The impact of systemic and copper pesticide applications on the phyllosphere microflora of tomatoes.

BACKGROUND: Contamination of tomatoes by Salmonella can occur in agricultural settings. Little is currently understood about how agricultural inputs such as pesticide applications may impact epiphytic crop microflora and potentially play a role in contamination events. We examined the impact of two materials commonly used in Virginia tomato agriculture: acibenzolar-S-methyl (crop protectant) and copper oxychloride (pesticide) to identify the effects these materials may exert on baseline tomato microflora and on the incidence of three specific genera; Salmonella, Xanthomonas and Paenibacillus. RESULTS: Approximately 186 441 16S rRNA gene and 39 381 18S rRNA gene sequences per independent replicate were used to analyze the impact of the pesticide applications on tomato microflora. An average of 3 346 677 (634 892 974 bases) shotgun sequences per replicate were used for metagenomic analyses. CONCLUSION: A significant decrease in the presence of Gammaproteobacteria was observed between controls and copper-treated plants, suggesting that copper is effective at suppressing growth of certain taxa in this class. A higher mean abundance of Salmonella and Paenibacillus in control samples compared to treatments may suggest that both systemic and copper applications diminish the presence of these genera in the phyllosphere; however, owing to the lack of statistical significance, this could also be due to other factors. The most distinctive separation of shared membership was observed in shotgun data between the two different sampling time-points (not between treatments), potentially supporting the hypothesis that environmental pressures may exert more selective pressures on epiphytic microflora than do certain agricultural management practices.

Large-scale bioreactor production of the herbicide-degrading Aminobacter sp. strain MSH1.

The Aminobacter sp. strain MSH1 has potential for pesticide bioremediation because it degrades the herbicide metabolite 2,6-dichlorobenzamide (BAM). Production of the BAM-degrading bacterium using aerobic bioreactor fermentation was investigated. A mineral salt medium limited for carbon and with an element composition similar to the strain was generated. The optimal pH and temperature for strain growth were determined using shaker flasks and verified in bioreactors. Glucose, fructose, and glycerol were suitable carbon sources for MSH1 (µ = 0.1 h(-1)); slower growth was observed on succinate and acetic acid (µ = 0.01 h(-1)). Standard conditions for growth of the MSH1 strain were defined at pH 7 and 25 °C, with glucose as the carbon source. In bioreactors (1 and 5 L), the specific growth rate of MSH1 increased from µ = 0.1 h(-1) on traditional mineral salt medium to µ = 0.18 h(-1) on the optimized mineral salt medium. The biomass yield under standard conditions was 0.47 g dry weight biomass/g glucose consumed. An investigation of the catabolic capacity of MSH1 cells harvested in exponential and stationary growth phases showed a degradation activity per cell of about 3 × 10(-9) µg BAM h(-1). Thus, fast, efficient, large-scale production of herbicide-degrading Aminobacter was possible, bringing the use of this bacterium in bioaugmentation field remediation closer to reality.

Effects of dissolved organic matter (DOM) at environmentally relevant carbon concentrations on atrazine degradation by Chelatobacter heintzii SalB.

The dissolved organic matter (DOM) is the term used for organic components of natural origin present in the soil solution and is probably the most available C-source that primes microbial activity in subsoils. Contrasting effects of organic C components on pesticide degradation have been reported; however, most studies have used model organic compounds with compositions and concentrations which differ substantially from those found in the environment. Degradation of atrazine (AT) by Chelatobacter heintzii SalB was monitored in liquid batch assays in the absence or presence of well-defined model C compounds (glucose, gluconate and citrate) as model DOM (mDOM) or complex, less-defined, environmental DOM solutions (eDOM: isolated humic substances, soil and plant residue extracts) at environmentally relevant concentrations. Glucose significantly increased AT degradation rate by more than a factor of 8 at and above 2.5 mg C L( - 1). Optical density measurements showed that this stimulation is related to microbial growth. Gluconate and citrate had no effects unless at non-relevant concentrations (1,000 mg DOC L( - 1)) at which stimulations (gluconate) or inhibitions (citrate) were found. The effects of eDOM added at 10 mg DOC L( - 1) on AT degradation were generally small. The AT degradation time was reduced by factors 1.4-1.9 in the presence of humic acids and eDOM from soils amended with plant residues; however, no effects were found for fulvic acids or eDOM from a soil leachate solution or extracted from unamended peat or forest soil. In conclusion, DOM supplied as both mDOM and eDOM did not inhibit AT degradation at environmentally relevant concentrations, and stimulation can be found for selected DOM samples and this is partly related to its effect on growth.

Aminobacter sp. MSH1 invades sand filter community biofilms while retaining 2,6-dichlorobenzamide degradation functionality under C- and N-limiting conditions.

Aminobacter sp. MSH1 is of interest for bioaugmentation of biofiltration units in drinking water treatment plants (DWTPs) due to its ability to degrade the groundwater micropollutant 2,6-dichlorobenzamide (BAM). Using a continuous flow chamber biofilm model, MSH1 was previously shown to colonize surfaces and degrade BAM at trace concentrations as low as 1 µg/L under the oligotrophic conditions found in DWTPs. In DWTP filtration units, MSH1 has to compete with the resident biofilm microbiota for space and nutrients. Using the same model, we examined how a sand filter community (SFC) affects MSH1's BAM-degrading activity and biofilm formation under C- and N-limiting conditions when fed with trace concentrations of BAM. MSH1 was inoculated simultaneously with the SFC (co-colonization mode) or after the SFC formed a biofilm (invasion mode). MSH1 successfully established in the SFC biofilm showing growth and activity. In co-colonization mode, MSH1 decreased in number in the presence of the SFC and formed isolated colonies, while specific BAM-degradation activity increased. In the invasion mode, MSH1 also decreased in numbers in the presence of the SFC but formed mixed colonies, while specific BAM degradation was unaffected. Our results show that MSH1 invades and performs successfully in an SFC biofilm under the oligotrophic conditions of DWTPs.

Changes in the bacterial microbiota in gut, blood, and lungs following acute LPS instillation into mice lungs.

INTRODUCTION: Previous reports have shown that the gastrointestinal (GI) bacterial microbiota can have profound effects on the lungs, which has been described as the "gut-lung axis". However, whether a "lung-gut" axis exists wherein acute lung inflammation perturbs the gut and blood microbiota is unknown. METHODS: Adult C57/Bl6 mice were exposed to one dose of LPS or PBS instillation (n=3 for each group) directly into lungs. Bacterial microbiota of the bronchoalveolar lavage fluid, blood, and cecum were determined using 454 pyrotag sequencing and quantitative polymerase chain reaction (qPCR) at 4 through 168 hours post-instillation. We then investigated the effects of oral neomycin and streptomycin (n=8) on the microbiota at 4 and 24 hours post LPS instillation versus control treatment (n=5 at baseline and 4 hours, n=7 at 24 hours). RESULTS: At 24 hours post LPS instillation, the total bacterial count was significantly increased in the cecum (P<0.05); whereas the total bacterial count in blood was increased at 4, 48, and 72 hours (P<0.05). Antibiotic treatment reduced the total bacteria in blood but not in the cecum. The increase in total bacteria in the blood correlated with Phyllobacteriaceae OTU 40 and was significantly reduced in the blood for both antibiotic groups (P<0.05). CONCLUSION: LPS instillation in lungs leads to acute changes in the bacterial microbiota in the blood and cecum, which can be modulated with antibiotics.

In glucose-limited continuous culture the minimum substrate concentration for growth, Smin, is crucial in the competition between the enterobacterium Escherichia coli and Chelatobacter heintzii, an environmentally abundant bacterium.

The competition for glucose between Escherichia coli ML30, a typical copiotrophic enterobacterium and Chelatobacter heintzii ATCC29600, an environmentally successful strain, was studied in a carbon-limited culture at low dilution rates. First, as a base for modelling, the kinetic parameters µ(max) and K(s) were determined for growth with glucose. For both strains, µ(max) was determined in batch culture after different precultivation conditions. In the case of C. heintzii, µ(max) was virtually independent of precultivation conditions. When inoculated into a glucose-excess batch culture medium from a glucose-limited chemostat run at a dilution rate of 0.075 h(-1) C. heintzii grew immediately with a µ(max) of 0.17 ± 0.03 h(-1). After five transfers in batch culture, µ(max) had increased only slightly to 0.18 ± 0.03 h(-1). A different pattern was observed in the case of E. coli. Inoculated from a glucose-limited chemostat at D = 0.075 h(-1) into glucose-excess batch medium E. coli grew only after an acceleration phase of ~3.5 h with a µ(max) of 0.52 h(-1). After 120 generations and several transfers into fresh medium, µ(max) had increased to 0.80 ± 0.03 h(-1). For long-term adapted chemostat-cultivated cells, a K(s) for glucose of 15 µg l(-1) for C. heintzii, and of 35 µg l(-1) for E. coli, respectively, was determined in (14)C-labelled glucose uptake experiments. In competition experiments, the population dynamics of the mixed culture was determined using specific surface antibodies against C. heintzii and a specific 16S rRNA probe for E. coli. C. heintzii outcompeted E. coli in glucose-limited continuous culture at the low dilution rates of 0.05 and 0.075 h(-1). Using the determined pure culture parameter values for K(s) and µ(max), it was only possible to simulate the population dynamics during competition with an extended form of the Monod model, which includes a finite substrate concentration at zero growth rate (s(min)). The values estimated for s(min) were dependent on growth rate; at D = 0.05 h(-1), it was 12.6 and 0 µg l(-1) for E. coli and C. heintzii, respectively. To fit the data at D=0.075 h(-1), s(min) for E. coli had to be raised to 34.9 µg l(-1) whereas s(min) for C. heintzii remained zero. The results of the mathematical simulation suggest that it is not so much the higher K(s) value, which is responsible for the unsuccessful competition of E. coli at low residual glucose concentration, but rather the existence of a significant s(min).