Growth of Acinetobacter calcoaceticus on ethanol

Recent advances in Emulsan production, purification, and application: Exploring bioemulsifiers unique potentials

Bioemulsifiers are compounds produced by microorganisms that reduce the interfacial forces between hydrophobic substances and water. Due to their potential in the pharmaceutical and food industries and their efficiency in oil spill remediation, they have been the subject of study in the scientific community while being safe, biodegradable, and sustainable compared to synthetic options. These biomolecules have high molecular weight and polymeric structures, distinguishing them from traditional biosurfactants. Emulsan, a bioemulsifier exopolysaccharide, is produced by Acinetobacter strains and is highly efficient in forming stable emulsions. Its low toxicity and high potential as an emulsifying agent promote its application in pharmaceutical and food industries as a drug-delivery vehicle and emulsion stabilizer. Due to the high environmental impact of oil spills, bioemulsifiers have great potential for environmental applications, such as bioremediation. This unique feature gives them a distinct mechanism of action in forming emulsions, resulting in minimal environmental impact. A better understanding of these aspects can improve the use of bioemulsifiers and environmental remediation in various industries. This review will discuss the production and characterization of Emulsan, focusing on recent advancements in cultivation conditions, purification techniques, compound identification, and ecotoxicity.

The Role of Microorganisms and Carbon-to-Nitrogen Ratios for Microbial Protein Production from Bioethanol

The global protein demand is rapidly increasing at rates that cannot be sustained, with projections showing 78% increased global protein needs by 2050 (361 compared to 202 million ton protein /year in 2017). In the absence of dedicated mitigation strategies, the environmental effects of our current food production system (relying on agriculture) are expected to surpass the planetary boundaries—the safe operating space for humanity—by 2050.

Patterns of virus growth across the diversity of life

Although viruses in their natural habitats add up to less than 10% of the biomass, they contribute more than 90% of the genome sequences [1]. These viral sequences or 'viromes' encode viruses that populate the Earth's oceans [2, 3] and terrestrial environments [4, 5], where their infections impact life across diverse ecological niches and scales [6, 7], including humans [8-10]. Most viruses have yet to be isolated and cultured [11-13], and surprisingly few efforts have explored what analysis of available data might reveal about their nature. Here, we compiled and analyzed seven decades of one-step growth and other data for viruses from six major families, including their infections of archaeal, bacterial and eukaryotic hosts [14-191]. We found that the use of host cell biomass for virus production was highest for archaea at 10%, followed by bacteria at 1% and eukarya at 0.01%, highlighting the degree to which viruses of archaea and bacteria exploit their host cells. For individual host cells, the yield of virus progeny spanned a relatively narrow range (10-1000 infectious particles per cell) compared with the million-fold difference in size between the smallest and largest cells. Furthermore, healthy and infected host cells were remarkably similar in the time they needed to multiply themselves or their virus progeny. Specifically, the doubling time of healthy cells and the delay time for virus release from infected cells were not only correlated (r = 0.71, p < 10-10, n = 101); they also spanned the same range from tens of minutes to about a week. These results have implications for better understanding the growth, spread and persistence of viruses in complex natural habitats that abound with diverse hosts, including humans and their associated microbes.

Identification and characterization of a carnitine transporter in Acinetobacter baumannii

The opportunistic pathogen Acinetobacter baumannii is able to grow on carnitine. The genes encoding the pathway for carnitine degradation to the intermediate malic acid are known but the transporter mediating carnitine uptake remained to be identified. The open reading frame HMPREF0010_01347 (aci01347) of Acinetobacter baumannii is annotated as a gene encoding a potential transporter of the betaine/choline/carnitine transporter (BCCT) family. To study the physiological function of Aci01347, the gene was deleted from A. baumannii ATCC 19606. The mutant was no longer able to grow on carnitine as sole carbon and energy source demonstrating the importance of this transporter for carnitine metabolism. Aci01347 was produced in Escherichia coli MKH13, a strain devoid of any compatible solute transporter, and the recombinant E. coli MKH13 strain was found to take up carnitine in an energy-dependent fashion. Aci01347 also transported choline, a compound known to be accumulated under osmotic stress. Choline transport was osmolarity-independent which is consistent with the absence of an extended C-terminus found in osmo-activated BCCT. We propose that the Aci01347 is the carnitine transporter mediating the first step in the growth of A. baumannii on carnitine.

Metabolism and Biodegradation of Spacecraft Cleaning Reagents by Strains of Spacecraft-Associated Acinetobacter

Spacecraft assembly facilities are oligotrophic and low-humidity environments, which are routinely cleaned using alcohol wipes for benchtops and spacecraft materials, and alkaline detergents for floors. Despite these cleaning protocols, spacecraft assembly facilities possess a persistent, diverse, dynamic, and low abundant core microbiome, where the Acinetobacter are among the dominant members of the community. In this report, we show that several spacecraft-associated Acinetobacter metabolize or biodegrade the spacecraft cleaning reagents of ethanol (ethyl alcohol), 2-propanol (isopropyl alcohol), and Kleenol 30 (floor detergent) under ultraminimal conditions. Using cultivation and stable isotope labeling studies, we show that ethanol is a sole carbon source when cultivating in 0.2 × M9 minimal medium containing 26 μM Fe(NH4)2(SO4)2. Although cultures expectedly did not grow solely on 2-propanol, cultivations on mixtures of ethanol and 2-propanol exhibited enhanced plate counts at mole ratios of ≤0.50. In support, enzymology experiments on cellular extracts were consistent with oxidation of ethanol and 2-propanol by a membrane-bound alcohol dehydrogenase. In the presence of Kleenol 30, untargeted metabolite profiling on ultraminimal cultures of Acinetobacter radioresistens 50v1 indicated (1) biodegradation of Kleenol 30 into products including ethylene glycols, (2) the potential metabolism of decanoate (formed during incubation of Kleenol 30 in 0.2 × M9), and (3) decreases in the abundances of several hydroxy- and ketoacids in the extracellular metabolome. In ultraminimal medium (when using ethanol as a sole carbon source), A. radioresistens 50v1 also exhibits a remarkable survival against hydrogen peroxide (∼1.5-log loss, ∼108 colony forming units (cfu)/mL, 10 mM H2O2), indicating a considerable tolerance toward oxidative stress under nutrient-restricted conditions. Together, these results suggest that the spacecraft cleaning reagents may (1) serve as nutrient sources under oligotrophic conditions and (2) sustain extremotolerances against the oxidative stresses associated with low-humidity environments. In perspective, this study provides a plausible biochemical rationale to the observed microbial ecology dynamics of spacecraft-associated environments.

Isolation and characterization of metaldehyde-degrading bacteria from domestic soils

Metaldehyde is a common molluscicide, used to control slugs in agriculture and horticulture. It is resistant to breakdown by current water treatment processes, and its accumulation in drinking water sources leads to regular regulatory failures in drinking water quality. To address this problem, we isolated metaldehyde-degrading microbes from domestic soils. Two distinct bacterial isolates were cultured, that were able to grow prototrophically using metaldehyde as sole carbon and energy source. One isolate belonged to the genus Acinetobacter (strain designation E1) and the other isolate belonged to the genus Variovorax (strain designation E3). Acinetobacter E1 was able to degrade metaldehyde to a residual concentration < 1 nM, whereas closely related Acinetobacter strains were completely unable to degrade metaldehyde. Variovorax E3 grew and degraded metaldehyde more slowly than Acinetobacter E1, and residual metaldehyde remained at the end of growth of the Variovorax E3 strain. Biological degradation of metaldehyde using these bacterial strains or approaches that allow in situ amplification of metaldehyde-degrading bacteria may represent a way forward for dealing with metaldehyde contamination in soils and water.

Growth and wax ester production of an Acinetobacter baylyi ADP1 mutant deficient in exopolysaccharide capsule synthesis

Acinetobacter baylyi ADP1 naturally produces wax esters that could be used as a raw material in industrial applications. We attempted to improve wax ester yield of A. baylyi ADP1 by removing rmlA, a gene involved in exopolysaccharide production. Growth rate, biomass formation and wax ester yield on 4-hydroxybenzoate were not affected, but the rmlA− strain grew slower on acetate, while reaching similar biomass and wax ester yield. The rmlA− cells had malformed shape and large size and grew poorly on glucose without expression of the gene for pyruvate kinase (pykF) from Escherichia coli. The pykF-expressing rmlA− strain had similar growth rate, lowered biomass formation and improved wax ester production on glucose as compared to the wild-type strain expressing pykF. Cultivation of the pykF-expressing rmlA− strain on an elevated glucose concentration in a medium supplemented with amino acids resulted in doubled molar wax ester yield and acetate production.

Growth and Polysaccharide Production by Methylocystis parvus OBBP on Methanol

Methylocystis parvus OBBP, an obligate methylotroph originally isolated as a methane-utilizing bacterium, was cultivated on methanol as a sole source of carbon. After adaptation to high methanol levels, this organism grew on methanol with a maximum specific growth rate of 0.65 h. The pH optimum for growth was between 7 and 9, and the temperature optimum was between 30 and 37 degrees C. Methanol concentrations higher than 5% (by weight) were toxic. Formaldehyde, at a concentration greater than 1 mM, inhibited growth. Formate was neither a substrate nor an inhibitor. An extracellular viscous heteropolysaccharide was produced during growth. The maximum production of the total biomass was 14.5 g (dry weight) per liter of broth. The dried biomass contained 22% (wt/wt) crude protein and 62% (wt/wt) polysaccharide. The main components of the polysaccharide were d-glucose (82%) and l-rhamnose (14%).

Self-Cycling Fermentation Applied to Acinetobacter calcoaceticus RAG-1

The self-cycling fermentation (SCF) technique was applied to a culture of Acinetobacter calcoaceticus RAG-1. This method was shown to result in synchronization of the cells, achieving a 77% improvement in cell synchrony over that of the batch case. Cellular occurrences, averaged out by asynchronous batch cultures, were magnified by the temporal alignment of metabolic events brought about by the synchronization associated with SCFs. The cell population doubled only once per cycle, thus establishing an equality between cycle time and doubling time. Parameters of interest were biomass concentration, total bioemulsifier (emulsan) production, cycle time, and residual carbon concentration. Cycle-to-cycle variation of these parameters was, in most cases, insignificant. Repeatability of doubling time estimates (based on 95% confidence intervals) was roughly 7 to 10 times better between cycles in an SCF than between batch replicates. The carbon substrate was completely utilized in all cases in which it was measured, giving this technique an advantage over chemostat-type fermentations. The dissolved-oxygen profiles monitored throughout a cycle were found to be repeatable. A characteristic shape, which can be related to the growth of the organism, was associated with each carbon source. The specific emulsan productivity of SCFs was found to be approximately 50 times greater than that of the batch process and 2 to 9 times greater than that of the chemostat, depending on the dilution rate considered. With respect to specific emulsan production, a 25-fold improvement over that in an immobilized cell system recently introduced was obtained. Thus, SCFs are a viable alternative to established fermentation techniques.

Influence of environmental parameters on polyphosphate accumulation in Acinetobacter sp

The regulation of and the optimum conditions for polyphosphate accumulation in Acinetobacter sp. were determined. Acinetobacter strain 210A accumulated polyphosphate in the presence of an intra- or extracellular energy source. The accumulation of polyphosphate during endogenous respiration was stimulated by streptomycin and inhibited by KCN. The highest amount of polyphosphate was found in cells in which energy supply was not limited, namely at low growth rates under sulphur limitation, and in the stationary phase of growth when either the nitrogen or the sulphur source was depleted. The phosphorus accumulation was not affected by the pH between 6.5 and 9. There was a pronounced effect of the temperature on phosphorus accumulation but is varied from strain to strain. Acinetobacter strain 210A accumulated more phosphate at low temperatures, strain B8 showed an optimum accumulation at 27.5 degrees C, while strain P accumulated phosphorus independently of the temperature. The optimum temperature for growth of Acinetobacter strains tested ranged from 25 to 33 degrees C, and the optimum pH was between 6 and 9.

Microbiological transformations of nabilone, a synthetic cannabinoid

A screening program was conducted to find microorganisms that modify the synthetic cannabinoid nabilone. After purification, the products from three cultures were analyzed by spectral methods to determine their chemical structures. An optically active 9S-hydroxy-6aR,10aR-trans cannabinoid was isolated from a culture of an unidentified soil bacterium designated A24007. From Bacillus cereus cultures were isolated a 9S,6'-dihydroxy-6aR,10aR-trans cannabinoid, a 9S-hydroxy-6'-keto-6aR,10aR-trans cannabinoid, a 9-keto-6'-hydroxy-6aS,10aS-trans cannabinoid, and a 6',9-diketo-6aS,10aS-trans cannabinoid. All of these products were optically active, as was a 9S-hydroxy-6aS,10AS-trans cannabinoid also isolated from B. cereus cultures. A series of acidic products were isolated from cultures of Nocardia salmonicolor. All of these products contained a carboxylic acid group at the terminal end of three-position alkyl side chains having varying numbers of carbon atoms. Two of the acidic products contained a 9-keto group, whereas all other carboxylic acid products were 9-hydroxy cannabinoids. The array of products obtained from incubation of nabilone indicates the usefulness of microbial transformations in the preparation of new cannabinoids.

Microbiological transformation of cannabinoids

Microorganisms were screened for their ability to modify 2 synthetic cannabinoid substrates (I and II). Structure analyses revealed that microorganisms transformed the substrates by (a) primary oxidation of the side chain, beta-oxidation of the side chain, ketone formation on the side chain or cyclohexene ring, (b) secondary hydroxylation on the side chain, (c) aromatization of the cyclohexene ring, and (d) tertiary hydroxylation at the b/c ring juncture.

Microbiological transformations of delta6a10a-tetrahydrocannabinol

A screening program was conducted to find microorganisms that catalyze transformation reactions with cannabinoids. Three hundred fifty-eight cultures, consisting of 97 bacteria, 175 actinomycetes, and 86 molds, were incubated in media containing 0.5 mg of Delta(6a,10a)-tetrahydrocannabinol (Delta(6a,10a)-THC) per ml. After 120 h of cultivation, ethyl acetate extracts of the cultures were examined by thin-layer chromatography (TLC) for transformation products. About 18% of the cultures modified Delta(6a,10a)-THC. The ability to modify the substrate did not predominate among any particular group of microorganisms. After purification, the products from three cultures were analyzed by high-resolution mass spectrometry, 100-mHz proton magnetic resonance spectrometry, ultraviolet spectrometry, and infrared spectrometry. These spectral data indicated that a Mycobacterium sp. oxidized Delta(6a,10a)-THC to cannabinol and a diastereomeric pair of 6a-hydroxy-Delta(10,10a)-THC isomers; a Streptomyces sp. and a Bacillus sp. oxidized Delta(6a,10a)-THC to 7-keto-Delta(6a,10a)-THC and 4'-hydroxy-Delta(6a,10a)-THC, respectively. The occurrence of these products and the presence of others that have not yet been isolated or identified indicate that microbial transformation may be a useful tool for the preparation of new cannabinoids that have desirable pharmacological properties.

Effect of growth rate and nutrient limitation on the composition and biomass yield of Acinetobacter calcoaceticus

Acinetobacter calcoaceticus was grown on ethanol in a chemostat as a model system for single-cell protein production. The substrate yield coefficient (Y(s), grams of biomass/gram of ethanol), protein yield coefficient (Y(p), grams of protein/gram of ethanol), and biomass composition were measured as a function of the specific growth rate. Nucleic acid, protein, Y(p), and Y(s) all increased at higher growth rates. Although protein content increased only 14% (from 53 to 67%), Y(p) almost doubled over the same range of growth rates. The increase in Y(p) was due to the higher protein content of the biomass and to higher values of Y(s). The higher values of Y(s) were attributed to maintenance metabolism, and the value of the maintenance coefficient was found to be 0.11 g of ethanol per g of cell per h. When A. calcoaceticus was cultivated under a phosphorus limitation protein content, Y(p) and Y(s) were lower than in carbon-limited cultures. It was concluded that a single-cell protein fermentation using A. calcoaceticus should be operated at a high growth rate under ethanol-limiting conditions in order to maximize both the protein content of the biomass and the amount of biomass and/or protein made from the substrate.

Active transport of alcohol in Corynebacterium acetophilum

The transport of alcohols was studied in Corynebacterium acetophilum, which was isolated as a strain growing well on acetate and ethanol. The transport of ethanol was found to be inducible by ethanol, n-propanol, n-butanol, and acetate, whereas transport of methanol occurred by noninducible passive diffusion. The entry of ethanol into the cells occurred against a concentration gradient and showed saturation kinetics with two K(m) values of 2.4 x 10(-5) M and 6.0 x 10(-5) M. Uptake of ethanol was inhibited by sodium azide, sodium cyanide, 2,4-dinitrophenol, and p-chloromercuribenzoate. The transport of ethanol was competitively inhibited by normal alcohols, but not by iso- or tert-alcohols. From these studies, we concluded that an inducible active alcohol transport system mediates the entry of ethanol, n-propanol, or n-butanol into the cells of C. acetophilum.