Kedong Ma

Open fermentative production of l-lactic acid with high optical purity by thermophilic Bacillus coagulans using excess sludge as nutrient

The development of a low-cost polymer-grade L-lactic acid production process was achieved in this study. Excess sludge hydrolyzate (ESH) was chosen as nutrient source for the objective of reducing nutrient cost in lactic acid production. 1% of ESH had high performance in lactic acid production relative to 2g/l yeast extract (YE) while the production cost of ESH was much lower than that of YE, indicating ESH was a promising substitute of YE. By employing a thermophilic strain of Bacillus coagulans (NBRC 12583), non-sterilized batch and repeated batch L-lactic acid fermentation was successfully performed, and the optical purity of L-lactic acid accumulated was more than 99%. Moreover, the factors associated with cell growth and lactic acid fermentation was investigated through a two-stage lactic acid production strategy. Oxygen played an important role in cell growth, and the optimal condition for cell growth and fermentation was pH 7.0 and 50°C.

Production of a lignocellulolytic enzyme system for simultaneous bio-delignification and saccharification of corn stover employing co-culture of fungi.

Aiming at improving the efficiency of transferring corn stover into sugars, an efficient lignocellulolytic enzyme system was developed and investigated by co-cultivation of the Coprinus comatus with Trichoderma reesei in a single bioreactor. The results showed that the lignocellulolytic enzyme activities of the co-culture exceeded that of the monoculture, suggesting synergistic interaction between two fungi. The highest laccase activity from the co-culture was 2.6-fold increase over that of the C. comatus monoculture and reached a peak 3days earlier. The maximum delignification obtained was 66.5% and about 82% of the original polysaccharides were converted into fermentable sugars by simultaneous bio-delignification and saccharification process. Correlation analysis showed that sugar yields were directly proportional to the lignin degradation. Our results suggested that co-fungi cultivation was a valuable technique for corn stover bioconversion, which could produce high efficiency of lignocellulolytic enzyme system as a cheaper alternative to commercial enzymes for industrial utilization.

Open fermentative production of fuel ethanol from food waste by an acid-tolerant mutant strain of Zymomonas mobilis.

The aim of present study was to develop a process for open ethanol fermentation from food waste using an acid-tolerant mutant of Zymomonas mobilis (ZMA7-2). The mutant showed strong tolerance to acid condition of food waste hydrolysate and high ethanol production performance. By optimizing fermentation parameters, ethanol fermentation with initial glucose concentration of 200 g/L, pH value around 4.0, inoculum size of 10% and without nutrient addition was considered as best conditions. Moreover, the potential of bench scales fermentation and cell reusability was also examined. The fermentation in bench scales (44 h) was faster than flask scale (48 h), and the maximum ethanol concentration and ethanol yield (99.78 g/L, 0.50 g/g) higher than that of flask scale (98.31 g/L, 0.49 g/g). In addition, the stable cell growth and ethanol production profile in five cycles successive fermentation was observed, indicating the mutant was suitable for industrial ethanol production.

Extracellular polymeric substances, microbial activity and microbial community of biofilm and suspended sludge at different divalent cadmium concentrations.

The differences between biofilm and suspended sludge (S-sludge) in extracellular polymeric substances (EPS), microbial activity, and microbial community in an anoxic-aerobic sequencing batch biofilm reactor (SBBR) at different concentrations of divalent cadmium (Cd(II)) were investigated. As the increase of Cd(II) concentration from 0 to 50mgL(-1), the specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR), and specific nitrate reduction rate (SNRR) of biofilm decreased from 4.85, 5.22 and 45mgNg(-1) VSSh(-1) to 1.54, 2.38 and 26mgNg(-1)VSSh(-1), respectively, and the SAOR, SNOR and SNRR of S-sludge decreased from 4.80, 5.02 and 34mgNg(-1)VSSh(-1) to 1.46, 2.20 and 17mgNg(-1)VSSh(-1), respectively. Biofilm had higher protein (PN) content in EPS than S-sludge. Contrast to S-sludge, biofilm could provide Nitrobacter vulgaris, beta proteobacterium INBAF015, and Pseudoxanthomonas mexicana with the favorable conditions of growth and reproduction.

Highly efficient production of optically pure l-lactic acid from corn stover hydrolysate by thermophilic Bacillus coagulans

A thermophilic strain Bacillus coagulans (NBRC 12714) was employed to produce l-lactic acid from corn stover hydrolysate in membrane integrated continuous fermentation. The strain NBRC 12714 metabolized glucose and xylose by the Embden-Meyerhof-Parnas pathway (EMP) and the pentose phosphate pathway (PPP), producing l-lactic acid with optical purity >99.5%. The overall l-lactic acid titer of 92g/l with a yield of 0.91g/g and a productivity of 13.8g/l/h were achieved at a dilution rate of 0.15h(-1). The productivity obtained was 1.6-fold than that of conventional continuous fermentation without cell recycling, and also was the highest among the relevant studies ever reported. These results indicated that the process developed had great potential for economical industrial production of l-lactic acid from lignocellulosic biomass.

Long-term effects of combined divalent copper and tetracycline on the performance, microbial activity and community in a sequencing batch reactor

The long-term effects of combined divalent copper (Cu(II)) and tetracycline (TC) on the performance, microbial activity and community in a sequencing batch reactor (SBR) were investigated. The addition of Cu(II), TC or mixed Cu(II)/TC caused the decrease of the organics and nitrogen removal efficiencies, and their decreased degrees were the lowest at the addition of mixed Cu(II)/TC. The increase of mixed Cu(II)/TC concentrations in the influent did not change the antagonistic effects between Cu(II) and TC on nitrifying and denitrifying activities. Nitrifiers had higher tolerances to Cu(II), TC and mixed Cu(II)/TC than denitrifiers. Compared to the addition of Cu(II) or TC alone, the microbial community richness was higher at the addition of mixed Cu(II)/TC, while the microbial community diversity was lower. The increased protein (PN) in extracellular polymeric substances (EPS) was a protective response of bacteria to Cu(II), TC and mixed Cu(II)/TC.

Bio-ethanol production by Zymomonas mobilis using pretreated dairy manure as a carbon and nitrogen source

Dairy manure contains high levels of cellulose, hemicellulose and a nitrogen source. These properties make dairy manure a potential biomass source for ethanol production. In this study, a dilute NaOH pretreatment and enzymatic hydrolysis were carried out for the degradation of lignocellulose from dairy manure. The response surface method and Box–Behnken design were first applied in order to optimize the NaOH pretreatment. Under the optimization conditions, 21.14 g L−1 of glucose and 9.48 g L−1 of xylose were obtained from continuous enzymolysis. The maximum ethanol concentration achieved reached 10.55 g L−1 when using ethanologenic Zymomonas mobilis without an additional nitrogen source. This produced a 71.91% ethanol yield from manure hydrolysate medium. These results demonstrate the economic benefits of using nitrogen from a dairy manure source for balancing the C/N ratio, without the need for an additional nitrogen source. The results from this study could extend beyond cellulosic ethanol for the production of other chemicals.

Brevibacillus halotolerans sp. nov., isolated from saline soil of a paddy field

Two novel aerobic bacteria, designated strains LAM0312T and LAM0313, were isolated from saline soil samples collected from a paddy field in Dezhou city, Shandong Province, China. Cells of these strains were Gram-stain-positive, sporogenous, rod-shaped and motile with peritrichous flagella. The optimal growth temperature and pH were 30 °C and pH 7.0-8.0. Strain LAM0312T was able to grow in the presence of 12 % (w/v) NaCl. The major fatty acids were anteiso-C15 : 0 and iso-C15 : 0. The dominant polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, glycolipids, five unidentitied lipids and phosphatidylmonomethylethanolamine. The cell-wall peptidoglycan was found to contain meso-diaminopimelic acid. The predominant menaquinone was identified as menaquinone-7. The G+C content of the genomic DNA of strains LAM0312T and LAM0313 was 45.0 and 46.0 mol%, respectively, as determined by the Tm method. 16S rRNA gene sequence similarity analysis indicated that the strains were closely related to Brevibacillus laterosporus DSM 25T and Brevibacillus fluminis JCM 15716T with 98.5 and 96.4 % sequence similarity, respectively. The DNA-DNA hybridization value between strain LAM0312T and LAM0313 was 92±0.6 % (reciprocal 90±0.2 %) and the value between strain LAM0312T and Brevibacillus laterosporus DSM 25T was 48±0.5 % (reciprocal 40±0.4 %). On the basis of the phenotypic, phylogenetic and chemotaxonomic characteristics, the two strains are proposed to represent a novel species of the genus Brevibacillus, for which the name Brevibacillus halotolerans sp. nov. is proposed. The type strain is LAM0312T (=ACCC 06527T=JCM 30849T).

Acinetobacter larvae sp. nov., isolated from the larval gut of Omphisa fuscidentalis

A Gram-stain-negative, non-spore-forming, non-motile and aerobic coccobacilli-shaped strain, designated BRTC-1T, was isolated from the gut of Omphisa fuscidentalis Hampson, which is a larva of a moth and was collected from Xishuangbanna Dai Autonomous Prefecture in China. The isolate was found to grow at NaCl concentrations of 0-5 % (w/v) (optimum: 0 %), 10-45 °C (optimum: 30-35 °C) and pH 5.0-9.0 (optimum: pH 6.0) on tryptic soy agar. Analysis of the 16S rRNA gene sequence indicated that the isolate belonged to the genus Acinetobacter and was most closely related to Acinetobacter rudis LMG 26107T, Acinetobacter guillouiae LMG 988T and Acinetobacter bereziniae LMG 1003T with 96.4, 96.3 and 96.3 % sequence similarity, respectively. The comparative sequence analyses of the rpoB and gyrB genes showed that BRTC-1T is distant from the species of the genus Acinetobacter with validly published names (≤84.0 and ≤82.0 % similarity, respectively). The average nucleotide identity and digital DNA-DNA hybridization values (≤77.0 and ≤22.8 %, respectively) between the whole-genome sequence of BRTC-1T and those of the known taxa were far below the thresholds used to discriminate bacterial species. The major fatty acids were determined to be C16 : 0, C18 : 1ω9c and C16 : 1ω7c/iso-C15 : 0 2-OH. The respiratory quinone was Q-9. The polar lipids were found to be diphosphatidyglycerol, phosphatidylglycerol, phosphatidylethanolamine, five phospholipids and one phosphatidylcholine. Based on its phenotypic and chemotaxonomic characteristics from this study, the isolate is concluded to represent a novel species of the genus Acinetobacter, for which the name Acinetobacter larvae sp. nov. is proposed. The type strain is BRTC-1T (=ACCC 19936T=JCM 31367T).