High immigration rates critical for establishing emigration-driven diversity in microbial communities.

Unraveling the mechanisms governing the diversity of ecological communities is a central goal in ecology. Although microbial dispersal constitutes an important ecological process, the effect of dispersal on microbial diversity is poorly understood. Here, we sought to fill this gap by combining a generalized Lotka-Volterra model with experimental investigations. Our model showed that emigration increases the diversity of the community when the immigration rate crosses a defined threshold, which we identified as Ineutral. We also found that at high immigration rates, emigration weakens the relative abundance of fast-growing species and thus enhances the mass effect and increases the diversity. We experimentally confirmed this finding using co-cultures of 20 bacterial strains isolated from the soil. Our model further showed that Ineutral decreases with the increase of species pool size, growth rate, and interspecies interaction. Our work deepens the understanding of the effects of dispersal on the diversity of natural communities.

Roles of sulfate-reducing bacteria in sustaining the diversity and stability of marine bacterial community.

Microbes play central roles in ocean food webs and global biogeochemical processes. Yet, the information available regarding the highly diverse bacterial communities in these systems is not comprehensive. Here we investigated the diversity, assembly process, and species coexistence frequency of bacterial communities in seawater and sediment across ∼600 km of the eastern Chinese marginal seas using 16S rRNA gene amplicon sequencing. Our analyses showed that compared with seawater, bacterial communities in sediment possessed higher diversity and experienced tight phylogenetic distribution. Neutral model analysis showed that the relative contribution of stochastic processes to the assembly process of bacterial communities in sediment was lower than that in seawater. Functional prediction results showed that sulfate-reducing bacteria (SRB) were enriched in the core bacterial sub-communities. The bacterial diversities of both sediment and seawater were positively associated with the relative abundance of SRB. Co-occurrence analysis showed that bacteria in seawater exhibited a more complex interaction network and closer co-occurrence relationships than those in sediment. The SRB of seawater were centrally located in the network and played an essential role in sustaining the complex network. In addition, further analysis indicated that the SRB of seawater helped maintain the high stability of the bacterial network. Overall, this study provided further comprehensive information regarding the characteristics of bacterial communities in the ocean, and provides new insights into keystone taxa and their roles in sustaining microbial diversity and stability in ocean.

Microbial communities and their roles in the Cenozoic sulfurous oil reservoirs in the Southwestern Qaidam Basin, Western China.

The latest discovery of sulfurous natural gas marked a breakthrough in the Cenozoic natural gas exploration in the southwestern margin of Qaidam Basin. The 16S rRNA analyses were performed on the crude oil samples from H2S-rich reservoirs in the Yuejin, Shizigou and Huatugou profiles, to understand the sulfurous gas origin, which was also integrated with carbon and hydrogen isotopes of alkane and sulfur isotopes of H2S collected from the Yingxiongling Area. Results show that the microorganisms in samples can survive in the hypersaline reservoirs, and can be classified into multiple phyla, including Proteobacteria, Planctomycetes, Firmicutes, Bacteroidetes, and Haloanaerobiaeota. Methanogens are abundant in all of the three profiles, while sulfate-reducing bacteria are abundant in Yuejin and Huatugou profiles, contributing to the methane and H2S components in the natural gas. The carbon, hydrogen and sulfur isotopes of sulfurous natural gas in the Yingxiongling Area show that the natural gas is a mixture of coal-type gas and oil-type gas, which was primarily derived from thermal degradation, and natural gas from the Yuejin and Huatugou profiles also originated from biodegradation. The isotopic analysis agrees well with the 16S rRNA results, i.e., H2S-rich natural gas from the Cenozoic reservoirs in the southwest margin of the Qaidam Basin was primarily of thermal genesis, with microbial genesis of secondary importance.

Response of Microbial Communities on Cathode with Different Potentials in a Single-Chamber Reactor.

Microbes use both organic and inorganic compounds as electron donors, with different electronic potentials, to produce energy required for growth in environments. Conventional studies on the effects of different electron donors on microbial community has been extensively studied with a set cathode potential. However, it remains under-researched how a microbial community response to the different redox potentials in different environments. Here, we incubated a lake sediment in a single-chamber reactor equipped with three working electrodes, i.e., with potentials of - 0.29 V, - 0.05 V versus standard hydrogen electrode and open-circuit, respectively. Results reveal that the structure of bacterial communities was highly similar for all closed-circuit electrodes (- 0.29 V, - 0.05 V), while differing significantly from those on open-circuit electrodes. We also show that specific bacteria were preferentially enriched by different electrode potentials, i.e., Pseudomonas and Rhodobacter preferentially grew on - 0.05 V and - 0.29 V cathode potentials, Azospirillum and Bosea preferentially grew on - 0.05 V; while Ferrovibrio, Hydrogenophaga, Delftia, and Sphingobium preferentially grew on - 0.29 V. In addition, microorganisms selectively enriched on open-circuit electrodes possess higher connectivity and closer relationship than microorganisms selectively enriched on closed-circuit electrode.

Improvement of Surface-Enhanced Raman Scattering Method for Single Bacterial Cell Analysis.

Surface-enhanced Raman scattering (SERS) is a useful tool for label-free analysis of bacteria at the single cell level. However, low reproducibility limits the use of SERS. In this study, for the sake of sensitive and reproducible Raman spectra, we optimized the methods for preparing silver nanoparticles (AgNPs) and depositing AgNPs onto a cell surface. We found that fast dropwise addition of AgNO3 into the reductant produced smaller and more stable AgNPs, with an average diameter of 45 ± 4 nm. Compared with that observed after simply mixing the bacterial cells with AgNPs, the SERS signal was significantly improved after centrifugation. To optimize the SERS enhancement method, the centrifugal force, method for preparing AgNPs, concentration of AgNPs, ionic strength of the solution used to suspend the cells, and density of the cells were chosen as impact factors and optimized through orthogonal experiments. Finally, the improved method could generate sensitive and reproducible SERS spectra from single Escherichia coli cells, and the SERS signals primarily arose from the cell envelope. We further verified that this optimal method was feasible for the detection of low to 25% incorporation of 13C isotopes by the cells and the discrimination of different bacterial species. Our work provides an improved method for generating sensitive and reproducible SERS spectra.

[Effects of Microbial Diversity on Soil Carbon Mineralization].

Soil microbial community plays an important role in ecosystem functions; however, little is known about the importance of microbial diversity to the ecosystems. In this study, serial dilution of soil suspension (10-1, 10-3, and 10-5) was performed and inoculated into the sterilized soils that form the broadleaf mixed forests in Pangquangou. The change in the carbon mineralization rate and the pattern of the carbon source utilization were studied by titration, Biolog Eco, and other experimental methods. The results show that after being incubated for six weeks, carbon mineralization rate, the cumulative amount of carbon mineralization, average well color development (AWCD), and diversity index (Shannon, McIntosh, and richness index) of D1 were significantly higher than those of the D5 treatment. The cumulative amount of carbon mineralization and AWCD was strongly and inversely correlated with richness. Principal component analysis and one-way ANOVA also indicated that the patterns of carbon source utilization of microbially diverse soil were different. Therefore, the loss of microbial diversity affects the carbon mineralization rate and the pattern of carbon source utilization, leading to functional changes in terrestrial ecosystems. In the management of forest soils, the effects of soil microbial diversity on ecosystem functions should be considered.

Aggravation of Helicobacter pylori stomach infections in stressed military recruits.

OBJECTIVE: To investigate the effect of military stress on immune response and Helicobacter pylori stomach infections. METHODS: In this prospective, observational study, the Symptom Checklist-90 questionnaire was completed by military recruits before and following a 3-month basic training programme. H. pylori immunoglobulin (Ig)G levels, C(14)-urea breath-test values and levels of cortisol, catecholamine, and certain humoral and cellular immune responses were measured before and after the basic training. RESULTS: For 60 military recruits, somatization, depression and paranoid ideation scores were significantly increased after, compared with before, basic training. Post-training H. pylori IgG detection revealed three additional cases of H. pylori infection. Post-training C(14)-urea breath-test values were significantly higher compared with before training - thus suggesting higher levels of H. pylori colonization in the stomach. Post-training cortisol and catecholamine levels were increased, while serum IgG levels were decreased; complement component (C)3 and C4 levels remained unchanged. Post-training CD4(+) and CD8(+) T-cell percentages and the CD4(+)/CD8(+) ratio were significantly reduced compared with before training. Serum interleukin (IL)-2 levels were lower and IL-10 levels were higher following training and there was a significant decrease in the IL-2/IL-10 ratio. CONCLUSION: Military stress may reduce humoral and cellular immune responses and may aggravate the severity of H. pylori infection.

Upregulation of Tim-3 on CD4(+) T cells is associated with Th1/Th2 imbalance in patients with allergic asthma.

T cell Ig and mucin domain-containing molecule-3 (Tim-3) is a negative regulator preferentially expressed on Th1 cells. Allergic asthma is a clinical syndrome well characterized by Th1/Th2 imbalance. To investigate the role of Tim-3 in the pathogenesis of asthma and its relationship with Th1/Th2 imbalance, a total of 40 patients with allergic asthma and 40 healthy controls were enrolled. Expression of Tim-3 and Th1/Th2 imbalance as well as the relationship between them was analyzed by flow cytometry and real-time PCR. Peripheral blood mononuclear cells (PBMCs) were cultured in vitro and anti-Tim-3 was used to block Tim-3 signaling; Th1/Th2 cytokines in the culture supernatant were detected by enzyme linked immunosorbent assay (ELISA). CD4(+) T cells and B cells were sorted and co-cultured in vitro, and anti-Tim-3 was used to block Tim-3 signaling; Total IgG/IgE in the culture supernatant was detected by ELISA. The mRNA level of T-bet and IFN-γ were significantly decreased in allergic asthma patients, while GATA-3 and IL-4 were significantly increased. Expression of Tim-3 on CD4(+) T cells was much higher in allergic asthma patients and it was negatively correlated with T-bet/GATA-3 ratio or IFN-γ/IL-4 ratio. Blocking of Tim-3 significantly increased Th1 cytokines (TNF-α and IFN-γ) and decreased Th2 cytokines (IL-4, IL-5, IL-13) in the culture supernatant of PBMCs. Blocking of Tim-3 dramatically reduced the production of IgG and IgE in the co-culture supernatant of CD4(+) T cells and B cells. In conclusion, Tim-3 was up-regulated in allergic asthma patients and related with the Th1/Th2 imbalance. Blocking of Tim-3 may be of therapeutic benefit by enhancing the Th1 cytokines response, down-regulating the Th2 cytokines response, and reducing IgG/IgE production.