Lixin Luo

Isolation and identification of algicidal compound from Streptomyces and algicidal mechanism to Microcystis aeruginosa.

The biological control of cyanobacterial harmful algal blooms (cyanoHABs) is important to promote human health, environmental protection, and economic growth. Active algicidal compounds and algicidal mechanisms should be identified and investigated to control cyanoHABs. In this study, the algicidal actinobacterium Streptomyces sp. L74 was isolated from the soil of a nearby pond which located in the center lake of Guanghzou Higher Education Mega Center. Results showed that the algicidal activities of cyanoHABs are mainly achieved via an indirect attack by producing algicidal compounds. All active algicidal compounds are hydrophilic substances that are heat and pH stable. In the present study, an active compound (B3) was isolated and purified by high-performance liquid chromatography and identified as a type of triterpenoid saponin (2-hydroxy-12-oleanene-3, 28-O-D-glucopyranosyl) with a molecular formula of C42H70O13 as determined by infrared spectrometry, electrospray ionization mass spectrometry, and nuclear magnetic resonance. Active algicidal compounds from Streptomyces sp. L74 were shown to disrupt the antioxidant systems of Microcystis aeruginosa cells.

Microbiota Dynamics Associated with Environmental Conditions and Potential Roles of Cellulolytic Communities in Traditional Chinese Cereal Starter Solid-State Fermentation.

ABSTRACT Traditional Chinese solid-state fermented cereal starters contain highly complex microbial communities and enzymes. Very little is known, however, about the microbial dynamics related to environmental conditions, and cellulolytic communities have never been proposed to exist during cereal starter fermentation. In this study, we performed Illumina MiSeq sequencing combined with PCR-denaturing gradient gel electrophoresis to investigate microbiota, coupled with clone library construction to trace cellulolytic communities in both fermentation stages. A succession of microbial assemblages was observed during the fermentation of starters. Lactobacillales and Saccharomycetales dominated the initial stages, with a continuous decline in relative abundance. However, thermotolerant and drought-resistant Bacillales, Eurotiales, and Mucorales were considerably accelerated during the heating stages, and these organisms dominated until the end of fermentation. Enterobacteriales were consistently ubiquitous throughout the process. For the cellulolytic communities, only the genera Sanguibacter, Beutenbergia, Agrobacterium, and Erwinia dominated the initial fermentation stages. In contrast, stages at high incubation temperature induced the appearance and dominance of Bacillus, Aspergillus, and Mucor. The enzymatic dynamics of amylase and glucoamylase also showed a similar trend, with the activities clearly increased in the first 7 days and subsequently decreased until the end of fermentation. Furthermore, β-glucosidase activity continuously and significantly increased during the fermentation process. Evidently, cellulolytic potential can adapt to environmental conditions by changes in the community structure during the fermentation of starters.

Analyzing the relation between the microbial diversity of DaQu and the turbidity spoilage of traditional Chinese vinegar

Vinegar is a traditional fermented condiment, and the microbial diversity of DaQu makes the quality of vinegar products. Recently, turbidity spoilage of vinegar sharply tampered with the quality of vinegar. In this study, the relation between the microbial diversity of DaQu and turbidity spoilage of vinegar was analyzed by plating technique, PCR–denaturing gradient gel electrophoresis (DGGE), and high-performance liquid chromatography (HPLC). The 16S rRNA sequencing and DGGE analysis indicated that Bacillus (Bacillus subtilis, Bacillus amyloliquefaciens, and Bacillus thuringiensis) and Lactobacillus (including Lactobacillus acidipiscis and Lactobacillus pobuzihii) species were the dominant contaminants in vinegar products. Meanwhile, DGGE analysis showed that the dominant bacteria in DaQu belonged to genera Bacillus, Lactobacillus, Pseudomonas, Weissella, Saccharopolyspora, Enterobacter, and Pantoea. However, only two yeast species (Pichia kudriavzevii and Saccharomycopsis fibuligera) and seven mold species including Aspergillus oryzae, Aspergillus niger, Aspergillus candidus, Rhizopus microspores, Eurotium herbariorum, Absidia corymbifera, and Eupenicillium javanicum were detected in the DaQu. The population level of fungi was below 5 log CFU/g in DaQu. The chemical and physical properties of vinegar and sediments were also determined. On the basis of a combined microbial diversity-chemical analysis, we demonstrated that turbidity spoilage of vinegar was a result of cooperation among the low population level and abundance of fungal species in DaQu, the suitable climate conditions, and the contaminants in vinegar. This is the first report to analyze the relation between the microbial diversity of DaQu and turbidity spoilage of vinegar.

Microbial diversity and their roles in the vinegar fermentation process.

Vinegar is one of the oldest acetic acid-diluted solution products in the world. It is produced from any fermentable sugary substrate by various fermentation methods. The final vinegar products possess unique functions, which are endowed with many kinds of compounds formed in the fermentation process. The quality of vinegar is determined by many factors, especially by the raw materials and microbial diversity involved in vinegar fermentation. Given that metabolic products from the fermenting strains are directly related to the quality of the final products of vinegar, the microbial diversity and features of the dominant strains involved in different fermentation stages should be analyzed to improve the strains and stabilize fermentation. Moreover, although numerous microbiological studies have been conducted to examine the process of vinegar fermentation, knowledge about microbial diversity and their roles involved in fermentation is still fragmentary and not systematic enough. Therefore, in this review, the dominant microorganism species involved in the stages of alcoholic fermentation and acetic acid fermentation of dissimilar vinegars were summarized. We also summarized various physicochemical properties and crucial compounds in disparate types of vinegar. Furthermore, the merits and drawbacks of vital fermentation methods were generalized. Finally, we described in detail the relationships among microbial diversity, raw materials, fermentation methods, physicochemical properties, compounds, functionality, and final quality of vinegar. The integration of this information can provide us a detailed map about the microbial diversity and function involved in vinegar fermentation.

Characterization of activity and microbial diversity of typical types of Daqu for traditional Chinese vinegar.

Daqu is a fermentation starter used in traditional Chinese vinegar production and determines the quality of the final vinegar products. In this study, the activity and microbial diversity of three typical types of Daqu were investigated using a nested PCR–denaturing gradient gel electrophoresis (DGGE) and plating technique. The bacterial DGGE profile and plate analysis indicated that the bacterial composition of Daqu was dominated by Bacillus sp., Pantoea sp., Saccharopolyspora sp., Enterobacter cloaceae and Cronobacter sakazakii, and lactic acid bacteria including Weissella sp., Pediococcus pentosaceus. DGGE analysis of fungal plates identified Aspergillus niger, Absidia corymbifera, Rhizopus sp. and Penicillium sp. as the predominant fungi involved in Daqu. However, DGGE results indicated that the bacterial microbiota of QC (Qing-Cha) and HX (Hong-Xin) were more complex than that of HR (Huai-Rang) Daqu. The total populations of microorganisms in QC were about 1 log CFU g−1 higher than in HR and HX Daqu. Moreover, the saccharifying power of QC was significantly higher than in HR and HX Daqu, and the liquefying power of QC was significantly higher than in HR, but slightly lower than in HX Daqu. Our results indicate that microbial diversity plays a crucial role in determining the activity of typical types of Daqu.

Environmental Factors Affecting Microbiota Dynamics during Traditional Solid-state Fermentation of Chinese Daqu Starter.

In this study, we investigated the microbiota dynamics during two industrial-scale traditional solid-state fermentation (SSF) processes of Daqu starters. Similar evolution profiles of environmental parameters, enzymatic activities, microbial amounts, and communities were observed during the medium temperature SSF (MTSSF) and low temperature SSF (LTSSF) processes. Orders of Rickettsiales and Streptophyta only dominated the initial 2 days, and Eurotiales only predominated from days 10 to 24, however, phylotypes of Enterobacteriales, Lactobacillales, Bacillales, Saccharomycetales, and Mucorales both prevailed throughout the MTSSF and LTSSF processes. Nevertheless, the pH in MTSSF process on day 5 were 5.28, while in LTSSF process (4.87) significantly lower (P < 0.05). The glucoamylase activities in MTSSF process dropped from 902.71 to 394.33 mg glucose g-1 h-1 on days 5 to 24, while significantly lower (P < 0.05) in LTSSF process and decreased from 512.25 to 268.69 mg glucose g-1 h-1. The relative abundance of Enterobacteriales and Lactobacillales in MTSSF process constituted from 10.30 to 71.73% and 2.34 to 16.68%, while in LTSSF process ranged from 3.16 to 41.06% and 8.43 to 57.39%, respectively. The relative abundance of Eurotiales in MTSSF process on days 10 to 24 decreased from 36.10 to 28.63%, while obviously higher in LTSSF process and increased from 52.00 to 72.97%. Furthermore, lower bacterial richness but higher fungal richness were displayed, markedly differences in bacterial communities but highly similarities in fungal communities were exhibited, during MTSSF process comparatively to the LTSSF process. Canonical correspondence analysis revealed microbial structure transition happened at thermophilic stages under environmental stress of moisture, pH, acidity, and pile temperature. These profound understanding might help to effectively control the traditional Daqu SSF process by adjusting relevant environmental parameters.

Evolution of bacterial consortia in an integrated tannery wastewater treatment process

In the present study, the dynamics of microbial communities and their abundance associated with each stage of a tannery wastewater treatment process were investigated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) combined with high throughput sequencing. Both PCR-DGGE and high throughput sequencing results reflected the bacterial succession in the integrated treatment process and phyla of Proteobacteria, Bacteroidetes and Firmicutes dominated throughout the integrated treatment process. However, Actinobacteria, Planctomycetes and Chlofoflexi only predominant the anoxic/oxic (A/O) process. The bacterial richness during the A/O process was higher than that in the pre-treatment process. Moreover, quantitative polymerase chain reaction (qPCR) analysis indicated that the absolute abundance of 16S rRNA genes in the biological treatment stages were higher than in other stages. Finally, redundancy analysis suggested that [Thermi] should be involved in NH4+–N removal and ammonia concentration had positive effects on the bacterial diversity. Overall, this study provided insight into the evolution of the bacterial community structure and diversity in integrated wastewater treatment processes and identified the correlations between the physicochemical characteristics of wastewater and bacterial community structures.

Unravelling diversity and metabolic potential of microbial consortia at each stage of leather sewage treatment

Activated sludge is essential for the biological wastewater treatment process and the identification of active microbes enlarges awareness of their ecological functions in this system. Microbial communities and their active members were investigated in activated sludge from a leather sewage treatment plant by a combined approach targeting both 16S rRNA and 16S rRNA genes. Although active bacteria obtained by RNA analysis exhibit similar diversity with DNA-based populations, the distribution of microbes significantly differed between the total and active communities. Several active taxa showed low abundance or even absence in the DNA-derived community. Moreover, microbial consortia, particularly bacterial communities, distinctly distributed at a particular treatment stage and both the total and active bacterial communities displayed high environmental sensitivity. Distributions of archaeal communities remained stable and the overrepresentations of active Cenarchaeaceae and Nitrosopumilaceae were potentially associated with ammonia oxidation across the treatment process. Furthermore, bacteria quantitatively dominate the microbial community in activated sludge and the 16S rRNA : 16S rRNA gene ratios of bacteria were positively correlated with the removal of contaminants. The results indicate that both dominant and low-abundance taxa with high potential activity play pivotal roles in removal of contaminants within sewage.

Chinese herb medicine against Sortase A catalyzed transformations, a key role in gram-positive bacterial infection progress.

Abstract Many Gram-positive bacteria can anchor their surface proteins to the cell wall peptidoglycan covalently by a common mechanism with Sortase A (SrtA), thus escaping from the host’s identification of immune cells. SrtA can complete this anchoring process by cleaving LPXTG motif conserved among these surface proteins and thus these proteins anchor on the cell wall. Moreover, those SrtA mutants lose this capability to anchor these relative proteins, with these bacteria no longer infectious. Therefore, SrtA inhibitors can be promising anti-infective agents to cure bacterial infections. Chinese herb medicines (CHMs) (chosen from Science Citation Index) have exhibited inhibition on SrtA of Gram-positive pathogens irreversibly or reversibly. In general, CHMs are likely to have important long-term impact as new antibacterial compounds and sought after by academia and the pharmaceutical industry. This review mainly focuses on SrtA inhibitors from CHMs and the potential inhibiting mechanism related to chemical structures of compounds in CHMs.

Paenibacillus aceti sp. nov., isolated from the traditional solid-state acetic acid fermentation culture of Chinese cereal vinegar.

A Gram-stain-negative, rod-shaped, motile, endospore-forming, facultatively anaerobic bacterium, designated strain L14T, was isolated from the traditional acetic acid fermentation culture of Chinese cereal vinegars. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain L14T was affiliated to the genus Paenibacillus, most closely related to Paenibacillus motobuensis MC10T with 97.8 % similarity. Chemotaxonomic characterization supported the allocation of the strain to the genus Paenibacillus. The polar lipid profile of strain L14T contained the major compounds diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. The predominant menaquinone was MK-7, and the major fatty acid components were anteiso-C15 : 0, iso-C15 : 0 and C16 : 0. The DNA G+C content of strain L14T was 49.9 mol%. The DNA-DNA relatedness value between strain L14T and P. motobuensis MC10T was 51.2 %. The results of physiological and biochemical tests allowed phenotypic differentiation of strain L14T from closely related species. On the basis of phenotypic and chemotaxonomic analyses, phylogenetic analysis and DNA-DNA relatedness values, strain L14T is considered to represent a novel species of the genus Paenibacillus, for which the name Paenibacillus aceti sp. nov. is proposed. The type strain is L14T (=CGMCC 1.15420T=JCM 31170T).