Spatial and Temporal Analysis of the Microbial Community in Slow Sand Filters Used for Treating Horticultural Irrigation Water

Abstract

An experimental slow sand filter (SSF) was constructed to study the spatial and temporal structure of a bacterial community suppressive to an oomycete plant pathogen, Phytophthora cryptogea. Passage of water through the mature sand column resulted in complete removal of zoospores of the plant pathogen. To monitor global changes in the microbial community, bacterial and fungal numbers were estimated on selective media, direct viable counts of fungal spores were made, and the ATP content was measured. PCR amplification of 16S rRNA genes and denaturing gradient gel electrophoresis (DGGE) were used to study the dynamics of the bacterial community in detail. The top layer (1 cm) of the SSF column was dominated by a variable and active microbial population, whereas the middle (50 cm) and bottom (80 cm) layers were dominated by less active and diverse bacterial populations. The major changes in the microbial populations occurred during the first week of filter operation, and these populations then remained to the end of the study. Spatial and temporal nonlinear mapping of the DGGE bands provided a useful visual representation of the similarities between SSF samples. According to the DGGE profile, less than 2% of the dominating bands present in the SSF column were represented in the culturable population. Sequence analysis of DGGE bands from all depths of the SSF column indicated that a range of bacteria were present, with 16S rRNA gene sequences similar to groups such as Bacillus megaterium, Cytophaga, Desulfovibrio, Legionella, Rhodococcus rhodochrous, Sphingomonas, and an uncharacterized environmental clone. This study describes the characterization of the performance, and microbial composition, of SSFs used for the treatment of water for use in the horticultural industry. Utilization of naturally suppressive population of microorganisms either directly or by manipulation of the environment in an SSF may provide a more reproducible control method for the future.Fungal plant diseases are a major problem within the horticultural industry, resulting in reduced yields and occasionally major crop damage. Contaminated irrigation water has long been recognized as an important source of fungal plant pathogens and is an important factor in disease spread on commercial horticultural nurseries (4). Water from many commonly used sources, such as rainwater from glasshouse roofs and, in particular, water stored in open reservoirs and ponds, can often contain large numbers of infective propagules of fungal plant pathogens, such as Pythium and Phytophthora spp. (1,4,34,46,48,53). A particularly high risk of disease spread is associated with the collection, recycling, and reuse of irrigation water, often referred to as recirculation (45,57,58), which is becoming more popular as attempts are increasingly being made to conserve valuable water supplies. Rapid dispersal of the pathogen in water is often achieved by asexual flagellate zoospores, and a key element for pathogen control is the removal of zoospores from water supplies. A wide...

Visualisation of the microbial colonisation of a slow sand filter using an Environmental Scanning Electron Microscope

“…Tentative identification suggested that the diatom could be either Gyrosigma or Nitzschia sp. The apparent scarcity of bacteria at this stage may partly be explained by the observation of Calvo-Bado et al (2003) who suggested that most of the microbial communities present within the slow sand filter were tightly attached to the sand grains within biofilms and that lower numbers existed as freeliving bacteria.…”

Differences in Microbial Activity and Microbial Populations of Peat Associated with Suppression of Damping-Off Disease Caused by Pythium sylvaticum

“…Denaturing gradient gel electrophoresis (DGGE) analysis was performed with a DCode mutation detection system (Bio-Rad, Hemel Hempstead, United Kingdom), using 160-by 160-by 1-mm gels of 8% (wt/vol) acrylamide (37:1 acrylamide:bisacrylamide) as described previously (8,40). Linear gradients of between 20% and 70% denaturant for bacterial amplifications and between 30% and 60% denaturant for fungal amplifications were formed by using a gradient maker (BDH, Lutterworth, United Kingdom), with 100% denaturant defined as 7 M urea and 40% (vol/vol) formamide.…”

“…PCR amplification of variable regions of the bacterial 16S or fungal 18S rRNA gene was performed with primers 341 (forward [5Ј-CCTA CGGGAGGCAGCAG-3Ј]) (8) and 534 (reverse [5Ј-ATTACCGCGGCTGCT G-3Ј]) (8) for bacterial amplifications and EF4 (forward [5Ј-GGAAGGGRTG TATTTATTAG-3Ј]) (55) and Fung (reverse [5Ј-ATTCCCCGTTACCCGTTG-3Ј]) (36) in a novel combination for fungal amplifications. Both forward primers were modified to include a 40-base 3Ј GC clamp (5Ј-CGCCCGCCGCGCGCG GCGGGCGGGGCGGGGGCACGGGGGG-3Ј) (40).…”

Review on the Fate and Mechanism of Nitrogen Pollutant Removal from Wastewater Using a Biological Filter

“…Biofilters afford many considerable advantages, including simple design and operation, low capital and operating costs, and a low requirement for energy and maintenance inputs [7]. During the past two decades, use of biofilter systems has developed rapidly, and biofilters have been widely used to remove various pollutants originating from aquatic environments [1,[8][9][10][11][12].…”