Comparison of bacterial community structures of terrestrial cyanobacterium Nostoc flagelliforme in three different regions of China using PCR-DGGE analysis

Metabolites Facilitating Adaptation of Desert Cyanobacteria to Extremely Arid Environments

Desert is one of the harshest environments on the planet, characterized by exposure to daily fluctuations of extreme conditions (such as high temperature, low nitrogen, low water, high salt, etc.). However, some cyanobacteria are able to live and flourish in such conditions, form communities, and facilitate survival of other organisms. Therefore, to ensure survival, desert cyanobacteria must develop sophisticated and comprehensive adaptation strategies to enhance their tolerance to multiple simultaneous stresses. In this review, we discuss the metabolic pathways used by desert cyanobacteria to adapt to extreme arid conditions. In particular, we focus on the extracellular polysaccharides and compatible solutes biosynthesis pathways and their evolution and special features. We also discuss the role of desert cyanobacteria in the improvement of soil properties and their ecological and environmental impact on soil communities. Finally, we summarize recent achievements in the application of desert cyanobacteria to prevent soil erosion and desertification.

Bacterial Communities Associated With Spherical Nostoc Macrocolonies

Species of the genus Nostoc (Cyanobacteria) can form large colonies of up to several centimeters in diameter that may represent a unique habitat for bacteria in freshwaters. Bacteria inside the colony are probably segregated from the surrounding water and largely dependent on the metabolism of this primary producer. However, the existence of a specific bacterial community associated with free-living representatives of Nostoc from lakes and streams is unknown. Here, we studied large Nostoc spp. colonies (ca. 2-10 cm in diameter) from two adjacent, high altitude aquatic environments and assessed the diversity, and community composition of the bacterial community associated with the inner gelatinous matrix (GM). Further, we compared this community with that of the lake's littoral zone where the colonies live or with the outer layer (OL) of the colony in samples collected from a stream. Alpha bacterial diversity in the inner GM of the colonies from both sites was lower than in the littoral zone or than in the OL. Significant differences in community composition were found between the inner and the OL, as well as between the inner GM, and the littoral zone. Further, these differences were supported by the putative metabolic processes of the bacterial communities. Our results indicate the existence of a specific bacterial community inside macrocolonies of Nostoc spp. and also imply that the inner environment exerts a strong selection. Finally, these large colonies represent not only a unique habitat, but probably also a hotspot of bacterial activity in an otherwise oligotrophic environment.

The physiological responses of terrestrial cyanobacteriumNostoc flagelliformeto different intensities of ultraviolet-B radiation

Nostoc flagelliforme is a pioneer organism in the desert and exerts important ecological functions. The habitats of N. flagelliforme are characterized by intense solar radiation, while the ultraviolet B (UV-B) tolerance has not been fully explored yet. To evaluate the physiological responses of N. flagelliforme to UV-B radiation, three intensities (1 W m⁻², 3 W m⁻² and 5 W m⁻²) were used, and the changes in photosynthetic pigments, cell morphology, mycosporine-like amino acids (MAAs) synthesis and cell metabolism were comparatively investigated. Under high UV-B intensity or long term radiation, chlorophyll a, allophycocyanin and phycocyanin were greatly decreased; scanning electron microscope observations showed that cell morphology significantly changed. To reduce the damage, cells synthesized a large amount of carotenoid. Moreover, three kinds of MAAs were identified, and their concentrations varied with the changes of UV-B intensity. Under 1 W m⁻² radiation, cells synthesized shinorine and porphyra-334 against UV-B, while with the increase of intensity, more shinorine turned into asterine-330. Metabolite profiling revealed the contents of some cytoprotective metabolites were greatly increased under 5 W m⁻² radiation. The principal component analysis showed cells exposed to UV-B were metabolically distinct from the control sample, and the influence on metabolism was particularly dependent on intensity. The results would improve the understanding of physiological responses of N. flagelliforme to UV-B radiation and provide an important theoretical basis for applying this organism to control desertification.

The findings would improve the understanding of physiological responses of N. flagelliforme to UV-B radiation.

Environmental Controls Over Actinobacteria Communities in Ecological Sensitive Yanshan Mountains Zone

The Yanshan Mountains are one of the oldest mountain ranges in the world. They are located in an ecologically sensitive zone in northern China near the Hu Huanyong Line. In this metagenomic study, we investigated the diversity of Actinobacteria in soils at 10 sites (YS1–YS10) on the Yanshan Mountains. First, we assessed the effect of different soil prtreatment on Actinobacteria recovery. With the soil pretreatment method: air drying of the soil sample, followed by exposure to 120°C for 1 h, we observed the higher Actinobacteria diversity in a relatively small number of clone libraries. No significant differences were observed in the Actinobacterial diversity of soils from sites YS2, YS3, YS4, YS6, YS8, YS9, or YS10 (P > 0.1). However, there were differences (P < 0.05) from the YS7 site and other sites, especially in response to environmental change. And we observed highly significant differences (P < 0.001) in Actinobacterial diversity of the soil from YS7 and that from YS4 and YS8 sites. The climatic characteristics of mean active accumulated temperature, annual mean precipitation, and annual mean temperature, and biogeochemical data of total phosphorus contributed to the diversity of Actinobacterial communities in soils at YS1, YS3, YS4, and YS5 sites. Compared to the climatic factors, the biogeochemical factors mostly contributed in shaping the Actinobacterial community. This work provides evidence that the diversity of Actinobacterial communities in soils from the Yashan Mountains show regional biogeographic patterns and that community membership change along the north-south distribution of the Hu Huanyong Line.

The impact of different DNA extraction methods on the analysis of microbial diversity of oral saliva from healthy youths by polymerase chain reaction-denaturing gradient gel electrophoresis

Background/purpose

Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), as a conventional molecular technique, was utilized to analyze the diversity of oral microbiota. However, studies found that the results of PCR-DGGE were affected by the DNA isolation method. This study compared QIAamp DNA Micro Kit extraction method with the phenol and chloroform extraction method for DNA isolation of saliva of healthy youths and analyzed PCR-DGGE fingerprints.

Materials and methods

In the first stage, samples were divided into two after collection from eight health youths. Two methods were used to isolate the DNA for PCR-DGGE analysis. In the second stage, another 16 samples were collected from 14 youths. The better method, QIAamp DNA Micro Kit, was used to isolate the DNA for PCR-DGGE analysis. The cluster analysis was performed with unweighted pair-group method with arithmetic means.

Results

The results in the first stage showed that the QIAamp DNA Micro Kit extraction method was more suitable for DNA extraction of saliva than the phenol-chloroform extraction method. In the second stage, the bands were changed into numbers “0”, “1”, and “2” to analyze the similarity of samples according to the bands' lightness. The similarity indices of different periods from the same individual showed that the microbiological composition was very similar (>0.95), while those from different individuals varied greatly (<0.90).

Conclusion

PCR-DGGE was more accurate in assessing oral microbial diversity by QIAamp DNA Micro Kit. Different individuals had large differences in oral microbial diversity but also had some common microbial dominant communities.