Wet deposition scavenges particles and particle-associated bacteria from the air column, but the impact of raindrops on various surfaces on Earth causes emission of surface-associated bacteria into the air column. Thus, after rainfall, these two mechanisms are expected to cause changes in airborne bacterial community composition (BCC). In this study, aerosol samples were collected at a suburban site in Seoul, Korea before and after three heavy rainfall events in April, May, and July 2011. BCC was investigated by pyrosequencing the 16S rRNA gene in aerosol samples. Interestingly, the relative abundance of non-spore forming Actinobacteria operational taxonomic units (OTUs) was always higher in post-rain aerosol samples. In particular, the absolute and relative abundances of airborne Propionibacteriaceae always increased after rainfall, whereas those of airborne Firmicutes, including Carnobacteriaceae and Clostridiales, consistently decreased. Marine bacterial sequences, which were temporally important in aerosol samples, also decreased after rainfall events. Further, increases in pathogen-like sequences were often observed in post-rain air samples. Rainfall events seemed to affect airborne BCCs by the combined action of the two mechanisms, with potentially adverse effects on human and plant health.
Bangladesh is currently the subject of the world's largest mass arsenic poisoning in history. Groundwater throughout Bangladesh
and West Bengal is contaminated with naturally occurring arsenic from the alluvial and deltaic sediments that form the region's
aquifers. It has been estimated that 75 million people are at risk of developing health effects associated with the ingestion
of arsenic. This project focuses on the use of microorganisms such as bacteria and algae to remove arsenic from water. Arsenic
in the arsenite form was used in the studies. Experiments were conducted with a common alga and wastewater bacteria. A common
green algae Scenedesmus abundans was used for determining arsenic uptake in batch experiments. Results of the experiments indicated that the algae biosorption
could be modeled by the conventional Langmuir isotherm model. Algae morphology studies indicated that the algae cells were
impacted due to the presence of arsenic as evidenced by clumping or loss of cell clusters. The wastewater bacteria also were
capable of high percent of arsenic removal. Results indicate that microbial uptake of arsenic may be a viable method of pretreatment
of arsenic contaminated water. However algae and sludge disposal would pose a problem and will have to be dealt with accordingly. 相似文献
The effects of Cd^2+ and Cu^2+ at 300 mg/L on anaerobic microbial communities that degrade 2-cholorophenol (2-CP) were examined. Based on the polymerase chain reaction (PCR) of 16S rDNA, bacterial community diversity and archaeal community structure were analyzed with denaturing gradient gel electrophoresis (DGGE) and cloning, respectively. Degradation capabilities of the anaerobic microbial community were drastically abated and the degradation efficiency of 2-CP was reduced to 60% after shock by Cu^2+ and Cd^2+, respectively. The bacterial community structure was disturbed and the biodiversity was reduced after shock by Cu^2+ and Cd^2+ for 3 d. Some new metal-resistant microbes which could cope with the new condition appeared. The sequence analysis showed that there existed common Archaea species in control sludge and systems when treated with Cu^2+ and Cd^2+, such as Methanothrix soehngenii, Methanosaeta concilii, uncultured euryarchaeote, and so on. Both the abundance and diversity of archaeal species were altered with addition of Cd^2+ and Cu^2+ at high concentration. Although the abundance of the predominant archaeal species decreased with Cd^2+ and Cu^2+ addition for 3 d, they recovered to some extent after 10 d. The diversity of archaeal species was remarkably reduced after recovery for 10 d and the shift in archaeal composition seemed to be irreversible. The 2-CP-degradation anaerobic system was more sensitive to Cu^2+ than Cd^2+. 相似文献
This study aimed to evaluate the suitability of two bioaerosol generation systems(dry and wet generation) for the aerosolization of microorganisms isolated from the International Space Station, and to calibrate the produced bioaerosols to fulfill the requirements of computational fluid dynamics model(CFD) validation. Concentration, stability, size distribution, agglomeration of generated bioaerosol and deposition of bioaerosols were analyzed. In addition, the dispersion of non-viable particles in the air was studied.Experiments proved that wet generation from microbial suspensions could be used for the production of well-calibrated and stabile bioaerosols for model validation. For the simulation of the natural release of fungal spores, a dry generation method should be used. This study showed that the used CFD model simulated the spread of non-viable particles fairly well. The mathematical deposition model by Lai and Nazaroff could be used to estimate the deposition velocities of bioaerosols on surfaces, although it somewhat underestimated the measured deposition velocities. 相似文献
Microorganisms are the most ancient cells on this planet and they include key phyla for understanding cell evolution and Earth
history, but, unfortunately, their microbial records are scarce. Here, we present a critical review of fossilized prokaryotic
and eukaryotic microorganisms entrapped in Cretaceous ambers (but not exclusively from this geological period) obtained from
deposits worldwide. Microbiota in ambers are rather diverse and include bacteria, fungi, and protists. We comment on the most
important microbial records from the last 25 years, although it is not an exhaustive bibliographic compilation. The most frequently
reported eukaryotic microfossils are shells of amoebae and protists with a cell wall or a complex cortex. Likewise, diverse
dormant stages (palmeloid forms, resting cysts, spores, etc.) are abundant in ambers. Besides, viral and protist pathogens
have been identified inside insects entrapped in amber. The situation regarding filamentous bacteria and fungi is quite confusing
because in some cases, the same record was identified consecutively as a member of these phylogenetically distant groups.
To avoid these identification errors in the future, we propose to apply a more resolute microscopic and analytical method
in amber studies. Also, we discuss the most recent findings about ancient DNA repair and bacterial survival in remote substrates,
which support the real possibility of ancient DNA amplification and bacterial resuscitation from Cretaceous resins. 相似文献
The aim of this work is to identify the range of applicability of Arrhenius type temperature dependence for Ammonia Oxidizing Bacteria (AOB) subjected to temperature time gradients through continuous titrimetric tests. An innovative online differential titrimetric technique was used to continuously monitor the maximum biologic ammonia oxidation rate of the biomass selected in a pilot scale membrane bioreactor, as a function of temperature time gradients. The monitoring technique is based on the measurement of alkalinity and hydrogen peroxide consumption rates in two parallel reactors operated in non-limiting substrate conditions for AOB; both reactors were continuously fed with mixed liquor and in one of them AOB were inhibited with allylthiourea. The effects of temperature decrease rates in the range 1 to 4°C·h−1 were evaluated by controlling the titrimetric reactor in the temperature range 10°C–20°C. The dependence of growth kinetics on temperature time gradients and the range of applicability of Arrhenius model for temperature dependency of AOB growth kinetics were assessed. The Arrhenius model was found to be accurate only with temperature gradients lower than 2°C·h−1. The estimated Arrhenius coefficients (θ) were shown to increase from 1.07 to 1.6 when the temperature decrease rate reached 4°C·h−1. 相似文献