Facultative Strain Research Articles

Isolation and Electrochemical Analysis of a Facultative Anaerobic Electrogenic Strain Klebsiella sp. SQ-1.

Electricigens decompose organic matter and convert stored chemical energy into electrical energy through extracellular electron transfer. They are significant biocatalysts for microbial fuel cells with practical applications in green energy generation, effluent treatment, and bioremediation. A facultative anaerobic electrogenic strain SQ-1 is isolated from sludge in a biotechnology factory. The strain SQ-1 is a close relative of Klebsiella variicola. Multilayered biofilms form on the surface of a carbon electrode after the isolated bacteria are inoculated into a microbial fuel cell device. This strain produces high current densities of 625 μA cm-2 by using acetate as the carbon source in a three-electrode configuration. The electricity generation performance is also analyzed in a dual-chamber microbial fuel cell. It reaches a maximum power density of 560 mW m-2 when the corresponding output voltage is 0.59 V. The facultative strain SQ-1 utilizes hydrous ferric oxide as an electron acceptor to perform extracellular electricigenic respiration in anaerobic conditions. Since facultative strains possess better properties than anaerobic strains, Klebsiella sp. SQ-1 may be a promising exoelectrogenic strain for applications in microbial electrochemistry.

Fecal Microbiota Analysis in Cats with Intestinal Dysbiosis of Varying Severity.

Recent studies have shown that the gut microbiota plays an important role in the pathogenesis of gastrointestinal diseases in various animal species. There are only limited data on the microbiome in cats with varying grades of dysbiosis. The purpose of the study was a detailed analysis of the quantitative and qualitative fecal microbiota spectrum in cats with intestinal dysbiosis of varying severity. The data obtained indicate that, depending on the dysbiosis severity in cats, the intestinal microbiome landscape changes significantly. It has been established that, depending on the dysbiosis severity, there is a shift in the balance between the Gram-positive and Gram-negative bacterial pools and in the nature of the isolation of specific bacteria forms, in the amount of obligate microbiota isolation, as well as individual facultative strains. When analyzing the serotyping of E. coli cultures isolated at various grades of intestinal dysbiosis severity, differences were found both in the isolation amount of various serotypes from one animal and in the prevalence of certain serotypes for each disease severity. A retrospective analysis of the fecal microbiota sensitivity in cats with dysbiosis to antibacterial drugs showed that, depending on the disease severity, the number of isolates sensitive to antibiotics increases significantly.

Cultivation-Assisted Genome of Candidatus Fukatsuia symbiotica; the Enigmatic "X-Type" Symbiont of Aphids.

Heritable symbionts are common in terrestrial arthropods and often provide beneficial services to hosts. Unlike obligate, nutritional symbionts that largely persist under strict host control within specialized host cells, heritable facultative symbionts exhibit large variation in within-host lifestyles and services rendered with many retaining the capacity to transition among roles. One enigmatic symbiont, Candidatus Fukatsuia symbiotica, frequently infects aphids with reported roles ranging from pathogen, defensive symbiont, mutualism exploiter, and nutritional co-obligate symbiont. Here, we used an in vitro culture-assisted protocol to sequence the genome of a facultative strain of Fukatsuia from pea aphids (Acyrthosiphon pisum). Phylogenetic and genomic comparisons indicate that Fukatsuia is an aerobic heterotroph, which together with Regiella insecticola and Hamiltonella defensa form a clade of heritable facultative symbionts within the Yersiniaceae (Enterobacteriales). These three heritable facultative symbionts largely share overlapping inventories of genes associated with housekeeping functions, metabolism, and nutrient acquisition, while varying in complements of mobile DNA. One unusual feature of Fukatsuia is its strong tendency to occur as a coinfection with H. defensa. However, the overall similarity of gene inventories among aphid heritable facultative symbionts suggests that metabolic complementarity is not the basis for coinfection, unless playing out on a H. defensa strain-specific basis. We also compared the pea aphid Fukatsuia with a strain from the aphid Cinara confinis (Lachninae) where it is reported to have transitioned to co-obligate status to support decaying Buchnera function. Overall, the two genomes are very similar with no clear genomic signatures consistent with such a transition, which suggests co-obligate status in C. confinis was a recent event.

Genome Analysis of Haplotype D of Candidatus Liberibacter Solanacearum.

Candidatus Liberibacter solanacearum (Lso) haplotype D (LsoD) is a suspected bacterial pathogen, spread by the phloem-feeding psyllid Bactericera trigonica Hodkinson and found to infect carrot plants throughout the Mediterranean. Haplotype D is one of six haplotypes of Lso that each have specific and overlapping host preferences, disease symptoms, and psyllid vectors. Genotyping of rRNA genes has allowed for tracking the haplotype diversity of Lso and genome sequencing of several haplotypes has been performed to advance a comprehensive understanding of Lso diseases and of the phylogenetic relationships among the haplotypes. To further pursue that aim we have sequenced the genome of LsoD from its psyllid vector and report here its draft genome. Genome-based single nucleotide polymorphism analysis indicates LsoD is most closely related to the A haplotype. Genomic features and the metabolic potential of LsoD are assessed in relation to Lso haplotypes A, B, and C, as well as the facultative strain Liberibacter crescens. We identify genes unique to haplotype D as well as putative secreted effectors that may play a role in disease characteristics specific to this haplotype of Lso.

Coupling heavy metal resistance and oxygen flexibility for bioremoval of copper ions by newly isolated Citrobacter freundii JPG1

The potential for bioremoval of copper ions was investigated by a novel strain of bacterium Citrobacter freundii JPG1, which was newly isolated from gold mining tailing in China and grew either aerobically or anaerobically. The strain cross-tolerated heavy metals of Ag+, Cd2+, Co2+, Cr6+, Cu2+ and Ni2+ and removed copper under both aerobic and anaerobic conditions with the stress of copper. Under aerobic conditions, the cells grew rapidly and exhibited higher biomass at low copper concentrations (<1 mmol L−1), while the growth of cells was almost completely inhibited at high copper concentrations (2 mmol L−1). However, the cell growths were less affected by copper under anaerobic conditions. Similarly, the copper-removal efficiency was affected by oxygen and the capability of copper removal by anaerobic cells was significantly higher than that of aerobic cells (P < 0.05). The quantitative measurement of extracellular biosorption and intercellular bioaccumulation of copper indicated that biosorption efficiencies for aerobic cells (37%) and anaerobic cells (38%) were similar but the bioaccumulation by anaerobic cells was almost ten-fold higher than that by aerobic cells, indicating bioaccumulation contributed most in copper reduction under anaerobic conditions. Overall, the results suggested the facultative strain C. freundii JPG1 had great potential in the treatment of copper-laden industrial wastewater under both aerobic and anaerobic conditions.

Microbial enhanced oil recovery in Baolige Oilfield using an indigenous facultative anaerobic strain Luteimonas huabeiensis sp. nov

A facultative strain Luteimonas huabeiensis sp. nov. HB-2 isolated from Baolige Oilfield of China was examined for its growth, biosurfactant production, hydrocarbon degradation and the effects on interfacial properties of oil recovery system. Specifically, the effects on reduction of fluid surface tension and oil viscosity, and on increase in emulsification activity for crude oil were evaluated. This was attributed to the combination of the strain's activities including the production of biosurfactants (cyclic lipopeptides) and the degradation of crude oil. The produced biosurfactants can effectively reduce the interfacial tension of oil-water and viscosity of crude oil. Meanwhile, the long-chain hydrocarbons (C20-C35) of crude oil also can be degraded by bacteria resulting in the increase in shorter chain (C10-C19). These activities demonstrated the suitability of strain HB-2 for application in microbial enhanced oil recovery (MEOR). This was confirmed by a laboratory-based core column flooding evaluation, showing an average increase of 11% in oil recovery, which was followed by an oilfield test involving two water injection wells and eight oil production wells over 16 months, resulting in a remarkable increase in the average single well oil production from 0.48 ton/day (without MEOR) to 1.77 ton/day with the highest reaching 9.5 ton/day by MEOR.

Draft Genome Sequence of Methylocella silvestris TVC, a Facultative Methanotroph Isolated from Permafrost.

ABSTRACTPermafrost environments play a crucial role in global carbon and methane cycling. We report here the draft genome sequence of Methylocella silvestris TVC, a new facultative methanotroph strain, isolated from the Siksik Creek catchment in the continuous permafrost zone of Inuvik (Northwest Territories, Canada).

Isolation of a facultative anaerobic exoelectrogenic strain LZ-1 and probing electron transfer mechanism in situ by linking UV/Vis spectroscopy and electrochemistry

A new facultative anaerobic exoelectrogenic strain LZ-1, belonging to Citrobacter freundii, has been isolated. This strain can produce current densities of 843.9 and 865.6μAcm−2 using citrate or acetate as carbon source in a three-electrode configuration. The electricity generation performance was also analyzed in a dual-chamber MFC system, reaching a maximum power density of 1233mWm−2. In addition to acetate and citrate, other carbon sources such as pyruvate, formate, acetate, citrate and fumarate could also be utilized to produce current by strain LZ-1. Data supports the presence of electroactive c-type cytochromes in C. freundii sp. when grown on ITO electrodes, by linking spectroscopy and electrochemistry in situ. Since facultative strains possess many desirable properties compared to anaerobic strains, strain LZ-1 represents a promising exoelectrogenic species in engineering of biological catalysts for microbial electrochemistry.

Three stage cultivation process of facultative strain of Chlorella sorokiniana for treating dairy farm effluent and lipid enhancement

Reserve lipids of microalgae are promising for biodiesel production. However, economically feasible and sustainable energy production from microalgae requires optimization of cultivation conditions for both biomass yield and lipid production of microalgae. Biomass yield and lipid production in microalgae are a contradictory problem because required conditions for both targets are different. Simultaneously, the mass cultivation of microalgae for biofuel production also depends extremely on the performance of the microalgae strains used. In this study a green unicellular microalgae Chlorella sorokiniana (DS6) isolated from the holding tanks of farm wastewater treatment plant using multi-step screening and acclimation procedures was found high-lipid producing facultative heterotrophic microalgae strain capable of growing on dairy farm effluent (DFE) for biodiesel feedstock and wastewater treatment. Morphological features and the phylogenetic analysis for the 18S rRNA identified the isolated strains. A novel three stage cultivation process of facultative strain of C. sorokiniana was examined for lipid production.

Screening of facultative strains of high lipid producing microalgae for treating surfactant mediated municipal wastewater

This study discusses a novel approach to simultaneously remove two types of hazardous chemicals, surfactants and nutrients, from municipal wastewater by culturing selected microalgae.

Degradation of dibutyl phthalate in refuse from different phases of landfill by its dominant bacterial strain, Enterobacter sp. T1

A facultative bacterial strain isolated from municipal solid waste (MSW) obtained from a simulated landfill bioreactor was found to have the ability to use dibutyl phthalate (DBP) as its sole source of carbon and energy. Based on its morphology, physiochemical characteristics, and 16S rDNA sequence, the strain was identified as Enterobacter sp. T1. Evaluation of the degradation of DBP in refuse collected during the initial, acidic, and methanogenic phases of landfill before and after inoculation with Enterobacter sp. T1 revealed that the degradation fits first-order kinetic models for refuse from all phases. The removal rate of DBP in the refuse of the methanogenic phase increased from 59.3% to 74.5% when Enterobacter T1 was added. The half-life of DBP in refuse from the methanogenic phase that was inoculated with Enterobacter T1 decreased by 36.7% relative to uninoculated samples, and the intermediate products monobutyl phthalate (MBP) and phthalic acid were detected in all samples. These results provide new evidence for the potential of applying Enterobacter sp. for phthalic acid ester-polluted area remediation.

Transferable Denitrification Capability of Thermus thermophilus

Laboratory-adapted strains of Thermus spp. have been shown to require oxygen for growth, including the model strains T. thermophilus HB27 and HB8. In contrast, many isolates of this species that have not been intensively grown under laboratory conditions keep the capability to grow anaerobically with one or more electron acceptors. The use of nitrogen oxides, especially nitrate, as electron acceptors is one of the most widespread capabilities among these facultative strains. In this process, nitrate is reduced to nitrite by a reductase (Nar) that also functions as electron transporter toward nitrite and nitric oxide reductases when nitrate is scarce, effectively replacing respiratory complex III. In many T. thermophilus denitrificant strains, most electrons for Nar are provided by a new class of NADH dehydrogenase (Nrc). The ability to reduce nitrite to NO and subsequently to N2O by the corresponding Nir and Nor reductases is also strain specific. The genes encoding the capabilities for nitrate (nar) and nitrite (nir and nor) respiration are easily transferred between T. thermophilus strains by natural competence or by a conjugation-like process and may be easily lost upon continuous growth under aerobic conditions. The reason for this instability is apparently related to the fact that these metabolic capabilities are encoded in gene cluster islands, which are delimited by insertion sequences and integrated within highly variable regions of easily transferable extrachromosomal elements. Together with the chromosomal genes, these plasmid-associated genetic islands constitute the extended pangenome of T. thermophilus that provides this species with an enhanced capability to adapt to changing environments.

Biodecolorization of textile dye effluent by Pseudomonas putida SKG-1 (MTCC 10510) under the conditions optimized for monoazo dye orange II color removal in simulated minimal salt medium

The decolorization studies were performed in orange II dye simulated minimal salt medium and textile effluent by a psychrotrophic Pseudomonas putida SKG-1 isolate. Maximum decolorization of initial 100 mg dye l−1 was achieved at optimum pH 8.0, 30 °C and 4.0% inoculum under static conditions during 96 h incubation. Supplementation with glucose at 0.4% (w/v) and ammonium sulfate (0.1%, w/v)) further enhanced dye decolorization to highest 92.8% within 96 h incubation. The strain was highly tolerant to dye up to 1000 mg l−1. Increasing dye concentration exerted inhibitory effect on bacterial growth and color removal. A direct correlation existed between bacterial growth and dye decolorization. Under above optimized conditions, 35.2% decolorization of unsterilized effluent by native microflora was achieved. The effluent decolorization marginally enhanced (41.3%) upon augmentation with P. putida, and substantially increased (50.2%) when supplemented with glucose and ammonium sulfate without augmentation. Maximum effluent decolorization of 69.5% occurred when supplemented with exogenous carbon and nitrogen source along with P. putida augmentation. Evidently, P. putida has great potential of textile effluent decolorization. GC–MS analysis indicated the formation of sulfanilic acid and 1,2 naphthoquinone as orange II biodegradation metabolites and FTIR analysis revealed the presence of carbonyl and hydroxyl groups. This facultative strain can be employed for sequential anaerobic-aerobic treatment strategy leading to effective dye decolorization anaerobically, and ultimate mineralization of textile dye effluent under aerobic conditions.

Could petroleum biodegradation be a joint achievement of aerobic and anaerobic microrganisms in deep sea reservoirs?

Several studies suggest that petroleum biodegradation can be achieved by either aerobic or anaerobic microorganisms, depending on oxygen input or other electron acceptors and appropriate nutrients. Evidence from in vitro experiments with samples of petroleum formation water and oils from Pampo Field indicate that petroleum biodegradation is more likely to be a joint achievement of both aerobic and anaerobic bacterial consortium, refining our previous observations of aerobic degradation. The aerobic consortium depleted, in decreasing order, hydrocarbons > hopanes > steranes > tricyclic terpanes while the anaerobic consortium depleted hydrocarbons > steranes > hopanes > tricyclic terpanes. The oxygen content of the mixed consortia was measured from time to time revealing alternating periods of microaerobicity (O2 ~0.8 mg.L-1) and of aerobicity (O2~6.0 mg.L-1). In this experiment, the petroleum biodegradation changed from time to time, alternating periods of biodegradation similar to the aerobic process and periods of biodegradation similar to the anaerobic process. The consortia showed preferences for metabolizing hydrocarbons > hopanes > steranes > tricyclic terpanes during a 90-day period, after which this trend changed and steranes were more biodegraded than hopanes. The analysis of aerobic oil degrading microbiota by the 16S rRNA gene clone library detected the presence of Bacillus, Brevibacterium, Mesorhizobium and Achromobacter, and the analysis of the anaerobic oil degrading microbiota using the same technique detected the presence of Bacillus and Acinetobacter (facultative strains). In the mixed consortia Stenotrophomonas, Brevibacterium, Bacillus, Rhizobium, Achromobacter and 5% uncultured bacteria were detected. This is certainly a new contribution to the study of reservoir biodegradation processes, combining two of the more important accepted hypotheses.

The role of the nitrate respiration element of Thermus thermophilus in the control and activity of the denitrification apparatus

The nitrate conjugative element (NCE) encodes the ability to respire nitrate in the facultative Thermus thermophilus NAR1 strain. This process is carried out by two heterotetrameric enzymes that catalyse the oxidation of NADH (Nrc) and the reduction of nitrate (Nar), whose expression is activated by the NCE-encoded transcription factors DnrS and DnrT. We report the presence of NCE in other facultative strains of T. thermophilus and analyse its role in subsequent steps of the denitrification pathway. We encountered that nrc mutants of denitrifying strains show a decrease in anaerobic growth rates not only with nitrate, but also with nitrite, NO and N(2)O, which is concomitant to their lower NADH oxidation activities in vitro. We show that nitrate, nitrite and NO are activating signals for transcription of nrc in these strains. Finally, we demonstrate that DnrS and DnrT are required for anaerobic growth not only with nitrate, but also with nitrite, NO and N(2)O. These data allow us to conclude that: (i) Nrc constitutes the main electron donor for the four reductases of the denitrification pathway, and (ii) the NCE controls the expression of the whole denitrification pathway and the repression of the aerobic respiration through the transcription factors DnrS and DnrT.

Utilization of the nitrate reductase enzymatic pathway to reduce enteric pathogens in chickens

Previous reports have shown that some bacteria, including Salmonella, use a dissimilatory nitrate reductase enzyme pathway (NREP) in anaerobic environments. This enzyme reduces nitrate to nitrite and has been shown to cometabolize chlorate to cytotoxic chlorite. The present investigations were performed to evaluate the susceptibility of a competitive exclusion culture (CE) to the experimental chlorate product (ECP). A commercially available CE product was evaluated for its nitrate reductase activity and therefore its chlorate sensitivity. Individual isolates (in triplicate) were cultured in 10 mL of Viande Levure broth containing 5 mM sodium nitrate or 10 mM sodium chlorate. Bacterial growth (optical density at 625 nm) was measured and 1-mL aliquots were removed concurrently for colorimetric determination of nitrate content at 0, 3, 6, and 24 h. Of the 15 different facultative strains, 11 had slight NREP utilization, 3 had moderate NREP utilization, and the remainder were NREP negative (with slight and moderate NREP utilization: >0.1 to <1.0 mM and >1.0 mM nitrate used within 6 h, respectively). Of the obligate anaerobes evaluated, 3 had slight NREP utilization and the remainder were NREP negative. In vivo studies utilizing both products (CE and ECP) in a horizontal transmission challenge model (seeders + contacts) showed significant reductions in Salmonella from 5.37 to 1.76 log10 cfu/g and 3.94 to 0.07 log10 cfu/g, respectively. The combined effect of the CE culture and an ECP are effective in killing these food-borne pathogens.

Apical periodontitis development and bacterial response to endodontic treatment. Experimental root canal infections in monkeys with selected bacterial strains.

In six monkeys, 160 root canals were inoculated with a combination of four bacterial strains belonging to species Streptococcus milleri, Peptostreptococcus anaerobius, Prevotella oralis, and Fusobacterium nucleatum. In two other monkeys, 24 root canals were inoculated with a five-strain combination consisting of these strains and a strain of Enterococcus faecalis. All strains were previously isolated from an infected monkey root canal. After 8-12 months, survival of the strains was recorded bacteriologically, and the reaction in the periapical region was radiographed. From 180 of 184 root canals, one or more of the bacterial strains were reisolated. The two facultative strains were more frequently reisolated than the anaerobic strains. Apical periodontitis was registered in the periapical region of more than 96% of root canals with reisolated bacteria but in none of those without reisolated bacteria. Endodontic treatment was carried out in two sessions with an interval of 14 d without interappointment dressings, and the effect was evaluated bacteriologically before and after each treatment. The chemo-mechanical treatment reduced significantly the number of strains and bacterial cells. The facultative bacteria were more resistant to the treatment than the anaerobic bacteria. The five-strain combination had a higher survival rate than the four-strain combination.

Facultative Sexual Reproduction Under Frequency-Dependent Selection on a Single Locus

The evolution of a facultative sexual strategy that simultaneously produced sexual and asexual individuals was studied theoretically, under negative frequency-dependence of fitness. The organism was considered to be diploid, characterized by two loci concerning fitness and determining sexual strategy, between which a certain degree of linkage existed. The locus concerning fitness was assumed to involve two alleles, resulting in three genotypes, the relative fitness of an individual being defined by a decreasing function of frequency of its own genotype on this locus in the population. The sexual reproductive strategy was considered to be determined by three alleles; asexual, obligate sexual and facultative sexual. Simulations under various linkages between loci and level of frequency dependence of fitness showed that a facultative sexual strategy was generally able to invade and increase in the population. In particular, when the level of frequency dependence was high to some degree, the facultative strain producing many sexual individuals tended to exclusively occupy the population. Namely, the frequency-dependent selection resulted in a predominance of obligate sexual strategy over asexual strategy, simultaneously causing a subordination of the former to the facultative sexual strategy. This indicated that the evolution of sex should be considered carefully with respect to the possibility of invasion of facultative sex.

A study of the prevalence of hydrogen peroxide generating Lactobacilli in bacterial vaginosis: the determination of H2O2 concentrations generated, in vitro, by isolated strains and the levels found in vaginal secretions of women with and without infection

The concentration of hydrogen peroxide in the vaginal secretions of normal women were compared with levels found in women infected with bacterial vaginosis (BV). The mean concentration found in 90 normal samples was 0.171 μg per ml, whereas in women with BV, the mean level was 0.04 mug per ml (P < 0.001). In vitro culture experiments using TMB agar showed that in normal women, 75% of Lactobacillus strains produced H2O2 and 25% did not, whereas in women 'infected' with BV. 14% of the isolates produced H2O2 and 86% did not (P < 0.001). Quantitative culture tests showed that both anaerobic and facultative strains of Lactobacilli isolated from normal women generated significantly higher levels of H2O2 than strains cultured from women with BV. Anaerobic strains isolated from normal women produced a mean level of 6.8 μg per ml, compared with the mean level of 1.4 μg per ml from women with BV. Facultative strains from normal women produced mean levels of 18.3 μg per ml compared with 2.4 μg per ml produced by strains from BV-infected women, which had been incubated under the same conditions (P < 0.001). There results indicate that Lactobacilli which produce H2O2 probably have a significant role in protecting the vaginal ecosystem from BV infection.

National survey of the in vitro spectrum of piperacillin-tazobactam tested against more than 40,000 aerobic clinical isolates from 236 medical centers

Hospital microbiology laboratories from 41 states participated in a bacterial antimicrobial susceptibility study comparing in vitro results generated by the standardized disk diffusion method. Over 41,000 freshly isolated aerobic and facultative strains, representing all specimen types (except stools and urines), were tested for their susceptibility to piperacillin-tazobactam and 21 other antimicrobial agents. Enterococcus spp. was the second or third most common isolate from intraabdominal, gynecologic, and cutaneous infections, confirming its growing importance as a nosocomial pathogen. Escherichia coli was the most frequent isolate overall, despite the exclusion of urinary tract specimens from the study. Pseudomonas aeruginosa was the second most prevalent species, ranking first in frequency of recovery from lower-respiratory-tract specimens. Piperacilin-tazobactam was the most active β-lactamase inhibitor combination tested against Gram-negative bacteria. Its activity against Gram-positive bacteria and Haemophilus influenzae was similar to that of ampicillin-sulbactam (95–97% susceptible). Imipenem and piperacillin-tazobactam displayed similar spectrums of activity against Gram-positive organisms and Haemophilus influenzae. Against Enterobacteriaceae, piperacillin-tazobactam and ceftazidime exhibited similarly wide spectrums of activity, but with some gaps, particularly among Enterobacter spp. and Citrobacter freundii, In this large-scale in vitro study, piperacillin-tazobactam and imipenem displayed the widest antimicrobial spectrums, inhibiting >90% of all isolates tested.