Production of a herbicide, 5-aminolevulinic acid, by Rhodobacter sphaeroides using the effluent of swine waste from an anaerobic digestor

Purple non-sulphur bacteria and plant production: benefits for fertilization, stress resistance and the environment

Purple non-sulphur bacteria (PNSB) are phototrophic microorganisms, which increasingly gain attention in plant production due to their ability to produce and accumulate high-value compounds that are beneficial for plant growth. Remarkable features of PNSB include the accumulation of polyphosphate, the production of pigments and vitamins and the production of plant growth-promoting substances (PGPSs). Scattered case studies on the application of PNSB for plant cultivation have been reported for decades, yet a comprehensive overview is lacking. This review highlights the potential of using PNSB in plant production, with emphasis on three key performance indicators (KPIs): fertilization, resistance to stress (biotic and abiotic) and environmental benefits. PNSB have the potential to enhance plant growth performance, increase the yield and quality of edible plant biomass, boost the resistance to environmental stresses, bioremediate heavy metals and mitigate greenhouse gas emissions. Here, the mechanisms responsible for these attributes are discussed. A distinction is made between the use of living and dead PNSB cells, where critical interpretation of existing literature revealed the better performance of living cells. Finally, this review presents research gaps that remain yet to be elucidated and proposes a roadmap for future research and implementation paving the way for a more sustainable crop production.

Sustainable and efficient sugar production from wheat straw by pretreatment with biogas digestate

The use of liquid fraction of biogas digestate (LFBD) instead of fresh water (hydrothermal) for the pretreatment of wheat straw was evaluated to improve the yield of released sugars during the following hydrolysis step. The pretreatments were conducted at temperatures of 130, 160, and 190 °C for 30 and 60 min. In most of the cases, pretreatment using LFBD led to higher glucose yields and higher total sugars concentrations, compared to those obtained after applying hydrothermal pretreatments. The increase of temperature resulted in an increase in sugars during the enzymatic hydrolysis. The highest yields of glucose (about 59%) were observed after treatments at 190 °C for 60 min, independently of which type of pretreatment was applied and at 190 °C for 30 min using LFBD. Treatment, with LFBD at 190 °C and for 60 min, resulted in glucose and xylose concentrations of 7.36 g L-1 and 2.41 g L-1, respectively, after the subsequent hydrolysis for 48 h. However, the FTIR analysis indicated that the crystallinity index remained rather constant after treatment. Both FTIR and compositional analysis showed that the removal of hemicelluloses was the main effect of the pretreatment.

Efficient hydrolysis and ethanol production from rice straw by pretreatment with organic acids and effluent of biogas plant

Effects of biogas effluent and its organic ingredients, i.e., acetic, butyric, lactic, and propionic acid, for the pretreatment of rice straw on enzymatic hydrolysis and ethanol production was studied.

Recent advances in microbial production of δ-aminolevulinic acid and vitamin B12

δ-aminolevulinate (ALA) is an important intermediate involved in tetrapyrrole synthesis (precursor for vitamin B12, chlorophyll and heme) in vivo. It has been widely applied in agriculture and medicine. On account of many disadvantages of its chemical synthesis, microbial production of ALA has been received much attention as an alternative because of less expensive raw materials, low pollution, and high productivity. Vitamin B12, one of ALA derivatives, which plays a vital role in prevention of anaemia has also attracted intensive works. In this review, recent advances on the production of ALA and vitamin B12 with novel approaches such as whole-cell enzyme-transformation and metabolic engineering are described. Furthermore, the direction for future research and perspective are also summarized.

Applications of photosynthetic bacteria for medical fields

The medical applications of photosynthetic bacteria are summarized. Photosynthetic bacteria can produce various types of physiological active substance such as vitamin B(12), ubiquinone (coenzyme Q10), 5-aminolevulinic acid (ALA), porphyrins and RNA. In particular, photosynthetic bacterial ALA was commercially applied to cancer diagnosis and treatment. Recently, ALA has been applied to the treatment of acne vulgaris and the suppression of the inflammatory response to coronary and iliac injuries. In addition, the recent applications of RNA from a marine photosynthetic bacterium as a medical supplement for immune improvement and suppression of infection are described. Furthermore, the feasible application of a biopolymer consisting of RNA from a photosynthetic bacterium as a drug delivery system (DDS) to cancer treatment is described.

Phenotypic and genotypic characterization of esterase-producing Ureibacillus thermosphaericus isolated from an aerobic digestor of swine waste

Eight closely related thermophilic strains were isolated from an aerobic and thermophilic treatment of swine wastes. The pleomorphic cells (short and long rods; cocci) showed peritrichous flagella, terminally swollen sporangium, and liberated spores exhibiting hairy appendages. The Gram reaction was negative for both young (4 h) and old (48 h) cultures. Several features, such as colonial morphology, growth between 35 degrees C and 65 degrees C, presence of catalase, presence of spores, and strictly aerobic metabolism (except for one strain), are similar to those found for the genus Bacillus. The inability of the strains to use sugars, except esculin, as source of carbon and energy and the whole cell fatty acid composition are similar to those found in Bacillus thermosphaericus DSM 10633. Sequence analysis of the 16S rRNA gene revealed 99.8%-99.9% identity for seven of the thermophilic strains with this species. A new genus, Ureibacillus, was recently proposed for type strain B. thermosphaericus DSM 10633 The last strain exhibits 97.8% and 97.3% identity with Ureibacillus terrenus DSM12654 and Bacillus sp. TP-84, respectively. Esterase activities were detected for all strains, and assays on p-nitrophenyl butyrate and p-nitrophenyl caprylate revealed that strains were more active on the shorter substrate.

Effects of levulinic acid on 5-aminolevulinic acid production in heterotrophic cultures of Chlorella regularis YA-603

To investigate the effects of levulinic acid (LA) on extracellular 5-aminolevulinic acid (ALA) accumulation, a heterotrophic culture of Chlorella regularis YA-603 in basal medium containing 0 to 60 mM of LA was carried out. It was found that the extracellular and total ALA concentrations increased, while the chlorophyll (CHL) concentration was the same above initial LA concentrations of 30 mM, with an increasing initial LA concentration up to 50 mM. In the presence of an initial LA concentration of 60 mM, however, the specific growth rate decreased markedly. This suggested that excessive LA exerted a negative effect on ALA production because it also directly affected cellular growth. The relationship between the initial LA and total ALA concentrations mentioned above indicates that LA could promote the ALA-producing activity. Kinetic analysis revealed that an LA concentration of between 30 to 50 mM in the culture broth gave the maximum specific production rate of ALA ((q(ALA))max). When LA was added repeatedly to maintain this optimum range of LA concentration, (q(ALA))max could be maintained at a relatively high level for a longer period, and the maximum concentration of ALA reached 3.86 mM.

Rhodobacter sphaeroides mutants which accumulate 5-aminolevulinic acid under aerobic and dark conditions

The photosynthetic bacterium Rhodobacter sphaeroides accumulates 5-aminolevulinic acid (ALA), which is a precursor in tetrapyrrole biosynthesis, under light illumination and upon addition of levulinic acid as an inhibitor of ALA dehydratase. To generate an industrial strain which produces ALA in the absence of light, we sequentially mutated R. sphaeroides CR-286 using N-methyl-N'-nitro-N-nitrosoguanidine (NTG). The mutant strains were screened by cultivating in the absence of light and assayed for ALA by the Ehrlich reaction in a 96-well microtiter plate. The mutant strain CR-386, derived from R. sphaeroides CR-286, was selected as a mutant that exhibited significant ALA accumulation. While CR-286 required light illumination for ALA production, CR-386 was able to accumulate 1.5 mM ALA in the presence of 50 mM glucose, 60 mM glycine, 15 mM levulinic acid and 1.0% (w/v) yeast extract under conditions of agitation in the absence of light. The mutant strain CR-450, derived from strain CR-386, was selected further as a mutant that exhibited significant ALA accumulation but no accumulation of aminoacetone, analogue of ALA. CR-450 accumulated 3.8 mM ALA under the same conditions. In the presence of 50 mM glucose, 60 mM glycine, 5 mM levulinic acid and 1.0% (w/v) yeast extract, the mutant strain CR-520, derived from strain CR-450, and strain CR-606, derived from strain CR-520, accumulated 8.1 mM and 11.2 mM ALA, respectively. In batch fermentation, the strain CR-606 accumulated 20 mM ALA over 18 h after the addition of glycine, levulinic acid, glucose and yeast extract.

Purification, characterization and gene cloning of 6-hydroxynicotinate 3-monooxygenase from Pseudomonas fluorescens TN5

6-Hydroxynicotinate 3-monooxygenase, a membrane-bound, 42-kDa monomeric enzyme from Pseudomonas fluorescens TN5 was purified and characterized. The enzyme catalyzes the oxidative decarboxylation of 6-hydroxynicotinate and depends on O2, NADH and FAD with the holoenzyme containing 1 M of FAD per 1 M of enzyme. The isolated enzyme was used for the synthesis of 2,5-dihydroxypyridine, a precursor for the chemical synthesis of 5-aminolevulinic acid, which is applied as a plant growth hormone, a herbicide and in cancer therapy. A 1.8-kbp DNA fragment, which contains the ORF encoding 6-hydroxynicotinic acid 3-monooxygenase, was cloned, sequenced and expressed in Escherichia coli. The deduced 385 amino acid sequence of the cloned ORF is in agreement with the enzyme molecular mass, amino acid sequence of an internal peptide, contains a putative FAD-binding site and is homologous to similar flavoproteins such as salicylate 1-monoxygenase.

Removal of phosphorus from oyster farm mud sediment using a photosynthetic bacterium, Rhodobacter sphaeroides IL106

Removal of phosphorous compounds from the mud sediment of an oyster farm was carried out by a series of bio-processes under anaerobic conditions. Anaerobic acidogenic fermentation of a mud sediment suspension (200 g wet wt/l artificial sea water) was initially carried out. With the addition of vitamins such as thiamine, nicotinic acid and biotin, acidogenic fermentation was enhanced to yield acetic acid of approximately 2 g/l. Furthermore, approximately 20 mg/l of PO4(3-) (10% of total phosphorus on mud weight) and 5300 mg/l of COD(Cr) (82% of organic matter on mud weight) were released into the culture broth after fermentation for 7 d. The supernatant of this culture broth was used to cultivate Rhodobacter sphaeroides IL106, a denitrifying photosynthetic bacterium. After 4 d, 3.32 g/l of biomass containing carotenoid and ubiquinone was obtained, and COD(Cr) and acetic acid were reduced by 58% and 72%, respectively. In addition, PO4(3-) was reduced by 97%, suggesting that the removal of PO4(3-) from the mud sediment might be possible by combining anaerobic acidogenic fermentation with R. sphaeroides cultivation.

Biodegradation and metabolism of unusual carbon compounds by anoxygenic phototrophic bacteria

Anoxygenic phototrophic bacteria play an important role in anaerobic nutritional cycles. The most readily used and widely studied carbon sources for growth of these bacteria are organic acids and a few carbohydrates. In this review we survey the growing knowledge on the metabolism of a number of other carbon sources, particularly polymers (starch, poly(3-hydroxyalkanoates)), aromatic compounds (natural and xenobiotic), one-carbon compounds, alcohols, aliphatic hydrocarbons and higher fatty acids, and their influence on various cellular activities of purple non-sulfur bacteria. We also discuss the possible exploitations in various biotechnological processes of this group of microorganisms while metabolizing unusual carbon compounds.