Nutritional Similarity between Leaf-Associated Nonpathogenic Bacteria and the Pathogen Is Not Predictive of Efficacy in Biological Control of Bacterial Spot of Tomato

It has been demonstrated that for a nonpathogenic, leaf-associated bacterium, effectiveness in the control of bacterial speck of tomato is correlated with the similarity in the nutritional needs of the nonpathogenic bacterium and the pathogen Pseudomonas syringae pv. tomato. This relationship was investigated further in this study by using the pathogen Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot of tomato, and a collection of nonpathogenic bacteria isolated from tomato foliage. The effects of inoculation of tomato plants with one of 34 nonpathogenic bacteria prior to inoculation with the pathogen X. campestris pv. vesicatoria were quantified by determining (i) the reduction in disease severity (number of lesions per square centimeter) in greenhouse assays and (ii) the reduction in leaf surface pathogen population size (log₁₀ of the number of CFU per leaflet) in growth chamber assays. Nutritional similarity between the nonpathogenic bacteria and X. campestris pv. vesicatoria was quantified by using either niche overlap indices (NOI) or relatedness in cluster analyses based upon in vitro utilization of carbon or nitrogen sources reported to be present in tomato tissues or in Biolog GN plates. In contrast to studies with P. syringae pv. tomato, nutritional similarity between the nonpathogenic bacteria and the pathogen X. campestris pv. vesicatoria was not correlated with reductions in disease severity. Nutritional similarity was also not correlated with reductions in pathogen population size. Further, the percentage of reduction in leaf surface pathogen population size was not correlated with the percentage of reduction in disease severity, suggesting that the epiphytic population size of X. campestris pv. vesicatoria is not related to disease severity and that X. campestris pv. vesicatoria exhibits behavior in the phyllosphere prior to lesion formation that is different from that of P. syringae pv. tomato.     

Enhancement of Population Size of a Biological Control Agent and Efficacy in Control of Bacterial Speck of Tomato through Salicylate and Ammonium Sulfate Amendments

Sodium salicylate and ammonium sulfate were applied to leaf surfaces along with suspensions of the biological control agents Pseudomonas syringae Cit7(pNAH7), which catabolizes salicylate, and Cit7, which does not catabolize salicylate, to determine whether enhanced biological control of bacterial speck of tomato could be achieved. Foliar amendment with salicylate alone significantly enhanced the population size and the efficacy of Cit7(pNAH7), but not of Cit7, on tomato leaves. Application of ammonium sulfate alone did not result in enhanced population size or biological control efficacy of either Cit7(pNAH7) or Cit7; however, when foliar amendments with both sodium salicylate and ammonium sulfate were applied, a trend toward further increases in population size and biological control efficacy of Cit7(pNAH7) was observed. This study demonstrates the potential of using a selective carbon source to improve the efficacy of a bacterial biological control agent in the control of a bacterial plant disease and supports previous conclusions that the growth of P. syringae in the phyllosphere is primarily carbon limited and secondarily nitrogen limited.     

Carbon Source Utilization Profiles for Microbial Communities from Hydrologically Distinct Zones in a Basalt Aquifer

Abstract The Eastern Snake River Plain aquifer has hydrologically distinct zones in basalt flow units and interbedded sediments. The zones that differ markedly in physical features (e.g., porosity and permeability) have similar groundwater chemistries. The primary objective of this study was to determine whether intervals within the aquifer that contrast on the basis of permeability have distinct communities of unattached microorganisms based on functional attributes. Aquifer sampling was conducted using a submersible pump to obtain whole-well (w) samples, and a straddle-packer pump (SPP) to obtain samples from specific aquifer intervals that were vertically distributed in the open borehole. The SPP intervals ranged from 4.6 to 6.1 m in length and were located from 142 to 198 m below land surface. A community-level physiological profile (CLPP) was used to determine functional characteristics of the microbial community in the groundwater samples based on the community response to 95 sole organic carbon sources. Surface soil samples at the site were analyzed in a similar manner for comparison. The total bacterial population in the groundwater samples was determined using acridine orange direct counts. Principal components analysis (PCA) of the CLPP dataset distinguished between surface soil and aquifer microbial communities. Soils scored low in the respiration of polymers, esters, and amines and high in bromosuccinate, when compared to aquifer samples. The W samples were distinct from SPP samples. The 180- to 198-m interval, with the lowest hydraulic conductivity of all intervals, yielded samples that grouped together by PCA and cluster analysis. Direct counts varied between 10⁴ and 10⁵ cells ml⁻¹, and showed no relationship to the depth of the sample or to the hydraulic conductivity of the sample interval. Differences between microbial communities based on respired carbon compounds were discerned in separate, hydrologically distinct intervals within the borehole, although these differences were slight. Differences among aquifer intervals were less apparent than differences between surface soils and groundwater, and may be related to variations in hydrologic properties over the intervals sampled. The results suggest that free-living microbial communities in basalt aquifers, as characterized by CLPP are relatively unaffected by wide ranges in hydraulic conductivity when other abiotic factors are essentially equal. Received: 14 December 1995; Revised: 12 April 1996     

Application of Carbon Source Utilization Patterns To Measure the Metabolic Similarity of Complex Dental Plaque Biofilm Microcosms

Biolog technology was applied to measure the metabolic similarity of plaque biofilm microcosms, which model the complex properties of dental plaque in vivo. The choice of Biolog plate, incubation time, and incubation conditions strongly influenced utilization profiles. For plaque biofilm microcosms, Biolog GP2 plates incubated anaerobically in an H₂-free atmosphere gave the clearest profile. To test the application of the Biolog GP2 assay, plaque microcosms were developed under different nutrient conditions in which the frequency of sucrose application was varied. Cluster analysis of Biolog GP2 data from 10 microcosm biofilms correlated with sucrose frequency. Aciduric bacteria (Streptococcus mutans plus lactobacilli) predominated in the plaques receiving high-frequency sucrose applications. Agreement between the Biolog GP2 groupings with nutrient and compositional changes suggests that Biolog analysis is a valuable technique for analyzing the metabolic similarity of dental plaque biofilm microcosms and other high-nutrient or predominantly anaerobic ecosystems.     

Relationship between Phylogeny and Pathotype for the Bacterial Blight Pathogen of Rice

Several transposable elements were isolated from the genome of Xanthomonas oryzae pv. oryzae. These elements and an avirulence gene isolated from X. oryzae pv. oryzae were used as hybridization probes for a collection of X. oryzae pv. oryzae strains from the Philippines. Each of the sequences was present in multiple copies in all strains examined and showed distinct patterns of hybridizing bands. Phenograms were derived from the restriction fragment length polymorphism data obtained for each of the individual probes and for pooled data from multiple probes. The phenograms derived from the different probes differed in topology and, on the basis of bootstrap analysis, were not equally robust. For all of the probes, including the avirulence gene, some groups (even some haplotypes) consisted of multiple races. The strains were grouped into four major clusters on the basis of the two probes giving the highest bootstrap values. These groups were inferred to represent phylogenetic lineages. Three of the six races of X. oryzae pv. oryzae appeared in more than one of the lineages, and another was present in two sublineages. For three of the races, strains representing different phenetic groups were inoculated on rice cultivars carrying 10 resistance genes. Two new races were differentiated, corresponding to pathogen lineages identified by DNA typing. On the basis of DNA and pathotypic analyses, together with information on the spatial and temporal distribution of the pathogen types from this and other studies, a general picture of X. oryzae pv. oryzae evolution in the Philippines is presented.     

Increased Light Availability Reduces the Importance of Bacterial Carbon in Headwater Stream Food Webs

Many ecosystems rely on subsidies of carbon and nutrients from surrounding environments. In headwater streams that are heavily shaded by riparian forests, allochthonous inputs from terrestrial systems often comprise a major part of the organic matter budget. Bacteria play a key role in organic matter cycling in streams, but there is limited evidence about how much bacterial carbon is actually assimilated by invertebrate and fish consumers, and how bacterial carbon assimilation varies among streams. We conducted stable isotope tracer additions of ¹³C-acetate, that is assimilated only by bacteria, and ¹⁵N-ammonium, that is assimilated by both bacteria and algae, in two small, shaded streams in the Adirondack region of New York State, USA. Our goal was to determine whether there is an important trophic link between bacteria and macroconsumers, and whether the link changes when the light environment is experimentally altered. In 2009, we evaluated bacterial carbon use in both streams with natural canopy cover using 10-day dual-isotope tracer releases. The canopy was then thinned in one stream to increase light availability and primary production and tracer experiments were repeated in 2010. As part of the tracer experiments, we developed a respiration assay to measure the δ ¹³C content of live bacteria, which provided critical information for determining how much of the carbon assimilated by invertebrate consumers is from bacterial sources. Some invertebrate taxa, including scraper mayflies (Heptagenia spp.) that feed largely on biofilms assimilated over 70% of their carbon from bacterial sources, whereas shredder caddisflies (Pycnopsyche spp.) that feed on decomposing leaves assimilated less than 1% of their carbon from bacteria. Increased light availability led to strong declines in the magnitude of bacterial carbon fluxes to different consumers (varying from ?17 to ?91% decrease across invertebrate taxa), suggesting that bacterial energy assimilation differs not only among consumer taxa but also within the same consumer taxa in streams with different ecological contexts. Our results demonstrate that fluxes of bacterial carbon to higher trophic levels in streams can be substantial, that is over 70% for some taxa, but that invertebrate taxa vary considerably in their reliance on bacterial carbon, and that local variation in carbon sources controls how much bacterial carbon invertebrates use.     

Ecological Similarity and Coexistence of Epiphytic Ice-Nucleating (Ice+) Pseudomonas syringae Strains and a Non-Ice-Nucleating (Ice-) Biological Control Agent

De Wit replacement series were used to study competitive interactions between epiphytic Ice⁺Pseudomonas syringae strains and the biological frost control agents Ice^-P. syringae TLP2del1 and Pseudomonas fluorescens A506. Mixtures containing two strains in different proportions but at a constant total population size were inoculated onto potato leaves. The population sizes of each strain and the total population size were determined when the community had reached equilibrium. A near-isogenic P. syringae strain pair exhibited an interaction similar to that expected for strains competing equally for limiting environmental resources. Replacement series with nonisogenic Ice⁺ and Ice^-P. syringae strain pairs suggested that these strains competed for limiting resources according to their relative competitive abilities. There was no evidence of any niche differentiation between the Ice⁺P. syringae strains and the Ice^-P. syringae strain. The growth responses of epiphytes following addition of nutrients to the phyllosphere indicated that the epiphytic P. syringae populations were nutrient limited and that, under growth chamber conditions, the populations were more limited by the availability of carbon than by the availability of nitrogen. Determination of in vitro carbon source utilization profiles provided further evidence for the lack of niche differentiation between the Ice⁺ and the Ice^-P. syringae strains. Niche overlap indices calculated for the Ice⁺P. syringae strains with respect to Ice^-P. syringae TLP2del1 were uniformly high, indicating ecological similarity, and were consistent with the observed low level of coexistence. The biological frost control agent P. fluorescens A506 replaced P. syringae. This was correlated with a high degree of niche overlap between these species.     

Bipolaris euphorbiae as a Biological Control Agent for Wild Poinsettia (Euphorbia heterophylla): Host-Specificity and Variability in Pathogen and Host Populations

Bipolaris euphorbiae (anamorphic Ascomycota: Pleosporaceae) has been studied since the early 1980s as a potential biocontrol agent of wild poinsettia (Euphorbia heterophylla), a noxious invader of soybean fields in Brazil. A new isolate (KLN05) was arbitrarily selected after the aggressiveness of six isolates of the fungus obtained from different sites was evaluated on wild poinsettias grown from seeds obtained from six different geographic origins in Brazil: Viçosa-state of Minas Gerais; Itabuna-state of Bahia; Niterói-state of Rio de Janeiro; Nova Laranjeira, Londrina and Foz do Iguaçú-state of Paraná. Bipolaris euphorbiae grew between 10 and 30 °C, with the optimum for colony growth at 25 °C. The best temperature range for conidial germination was between 20 and 30 °C. Conidial germination was not inhibited by mixing conidia with imazethapyr (106 g of active ingredient [a.i.]/l), glyphosate (720 g of a.i./kg), fomesafen (250 g of a.i./l), carfentrazone (400 g of a.i./l), atrazine (500 g of a.i./l) and glyphosate+carfentrazone (720 g of a.i/kg+400 g of a.i/l). Bipolaris euphorbiae was inoculated on plants belonging to 32 species of 12 different plant families and was only capable of infecting E. heterophylla.     

Bacterial Community Structure in Relation to the Carbon Environments in Lettuce and Tomato Rhizospheres and in Bulk Soil

Abstract Crop roots provide dynamic nutrient environments within agroecosystems that can influence the relative abundance and activity of oligotrophic and copiotrophic microorganisms. Copiotrophic organisms grow in carbon (C)-rich environments and their distribution implies that C abundance favors their survival. Survival of oligotrophic organisms is dependent on their ability to multiply and maintain activity in habitats of low C flux. To determine if spatial variation in available C along the root coincides with different physiological groups of bacteria, we isolated bacteria from the rhizosphere at different locations along the tap root of lettuce and tomato plants grown under greenhouse and field conditions. In all five experiments, the overall numbers of both oligotrophs and copiotrophs were high at the upper portions of the root and lower at tip locations and in the bulk soil environment. Consistent patterns in the ratio of copiotrophic to oligotrophic (C:O) bacteria along the roots of lettuce and tomato were obtained and clearly showed that the C:O ratio was different for these two crop species. With lettuce, C:O ratios were high at the root tip (1.22 to 1.61) and upper mid-root locations (0.90 to 1.30), intermediate at the lower mid-root locations (0.73 to 0.95), and low at the root base (0.56 to 0.76). With tomato, C:O ratios were low at root tip locations (0.50 to 0.68) and high at mid and base locations along the root (1.20 to 1.28). These differences may reflect qualitative and quantitative differences in root exudates between these crop species. In our experiments, nitrogen (N) concentrations and lateral branch sites, providing C sources, were important factors influencing bacterial populations in the rhizosphere of lettuce and tomato. Competitive interactions between microorganisms and physiological constraints with respect to substrate affinity may be two important mechanisms influencing bacterial populations and structure of rhizosphere communities. Received: 14 August 1996; Accepted: 10 December 1996     

Suppression of the Bacterial Spot Pathogen Xanthomonas euvesicatoria on Tomato Leaves by an Attenuated Mutant of Xanthomonas perforans

A bacteriocin-producing strain of the bacterial spot of tomato plant pathogen, Xanthomonas perforans, with attenuated pathogenicity was deployed for biocontrol of a bacteriocin-sensitive strain of the genetically closely related bacterial spot of tomato plant pathogen, X. euvesicatoria. The attenuated mutant (91-118ΔopgHΔbcnB) of X. perforans was tested in leaf tissue and shown to significantly inhibit internal populations of the wild-type X. euvesicatoria strain although significantly less than the wild-type 91-118 strain, whereas in a phyllosphere inhibition assay, the mutant strain reduced epiphytic populations comparably to 91-118. Thus, the attenuated mutant limited the sensitive bacterium more efficiently on the leaf surface than inside the leaf. In field experiments, weekly application of 91-118ΔopgHΔbcnB significantly reduced X. euvesicatoria populations compared to the growers’ standard control (copper hydroxide and mancozeb applied weekly and acibenzolar-S-methyl applied every 2 weeks). The biological control agent, 91-118ΔopgHΔbcnB, applied every 2 weeks also significantly reduced X. euvesicatoria populations in one season but was not significantly different from the growers’ standard control. Potentially, attenuated pathogenic strains could be deployed as biological control agents in order to improve disease control of foliar plant pathogens.Bacterial spot of tomato is incited by several Xanthomonas spp., including Xanthomonas euvesicatoria, X. perforans, and X. vesicatoria (13). On tomato plants, three races, designated tomato race 1 (T1), T2, and T3, were originally identified based on their reactions on three tomato genotypes (22, 23, 33, 37). These races, T1, T2, and T3, are principally members of X. euvesicatoria, X. vesicatoria, and X. perforans, respectively. Control of bacterial spot of tomato is extremely difficult when moderate-to-high temperatures and high moisture conditions exist. The disease causes significant damage to the crop, resulting in major losses (27). Management is primarily limited to bactericides, such as fixed coppers (3, 20, 32); however, copper-tolerant strains have become prevalent (31, 32) and chemical control alone is insufficient to control the disease under optimal weather conditions. Additionally, the use of copper compounds has led to soil contamination in some instances (16).Recently, there has been increased interest in integrated biological control strategies for bacterial diseases (5, 7, 11, 19, 23). However, optimization of biocontrol agents for consistent disease suppression for many bacterial diseases has been difficult. Studies are increasing our understanding of the ecology of nonpathogenic saprophytes as biocontrol agents, but their selection is limited to labor-intensive protocols. New biological control strategies are currently being sought, including the use of bacteriocins, bacteriophages, and attenuated plant pathogens (4, 5, 7, 9, 11, 23, 26, 35, 38).For many years, only X. euvesicatoria (T1) was present on tomato plants in Florida. In 1991, X. perforans (T3) appeared in Florida tomato fields (15) and eventually became the prevalent race (14). Following that observation, Jones et al. (12) demonstrated that when X. perforans and X. euvesicatoria were coinoculated onto tomato plants in the field, X. perforans displaced X. euvesicatoria and became the predominant strain. Further studies revealed that the competitive nature of X. perforans was due in large part to its antagonism toward X. euvesicatoria strains (9, 12, 36). Tudor-Nelson et al. (36) identified three different bacteriocins, designated BCN-A, BCN-B, and BCN-C, which were found to confer the ability to inhibit X. euvesicatoria strains in plate assays. Hert et al. (9) determined that these bacteriocins provided X. perforans strains with a competitive advantage in the greenhouse and field and that a mutant X. perforans strain expressing only BCN-A and BCN-C was most effective in displacing X. euvesicatoria and outcompeted wild-type (WT) X. perforans. Field experiments conducted with a nonpathogenic Hrp⁻ strain of X. perforans as a potential biocontrol agent for controlling X. euvesicatoria resulted in marginal control (18). Although the WT X. perforans strain has a competitive advantage over X. euvesicatoria populations, Hrp⁻ mutants such as that used in the study by Liu (18) do not appear to have the necessary competitiveness to suppress X. euvesicatoria populations.Previous research has focused on colonization of the plant by biocontrol agents to determine the relationship between invasion efficiency and biological control efficacy. For example, Frey et al. (8) achieved only low-to-moderate levels of biological control of a WT bacteriocin-sensitive strain of Ralstonia solanacearum when using a bacteriocin-producing nonpathogenic Hrp⁻ mutant strain of R. solanacearum. However, control using a moderately pathogenic hrp mutant (hrcV) capable of higher levels of colonization of the root and stem achieved greater disease suppression (6). Etchebar et al. (6) suggested that there was a positive correlation between colonization of the xylem by the hrp mutant and the level of control of WT R. solanacearum. As a result of previous studies showing that nonpathogenic strains of X. perforans only provide low levels of biological control (18), we hypothesized that using an attenuated pathogenic bacteriocin-producing strain of X. perforans rather than a nonpathogenic strain may increase the efficiency of control under field conditions.In this study, our strategy was to use an attenuated mutant of X. perforans that colonizes leaf tissue more effectively than nonpathogenic strains do and potentially provides more effective colonization and increases the likelihood for interaction between X. perforans and X. euvesicatoria. We selected strain 91-118ΔopgHΔbcnB as the biocontrol agent since it was previously shown that deletion of the osmoregulated periplasmic glucan gene opgH resulted in a pathogenic phenotype with a significantly reduced ability to cause disease and internal colonization in susceptible tomato tissue (22). The selected mutant also lacked BcnB activity based on a previous study in which BcnB appeared to negatively affect competitive ability in that a ΔbcnB mutant was more effective at colonizing tomato leaves in field experiments than WT X. perforans was (9).     

Metabolism of Phosphonoacetate as the Sole Carbon and Phosphorus Source by an Environmental Bacterial Isolate

A gram-negative bacterium isolated from activated sludge was able to utilize up to 25 mM phosphonoacetate as the sole carbon and phosphorus source, with simultaneous excretion of virtually equimolar levels of phosphate. 2-Aminoethylphosphonate was similarly utilized with equivalent growth rates and cellular yields, while 3-aminopropyl-, 4-aminobutyl-, methyl-, ethyl-, and phenylphosphonates served only as phosphorus sources.     

Utilization of Glyphosate as Phosphate Source: Biochemistry and Genetics of Bacterial Carbon-Phosphorus Lyase

SUMMARY

After several decades of use of glyphosate, the active ingredient in weed killers such as Roundup, in fields, forests, and gardens, the biochemical pathway of transformation of glyphosate phosphorus to a useful phosphorus source for microorganisms has been disclosed. Glyphosate is a member of a large group of chemicals, phosphonic acids or phosphonates, which are characterized by a carbon-phosphorus bond. This is in contrast to the general phosphorus compounds utilized and metabolized by microorganisms. Here phosphorus is found as phosphoric acid or phosphate ion, phosphoric acid esters, or phosphoric acid anhydrides. The latter compounds contain phosphorus that is bound only to oxygen. Hydrolytic, oxidative, and radical-based mechanisms for carbon-phosphorus bond cleavage have been described. This review deals with the radical-based mechanism employed by the carbon-phosphorus lyase of the carbon-phosphorus lyase pathway, which involves reactions for activation of phosphonate, carbon-phosphorus bond cleavage, and further chemical transformation before a useful phosphate ion is generated in a series of seven or eight enzyme-catalyzed reactions. The phn genes, encoding the enzymes for this pathway, are widespread among bacterial species. The processes are described with emphasis on glyphosate as a substrate. Additionally, the catabolism of glyphosate is intimately connected with that of aminomethylphosphonate, which is also treated in this review. Results of physiological and genetic analyses are combined with those of bioinformatics analyses.     

Bacterial Cooperation Causes Systematic Errors in Pathogen Risk Assessment due to the Failure of the Independent Action Hypothesis

The Independent Action Hypothesis (IAH) states that pathogenic individuals (cells, spores, virus particles etc.) behave independently of each other, so that each has an independent probability of causing systemic infection or death. The IAH is not just of basic scientific interest; it forms the basis of our current estimates of infectious disease risk in humans. Despite the important role of the IAH in managing disease interventions for food and water-borne pathogens, experimental support for the IAH in bacterial pathogens is indirect at best. Moreover since the IAH was first proposed, cooperative behaviors have been discovered in a wide range of microorganisms, including many pathogens. A fundamental principle of cooperation is that the fitness of individuals is affected by the presence and behaviors of others, which is contrary to the assumption of independent action. In this paper, we test the IAH in Bacillus thuringiensis (B.t), a widely occurring insect pathogen that releases toxins that benefit others in the inoculum, infecting the diamondback moth, Plutella xylostella. By experimentally separating B.t. spores from their toxins, we demonstrate that the IAH fails because there is an interaction between toxin and spore effects on mortality, where the toxin effect is synergistic and cannot be accommodated by independence assumptions. Finally, we show that applying recommended IAH dose-response models to high dose data leads to systematic overestimation of mortality risks at low doses, due to the presence of synergistic pathogen interactions. Our results show that cooperative secretions can easily invalidate the IAH, and that such mechanistic details should be incorporated into pathogen risk analysis.     

Carbon Translocation in the Tomato: Carbon Import and Fruit Growth

The rates of carbon import by fruits were measured over 48 has the sum of the change in the total organic carbon contentof the fruit and the respiratory loss of carbon. Over a rangeof fruit sizes from 20–90 per cent of the maximum volumethe smaller fruits imported carbon at an absolute rate (mgCfruit^–1 h^–1) nearly twice that of the larger fruits.The imported leaf assimilates, identified as the ¹⁴C-compoundsalong the pathway between a ¹⁴CO₂-fed leaf and a young fruit,comprised 90 per cent sucrose and 10 per cent glutamic acid,aspartic acid and malic acid. Within the fruit the imported¹⁴C-sucrose was hydrolysed into hexoses. The changes in thelevels of starch and insoluble residue in the fruit were positivelycorrelated with the carbon import rates. In the largest fruitswith the lowest import rates, there was breakdown of insolubleresidue and less accumulation of starch, but a significant increasein the level of sucrose. The sink strength of a tomato fruitis dependent more on sink activity than on sink size.     

Cell-Size Homeostasis and the Incremental Rule in a Bacterial Pathogen

How populations of growing cells achieve cell-size homeostasis remains a major question in cell biology. Recent studies in rod-shaped bacteria support the “incremental rule” where each cell adds a constant length before dividing. Although this rule explains narrow cell-size distributions, its mechanism is still unknown. We show that the opportunistic pathogen Pseudomonas aeruginosa obeys the incremental rule to achieve cell-length homeostasis during exponential growth but shortens its cells when entering the stationary phase. We identify a mutant, called frik, which has increased antibiotic sensitivity, cells that are on average longer, and a fraction of filamentous cells longer than 10 μm. When growth slows due to entry in stationary phase, the distribution of frik cell sizes decreases and approaches wild-type length distribution. The rare filamentous cells have abnormally large nucleoids, suggesting that a deficiency in DNA segregation prevents cell division without slowing the exponential elongation rate.     

The Relation between Oral Candida Load and Bacterial Microbiome Profiles in Dutch Older Adults

Currently there are no evidence-based ecological measures for prevention of overgrowth and subsequent infection by fungi in the oral cavity. The aim of this study was to increase our knowledge on fungal-bacterial ecological interactions. Salivary Candida abundance of 82 Dutch adults aged 58-80 years was established relative to the bacterial load by quantitative PCR analysis of the Internal Transcribed (ITS) region (Candida) and 16S rDNA gene (bacteria). The salivary microbiome was assessed using barcoded pyrosequencing of the bacterial hypervariable regions V5-V7 of 16S rDNA. Sequencing data was preprocessed by denoising and chimera removal, clustered in Operational Taxonomic Units (OTUs) and assigned to taxonomy. Both OTU-based (PCA, diversity statistics) and phylogeny-based analyses (UniFrac, PCoA) were performed. Saliva of Dutch older adults contained 0-4 × 10(8) CFU/mL Candida with a median Candida load of 0.06%. With increased Candida load the diversity of the salivary microbiome decreased significantly (p<0.001). Increase in the Candida load correlated positively with class Bacilli, and negatively with class Fusobacteria, Flavobacteria, and Bacteroidia. Microbiomes with high Candida load were less diverse and had a distinct microbial composition towards dominance by saccharolytic and acidogenic bacteria - streptococci. The control of the acidification of the oral environment may be a potential preventive measure for Candida outgrowth that should be evaluated in longitudinal clinical intervention trials.     

Substrate Utilization Profiles of Bacterial Strains in Plankton from the River Warnow, a Humic and Eutrophic River in North Germany

Bacteria are very important degraders of organic substances in aquatic environments. Despite their influential role in the carbon (and many other element) cycle(s), the specific genetic identity of active bacteria is mostly unknown, although contributing phylogenetic groups had been investigated. Moreover, the degree to which phenotypic potential (i.e., utilization of environmentally relevant carbon substrates) is related to the genomic identity of bacteria or bacterial groups is unclear. The present study compared the genomic fingerprints of 27 bacterial isolates from the humic River Warnow with their ability to utilize 14 environmentally relevant substrates. Acetate was the only substrate utilized by all bacterial strains. Only 60% of the strains respired glucose, but this substrate always stimulated the highest bacterial activity (respiration and growth). Two isolates, both closely related to the same Pseudomonas sp., also had very similar substrate utilization patterns. However, similar substrate utilization profiles commonly belonged to genetically different strains (e.g., the substrate profile of Janthinobacterium lividum OW6/RT-3 and Flavobacterium sp. OW3/15-5 differed by only three substrates). Substrate consumption was sometimes totally different for genetically related isolates. Thus, the genomic profiles of bacterial strains were not congruent with their different substrate utilization profiles. Additionally, changes in pre-incubation conditions strongly influenced substrate utilization. Therefore, it is problematic to infer substrate utilization and especially microbial dissolved organic matter transformation in aquatic systems from bacterial molecular taxonomy.