Efficient secretion of (R)-3-hydroxybutyric acid from Halomonas sp. KM-1 cultured with saccharified Japanese cedar under microaerobic conditions

Daily Intake of D-β-Hydroxybutyric Acid (D-BHB) Reduces Body Fat in Japanese Adult Participants: A Randomized, Double-Blind, Placebo-Controlled Study

Currently, there is considerable interest in ketone metabolism owing to the benefits for human health. Conventionally, strict dietary restrictions on carbohydrates are required to increase plasma ketone levels, while supplementation with D-β-hydroxybutyric acid (D-BHB) can easily increase plasma ketone levels. We hypothesized that a daily intake of D-BHB could promote weight loss, especially through fat reduction. Herein, D-BHB (OKETOATM) was produced via a proprietary fermentation process from sugar. In this randomized, double-blind, placebo-controlled study, we assessed the safety and fat-reduction effects after 12 wk of daily ingestion of D-BHB (2.9 g) in 22 healthy Japanese adults and 22 control participants. Blood samples were collected pre- and post-treatment. Blood chemistry, anthropometric variables, and the body composition of the participants were investigated. Data analysis revealed that visceral fat at 12 wk significantly decreased by 9.0 cm2 (p=0.037), as evidenced by analysis of covariance. Blood parameters and body condition showed no significant differences between the two groups, and the participants reported no adverse effects or discomfort. Furthermore, data were analyzed by regrouping the participants. After removing one suspicious diabetes participant, all others showed significant decreases in visceral fat, body weight, BMI, and fat weight. Additionally, those aged under 50 y old had significantly decreased abdominal circumference and body fat percentage, in addition to visceral fat, body weight, BMI, and fat weight. Overall, our findings indicate that daily D-BHB intake may reduce body fat without dieting or exercise intervention. This study was registered with the UMIN Clinical Trials Registry as UMIN000045322.

Establishment of genetic tools for genomic DNA engineering of Halomonas sp. KM-1, a bacterium with potential for biochemical production

Halomonas species are halophilic and alkaliphilic bacteria, which exhibit potential for industrial production of a variety of chemicals, such as polyhydroxyalkanoates and ectoine, by fermentation because of their favorable characteristics, including high-density culturing capacity and low risk of contamination. However, genetic tools to modify the metabolism of Halomonas for suitable fermentation performance are limited. In this study, we developed two independent basic vectors for Halomonas, named pUCpHAw and pHA1AT_32, consisting of ori regions from two plasmids isolated from Halomonas sp. A020, and chloramphenicol- and tetracycline-resistant genes as cloning markers, respectively. These vectors can independently transform and co-transform the Halomonas sp. KM-1 (KM-1). A protein that was highly and constitutively accumulated was identified as a hemolysin coregulated protein (Hcp) based on proteome analysis of KM-1. Using the hcp promoter, various genes, such as phaA and EGFP, were highly expressed. To establish a gene disruption system, the Streptococcus pyogenes cas9 gene and guide RNA for the pyrF gene, a yeast URA3 homologue, were expressed in pUCpHAw and pHA1AT_32, respectively. As a result, gene disruption mutants were isolated based on phenotypes, 5-fluoroorotic acid resistance, and uracil auxotrophy. A combination of KM-1 and these vectors could be a suitable platform for industrial chemical and protein production.

Consolidated microbial production of four-, five-, and six-carbon organic acids from crop residues: Current status and perspectives

The production of platform organic acids has been heavily dependent on petroleum-based industries. However, petrochemical-based industries that cannot guarantee a virtuous cycle of carbons released during various processes are now facing obsolescence because of the depletion of finite fossil fuel reserves and associated environmental pollutions. Thus, the transition into a circular economy in terms of the carbon footprint has been evaluated with the development of efficient microbial cell factories using renewable feedstocks. Herein, the recent progress on bio-based production of organic acids with four-, five-, and six-carbon backbones, including butyric acid and 3-hydroxybutyric acid (C4), 5-aminolevulinic acid and citramalic acid (C5), and hexanoic acid (C6), is discussed. Then, the current research on the production of C4-C6 organic acids is illustrated to suggest future directions for developing crop-residue based consolidated bioprocessing of C4-C6 organic acids using host strains with tailor-made capabilities.

Aerobic Denitrification and Heterotrophic Sulfur Oxidation in the Genus Halomonas Revealed by Six Novel Species Characterizations and Genome-Based Analysis

Bacteria of Halomonas are widely distributed in various environments and play a substantial role in the nutrient cycle. In this report, 14 strains capable of aerobic denitrification and heterotrophic sulfur oxidation were isolated from different habitats. Based on the phenotypic, genotypic, and chemotaxonomic analyses, these strains were considered to represent six novel species of the genus Halomonas, for which the names Halomonas zhangzhouensis sp. nov. type strain CXT3-11T ( = MCCC 1A11036T = KCTC 72087T), Halomonas aerodenitrificans sp. nov. CYD-9T ( = MCCC 1A11058T = KCTC 72088T), Halomonas sulfidoxydans sp. nov. CYN-1-2T ( = MCCC 1A11059T = KCTC 72089T), Halomonas ethanolica sp. nov. CYT3-1-1T ( = MCCC 1A11081T = KCTC 72090T), Halomonas sulfidivorans sp. nov. NLG_F1ET ( = MCCC 1A13718T = KCTC 72091T), and Halomonas tianxiuensis sp. nov. BC-M4-5T ( = MCCC 1A14433T = KCTC 72092T) are proposed. Intriguingly, they formed a unique group with 11 other species designated as the "H. desiderata group." To better understand their featured metabolisms, genes involved in denitrification and sulfur oxidation were analyzed, along with 193 other available genomes of the whole genus. Consistently, complete denitrification pathways were confirmed in the "H. desiderata group," in which napA, narG, nirS, norB, and nosZ genes coexist. Their nitrite reductase NirS formed a unique evolutionary lineage, distinguished from other denitrifiers in Halomonas. In addition, diverse occurrence patterns of denitrification genes were also observed in different phylogenetic clades of Halomonas. With respect to sulfur oxidation, fccAB genes involved in sulfide oxidation commonly exist in the "H. desiderata group," while sqr genes are diverse and can be found in more species; sqr genes co-occurred with fccAB in eight strains of this study, contributing to more active sulfide oxidation. Besides, the tsdA gene, which encodes an enzyme that oxidizes thiosulfate to tetrathionate, is ubiquitous in the genus Halomonas. The widespread presence of sqr/fccAB, pdo, and tsdA in Halomonas suggests that many Halomonas spp. can act as heterotrophic sulfur oxidizers. These results provide comprehensive insights into the potential of denitrification and sulfur oxidation in the whole genus of Halomonas. With regard to the global distribution of Halomonas, this report implies their unneglectable role in the biogeochemical cycle.

Polyhydroxyalkanoate nanoparticles produced by marine bacteria cultivated on cost effective Mediterranean algal hydrolysate media

Algae are omnipresent in all seas and oceans, which make thema target for many applications such as bio-fertilizers, fish feeding and removal of heavy metals. In the present study, different algal species were examined as sustainable alternatives substrates for PHA production by Halomonas sp. Several media simulations were utilized to achieve high polymer productivity. The maximum poly(3-hydroxybutyrate) (PHB) concentrations were determined by using Corallina mediterranea hydrolysates as a carbon and nitrogen source. The isolates Halomonas pacifica ASL10 and Halomonas salifodiane ASL11 were found to be able to produce PHA by 67 % wt and 63 % wt CDW, respectively. PHB nanoparticles (NPs) had high zeta potential values and small particle sizes. These properties make it suitable for several drug delivery and pharmaceutical applications. Interestingly, NPs showed a potent antibacterial activity against several reference strains. The antibacterial efficacy of PHA-NPs has not been previously studied, thus this study opens a promising use of PHA-NPs.

Efficient production and secretion of oxaloacetate from Halomonas sp. KM-1 under aerobic conditions

The alkaliphilic, halophilic bacterium Halomonas sp. KM-1 can utilize glucose for the intracellular storage of the bioplastic poly-(R)-3-hydroxybutyric acid (PHB) and extracellular secretion of pyruvate under aerobic conditions. In this study, we investigated the effects of sodium chloride concentration on PHB accumulation and pyruvate secretion in the KM-1 strain and, unexpectedly, observed that oxaloacetate, an important intermediate chemical in the TCA cycle, glycogenesis, and aspartic acid biosynthesis, was secreted. We then further analyzed oxaloacetate productivity after changing the sodium chloride additive concentration, additive time-shift, and culture temperature. In 42-h batch-cultivation experiments, we found that wild-type Halomonas sp. KM-1 secreted 39.0 g/L oxaloacetate at a rate of 0.93 g/(L h). The halophilic bacteria Halomonas has already gained attention for industrial chemical-production processes owing to its unique properties, such as contamination-free culture conditions and a tolerance for high substrate concentrations. Moreover, no commercial scale oxaloacetate production was previously reported to result from bacterial fermentation. Oxaloacetate is an important intermediate chemical in biosynthesis and is used as a health food based on its role in energy synthesis. Thus, these data provided important insights into the production of oxaloacetate and other derivative chemicals using this strain.

Efficient production and secretion of pyruvate from Halomonas sp. KM-1 under aerobic conditions

The alkaliphilic, halophilic bacterium Halomonas sp. KM-1 can utilize both hexose and pentose sugars for the intracellular storage of bioplastic poly-(R)-3-hydroxybutyric acid (PHB) under aerobic conditions. In this study, we investigated the effects of the sodium nitrate concentration on PHB accumulation in the KM-1 strain. Unexpectedly, we observed the secretion of pyruvate, a central intermediate in carbon- and energy-metabolism processes in all organisms; therefore, pyruvate is widely used as a starting material in the industrial biosynthesis of pharmaceuticals and is employed for the production of crop-protection agents, polymers, cosmetics, and food additives. We then further analyzed pyruvate productivity following changes in culture temperature and the buffer concentration. In 48-h batch-cultivation experiments, we found that wild-type Halomonas sp. KM-1 secreted 63.3 g/L pyruvate at a rate of 1.32 g/(L·h), comparable to the results of former studies using mutant and recombinant microorganisms. Thus, these data provided important insights into the production of pyruvate using this novel strain.

Improvement of (R)-3-hydroxybutyric acid secretion during Halomonas sp. KM-1 cultivation with saccharified Japanese cedar by the addition of urea

Japanese cedar (Cryptomeria japonica) is a major species in artificial Japanese forests. The Halomonas sp. KM-1 was recently isolated and found to grow effectively on saccharified Japanese cedar wood, resulting in the intracellular storage of poly-(R)-3-hydroxybutyric acid (PHB) under aerobic conditions. Under microaerobic conditions, the extracellular secretion of (R)-3-hydroxybutyric acid ((R)-3-HB) led to the degradation of intracellular PHB. In this study, the production of PHB and the secretion of (R)-3-HB using saccharified Japanese cedar were much improved in cultures that were grown in the presence of urea. The level of intracellular PHB production after 36 h under aerobic cultivation was 23·6 g l(-1) ; after shifting to microaerobic conditions for 24 h, the (R)-3-HB concentration in the medium reached 21·1 g l(-1) . Thus, KM-1 efficiently utilizes saccharified Japanese cedar to produce PHB and secretes (R)-3-HB, making it a practical candidate for use in the industrial production of (R)-3-HB.

SIGNIFICANCE AND IMPACT OF THE STUDY

Japanese cedar is a major species grown in artificial Japanese forests, and its thinning is crucial for the health of artificial forests and the Japanese economy. Halomonas sp. KM-1 grew effectively on saccharified Japanese cedar wood, resulting in intracellular storage of poly-(R)-3-hydroxybutyric acid (PHB) under aerobic conditions. Under microaerobic conditions, extracellular secretion of (R)-3-hydroxybutyric acid ((R)-3-HB) caused intracellular PHB degradation. (R)-3-HB is a chiral compound that is useful in the chemical, health food and pharmaceutical industries. The production of PHB and secretion of (R)-3-HB using saccharified wood was dramatically improved, which may positively affect its future industrial production.

Production of poly(3-hydroxybutyrate) by Halomonas boliviensis in an air-lift reactor

Background

Microbial polyesters, also known as polyhydroxyalkanoates (PHAs), closely resemble physical and mechanical features of petroleum derived plastics. Recombinant Escherichia coli strains are being used in industrial production of PHAs in Stirred Tank Bioreactors (STRs). However, use of Air-Lift Reactors (ALRs) has been known to offer numerous technical operating options over STRs, and as such has been successfully implemented in many bioprocesses. Halomonas boliviensis is a halophilic bacterium that is known to assimilate various carbohydrates and convert them into a particular type of PHA known as poly(3-hydroxybutyrate) (PHB). Owing to this capability, it has been used to synthesize the polyester using hydrolysates of starch or wheat bran in stirred tank bioreactors.

Results

This research article firstly describes the production of PHB in shake flasks by H. boliviensis using different combinations of carbohydrates and partially hydrolyzed starch as carbon sources. The highest PHB yields, between 56 and 61 % (wt.), were achieved when either starch hydrolysate or a mixture of glucose and xylose were used as carbon sources. The starch hydrolysate obtained in this study was then used as carbon source in an ALR. The largest amount of PHB, 41 % (wt.), was attained after 24 hrs of cultivation during which maltose in the hydrolysate was assimilated more rapidly than glucose during active cell growth; however, the rate of assimilation of both the carbohydrates was found to be similar during synthesis of PHB. An incomplete pentose phosphate pathway, which lacks 6-phosphogluconate dehydrogenase, was deduced from the genome sequence of this bacterium and may result in the characteristic assimilation of glucose and maltose by the cells.

Conclusions

This study showed that the production of PHB by H. boliviensis using cheap substrates such as starch hydrolysate in a simple production system involving an ALR is feasible. Both maltose and glucose in the hydrolysate induce cell growth and PHB synthesis; most likely the cells balance adequately CoA and NAD(P)H during the assimilation of these carbohydrates. The combination of cheap substrates, simple production systems and the use of non-strict sterile conditions by the halophile H. boliviensis are desirable traits for large scale production of PHB, and should lead to a competitive bioprocess.

Electronic supplementary material

The online version of this article (doi:10.1186/s40709-015-0031-6) contains supplementary material, which is available to authorized users.

Efficient secretion of (R)-3-hydroxybutyric acid from Halomonas sp. KM-1 by nitrate fed-batch cultivation with glucose under microaerobic conditions

To establish a sustainable society, commodity chemicals need to be developed from biomass resources. Recently, (R)-3-hydroxybutyric acid ((R)-3-HB), a monomer of bioplastic poly-(R)-3-hydroxybutyric acid (PHB), has attracted attention for its possible use in the chemical industry. Halophilic bacteria have been considered for bioprocess applications due to certain characteristics such as the ability to grow in media containing high levels of the starting carbon source and the ability to be rarely contaminated. A halophilic bacterium Halomonas sp. KM-1 stores PHB intracellularly under aerobic conditions and secretes (R)-3-HB under microaerobic conditions. In this study, we optimized culture conditions to maximize (R)-3-HB secretion by KM-1 cells. By a simple nitrate fed-batch cultivation, Halomonas sp. KM-1 secreted 40.3g/L (R)-3-HB with a productivity of 0.48g L(-1)h(-1) with 20% (w/v) glucose. This level is one of the highest recorded productivity of (R)-3-HB to date.