No abstract

Filamentous anoxygenic phototrophs (FAPs) are abundant members of microbial mat communities inhabiting neutral and alkaline geothermal springs. Natural populations of FAPs related to Chloroflexus spp. and Roseiflexus spp. have been well characterized in Mushroom Spring, where they occur with unicellular cyanobacteria related to Synechococcus spp. strains A and B 0 . Metatranscriptomic sequencing was applied to the microbial community to determine how FAPs regulate their gene expression in response to fluctuating environmental conditions and resource availability over a diel period. Transcripts for genes involved in the biosynthesis of bacteriochlorophylls (BChls) and photosynthetic reaction centers were much more abundant at night. Both Roseiflexus spp. and Chloroflexus spp. expressed key genes involved in the 3-hydroxypropionate (3-OHP) carbon dioxide fixation bi-cycle during the day, when these FAPs have been thought to perform primarily photoheterotrophic and/or aerobic chemoorganotrophic metabolism. The expression of genes for the synthesis and degradation of storage polymers, including glycogen, polyhydroxyalkanoates and wax esters, suggests that FAPs produce and utilize these compounds at different times during the diel cycle. We summarize these results in a proposed conceptual model for temporal changes in central carbon metabolism and energy production of FAPs living in a natural environment. The model proposes that, at night, Chloroflexus spp. and Roseiflexus spp. synthesize BChl, components of the photosynthetic apparatus, polyhydroxyalkanoates and wax esters in concert with fermentation of glycogen. It further proposes that, in daytime, polyhydroxyalkanoates and wax esters are degraded and used as carbon and electron reserves to support photomixotrophy via the 3-OHP bi-cycle.

An uncultured member of the phylum Chlorobi, provisionally named ‘Candidatus Thermochlorobacter aerophilum’, occurs in the microbial mats of alkaline siliceous hot springs at the Yellowstone National Park. ‘Ca. T. aerophilum’ was investigated through metagenomic and metatranscriptomic approaches. ‘Ca. T. aerophilum’ is a member of a novel, family-level lineage of Chlorobi, a chlorophototroph that synthesizes type-1 reaction centers and chlorosomes similar to cultivated relatives among the green sulfur bacteria, but is otherwise very different physiologically. ‘Ca. T. aerophilum’ is proposed to be an aerobic photoheterotroph that cannot oxidize sulfur compounds, cannot fix N2, and does not fix CO2 autotrophically. Metagenomic analyses suggest that ‘Ca. T. aerophilum’ depends on other mat organisms for fixed carbon and nitrogen, several amino acids, and other important nutrients. The failure to detect bchU suggests that ‘Ca. T. aerophilum’ synthesizes bacteriochlorophyll (BChl) d, and thus it occupies a different ecological niche than other chlorosome-containing chlorophototrophs in the mat. Transcription profiling throughout a diel cycle revealed distinctive gene expression patterns. Although ‘Ca. T. aerophilum’ probably photoassimilates organic carbon sources and synthesizes most of its cell materials during the day, it mainly transcribes genes for BChl synthesis during late afternoon and early morning, and it synthesizes and assembles its photosynthetic apparatus during the night.

Microbial eukaryotes fulfill key ecological positions in marine food webs. Molecular approaches that connect protistan diversity and biogeography to their diverse metabolisms will greatly improve our understanding of marine ecosystem function. The majority of molecular-based studies to date use 18S rRNA gene sequencing to characterize natural microbial assemblages, but this approach does not necessarily discriminate between active and non-active cells. We incorporated RNA sequencing into standard 18S rRNA gene sequence surveys with the purpose of assessing those members of the protistan community contributing to biogeochemical cycling (active organisms), using the ratio of cDNA (reverse transcribed from total RNA) to 18S rRNA gene sequences within major protistan taxonomic groups. Trophically important phytoplankton, such as diatoms and chlorophytes exhibited seasonal trends in relative activity. Additionally, both radiolaria and ciliates displayed previously unreported high relative activities below the euphotic zone. This study sheds new light on the relative metabolic activity of specific protistan groups and how microbial communities respond to changing environmental conditions.

The phototrophic microbial mat community of Mushroom Spring, an alkaline siliceous hot spring in Yellowstone National Park, was studied by metatranscriptomic methods. RNA was extracted from mat specimens collected at four timepoints during light-to-dark and dark-to-light transitions in one diel cycle, and these RNA samples were analyzed by both pyrosequencing and SOLiD technologies. Pyrosequencing was used to assess the community composition, which showed that B84% of the rRNA was derived from members of four kingdoms Cyanobacteria, Chloroflexi, Chlorobi and Acidobacteria. Transcription of photosynthesis-related genes conclusively demonstrated the phototrophic nature of two newly discovered populations; these organisms, which were discovered through metagenomics, are currently uncultured and previously undescribed members of Chloroflexi and Chlorobi. Data sets produced by SOLiD sequencing of complementary DNA provided 4100-fold greater sequence coverage. The much greater sequencing depth allowed transcripts to be detected from B15 000 genes and could be used to demonstrate statistically significant differential transcription of thousands of genes. Temporal differences for in situ transcription patterns of photosynthesis-related genes suggested that the six types of chlorophototrophs in the mats may use different strategies for maximizing their solar-energy capture, usage and growth. On the basis of both temporal pattern and transcript abundance, intra-guild gene expression differences were also detected for two populations of the oxygenic photosynthesis guild. This study showed that, when community-relevant genomes and metagenomes are available, SOLiD sequencing technology can be used for metatranscriptomic analyses, and the results suggested that this method can potentially reveal new insights into the ecophysiology of this model microbial community.

BackgroundThe prevalence of HIV among men who have sex with men (MSM) has become a significant public health challenge. The aim was to comprehensively estimate the national prevalence of HIV among MSM and its time trends through a large-scale systematic analysis.MethodsSystematic search of Cochrane Library, PubMed, EMBASE, CNKI, VIP, and Wanfang Data databases without language restriction for studies on the prevalence of HIV among MSM published before Dec.31, 2018. Studies were eligible for inclusion if they were published in the peer-reviewed literature and used validated assessment methods to assess the prevalence of HIV among MSM. Estimates were pooled using random-effects analysis.ResultsData were extracted from 355 cross-sectional studies (571,328 individuals) covered 59 cities from 30 provinces and municipalities of China. The overall national prevalence of HIV among MSM from 2001 to 2018 was estimated to be 5.7% (95% CI: 5.4–6.1%), with high between-study heterogeneity (I2 = 98.0%, P <  0.001). Our study showed an increased tendency in the HIV prevalence as time progressed by meta-regression analysis (I2 = 95.9%, P <  0.0001). HIV prevalence was the highest in those aged 50 years and older with HIV prevalence of 19.3% (95%CI: 13.1-27.4%, N = 13). HIV was more prevalent in the illiterate population (16.8%), than in those who had received an education. Although the internet was a major venue for Chinese MSM seeking male sex partners (35.6, 95%CI: 32.3-39.9%, N = 101), seeking MSM in bathhouses/saunas had the highest associated prevalence of HIV (13.4, 95%CI: 10.3-17.1%, N = 22). The HIV prevalence among MSM varied by location: compared with other regions in China, HIV was highly prevalent among MSM in the southwest (10.7, 95%CI: 9.3-12.2%, N = 91). Compared to participants who sometimes or always used condoms, participants who had never used a condom in the past 6 months had a higher risk of HIV infection, with odds ratios of 0.1 (95%CI: 0.08-0.14).ConclusionsOur analysis provided reliable estimates of China’s HIV burden among MSM, which appears to present an increasing national public health challenge. Effective government responses are needed to address this challenge and include the implementation of HIV prevention.

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FDG-PET is especially effective in detecting patients with elevated thyroglobulin levels and normal radioiodine WBS; FDG-PET/CT is a more sensitive method in the follow-up of thyroid cancer recurrence or metastases, particularly in those with negative WBS.