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The hyporheic zone of stream ecosystems is a critical habitat for microbial communities. However, the factors influencing hyporheic bacterial communities along spatial and seasonal gradients remain poorly understood. We sought to characterize patterns in bacterial community composition among the sediments of a small stream in southern Ontario, Canada. We used sampling cores to collect monthly hyporheic water and sediment microbial communities in 2006 and 2007. We described bacterial communities terminal-restriction fragment length polymorphism (TRFLP) and tested for spatial and seasonal relationships with physicochemical parameters using multivariate statistics. Overall, the hyporheic zone appears to be a DOC, oxygen, and nitrogen sink. Microbial communities were distinct from those at the streambed surface and from soil collected in the adjacent watershed. In the sediments, microbial communities were distinct between the fall, spring, and summer seasons, and bacterial communities were more diverse at streambed surface and near-surface sites compared with deeper sites. Moreover, bacterial communities were similar between consecutive fall seasons despite shifting throughout the year, suggesting recurring community assemblages associated with season and location in the hyporheic zone. Using canonical correspondence analysis, seasonal patterns in microbial community composition and environmental parameters were correlated in the following way: temperature was related to summer communities; DOC (likely from biofilm and allochthonous inputs) influenced most fall communities; and nitrogen associated strongly with winter and spring communities. Our results also suggest that labile DOC entering the hyporheic zone occurred in concert with shifts in the bacterial community. Generally, seasonal patterns in hyporheic physicochemistry and microbial biodiversity remain largely unexplored. Therefore, we highlight the importance of seasonal and spatial resolution when assessing surface- and groundwater interactions in stream ecosystems. [ABSTRACT FROM AUTHOR]

Colour discharges are gaining renewed focus in the pulp and paper industry as increasingly strict regulatory limits are placed on wastewater quality and aesthetics. In-mill process improvements, such as ECF bleaching and oxygen delignification, have decreased wastewater colour loadings. However, a survey of 12 pulp and paper mill systems found that effluent treatment using aerated stabilisation basins (ASB) leads to average increases in colour of 20-40%. In some instances, this phenomenon may even double the influent colour levels. Activated sludge systems did not produce a colour increase. The measured increases that follow ASB secondary treatment may be sufficient for a mill to fail prescribed discharge standards. A detailed field survey focusing on sections of an integrated bleached kraft mill ASB treatment system was undertaken. The average increase in colour at the final point of discharge was 45%. The major changes in colour concentration occurred in the inlet to the main treatment pond, and in polishing ponds that followed the main treatment pond. Both of these areas receive little or no aeration. No significant change was observed in the highly aerated main pond. These results, along with literature reports, suggested that redox conditions play a major role in influencing colour behaviour. To test this, two series of paired continuously stirred reactors were used to treat whole mill effluent from two ECF bleached kraft mills in parallel. The first series initially treated under anaerobic conditions, followed by an aerobic reactor, while the second series reversed this order. With the initial anaerobic stage, effluent colour increased by 18% and 19% for the first and second series respectively. Subsequent treatment by aerobic bacteria further increased colour by 14% and 6%, for a total increase of 32% and 25%. Initial aerobic treatment, however, did not lead to any significant change in colour for either effluent. Further anaerobic treatment following aerobic conditions produced only small increases in colour. These results are consistent with the ASB and activated sludge system survey, suggesting that anaerobic conditions at the head of treatment systems initiate the observed increases in effluent colour in ASB treatment systems. [ABSTRACT FROM AUTHOR]

Horizontal gene transfer in the Bacteria has been demonstrated to occur under natural conditions. The ecological impact of gene transfer events depends on the new genetic material being expressed in recipient organisms, and on natural selection processes operating on these recipients. The phylogenetic distribution of cbaAB genes for chlorobenzoate 3,4-(4,s)-dioxygenase, which are carried within Tn5271 on the IncPβ plasmid pBRC60, was investigated using isolates from freshwater microcosms and from the Niagara River watershed. The latter included isolates from surface water, groundwater and bioremediation reactor samples. The cbaAB genes have become integrated, through interspecific transfer, primarily into species of the β Proteobacteria (44/48 isolates). Only four isolates, identified as Pseudomonas fluorescens (3/48) and Xantlromonas maltophilia(1/48), belonged to the ϒ Proteobacteria, despite the observation that pBRC60 was capable of mobilizing these genes into a wide range of β and Proteobacteria in the laboratory. The natural host range correlated with the distribution of the meta-ring-fission pathway for metabolism of protocatechuates formed when the cbnAB genes were expressed (45/48 isolates). We proposed the hypothesis that natural selection has favoured recipients that successfully integrate the activity of the transferred dioxygenase with the conserved meta ring-fission pathway. The hypothesis was tested by transferring a plasmid construct containing the cbnAB genes into type strains representative of the β and ϒ Proteobacteria. The concept of applying mobile catabolic genes to probe the phylogenetic distribution of compatible degradative pathways is discussed. [ABSTRACT FROM AUTHOR]

1. Studies of hyporheic microbial ecology have suggested an important role for hyporheic microbial processes in stream ecosystem functioning. Using evidence from microbial communities in other aquatic habitats, some predictions are made concerning the diversity of microbial types and microbial processes likely to occur in the hyporheic zone, and the relative importance of these various types to the hyporheic ecosystem. 2. It is predicted that the biofilm growth form of interstitial micro-organisms will create a variety of microniches, allowing coexistence of a great diversity of microbial types, and promoting the activity of some otherwise poor competitors. It is further predicted that the confluence of reduced groundwaters and aerobic surface waters will favour chemolithotrophic processes in the hyporheic zone, but that these will contribute significantly to hyporheic production only if surface water is very low in dissolved organic carbon, or the groundwater is extremely reduced, such as by the influence of riparian wetlands. A variety of anaerobic respiratory pathways, such as nitrate, ferric ion, sulphate and even methanogenic respiration will be employed in the hyporheic zone, with biofilm dynamics permitting these to occur even in aerobic sediments. Anaerobic pathways may account for a significant proportion of total hyporheic organic matter mineralization. 3. The role of fungi in hyporheic dynamics is, as yet, almost completely unstudied. However, it is expected that they will be important in breaking down buried particulate organic matter (POM), which may account for a large proportion of total stream POM. 4. Physicochemical conditions in hyporheic sediments appear to be highly heterogeneous, and this heterogeneity may be very important in the cycling of certain nutrients, especially nitrogen, which involves a series of steps requiring different conditions. 5. Various new techniques are now available by which biofilm dynamics and in situ microbial processes may be measured. Studies are recommended of intact microbial communities both at the microscale of the biofilm and at the scale of the heterogeneities occurring in hyporheic sediments. Studies are needed that measure actual rates of microbial processes under in situ conditions. [ABSTRACT FROM AUTHOR]

This paper forms part of series of biological treatment colour behaviour studies. Surveys across a range of mills have observed colour increases in aerated stabilisation basins of 20-45%. Much of the colour formation has been demonstrated to occur in high molecular mass effluent organic constituents (HMM) present in bleach plant effluents. Removing material greater than 3,000 Da essentially eliminated the colour forming ability in both E and D stage wastewaters. We have also shown that pulp and paper sludges contain anaerobic bacteria capable of reducing humic like materials. Colour formation was correlated to the anoxic conditions and the availability of readily biodegradable organic constituents during the wastewater treatment process. Overall, these studies suggest that colour formation in pulp and paper biological treatment systems may be caused by anaerobic bacteria using HMM material from the bleaching effluents as an electron acceptor for growth. This leads to the reduction of the material, which in turn leads to non-reversible internal changes, such as intra-molecular polymerisation or formation of chromophonc functional groups. [ABSTRACT FROM AUTHOR]

The pulp and paper industry largely depends on the biodegradation activities of heterotrophic bacteria to remove organic contaminants in wastewater prior to discharge. Our recent discovery of extensive cyanobacterial communities in pulp and paper waste treatment systems led us to investigate the potential impacts of cyanobacterial exudates on growth and biodegradation efficiency of three bacterial heterotrophs. Each of the three assessed bacteria represented different taxa commonly found in pulp and paper waste treatment systems: a fluorescent Pseudomonad, an Ancylobacter aquaticus strain, and a Ralstonia eutropha strain. They were capable of utilizing phenol, dichloroacetate (DCA), or 2,4-dichlorophenoxyacetic acid (2,4-D), respectively. Exudates from all 12 cyanobacterial strains studied supported the growth of each bacterial strain to varying degrees. Maximum biomass of two bacterial strains positively correlated with the total organic carbon content of exudate treatments. The combined availability of exudate and a known growth substrate (i.e., phenol, DCA, or 2,4-D) generally had a synergistic affect on the growth of the Ancylobacter strain, whereas mixed effects were seen on the other two strains. Exudates from four representative cyanobacterial strains were assessed for their impacts on phenol and DCA biodegradation by the Pseudomonas and Ancylobacter strains, respectively. Exudates from three of the four cyanobacterial taxa repressed phenol biodegradation, but enhanced DCA biodegradation. These dissimilar impacts of cyanobacterial exudates on bacterial degradation of contaminants suggest a species-specific association, as well as a significant role for cyanobacteria during the biological treatment of wastewaters. [ABSTRACT FROM AUTHOR]

This study investigated the effects of cyanobacteria from pulp-and-paper waste-treatment systems on biological toxicity removal and biodegradation of certain wastewater contaminants. In field and batch studies, using the Microtox® assay, cyanobacterial biomass and final wastewater toxicity were significantly correlated. In softwood-based wastewater, a decrease in toxicity was negatively correlated with cyanobacterial biomass, but the correlation was positive in hardwood-based wastewater. In the softwood-based wastewater, toxicity remained higher in the light than it was in the dark, whereas in hardwood-based wastewater, toxicity was lower in the light than it was in the dark. All of these results were light-dependent, suggesting that the photosynthetic growth of cyanobacteria is required to induce significant effects. When grown in mixed cultures with bacterial degraders, cyanobacteria from pulp-and-paper waste-treatment systems generally impeded the biodegradation of the wastewater contaminants phenol and dichloroacetate (DCA). However, there was one case where the cyanobacterium Phormidium insigne improved the bacterial degradation of DCA. Doubling inorganic nutrient concentrations did not improve phenol or DCA biodegradation in the majority of cases, indicating that nutrient competition is not a major factor. These data suggest that cyanobacteria play an important role during the biological treatment of contaminants, and, hence, toxicity removal in pulp-and-paper waste-treatment systems.Key words: cyanobacteria, heterotrophic bacteria, biodegradation, pulp and paper waste-treatment, wastewater toxicity. [ABSTRACT FROM AUTHOR]

The integration of shade trees in coffee production can positively contribute to increased yields in these cropping systems. However, little work has examined nutrient-microbial dynamics in the rhizosphere of coffee under shade trees. In this study, we compared nutrient concentrations and nitrifier populations in rhizosphere soil of coffee under shade and in monoculture as well as in rhizosphere versus bulk soils. Our study was performed in a low altitude, wet coffee zone of Costa Rica, at a 12-year-old agroforestry experimental farm with coffee ( Coffea arabica ) grown under full sun and under the commonly used dinitrogen (N 2 ) fixing shade tree, Erythrina poeppigiana . Rhizosphere and bulk soils were collected and analyzed for inorganic N, available P, exchangeable base cations and pH status. Real-time PCR was used to determine the relative abundance of ammonia oxidizing bacteria (AOB). We show a nutrient increase (11–158%), particularly nitrates, in the rhizosphere soil compared to bulk soil of coffee. Moreover, this accumulation was greater in the rhizosphere of coffee associated with E. poeppigiana than under monoculture. AOB abundance was strongly related to soil pH ( r = 0.83; P = 0.002) across both treatments, while AOB abundance varied with soil ammonium:nitrate ratios ( r = −0.82; P = 0.0420) exclusively under monoculture coffee. Our study, for the first time to our knowledge, illustrates soil nutrient differences and nutrient–microbial relationships under coffee in monoculture and in a N 2 -fixing shade tree system. [ABSTRACT FROM AUTHOR]