Two novel cationic antifungal peptides isolated from Bacillus pumilus HN-10 and their inhibitory activity against Trichothecium roseum.

Public concern for food safety and environmental issues and the increase in fungicide-resistant pathogen have enhanced the interest in developing alternative methods to fungicides to control postharvest fruit decay. In this study, a bacterial strain isolated from stale potato vermicelli was identified as Bacillus pumilus HN-10 based on morphological characteristics and 16S rRNA gene sequence analysis. Furthermore, two novel cationic antifungal peptides named P-1 and P-2 were purified from B. pumilus HN-10 using macroporous adsorbent resin AB-8, Sephadex G-100 chromatography, and reversed-phase high-performance liquid chromatography. The primary structure of P-1 and P-2, which were proved to be novel antifungal peptides by BLAST search in NCBI database, was PLSSPATLNSR and GGSGGGSSGGSIGGR with a molecular weight of 1142.28 and 1149.14 Da, respectively, as indicated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Both P-1 and P-2 exhibited strong antifungal activity against Trichothecium roseum with minimum inhibitory concentrations starting from 1 µg/mL. The two novel antifungal peptides were stable below 80 °C for 2 h, but lost their activity in 15 min at 121 °C. In addition, they were resistant to the proteolytic action of pepsin, trypsin, and papain, and stable within a wide range of pH (2.0-12.0). These results showed that P-1 and P-2 are novel cationic antifungal peptides with specific activity against T. roseum.

Enhanced ß-galactosidase production of Aspergillus oryzae mutated by UV and LiCl.

In order to breed a high-yield ß-galactosidase-producing strain, Aspergillus oryzae was used as the parent strain and mutagenized with ultraviolet (UV) and UV plus lithium chloride (LiCl), respectively. After being mutagenized by UV, the ß-galactosidase activity of mutant UV-15-20 reached 114.08 U/mL, which revealed a 49.22% increase compared with the original strain. A mutant UV-LiCl-38 with high ß-galactosidase activity (121.42 U/mL) was obtained after compound mutagenesis of UV and LiCl; the ß-galactosidase activity of this mutant was 58.82% higher than that of the parent strain. Subculture testing indicated that UV-15-20 and UV-LiCl-38 had good hereditary stability and may be ideal strains for the production of ß-galactosidase. Additionally, it was demonstrated that compound mutagenesis with UV and LiCl is an effective mutation method for breeding industrially interesting strains.

Microbial succession and its correlation with the dynamics of flavor compounds involved in the fermentation of Longxi bacon.

Introduction: Longxi bacon is a traditional fermented meat from Gansu province, China. The ripening process of the bacon is crucial for quality and flavor. The aim of this study was to gain deeper knowledges on the bacterial and fungal community diversity and the changes of chemical components including fatty acids and volatile compounds at different time points during the ripening of the bacon and to understand the relationship between microbial profiles and the chemical components related the bacon flavor. Methods: Bacon samples were collected from days 0, 15, 30, 60 and 90. The bacterial and fungal compositions were analyzed with next generation sequencing targeting the 16S rDNA loci for bacteria and ITS loci for fungi. The fatty acids and the volatile components were analyzed by headspace solid phase micro extraction followed by gas chromatography/mass spectrometry (HS-SPME-GC/MS). Results: We found that the abundance of bacteria in bacon was higher than that of fungi, and Psychrobacter, Brochothrix, Phoma and Trichoderma was the dominant bacon's population. The largest contributors of volatiles were aldehydes, ketones and esters, and the main fatty acids were palmitic, oleic and linoleic acids. Pearson correlation analysis between microbial succession and key flavor substances showed that the production of Longxi bacon flavor is the result of a combination of bacteria and fungi. Ten bacteria genera and six fungi genera were determined as functional core microbiota for the flavor production based their dominance and functionality in microbial community. In addition, bacteria and fungi are involved in the oxidation and hydrolysis of fatty acids during the ripening of bacon, which also contributes to the formation of bacon flavor. Discussion: This study provides a comprehensive analysis of the key microbiota involved in shaping bacon's distinctive flavor. Here, the results presented should provide insight into the influence of the microenvironment on the microbial community in bacon and lay a foundation for further investigations into the food ecology of bacon.

Analysis of compensatory substitution and gene evolution on the MAGEA/CSAG-palindrome of the primate X chromosomes.

The human X chromosome contains a large number of inverted repeat DNA palindromes. Although arbitrary substitutions destroyed the inverted repeat structure of MAGEA/CSAG-palindrome during the evolutionary process of the primates, most of the substitutions are compensatory. Using maximum parsimony, it is demonstrated that the compensatory substitutions are prone to occur between bases with similar structures on the human, chimpanzee and orangutan MAGEA/CSAG-palindromes. Furthermore, it is found that MAGEA/CSAG genes also exist in orangutan and rhesus monkey palindromes by homologous searching. This suggests that the MAGEA/CSAG-palindrome might predate the divergence of human and other primate lineages. Comparative sequence analysis of the arms and genes on the primate MAGEA/CSAG-palindromes provides possible evidence of subsequently arm to arm gene conversion. These compensatory substitutions on the MAGEA/CSAG-palindrome of the primate X chromosomes play an important role in maintaining their structural symmetry during the process of formation.

Wavelet analysis of DNA walks on the human and chimpanzee MAGE/CSAG-palindromes.

The palindrome is one class of symmetrical duplications with reverse complementary characters, which is widely distributed in many organisms. Graphical representation of DNA sequence provides a simple way of viewing and comparing various genomic structures. Through 3-D DNA walk analysis, the similarity and differences in nucleotide composition, as well as the evolutionary relationship between human and chimpanzee MAGE/CSAG-palindromes, can be clearly revealed. Further wavelet analysis indicated that duplicated segments have irregular patterns compared to their surrounding sequences. However, sequence similarity analysis suggests that there is possible common ancestor between human and chimpanzee MAGE/CSAG-palindromes. Based on the specific distribution and orientation of the repeated sequences, a simple possible evolutionary model of the palindromes is suggested, which may help us to better understand the evolutionary course of the genes and the symmetrical sequences.