Assessment of Bacterial and Fungal Aerosol in Different Residential Settings

The concentration and size distribution of bacterial and fungal aerosol was studied in 15 houses. The houses were categorized into three types, based on occupant density and number of rooms: single room in shared accommodation (type I), single bedroom flat in three storey buildings (type II) and two or three bedroomed houses (type III). Sampling was undertaken with an Anderson six-stage impactor during the summer of 2007 in the living rooms of all the residential settings. The maximum mean geometric concentration of bacterial (5,036 CFU/m³, ± 2.5, n?=?5) and fungal (2,124 CFU/m³, ± 1.38, n?=?5) aerosol were in housing type III. The minimum levels of indoor culturable bacteria (1,557 CFU/m³, ±1.5, n?=?5) and fungal (925 CFU/m³, ±2.9, n?=?5) spores were observed in housing type I. The differences in terms of total bacterial and fungal concentration were less obvious between housing types I and II as compared to type III. With reference to size distribution, the dominant stages for culturable bacteria in housing types I, II and III were stage 3 (3.3–4.7 μm), stage 1 (7 μm and above) and stage 5 (1.1–2.1 μm), respectively. Whereas the maximum numbers of culturable fungal spores were recovered from stage 2 (4.7–7 µm), in housing type I, and from stage 4 (2.1–3.3 μm) in both type II and III houses. The average geometric mean diameter of bacterial aerosol was largest in type I (4.7 μm), followed by type II (3.89 μm) and III (1.96 μm). Similarly, for fungal spores, type I houses had the highest average mean geometric diameter (4.5 μm), while in types II and III the mean geometric diameter was 3.57 and 3.92 μm, respectively. The results indicate a wide variation in total concentration and size of bioaerosols among different residential settings. The observed differences in the size distributions and concentrations reflect their variable airborne behaviour and, as a result, different risks of respiratory exposure of the occupants to bioaerosols in various residential settings.     

Evidence of Elevated Ozone Concentrations on Forested Slopes of the Lower Fraser Valley, British Columbia, Canada

During the summers of 2001 and 2002, hourly average ozone concentrations were measured at three sites of differing elevation (188, 588, and 1221 m.a.s.l.) on the forested south-facing slopes of the Lower Fraser Valley (LFV), British Columbia. Sites experienced ozone concentrations ranging from 0 to 88 ppb in 2001, and 0 to 96 ppb in 2002. Daily patterns were in agreement with previous studies showing morning increases and late afternoon peaks. Reduced diurnal variation increased the exposure of higher-elevation forested sites. An upper-level ridge coinciding with a thermal coastal trough caused above-average ozone concentrations, and the ‘maximum acceptable’ 1-hour National Ambient Air Quality Objective (AQO) of 82 ppb to be exceeded. Maximum ozone concentrations and AQO exceedance frequency both increased with distance eastward in the valley. A preliminary survey of ozone-like injury symptoms on native shrubs suggested that the elevated ozone levels occurring in the LFV may cause injury to forest plants.     

Survival of bacterial DNA and culturable bacteria in archived soils from the Rothamsted Broadbalk experiment

Dried soil samples from many sources have been stored in archives world-wide over the years, but there has been little research on their value for studying microbial populations. Samples collected since 1843 from the Broadbalk field experiment on crop nutrition at Rothamsted have been used to document changes in the structure and composition of soils as agricultural practices evolve, also offering an invaluable record of environmental changes from the pre- to post-industrial era in the UK. To date, the microbial communities of these soils have not been studied, in part due to the well-documented drop in bacterial culturability in dried soils. However, modern molecular methods based on PCR amplification of DNA extracted directly from soil do not require bacterial cells to be viable or intact and may allow investigations into the legacy of bacteria that were present at the time of sample collection.

In a preliminary study, to establish if dried soils can provide a historical record of bacterial communities, samples from the Broadbalk soil archive dating back to 1868 were investigated and plots treated with either farmyard manure (FYM) or inorganic fertilizer (NPK) were compared. As anticipated, the processes of air-drying and milling greatly reduced bacterial viability whilst DNA yields declined less and may be preserved by desiccation. A higher proportion of culturable bacteria survived the archiving process in the FYM soil, possibly protected by the increased soil organic matter. The majority of surviving bacteria were firmicutes, whether collected in 2003 or in 1914, but a wide range of genera was detected in DNA extracted from the samples using PCR and DGGE of 16S rRNA genes. Analysis of DGGE band profiles indicated that the two plots maintained divergent populations. Sequence analysis of bands excised from DGGE gels, from a sample collected in 1914, revealed DNA from - and β-proteobacteria as well as firmicutes. PCR using primers specific for ammonia oxidizing bacteria showed similar band profiles across the two treatments in recently collected samples, however older samples from the NPK plot showed greater divergence. Primers specific for the genus Pseudomonas were designed and used in real-time quantitative PCR to indicate that archived soil collected in 1868 contained 10-fold less pseudomonad DNA than fresh soil, representing around 10⁵ genomes g⁻¹ soil. Prior to milling, dramatically less pseudomonad DNA was extracted from recently collected air-dried soil from the NPK compared to the FYM plot; otherwise, the two plots followed similar trends. Overall bacterial abundance, diversity and survival during the archiving process differed in the two soils, possibly due to differences in clay and soil organic matter content. Nevertheless, the results demonstrate that air-dried soils can protect microbial DNA for more than 150 years and offer an invaluable resource for future research.     

Starving the soil of plant inputs for 50 years reduces abundance but not diversity of soil bacterial communities

If soil communities rely on plant-derived carbon, is biodiversity lost when this primary source is removed? Soil microbial and mesofaunal communities at the Rothamsted Highfield site were compared under a mixed grass sward, arable rotation and a section maintained as a bare-fallow for the past 50 years by regular tillage. Organic matter reserves have been degraded and microbial and mesofaunal numbers and mite diversity have declined in this unique bare-fallow site, where fresh carbon inputs have been drastically reduced. However, it supports a species-rich metabolically active bacterial community of similar diversity to that in soil maintained as grass sward. Thus in contrast to soil mesofauna, bacterial diversity (but not abundance) is apparently independent of plant inputs.     

Seasonal speedup along the western flank of the Greenland Ice Sheet

It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice-bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic-scale view, spanning ice-sheet to outlet-glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups (50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller (<15%). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet-glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice-sheet flow.     

Aerobic microbial respiration in 86-million-year-old deep-sea red clay

Microbial communities can subsist at depth in marine sediments without fresh supply of organic matter for millions of years. At threshold sedimentation rates of 1 millimeter per 1000 years, the low rates of microbial community metabolism in the North Pacific Gyre allow sediments to remain oxygenated tens of meters below the sea floor. We found that the oxygen respiration rates dropped from 10 micromoles of O(2) liter(-1) year(-1) near the sediment-water interface to 0.001 micromoles of O(2) liter(-1) year(-1) at 30-meter depth within 86 million-year-old sediment. The cell-specific respiration rate decreased with depth but stabilized at around 10(-3) femtomoles of O(2) cell(-1) day(-1) 10 meters below the seafloor. This result indicated that the community size is controlled by the rate of carbon oxidation and thereby by the low available energy flux.     

The transmission of geminiviruses by Bemisia tabaci

The cosmopolitan whitefly species, Bemisia tabaci (Gennadius) and Trialeurodes taporariorum (Westwood) have always been regarded as pests to a large range of worldwide crops. Both species are capable of transmitting plant viruses, with T. vaporariorum being the vector of only a few ‘clostero’-like viruses and B. tabaci the vector of viruses in several groups. The largest group of viruses transmitted by B. tabaci are the geminiviruses and B. tabaci is known to transmit around 60 members. Until recently, B. tabaci had been associated with only a limited range of host plants within any one region, although its total potential host range was large. Virus transmission was confined within the plant host range of each regional population of B. tabaci. The emergence of the polyphagous ‘B’ biotype of B. tabaci with its increased host range of more than 600 plant species, has resulted in geminiviruses infecting previously unaffected crops. As the ‘B’ biotype spreads further into Europe, European field and glasshouse crops have been shown to be susceptible to whitefly-transmitted viruses already endemic to other parts of the world. More than 20 colonies of B. tabaci, including both ‘B’ and non-‘B’ biotypes from disparate global locations have been compared for their ability to transmit more than 20 geminiviruses. All but two highly host-specific colonies were capable of transmitting most geminiviruses tested. However, some viruses were transmitted more efficiently than others. The virus coat protein or capsid is essential for vector recognition and transmission. By comparing transmissible viruses at the molecular level to viruses that are no longer whitefly-transmissible, the active epitope on the virus coat protein could be identified for designing future virus control strategies.