Total (as opposed to culturable) bacterial number counts are reported for four sites in the United Kingdom measured during campaigns over four separate seasons. These are interpreted in relation to simple climatic factors, i.e. temperature, wind speed and wind direction. Temperature has a marked effect at all four sites with data for a rural coastal site conforming best to a simple exponential model. Data for the other rural and urban locations show a baseline similar to that determined at the coastal rural location, but with some very significant positive excursions. The temperature dependence of bacterial number is found to conform to that typical of bacterial growth rates. At the coastal rural location, bacterial numbers normalised for temperature show no dependence on wind speed whilst at the inland sites there is a decrease with increasing wind speed of the form expected for a large area source. Only one site appeared to show a systematic relationship of bacterial concentrations to wind direction that being a site in the suburbs of Birmingham with highest number concentrations observed on a wind sector approaching from the city centre. PCR techniques have been used to identify predominant types of bacteria and results are presented which show that Bacillus was the dominant genus observed at the three inland sites during the winter and summer seasons. Pseudomonas appeared with comparable frequency at certain sites and seasons. There was in general a greater diversity of bacteria at the coastal site than at the inland sites.
Resistance to Cr(VI) is usually associated with its cellular exclusion, precluding enrichment techniques for the isolation of organisms accumulating Cr(VI) via bioreduction to insoluble Cr(III). A technique was developed to screen for potential Cr(VI) reduction in approx. 2000 isolates from a coastal environment, based on the non-specific reduction of selenite and tellurite to Se0 and Te0, and reduction of tetrazolium blue to insoluble blue formazan. The most promising strains were further screened in liquid culture, giving three, which were identified by 16S rRNA sequence analysis as Bacillus pumilus, Exiguobacterium aurantiacum and Pseudomonas synxantha, all of which reduced 100 microM Cr(VI) anaerobically, without growth. The respective removal of Cr(VI) was 90% and 80% by B. pumilus and E. aurantiacum after 48 h and 80% and by P. synxantha after 192 h. With the gram positive strains Cr(VI) promoted loss of flagella and, in the case of B. pumilus, lysis of some cells, but Cr was deposited as an exocellular precipitate which was identified as containing Cr and P using energy dispersive X-ray microanalysis (EDAX). This prompted the testing of Citrobacter sp. N14 (subsequently re-assigned by 16S rRNA sequence analysis and biochemical studies as a strain of Serratia) which bioprecipitates metal cation phosphates via enzymatically-liberated phosphate. This strain reduced Cr(VI) at a rate comparable to that of P. synxantha but Cr(III) was not bioprecipitated where La(III) was removed as LaPO4, even though a similar amount of phosphate was produced in the presence of Cr(III). Since B. pumilus removed most of the Cr(VI), with the formation of cell-bound CrPO4 implicated, this suggests that this strain could have future bioprocess potential.
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