Microbial Population Dynamics Research Articles

Temporal Profiles of Soil Properties and Performance of Amaranthus Grown on Farm Yard Manure-mediated Crude Oil Polluted Soil

An experiment was conducted in the plant house of the Department of Crop, Soil and Pest management, Federal University of Technology, Akure, Nigeria, to examine the efficacy of manuring and incubation periods on the amelioration of the toxic effects of crude oil contamination on soil properties and Amaranthus performance. The time dynamics of physical, chemical and microbial population of the manured mediated crude oil contamination were observed following 270 days (9 months) of incubation. Bonny light crude oil was applied at zero and 5% (0 and 325 ml per pot) to the containerized (pot) soil which were amended with Farm Yard Manure (FYM) at 0 and 40 g per pot. The manure-mediated crude oil polluted containerized soil were incubated for periods of 0, 2, 4, 6 and 9 months. Treatments were arranged using Completely Randomised Design (CRD) with three replications. The toxicity of the crude oil pollution and its capacity to support plant growth was assessed via germination, seedling survival and growth of Amaranthus at the various periods of incubation. Data were also collected on soil biological, physical and chemical properties at the various sampling dates (periods of incubation). Application of organic fertilizer to crude oil-contaminated soil produced significant influence on soil chemical properties, microflora populations, and on the growth characters of Amaranthus. Organic amendment of crude oil contamination at two rates of organic fertilizer produced increases in soil pH and its contents of organic matter, N, P and K, and the colony sizes of microflora populations, and improved root, shoot biomass and leaf development of Amaranthus. Soil application of of crude oil affected soil chemical properties via decreases in soil pH, organic matter, N, P and K) and the colony sizes of microflora populations (bacterium, yeast and fungi counts). Crude oil contamination inhibited seed germination and growth of Amaranthus from the commencement of experiment to 4 weeks after treatment application. The time changes in soil elemental concentrations and biological populations following contamination with crude oil was monitored. Data obtained on soil chemical constituents (pH, organic matter, CEC) biological populations were fitted to correlation and regression models. The observed trendlines in time-dependent elemental concentration and soil biological populations were described by power, logarithmic and polynomial relations with high R2values. The initial declining trends in values with time up to the forth months after crude oil application were followed by a little linear increases in soil chemical properties and microbial population with time. These trends were consistent for both soil chemical properties and microbial population. The nature of the trends (polynomial function as best fit) indicate that the responses were not sole function of a factor but suggest synergy among factors responsible for the decay of petroleum hydrocarbon compounds and hence its toxicity to soil chemical properties and biological activities. The study showed that soil microbiological population (diversity) may be useful tools for assessing the effect of petroleum hydrocarbon contamination on soil and environmental health.

Gene flow in microbial communities could explain unexpected patterns of synonymous variation in the Escherichia coli core genome.

ABSTRACTResearchers contest the importance of gene flow in bacterial core genomes, as traditionalists view microbes as predominantly clonal, asexually reproducing organisms. Contrary to the traditional perspective, Escherichia coli core genes vary greatly in their levels of synonymous genetic diversity. This observation indicates that the relative importance of evolutionary forces such as mutation, selection, and recombination varies from gene to gene. In this paper, I highlight why the synonymous diversity observation is broadly relevant to researchers interested in the evolutionary dynamics of microbial populations and communities. I explain how a model of evolution called the coalescent relates neutral diversity (i.e. mutations with negligible fitness effects) to mutation rates, evolutionary time, and a parameter called effective population size. I then describe the possible ways in which mutation, selection, and recombination can explain observed patterns of synonymous diversity in E. coli. Finally, I describe a model for E. coli genome evolution in which different loci are subject to varying levels of gene flow among co-occurring microbes and viruses in the environment. Researchers can falsify the gene flow hypothesis by sequencing genes and strains isolated from stable microbiomes or by carrying out evolution experiments that trace gene genealogies in real-time.

Solids Retention Time Dependent Phototrophic Growth and Population Changes in Chemostat Cultivation Using Wastewater

There has been renewed interest in using algae for wastewater polishing and treatment in recent years. Because solids retention time (SRT) is a key design and operating parameter in bioreactor operation, this research determined the effect of SRT on phototrophic growth and microbial population dynamics in continuous-flow chemostat systems. There was a unique feature of phototrophic growth that differed from chemotrophic growth in chemostat. It was found that the phototrophic biomass concentration increased proportionally as SRT increased from 3 to 9 days. Regardless of the change in SRT, a step function model was successfully applied with the predicted phototrophic production rate of 4.5 ± 0.9 g/m(2)·d at the light intensity of 68.5 μmol/m(2)·s. Even though the continuous-flow systems were initially seeded with a 1:1 mixture of green algae and cyanobacteria, Chlorella vulgaris always dominated (98%) in the continuous-flow chemostat systems under steady-state conditions.

Evolution of Drug Resistance in Bacteria.

Resistance to antibiotics is an important and timely problem of contemporary medicine. Rapid evolution of resistant bacteria calls for new preventive measures to slow down this process, and a longer-term progress cannot be achieved without a good understanding of the mechanisms through which drug resistance is acquired and spreads in microbial populations. Here, we discuss recent experimental and theoretical advances in our knowledge how the dynamics of microbial populations affects the evolution of antibiotic resistance . We focus on the role of spatial and temporal drug gradients and show that in certain situations bacteria can evolve de novo resistance within hours. We identify factors that lead to such rapid onset of resistance and discuss their relevance for bacterial infections.

Terrestrial Arthropod Profile and Soil Microbial Population Dynamics on Cabbage Cropping as Affected by Application of Trichoderma Microbial Inoculant (TMI) in Sariaya, Quezon, Philippines

A two-season study was conducted in a cabbage farmer’s field in Sariaya, Quezon Province, Philippines to determine the impact of Trichoderma microbial inoculant (TMI) application on above-ground terrestrial arthropod profile. Soil microflora population dynamics, soil chemical properties, the nitrogen and phosphate crop uptake, and disease incidence were monitored for the first season only. TMI treatment was compared with farmer’s practice (FP, control) that involved insecticide treatment following an RCBD with three replicates. Target organisms were simultaneously monitored at 40, 60 and 85 days after transplanting (DAT). This is the first report on simultaneously studying these components of the cabbage agroecosystem.Combined seasons’ data showed higher arthropod counts in TMI plots, with predators significantly higher at third sampling-first season and parasite population first sampling-second season. Insect damage was observed on all plants indicating herbivore infestation, despite insecticide spraying in FP. Marketable yield was significantly greater in TMI plots based on combined seasons’data.Trichoderma invaded cabbage roots and existed as an endophyte throughout the life of the crop. It also significantly reduced disease incidence, increased N uptake despite reduced fertilizer application compared with FP. No change in culturable bacterial and fungal population was observed except for a transient increase in fungal population following TMI application.Further testing on other crucifers should be done to determine their reaction against major insect pests and on functional microbial groups

Microbial population dynamics and profiling of quorum sensing agents in membrane bioreactor

The biofilm formation on membrane surface in a membrane bioreactor (MBR) leads to membrane biofouling and retards the filtration performance. Researchers have been focused towards investigating the physicochemical fouling control strategies ignoring the microbiological mechanism and agents responsible for biofouling. The study aimed at investigating the signal molecules like N-acyl homoserine lactones and dominant bacterial diversity responsible for cell to cell communication, known as quorum sensing which allow them to coordinate gene expression and regulate virulence, leading to formation of mature biofilm. Dominant strains were isolated from the activated sludge of MBR and screened for the ability to produce AHLs as signal molecules, using two biosensors, Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136. 16S rRNA sequencing approach was used for identification of dominant bacterial diversity along with QS strains. Among AHLs producing strains, maximum biofilm formation ability was indicated by Pseudomonas kilonensis and Psychrobacter sp. All bacterial strains showed different biofilm forming tendencies, irrespective of their growth rate, verifies the role of QS agents responsible for biofilm development. The presence of short and medium chain AHLs (C4-HSL, C6-HSL and C8-HSL) was confirmed using HPLC. Production of AHLs and dominance of quorum sensing strains in activated sludge authenticate the key role of these substances in biofilm production and thereby membrane bio-fouling.

Fermentation and microbial population dynamics during the ensiling of native grass and subsequent exposure to air.

To study the microbial population and fermentation dynamics of large needlegrass (LN) and Chinese leymus (CL) during ensiling and subsequent exposure to air, silages were sampled and analyzed using culture-based techniques and denaturing gradient gel electrophoresis (DGGE). A total of 112 lactic acid bacteria (LAB) strains were isolated and identified using the 16S rRNA sequencing method. Lactic acid was not detected in the first 20 days in LN silage and the pH decreased to 6.13 after 45 days of ensiling. The temperature of the LN silage increased after approximately 30 h of air exposure and the CL silage showed a slight temperature variation. Enterococcus spp. were mainly present in LN silage. The proportion of Lactobacillus brevis in CL silage increased after exposure to air. LN silage with a higher proportion of Enterococcus spp. and propionic acid concentration did not show higher fermentation quality or aerobic stability than CL silage, which had a higher concentration of acetic acid, butyric acid and increased proportion of L. brevis after exposure to air.

An evidence-based framework for predicting the impact of differing autotroph-heterotroph thermal sensitivities on consumer-prey dynamics.

Increased temperature accelerates vital rates, influencing microbial population and wider ecosystem dynamics, for example, the predicted increases in cyanobacterial blooms associated with global warming. However, heterotrophic and mixotrophic protists, which are dominant grazers of microalgae, may be more thermally sensitive than autotrophs, and thus prey could be suppressed as temperature rises. Theoretical and meta-analyses have begun to address this issue, but an appropriate framework linking experimental data with theory is lacking. Using ecophysiological data to develop a novel model structure, we provide the first validation of this thermal sensitivity hypothesis: increased temperature improves the consumer's ability to control the autotrophic prey. Specifically, the model accounts for temperature effects on auto- and mixotrophs and ingestion, growth and mortality rates, using an ecologically and economically important system (cyanobacteria grazed by a mixotrophic flagellate). Once established, we show the model to be a good predictor of temperature impacts on consumer–prey dynamics by comparing simulations with microcosm observations. Then, through simulations, we indicate our conclusions remain valid, even with large changes in bottom-up factors (prey growth and carrying capacity). In conclusion, we show that rising temperature could, counterintuitively, reduce the propensity for microalgal blooms to occur and, critically, provide a novel model framework for needed, continued assessment.

Microbial population dynamics during long-term sludge adaptation of thermophilic and mesophilic sequencing batch digesters treating sewage fine sieved fraction at varying organic loading rates

BackgroundIn this research, the feasibility of, and population dynamics in, one-step anaerobic sequencing batch reactor systems treating the fine sieved fraction (FSF) from raw municipal wastewater was studied under thermophilic (55 °C) and mesophilic (35 °C) conditions. FSF was sequestered from raw municipal wastewater, in the Netherlands, using a rotating belt filter (mesh size 350 micron). FSF is a heterogeneous substrate that mainly consists of fibres originating from toilet paper and thus contains a high cellulosic fraction (60–80 % of total solids content), regarded as an energy-rich material.ResultsResults of the 656-day fed-batch operation clearly showed that thermophilic digestion was more stable, applying high organic loading rates (OLR) up to 22 kg COD/(m3 day). In contrast, the mesophilic digester already failed applying an OLR of 5.5 kg COD/(m3 day), indicated by a drop in pH and increase in volatile fatty acids (VFAs). The observed viscosity values of the mesophilic sludge were more than tenfold higher than the thermophilic sludge. 454-pyrosequencing of eight mesophilic and eight thermophilic biomass samples revealed that Bacteroides and aceticlastic methanogen Methanosaeta were the dominant genera in the mesophilic digester, whereas OP9 lineages, Clostridium and the hydrogenotrophic methanogen Methanothermobacter dominated the thermophilic one.ConclusionsOur study suggests that applying thermophilic conditions for FSF digestion would result in a higher biogas production rate and/or a smaller required reactor volume, comparing to mesophilic conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0355-3) contains supplementary material, which is available to authorised users.

Performance, carotenoids yield and microbial population dynamics in a photobioreactor system treating acidic wastewater: Effect of hydraulic retention time (HRT) and organic loading rate (OLR)

Effects of hydraulic retention time (HRT) and influent organic loading rate (OLR) were investigated in a photobioreactor containing PNSB (Rhodopseudomonas palustris)-chemoheterotrophic bacteria to treat volatile fatty acid wastewater. Pollutants removal, biomass production and carotenoids yield in different phases were investigated in together with functional microbial population dynamics. The results indicated that properly decreasing HRT and increasing OLR improved the nutrient removal performance as well as the biomass and carotenoids productions. 85.7% COD, 89.9% TN and 91.8% TP removals were achieved under the optimal HRT of 48h and OLR of 2.51g/L/d. Meanwhile, the highest biomass production and carotenoids yield were 2719.3mg/L and 3.91mg/g-biomass respectively. In addition, HRT and OLR have obvious impacts on PNSB and total bacteria dynamics. Statistical analyses indicated that the COD removal exhibited a positive relationship with OLR, biomass and carotenoids production. PNSB/total bacteria ratio had a positive correlation with the carotenoids yield.

Effects of controlling ripening conditions on the dynamics of the native microbial population of Mexican artisanal Cotija cheese assessed by PCR-DGGE

Diversity and dynamics of autochthonous microbiota of Cotija, a traditional Mexican raw-milk cheese that resembles Parmesan, were compared in cheeses during 90 days of ripening under traditional and controlled conditions (temperature and relative humidity). Molecular assessments by PCR-DGGE 26S and 16S rRNA encoding regions were performed on various sections of the cheese at different ripening times. A complex microbial profile was found differentially distributed in the cheese. Several spices of lactic-acid-bacteria (LAB) from the genera Leuconostoc, Lactobacillus, Weissella, Aerococcus, Enterococcus, Carnobacterium and the yeasts Candida etchellsii, Pichia kudriavzevii and Moniliella suaveolens were found in the cheese matrix, with Leuconostoc mesenteroides being dominant. The cheese surface was populated by some of these microorganisms before the characteristic crust was formed, but Kluyveromyces lactis, Kodamaea ohmeri together with non-lactic-acid-bacteria (nLAB) Psychrobacter celer and Corynebacter variabile became distinctive in this part of the cheese. The microbial spatial/temporal variations showed similar patterns in samples from both ripening conditions, which suggested a robust ecosystem that is likely responsible for the safety, sensorial richness, and potential bio-functionality of Cotija. This knowledge could open the possibility for standardizing the ripening operation to avoid defects and improve the marketing of the product.

Evaluation of aerobic co-composting of penicillin fermentation fungi residue with pig manure on penicillin degradation, microbial population dynamics and composting maturity

Improper treatment of penicillin fermentation fungi residue (PFFR), one of the by-products of penicillin production process, may result in environmental pollution due to the high concentration of penicillin. Aerobic co-composting of PFFR with pig manure was determined to degrade penicillin in PFFR. Results showed that co-composting of PFFR with pig manure can significantly reduce the concentration of penicillin in PFFR, make the PFFR-compost safer as organic fertilizer for soil application. More than 99% of penicillin in PFFR were removed after 7-day composting. PFFR did not affect the composting process and even promote the activity of the microorganisms in the compost. Quantitative PCR (qPCR) indicated that the bacteria and actinomycetes number in the AC samples were 40–80% higher than that in the pig-manure compost (CK) samples in the same composting phases. This research indicated that the aerobic co-composting was a feasible PFFR treatment method.

Changes in microbial diversity of brined green asparagus upon treatment with high hydrostatic pressure

The application of high hydrostatic pressure (HHP, 600MPa, 8min) on brined green asparagus and the changes in bacterial diversity after treatments and during storage at 4°C (30days) or 22°C (10days) were studied. HHP treatments reduced viable cell counts by 3.6 log cycles. The residual surviving population did not increase during storage at 4°C. However, bacterial counts significantly increased at 22°C by day 3, leading to rapid spoilage. The microbiota of green asparagus was composed mainly by Proteobacteria (mainly Pantoea and Pseudomonas), followed by Firmicutes (mainly Lactococcus and Enterococcus) and to a less extent Bacteroidetes and Actinobacteria. During chill storage of untreated asparagus, the relative abundance of Proteobacteria as well as Enterococcus and Lactococcus decreased while Lactobacillus increased. During storage of untreated asparagus at 22°C, the abundance of Bacteroidetes decreased while Proteobacteria increased during late storage. The HHP treatment determined a reduction of the Proteobacteria both early after treatment and during chill storage. In the HHP treated samples stored at 22°C, the relative abundance of Pseudomonas rapidly decreased at day 1, with an increase of Bacteroidetes. This was followed by a marked increase in Enterobacteriaceae (Escherichia) simultaneously with increase in viable counts and spoilage. Results from the study indicate that the effect of HHP treatments on the viability of microbial populations in foods also has an impact on the dynamics of microbial populations during the storage of the treated foods.

Microbial population dynamics in response to increasing loadings of pre-hydrolyzed pig manure in an expanded granular sludge bed

In recent years, pig manure (PM) has been regarded as a valuable substrate for energy and resource recovery via bioprocesses such as anaerobic digestion (AD), however, the efficiency of digesting raw PM is limited by the presence of refractory compounds. In this study, we applied a series of pretreatment on raw PM, consisting of subsequent thermochemical pretreatment, enzymatic hydrolysis, tyndallization and filtration. The liquid PM hydrolysates were fed to an expanded granular sludge bed (EGSB) for the production of biogas. The general performance and population dynamics of the EGSB reactor were assessed during an extended operational period of 339 days. An efficient and stable digestion process was achieved under high organic loading rates (OLRs) up to 21 kg-COD/(m3·d), agreeing with a sludge loading rate of 0.75 kg-COD/(kg-VSS·d), 1600 mg-NH4+-N/L and 17 mg/L of free ammonia nitrogen. The tyndallization decreased the total amount of active cells from 1 × 108 to 1 × 102 CFU/ml. Hence, bio-augmentation with pigs' intestinal microbiota was absent and the community dynamics were mainly credited to the composition of the substrate (i.e. PM hydrolysates) and the environmental conditions inside the reactor. The results showed the influence of both the seed community and the imposed loading rates on the evolutionary trajectory of the EGSB microbial community. Four bacterial genera (Clostridium, Cytophaga, Bacillus and Bacteroides) and two methanogenic genera (Methanosaeta and Methanobacterium) dominated the communities. An obvious shift from aceticlastic Methanosaeta to hydrogenotrophic Methanobacterium appeared when the OLR was increased to over 10 kg-COD/(m3·d).

A polyphasic approach to study the dynamics of microbial population of an organic wheat sourdough during its conversion to gluten-free sourdough.

To develop a method for organic gluten-free (GF) sourdough bread production, a long-term and original wheat sourdough was refreshed with GF flours. The dynamics of the sourdough microbiota during five months of back-slopping were analyzed by classical enumeration and molecular methods, including PCR-temporal temperature gel electrophoresis (PCR-TTGE), multiplex PCR, and pulsed field gel electrophoresis (PFGE). The results showed that the yeast counts remained constant, although Saccharomyces cerevisiae, present in the initial wheat sourdough, was no longer detected in the GF sourdough, while lactic acid bacteria (LAB) counts increased consistently. In the first phase, which was aimed at obtaining a GF sourdough from wheat sourdough, Lactobacillus sanfranciscensis, L. plantarum, and L. spicheri were the main LAB species detected. During the second phase, aimed at maintaining the GF sourdough, the L. plantarum and L. spicheri populations decreased whereas L. sanfranciscensis persisted and L. sakei became the predominant species. Multiplex PCRs also revealed the presence of several L. sakei strains in the GF sourdough. In a search for the origin of the LAB species, PCR-TTGE was performed on the flour samples but only L. sanfranciscensis was detected, suggesting a flour origin for this typical sourdough species. Thus, while replacement of the wheat flour by GF flour influenced the sourdough microbiota, some of the original sourdough LAB and yeast species remained in the GF sourdough.

Monitoring microbial metabolites using an inductively coupled resonance circuit

We present a new approach to monitor microbial population dynamics in emulsion droplets via changes in metabolite composition, using an inductively coupled LC resonance circuit. The signal measured by such resonance detector provides information on the magnetic field interaction with the bacterial culture, which is complementary to the information accessible by other detection means, based on electric field interaction, i.e. capacitive or resistive, as well as optical techniques. Several charge-related factors, including pH and ammonia concentrations, were identified as possible contributors to the characteristic of resonance detector profile. The setup enables probing the ionic byproducts of microbial metabolic activity at later stages of cell growth, where conventional optical detection methods have no discriminating power.

The evolutionary advantage of haploid versus diploid microbes in nutrient-poor environments

Sexual eukaryotic organisms are characterized by haploid and diploid nuclear phases. In many organisms, growth and development occur in both haploid and diploid phases, and the relative length of these phases exhibits considerable diversity. A number of hypotheses have been put forward to explain the maintenance of this diversity of life cycles and the advantage of being haploid versus that of being diploid. The nutrient-limitation hypothesis postulates that haploid cells, because they are small and thus have a higher surface area to volume ratio, are advantageous in nutrient-poor environments. In this paper, we examine this hypothesis theoretically and determine the conditions under which it holds. On the basis of our analysis, we make the following predictions. First, the relative advantages of different ploidy levels strongly depend on the ploidy-dependent energy conversion efficiency and the scaling of mortality with cell size. Specifically, haploids enjoy a higher intrinsic population growth rate than diploids do under nutrient-poor conditions, but under nutrient-rich conditions the intrinsic population growth rate of diploids is higher, provided that the energy conversion efficiency of diploids is higher than that of haploids and the scaling of mortality with cell size is weak. Second, differences in nutrient concentration in the inflowing medium have almost no effect on the relative advantage of ploidy levels at population equilibrium. Our study illustrates the importance of explicit modeling of microbial life history and population dynamics to understand the evolution of ploidy levels.

A novel process-based model of microbial growth: self-inhibition in Saccharomyces cerevisiae aerobic fed-batch cultures.

BackgroundMicrobial population dynamics in bioreactors depend on both nutrients availability and changes in the growth environment. Research is still ongoing on the optimization of bioreactor yields focusing on the increase of the maximum achievable cell density.ResultsA new process-based model is proposed to describe the aerobic growth of Saccharomyces cerevisiae cultured on glucose as carbon and energy source. The model considers the main metabolic routes of glucose assimilation (fermentation to ethanol and respiration) and the occurrence of inhibition due to the accumulation of both ethanol and other self-produced toxic compounds in the medium. Model simulations reproduced data from classic and new experiments of yeast growth in batch and fed-batch cultures. Model and experimental results showed that the growth decline observed in prolonged fed-batch cultures had to be ascribed to self-produced inhibitory compounds other than ethanol.ConclusionsThe presented results clarify the dynamics of microbial growth under different feeding conditions and highlight the relevance of the negative feedback by self-produced inhibitory compounds on the maximum cell densities achieved in a bioreactor.

Volume ratios between the thermophilic and the mesophilic digesters of a temperature-phased anaerobic digestion system affect their performance and microbial communities

An experimental temperature-phased anaerobic digestion (TPAD) system, with the thermophilic digester operated at neutral pH and with a balanced acidogenesis and methanogenesis (referred to as NT-TPAD), was evaluated with respect to the microbial communities and population dynamics of methanogens when digesting dairy cattle manure at 15-day overall system hydraulic retention time (HRT). When fed a manure slurry of 10% total solid (TS), similar system performance, 36-38% volatile solid (VS) removal and 0.21-0.22 L methane g(-1) VS fed, was achieved between a 5-day and 7.5-day HRT for the thermophilic digester. However, the thermophilic digester achieved a greater volumetric biogas yield when operated at a 5-day RT than at a 7.5-day HRT (6.3 vs. 4.7 L/L/d), while the mesophilic digester had a stable volumetric biogas yield (about 1.0 L/L/d). Each of the digesters harbored distinct yet dynamic microbial populations, and some of the methanogens were significantly correlated with methane productions. Methanosarcina and Methanosaeta were the most important methanogenic genera in the thermophilic and the mesophilic digesters, respectively. The microbiological findings may help understand the metabolism that underpins the anaerobic processes within each of the two digesters of TPAD systems when fed dairy manure.

Predictive Studies Suggest that the Risk for the Selection of Antibiotic Resistance by Biocides Is Likely Low in Stenotrophomonas maltophilia.

Biocides are used without restriction for several purposes. As a consequence, large amounts of biocides are released without any control in the environment, a situation that can challenge the microbial population dynamics, including selection of antibiotic resistant bacteria. Previous work has shown that triclosan selects Stenotrophomonas maltophilia antibiotic resistant mutants overexpressing the efflux pump SmeDEF and induces expression of this pump triggering transient low-level resistance. In the present work we analyze if two other common biocides, benzalkonium chloride and hexachlorophene, trigger antibiotic resistance in S. maltophilia. Bioinformatic and biochemical methods showed that benzalkonium chloride and hexachlorophene bind the repressor of smeDEF, SmeT. Only benzalkonium chloride triggers expression of smeD and its effect in transient antibiotic resistance is minor. None of the hexachlorophene-selected mutants was antibiotic resistant. Two benzalkonium chloride resistant mutants presented reduced susceptibility to antibiotics and were impaired in growth. Metabolic profiling showed they were more proficient than their parental strain in the use of some dipeptides. We can then conclude that although bioinformatic predictions and biochemical studies suggest that both hexachlorophene and benzalkonium chloride should induce smeDEF expression leading to transient S. maltophilia resistance to antibiotics, phenotypic assays showed this not to be true. The facts that hexachlorophene resistant mutants are not antibiotic resistant and that the benzalkonium chloride resistant mutants presenting altered susceptibility to antibiotics were impaired in growth suggests that the risk for the selection (and fixation) of S. maltophilia antibiotic resistant mutants by these biocides is likely low, at least in the absence of constant selection pressure.