BackgroundThe production of secondary metabolites with antibiotic properties is a common characteristic to entomopathogenic bacteria Xenorhabdus spp. These metabolites not only have diverse chemical structures but also have a wide range of bioactivities with medicinal and agricultural interests such as antibiotic, antimycotic and insecticidal, nematicidal and antiulcer, antineoplastic and antiviral. It has been known that cultivation parameters are critical to the secondary metabolites produced by microorganisms. Even small changes in the culture medium may not only impact the quantity of certain compounds but also the general metabolic profile of microorganisms. Manipulating nutritional or environmental factors can promote the biosynthesis of secondary metabolites and thus facilitate the discovery of new natural products. This work was conducted to evaluate the influence of nutrition on the antibiotic production of X. bovienii YL002 and to optimize the medium to maximize its antibiotic production.ResultsNutrition has high influence on the antibiotic production of X. bovienii YL002. Glycerol and soytone were identified as the best carbon and nitrogen sources that significantly affected the antibiotic production using one-factor-at-a-time approach. Response surface methodology (RSM) was applied to optimize the medium constituents (glycerol, soytone and minerals) for the antibiotic production of X. bovienii YL002. Higher antibiotic activity (337.5 U/mL) was obtained after optimization. The optimal levels of medium components were (g/L): glycerol 6.90, soytone 25.17, MgSO4·7H2O 1.57, (NH4)2SO4 2.55, KH2PO4 0.87, K2HPO4 1.11 and Na2SO4 1.81. An overall of 37.8% increase in the antibiotic activity of X. bovienii YL002 was obtained compared with that of the original medium.ConclusionsTo the best of our knowledge, there are no reports on antibiotic production of X. boviebii by medium optimization using RSM. The results strongly support the use of RSM for medium optimization. The optimized medium not only resulted in a 37.8% increase of antibiotic activity, but also reduced the numbers of experiments. The chosen method of medium optimization was efficient, simple and less time consuming. This work will be useful for the development of X. bovienii cultivation process for efficient antibiotic production on a large scale, and for the development of more advanced control strategies on plant diseases.
Heavy metal pollution has become a widespread environmental problem due to rapid economic development. The phylogenetic diversity and structure of microbial communities in lead (Pb)-contaminated Lou soils were investigated using Illumina MiSeq sequencing of 16S rRNA genes. The presence of Pb in soil showed weak impact on the diversity of soil bacteria community, but it influenced the abundance of some genera of bacteria, as well as soil physicochemical properties. We found significant differences in the relative abundances of heavy-metal-resistant bacteria such as Bacillus, Streptococcus, and Arthrobacter at the genus level. Available Pb and total Pb negatively correlated with soil organic matter but positively affected available phosphorus. The abundance of main bacteria phyla was highly correlated with total Pb. The relative abundance of Gemmatimonadetes, Nitrospirae, and Planctomycetes was negatively correlated with total Pb. Collectively, Pb influences both the microbial community composition and physicochemical properties of soil.
The aim of this study was to investigate the sensory indicators, biogenic amine contents, and bacterial community structure and diversity of chilled chicken stored at 4°C under aerobic conditions. Bacterial diversity and dominant bacteria were analyzed using high‐throughput sequencing technique (HTS). The relationship between biogenic amine contents and microbial community structure was studied. The results showed that contents of putrescine and cadaverine increased significantly with storage time. Proteobacteria was absolutely dominant flora at the phylum level. The predominant spoilage bacteria found in chicken thighs were
Pseudomonas
,
Acinetobacter
,
Aeromonas
,
Shewanella
, and
Yersinia
, and the difference with chicken breasts was related to the presence of
Myroides
and absence of
Yersinia
.
Myroides
,
Yersinia
, and
Shewanella
were reported for the first time as an important contributor to the spoilage‐related microflora
.
Bacterial diversity and richness indices showed fluctuating and decreasing trend with storage time. The redundancy analysis showed that the relative abundance of
Pseudomonas
,
Yersinia
, and
Janthinobacterium
was positively related to the contents of putrescine, cadaverine, and tyramine, while
Shewanella
and
Aeromonas
showed positive relationship with putrescine content. Furthermore, positive relationship of
Myroides
and
Desulfovibrio
with the contents of cadaverine and tyramine was proposed for the first time. The key findings of this study can provide experimental data for food safety monitoring during refrigerated storage and preservation for poultry meat products.
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