than that for attack strength B. Using Vaseline-coating, we demonstrated that, in the first encounter fight, the 3H-2B was emitted by the dominant male.

Role of citritase in acetoin formation by Streptococcus diacetilactis and Leuconostoc citrovorum

Harvey, R. J. (University of California, Davis) and E. B. Collins. Role of citritase in acetoin formation by Streptococcus diacetilactis and Leuconostoc citrovorum. J. Bacteriol. 82:954-959. 1961.-Cell-free extracts of Streptococcus diacetilactis and Leuconostoc citrovorum converted citrate to acetate, oxalacetate, pyruvate, carbon dioxide, and acetoin. The products, stoichiometry, and cofactor requirements of the citrate-splitting reaction were identical to those reported for citritase. Coenzyme A was not required; the reaction was stimulated by magnesium or manganous ions, and inhibited by calcium ions. In S. diacetilactis the enzyme is constitutive; it has been found inducible in all other organisms that have been studied. Ten strains of S. diacetilactis, three strains of Leuconostoc, and one strain of S. liquefaciens contained the enzyme; 21 strains of S. cremoris and 3 strains of S. lactis did not. Cell-free extracts of S. diacetilactis and L. citrovorum converted pyruvate to acetoin and carbon dioxide in the presence of manganous ions and thiamine pyrophosphate.

PYRUVATE FERMENTATION BY STREPTOCOCCUS FAECALIS

Deibel, R. H. (American Meat Institute Foundation, Chicago, Ill.), and C. F. Niven, Jr. Pyruvate fermentation by Streptococcus faecalis. J. Bacteriol. 88:4-10. 1964.-Streptococcus faecalis, as opposed to S. faecium, utilizes pyruvate as an energy source for growth. The fermentation is adaptive, as demonstrated by growth experiments in a casein-hydrolysate medium and the fermentation of pyruvate by cell suspensions. The principal products of pyruvate catabolism were acetoin, CO(2), and lactic, acetic, and formic acids, although carbon recoveries were low due to the formation of slime. End-product analyses suggested that both the phosphoroclastic and dismutation systems were active in pyruvate breakdown. Studies with cell-free extracts indicated a thiamine diphosphate requirement for active pyruvate catabolism. The involvement of lipoic acid in the phosphoroclastic system was investigated, and, although inconclusive results were obtained, no association of this cofactor with phosphoroclastic activity could be made.

ROLES OF CITRATE AND ACETOIN IN THE METABOLISM OF STREPTOCOCCUS DIACETILACTIS

Harvey, R. J. (University of California, Davis), and E. B. Collins. Roles of citrate and acetoin in the metabolism of Streptococcus diacetilactis. J. Bacteriol. 86:1301-1307. 1963.-Streptococcus diacetilactis was unable to use citrate as a source of energy for growth, but the addition of citrate to a lactose-containing medium increased the specific growth rate 35%. Besides serving as the precursor of acetoin, some of the pyruvate formed from citrate was incorporated into cell material, primarily into lipids. A constant fraction of the weight of new cells was synthesized from the pyruvate formed from citrate. The rate of entry of citrate into cells was independent of the growth rate, and the usual result was that more pyruvate was formed from citrate than was required for cell synthesis. All excess pyruvate was converted to acetoin. Thus, acetoin formation acts as a detoxification mechanism, a means of removing intracellular pyruvate not required for synthesis of cell material.

[The quantitative composition of natural and technologically changed aromas of plants. II. Aroma compounds in oranges and their changes during juice processing (author's transl)]

After enzyme inhibition with methanol the original volatile compounds of the fruits were investigated in order to compare the quantitative composition of the aroma substances in orange fruits and juices. Aroma compounds of fresh, flash pasteurized and pasteurized juices were analysed. After aroma enrichment by liquid-liquid extraction, prefractionation of the flavor compounds by column chromatography on silicagel 56 flavor substances in the fruits and in the different juices were identified and determined by gas chromatography and mass spectrometry. In comparison to their content in the fruits only 10% of the terpenic hydrocarbons and about 30-66% of the esters were found on average in the fruits. Among the secondary flavor substances, which were not present or present only in traces in the fruits, but showed in juices concentrations up to 0,2 ppm, were 4-terpinenol, carveol and tr-2,8-menthadien-1-ol. After a thermic treatment also 3-hydroxy-2-butanone and 3-methyl-2-buten-1-ol were identified.

[Taxonomic importance of fermentation balances of Enterobacteriaceae (author's transl)]

Fermentation balances have been studied on 66 strains from 9 taxa of Enterobacteriaceae. In addition, 6 strains of Aeromonas have been investigated. Among these fermentation balances, 7 types could be distinguished. It was shown, that the taxa of Enterobacteriaceae differed with respect to the balance types involved. This is true especially for VP-positive taxa. For example, Hafnia, the Klebsiella-Enterobacter-Serratia group, Enterobacter cloacae and Erwinia are to some extend characterized by different balance types. The groups of Enterobacteriaceae with plain acid fermentation are apperently more homogenous with respect to fermentation balances. Balances are, however, not suited for classification, because no balance type turned out to be absolutely group specific. The fermentation balances of our strains of Aeromonas are closely related to the acid-type balances of Enterobacteriaceae. A numerical classification of the data showed, that this method is most potent in sorting multivariate data. A basic agreement of both techniques, the subjective and the numerical subdivision, was found. The first one, however, tends to overemphasize differences among the types. A comparison between the quantitative data of fermentation balances and the corresponding diagnostic tests (MR, VP, Gas) gives information on the reliabiity of the latter.

Enzymes of 2-oxo acid degradation and biosynthesis in cell-free extracts of mixed rumen micro-organisms

The enzymes of 2-oxo acid decarboxylation and 2-oxo acid synthesis (EC 1.2.7.1 and EC 1.2.7.2) were isolated and partially purified from cell-free extracts of rumen micro-organisms. The lyase was active with pyruvate, 3-hydroxypyruvate and 2-oxobutyrate. The synthase was active with acetate, 2-oxoglutarate or succinate. Pyruvate synthase was separated from pyruvate lyase by Sephadex G-200 gel filtration. With Sephadex filtration, approximate mol.wts. of 310000 and 210000 were determined for pyruvate lyase and pyruvate synthase respectively.

Some Factors Influencing the Efficiency of Production of Acetylmethylcarbinol by Rhizopus nigricans

Incubation time had no effect on the efficiency ratio [dry weight-acetylmethylcarbinol (AMC)] during the incubation times tested. The mycelium was more efficient in synthetic media at pH 3 and 4 than at pH 5 and 6. Mycelium also produced AMC more efficiently in apple juice and in synthetic media containing yeast extract or vitamins, especially thiamine. KCl, MgSO 4 , and KH 2 PO 4 had significant suppressing effects on AMC production in a synthetic medium.

Survey of Selected Filamentous Fungi for Voges-Proskauer Reactions

Of 16 filamentous fungi surveyed for Voges-Proskauer reactants, 81.2% were found to be positive. The total group fell into three classes: those producing considerable acetylmethylcarbinol (AMC), those producing a small amount, and those producing no AMC. Oidium lactis had a highly significant effect upon lowering the amount of Voges-Proskauer reactants produced by Rhizopus nigricans .

ACETYLMETHYLCARBINOL PRODUCTION AND THE CLASSIFICATION OF AEROMONADS ASSOCIATED WITH ULCERATIVE DISEASES OF ECTOTHERMIC VERTEBRATES

Page , L. A. (Biological Research Institute, San Diego, and University of California, Davis). Acetylmethylcarbinol production and the classification of aeromonads associated with ulcerative diseases of ectothermic vertebrates. J. Bacteriol. 84: 772–777. 1962.—Quantitative colorimetric tests were made for acetylmethylcarbinol (AMC) production by 14 Aeromonas isolates from ulcerous lesions of snakes, lizards, frogs, and other animals, and by 27 cultures of “identified” aeromonads. The tests revealed that: (i) some strains failed to produce AMC, while the other strains produced AMC in amounts of 5 to > 100 μg/ml of culture; (ii) the reagents employed in the standard method of Barritt failed to detect AMC in concentrations below 35 μg/ml; and (iii) certain strains reported as producing AMC at 23 C and not at 37 C (or vice versa) produced AMC at both temperatures, but at one temperature produced AMC at a level below the sensitivity of the qualitative test. The strains representing the two biotypes could not be distinguished on the basis of their morphology, habitat, pathogenicity for mice or snakes, or serological specificity. Therefore, the Aeromonas classification proposed by Ewing, Hugh, and Johnson, who incorporated the two biotypes into one species, was followed, and the new isolates were designated A. hydrophila .