Structural and functional insights into the role of a cupin superfamily isomerase in the biosynthesis of Choi moiety of aeruginosin.

The 2-carboxy-6-hydroxyoctahydroindole (Choi) moiety is a hallmark of aeruginosins, a class of cyanobacterial derived bioactive linear tetrapeptides that possess antithrombotic activity. The biosynthetic pathway of Choi has yet to be resolved. AerE is a cupin superfamily enzyme that was shown to be involved in the biosynthesis of Choi, but its exact role remains unclear. This study reports the functional characterization and structural analyses of AerE. Enzymatic observation reveals that AerE can dramatically accelerate 1,3-allylic isomerization of the non-aromatic decarboxylation product of prephenate, dihydro-4-hydroxyphenylpyruvate (H2HPP). This olefin isomerization reaction can occur non-enzymatically and is the second step of the biosynthetic pathway from prephenate to Choi. The results of comparative structural analysis and substrate analogue binding geometry analysis combined with the results of mutational studies suggest that AerE employs an induced fit strategy to bind and stabilize the substrate in a particular conformation that is possibly favorable for 1,3-allylic isomerization of H2HPP through coordinate bonds, hydrogen bonds, π-π conjugation interaction and hydrophobic interactions. All of these interactions are critical for the catalytic efficiency.

[Characterization and optimization of a heterotrophic bacterium for sulfide degradation].

The emission of hydrogen sulfide in the waste gas from slaughter plant, fishmeal feed processing and some other food industrial processing could cause serious air pollution to the surrounding environment. The purpose of this study was to screen heterotrophic bacterium strains for the removal of hydrogen sulfide odor. One heterotrophic bacterial mutant ZJNB-B3 was derived from the sulfide degrader Bacillus cereus XJ-2 and its sulfide removal efficiency was 97%. Based on the morphology studies, biochemical tests and 16S rRNA gene analysis, the strain was identified as Bacillus cereus ZJNB-B3. The NCBI GenBank accession number is MF679650. Batch tests showed that the strain tolerated up to 300 mg/L of toxic S²â» concentration. Response surface methodology was applied to optimize the conditions of degradation of sulfide. The optimal parameters were as follows: initial sulfide concentration 211.8 mg/L, initial pH 6.72, inoculum volume 5.04%, and incubation temperature 30 ℃. The accumulated sulfate concentration was 63.8 mg/L and the sulfide removal efficiency was 97.3% after 48 h incubation. No sulfuric acid was generated during sulfide oxidation by the strain. Sulfide could be removed effectively by this strain under mild pH conditions. The results suggested that the strain may have great industrial application potential. This study provides the fundamentals for the removal of hydrogen sulfide gas.

Identification of a yeast strain able to oxidize and remove sulfide high efficiently.

Hydrogen sulfide is a common odor gas of volatile sulfur-containing compound. The emission of hydrogen sulfide in the waste gas from industrial processing and agricultural operations could cause air pollution to the surrounding environment. The aim of this study was screening and isolation of wild yeast strains from the sludge of sewage pool in the fishmeal processing plant to remove hydrogen sulfide odor. A yeast strain ZJY-7 was obtained. Its hydrogen sulfide removal efficiency was 97.1 %. The morphology studies were investigated using microscope and scanning electron microscope. The yeast isolate was then identified by biochemical tests using API 20 C AUX strip and sequencing 26S rDNA genes. Both biochemical tests analysis and the molecular identification indicated that the yeast isolate ZJY-7 was Candida tropicalis ZJY-7. The NCBI GenBank accession number is KX259479. Batch tests showed that the yeast strain tolerated up to 300 mg/l of dissolved S2- concentration. The yeast also tolerated a wide pH range (2.5-9.0). The optimal initial sulfide concentration of C. tropicalis ZJY-7 on sulfide oxidation and sulfate generation was 200 mg/l, and at initial pH value 6. The highest accumulated sulfate was 91.8 mg/l at 48 h. These results broadened the range of sulfide-oxidizing organism and new application of C. tropicalis on the control of hydrogen sulfide odor pollution. The yeast may have potential to be used in bioreactor for removal of hydrogen sulfide gas.

Influence of hydroxypropyl methylcellulose edible coating on fresh-keeping and storability of tomato.

The effect of application of cellulose-based edible coating, hydroxypropyl methylcellulose (HPMC) to mature-green tomatoes on the firmness and color was investigated. Tomatoes were stored at 20 degrees C for up to 18 days. Firmness decreased as storage time increased in all treatments. However, application of HPMC edible coating delayed softening of tomatoes during 18 days of storage at 20 degrees C. At days 7, 13 and 18, the firmness of tomatoes coated with HPMC was significantly (P < or = 0.05) greater than the firmness of uncoated tomatoes. The study also confirmed that HPMC coatings could significantly (P < or = 0.05) delay the changes in color of tomatoes stored at 20 degrees C. The ripening of tomatoes from the pink stage to the red stage was successfully retarded. HPMC coating could extend the shelf life of fresh tomatoes. The retardation of the rate of loss of firmness could reduce the economic loss that would result from spoilage by mechanical injury during transportation of tomatoes.