Seasonal taxonomic composition of microbial communal shaping the bioaerosols milieu of the urban city of Lanzhou

Here, the taxonomical composition and seasonal dynamics of airborne microbial communities were described in the urban city of Lanzhou, Northwest China. Year-long samples were studied in two filter membranes (Quartz and PTFE). Higher microbial loads were reported in the PTFE than in the quartz filter. Onefold decrease was reported in bacterial loads in spring and summer than winter and autumn for both filters. The fungal loadings were lowest during winter and highest during autumn, followed by summer. The microbial communities included Actinobacteria and Proteobacteria, Ascomycota, and Basidiomycota as major components. Maximum abundance of the members from Gammaproteobacteria, Coriobacteria and Clostridia were studied in all seasons on PTFE membrane, followed by, Erysipelotrichia, Negativicutes and Fusobacteria. Members of Actinobacteria and Bacilli showed higher abundance in spring and winter, with a small proportion during autumn. Members of Clostridia, Gammaproteobacteria, Bacilli, and Actinobacteria showed maximum abundance on the quartz filter in all the seasons. Similarly, on the PTFE, fungi including Dothideomycetes and Agaricomycetes were dominant, followed by Saccharomycetes during summer and winter. The result showed that PM_2.5, SO₄^2-, NO₂^-, Na⁺, EC, and OC are important environmental parameters influencing the seasonal microbial community. However, the relation of the microbiome with the environment cannot be confidently defined because the environmental factors are changeable and yet interrelated.

Concentration, sources and wet deposition of dissolved nitrogen and organic carbon in the Northern Indo-Gangetic Plain during monsoon

Precipitation represents an important phenomenon for carbon and nitrogen deposition. Here, the concentrations and fluxes of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) with their potential sources were analyzed in wet precipitation during summer monsoon from the Northern Indo-Gangetic Plain (IGP), important but neglected area. The volume-weighted mean (VWM) concentration of DOC and TDN were 687.04 and 1210.23 µg/L, respectively. Similarly, the VWM concentration of major ions were in a sequence of NH₄⁺ > Ca²⁺ > SO₄^2- > Na⁺ > K⁺ > NO₃^- > Cl^- > Mg²⁺ > F^- > NO₂^-, suggesting NH₄⁺ and Ca²⁺ from agricultural activities and crustal dust played a vital role in precipitation chemistry. Moreover, the wet deposition flux of DOC and TDN were 9.95 and 17.06 kg/(ha⋅year), respectively. The wet deposition flux of inorganic nitrogen species such as NH₄⁺-N and NO₃^--N were 14.31 and 0.47 kg/(ha⋅year), respectively, demonstrating the strong influence of emission sources and precipitation volume. Source attribution from different analysis suggested the influence of biomass burning on DOC and anthropogenic activities (agriculture, animal husbandry) on nitrogenous species. The air-mass back trajectory analysis indicated the influence of air masses originating from the Bay of Bengal, which possibly carried marine and anthropogenic pollutants along with the biomass burning emissions to the sampling site. This study bridges the data gap in the less studied part of the northern IGP region and provides new information for policy makers to deal with pollution control.

Bacterial Diversity and Communities Structural Dynamics in Soil and Meltwater Runoff at the Frontier of Baishui Glacier No.1, China

Comprehensive knowledge of bacterial ecology mainly in supraglacial habitats is pivotal particularly at the frontier of accelerated glacier retreat. In this study, bacterial diversity and community composition in glacial soil and meltwater runoff at the frontier of Baishui Glacier No.1 were evaluated using high throughput sequencing. Significant variations in the physiochemical parameters formed an ecological gradient between soil and meltwater runoff. Based on the richness and evenness indexes, the bacterial diversity was relatively higher in soil compared with meltwater runoff. Hierarchical clustering and bi-plot ordination revealed that the taxonomic composition of soil samples was highly similar and significantly influenced by the ecological parameters than the meltwater runoff. The overall relative abundance trend of bacterial phyla and genera were greatly varied in soil and water samples. The relative abundance of Proteobacteria was higher in water runoff samples (40.5-87%) compared with soil samples (32-52.7%). Proteobacteria, Firmicutes, and a little part of Cyanobacteria occupied a major portion of water runoff while the soil was dominated by Acidobacteria (6-16.2%), Actinobacteria (5-16%), Bacteroidetes (0.5-8.8%), and Cyanobacteria (0.1-8.3%) besides Proteobacteria and Firmicutes. Higher numbers of biomarkers were found in soil group compared with the water group. The study area is diverse in terms of richness, while community structures are not evenly distributed. This study provides a preliminary understanding of the bacterial diversity and shifts in community structure in soil and meltwater runoff at the frontier of the glacial. The findings revealed that the environmental factors are a significantly strong determinant of bacterial community structures in such a closely linked ecosystem.

Microbial mercury methylation in the cryosphere: Progress and prospects

Mercury (Hg) is one of the most toxic heavy metals, and its cycle is mainly controlled by oxidation-reduction reactions carried out by photochemical or microbial process under suitable conditions. The deposition and accumulation of methylmercury (MeHg) in various ecosystems, including the cryospheric components such as snow, meltwater, glaciers, and ice sheet, and subsequently in the food chain pose serious health concerns for living beings. Unlike the abundance of knowledge about the processes of MeHg production over land and oceans, little is known about the sources and production/degradation rate of MeHg in cryosphere systems. In addition, processes controlling the concentration of Hg and MeHg in the cryosphere remains poorly understood, and filling this scientific gap has been challenging. Therefore, it is essential to study and review the deposition and accumulation by biological, physical, and chemical mechanisms involved in Hg methylation in the cryosphere. This review attempts to address knowledge gaps in understanding processes, especially biotic and abiotic, applicable for Hg methylation in the cryosphere. First, we focus on the variability in Hg concentration and mechanisms of Hg methylation, including physical, chemical, microbial, and biological processes, and transportation in the cryosphere. Then, we elaborate on the mechanism of redox reactions and biotic and abiotic factors controlling Hg methylation and biogeochemistry of Hg in the cryosphere. We also present possible mechanisms of Hg methylation with an emphasis on microbial transformation and molecular function to understand variability in Hg concentration in the cryosphere. Recent advancements in the genetic and physicochemical mechanisms of Hg methylation are also presented. Finally, we summarize and propose a method to study the unsolved issues of Hg methylation in the cryosphere.

Culture-dependent diversity of bacteria from Laohugou glacier, Qilian Mts., China and their resistance against metals

In the current study, psychrophilic, endolithic, and epilithic bacterial strains were isolated and characterized from the nonpolar Laohugou glacier (LHG) no. 12, the largest valley glacier in the western Qilian Mts. located on the northeastern edge of the Tibetan Plateau. Five different types of samples, rocks, soil, glacial water, ice/snow, and cryoconite, were collected. A total of 48 bacterial strains were isolated by using the R2A bacterial cultural medium. The findings revealed that the Gram-positive bacteria 41 (85.4%) dominated the Gram-negative bacteria 7 (14.6%) in this extremely harsh environment. Molecular characterization based on 16S ribosomal RNA gene sequencing exhibited that the obtained isolates belong to four phyla, among which the diversity of Firmicutes (58.33%) was higher followed by Actinobacteria (23.0%), Proteobacteria (14.6%), and least diversity was reported in Euryarchaeota (4.2%). The bacterial communities were most dominant in soil samples followed by cryoconite sample and least dominant in the ice and snow samples. Moreover, the obtained bacterial isolates were found resistant to high concentrations of heavy metals (Cr³⁺ , Cd²⁺ , Hg²⁺ , and Ar³⁺ ) and sodium chloride, and, therefore, exhibited polyextremophilic characteristics. LHG no. 12 is rich in bacterial and archaeal diversities and provides a potentially curious site for further in-depth exploration of microbial diversity and their biotechnological applications.

Spatial and temporal distribution of total mercury in atmospheric wet precipitation at four sites from the Nepal-Himalayas

The studies on global pollutant mercury (Hg), which is of public concern due to its high toxicity and capacity to long-range transport via atmospheric circulation, is poorly characterized in wet deposition over the Nepal-Himalayas region. Therefore, in order to understand the concentration levels, spatial distribution and seasonal variation of total Hg, 333 precipitation samples were collected from south to north: Kathmandu (1314 m a.s.l.), Dhunche (2065 m a.s.l.), Dimsa (3078 m a.s.l.) and Gosainkunda (4417 m a.s.l.) characterized as urban, rural, remote forest and remote alpine sites, respectively, for over one-year period. The highest Hg concentration was found in Kathmandu comparable to the urban sites worldwide, and significantly lower concentrations at other three sites demonstrated similar levels as in rural and remote alpine sites worldwide. Higher wet deposition fluxes of 34.91 and 15.89 μg m^-2 year^-1 were found in Kathmandu and Dhunche respectively, due to higher precipitation amount. Clear and distinct seasonal differences were observed with higher concentrations in non-monsoon and lower values in monsoon periods due to less scavenging and high pollutant concentration loadings during the dry period. The positive correlation of Hg flux and precipitation amount with Hg concentration suggested that both precipitation amount and Hg concentration plays a vital role in Hg deposition in the central Himalayan region. Enrichment factor (EF_Hg) indicated that the anthropogenic emission sources play a significant role for Hg enrichment and a high ratio of EF_monsoon to EF_non-monsoon (>2.18) suggested that the anthropogenic atmospheric mercury could likely be long-range transported from south Asian regions to the Himalayas during the monsoon season. In addition, our results showed that the major ionic compositions (e.g., SO₄^2-, NO₃^-, NH₄⁺, K⁺, Ca²⁺) could influence Hg concentration in wet precipitation. The anthropogenic sources of Hg such as biomass and fossil fuel combustion, crustal aerosols may contribute to the Hg concentration in wet precipitation over the central Himalayas.

Insight into Enzymatic Degradation of Corn, Wheat, and Soybean Cell Wall Cellulose Using Quantitative Secretome Analysis of Aspergillus fumigatus

Lignocelluloses contained in animal forage cannot be digested by pigs or poultry with 100% efficiency. On contrary, Aspergillus fumigatus, a saprophytic filamentous fungus, is known to harbor 263 glycoside hydrolase encoding genes, suggesting that A. fumigatus is an efficient lignocellulose degrader. Hence the present study uses corn, wheat, or soybean as a sole carbon source to culture A. fumigatus under animal physiological condition to understand how cellulolytic enzymes work together to achieve an efficient degradation of lignocellulose. Our results showed that A. fumigatus produced different sets of enzymes to degrade lignocelluloses derived from corn, wheat, or soybean cell wall. In addition, the cellulolytic enzymes produced by A. fumigatus were stable under acidic condition or at higher temperatures. Using isobaric tags for a relative and absolute quantification (iTRAQ) approach, a total of ∼600 extracellular proteins were identified and quantified, in which ∼50 proteins were involved in lignocellulolysis, including cellulases, hemicellulases, lignin-degrading enzymes, and some hypothetical proteins. Data are available via ProteomeXchange with identifier PXD004670. On the basis of quantitative iTRAQ results, 14 genes were selected for further confirmation by RT-PCR. Taken together, our results indicated that the expression and regulation of lignocellulolytic proteins in the secretome of A. fumigatus were dependent on both nature and complexity of cellulose, thus suggesting that a different enzyme system is required for degradation of different lignocelluloses derived from plant cells. Although A. fumigatus is a pathogenic fungus and cannot be directly used as an enzyme source, as an efficient lignocellulose degrader its strategy to synergistically degrade various lignocelluloses with different enzymes can be used to design enzyme combination for optimal digestion and absorption of corn, wheat, or soybean that are used as forage of pig and poultry.