Bacterial Colony Morphology Research Articles

Generalized spectral light scatter models of diverse bacterial colony morphologies.

An optical forward-scatter model was generalized to encompass the diverse nature of bacterial colony morphologies and the spectral information. According to the model, the colony shape and the wavelength of incident light significantly affect the characteristics of a forward elastic-light-scattering pattern. To study the relationship between the colony morphology and the scattering pattern, three-dimensional colony models were generated in various morphologies. The propagation of light passing through the colony model was then simulated. In validation of the theoretical modeling, the scattering patterns of three bacterial genera, Staphylococcus, Exiguobacterium and Bacillus, which grow into colonies having convex, crateriform and flat elevations, respectively, were qualitatively compared to the simulated scattering patterns. The strong correlations observed between simulated and experimental patterns validated the scatter model. In addition, spectral effect on the scattering pattern was studied using the scatter model, and experimentally investigated using Staphylococcus, whose colony has circular form and convex elevation. Both simulation and experiment showed that changes in wavelength affected the overall pattern size and the number of rings.

Identifikasi Penyakit Bakterial Pada Benih Sidat (Anguilla marmorata) di Balai Budidaya Air Tawar Tatelu

This study aimed to identify the bacterial disease in cultured eel elvers (Anguilla marmorata). The samples used for this study were taken from the Tatelu Freshwater Aquaculture Center. The samples taken were elvers (juvenile life stage of A. marmorata) which showed clinical symptoms of bacterial infection such as bleeding in the chest, abdomen, and the base of the fin, passive movement, weakness, and loss of balance of the body, loss of appetite, some wounds on back fin, chest, and tail, and the body was not slippery/shiny. Three elvers with the size of 4-6 cm, and weigh about 0.2 g were taken as samples. The organ chosen to be targeted for isolation was head kidney. Each sample was isolated twice as replicates and streaked on Triptic Soy Agar (TSA) medium. First replicates were identified in the Tatelu Health Lab of Freshwater Aquaculture, and the second replicates were identified in North Sulawesi Provincial Health Lab. Bacterial identification was done through a series of observations and morphology of bacterial colonies through gram stain, followed by biochemical tests through oxidase test, catalase test, Triple Sugar Iron Agar (TSIA) test, H2S production test, motility test, O/F test, and Simmons Citrate Agar (SCA) test. Water quality parameters that were measured included temperature, disolve oxygen, pH, and ammonia. Based on identification of bacteria in cultured elvers in Tatelu Freshwater Aquaculture Center, the elver samples had been infected with bacterial Aeromonas hydrophila. Keywords: elver, identification, Aeromonas hydrophila, Tatelu Freshwater Aquaculture Center

Rapid nondestructive measurement of bacterial cultures with 3D interferometric imaging

The agar culture plate has played a crucial role in bacteriology since the origins of the discipline and is a staple bioanalytical method for efforts ranging from research to standard clinical diagnostic tests. However, plating, inoculating, and waiting for microbes to develop colonies that are visible is time-consuming. In this work, we demonstrate white-light interferometry (WLI) as a practical tool for accelerated and improved measurement of bacterial cultures. High resolution WLI surface profile imaging was used for nondestructive characterization and counting of bacterial colonies on agar before they became visible to the naked eye. The three-dimensional (3D) morphology of Gram-negative (Pseudomonas fluorescens) and Gram-positive (Bacillus thuringiensis) bacterial species were monitored with WLI over time by collecting surface profiles of colonies on agar plates with high vertical resolution (3–5 nanometers) and large field of view (3–5 mm). This unique combination of sensitive vertical resolution and large field of view uniquely provided by WLI enables measurement of colony morphologies and nondestructive monitoring of hundreds of microcolonies. Individual bacteria were imaged within the first few hours after plating and colonies were accurately counted with results comparing favorably to counts made by traditional methods that require much longer wait times. Nondestructive imaging was used to track single cells multiplying into small colonies and the volume changes over time in these colonies were used to measure their growth rates. Based on the results herein, bioimaging with WLI was demonstrated as a novel rapid bacterial culture assay with several advantageous capabilities. Fast nondestructive counting of colony-forming units in a culture and simultaneous measurement of bacterial growth rates and colony morphology with this method may be beneficial in research and clinical applications where current methods are either too slow or are destructive.

Spatiotemporal establishment of dense bacterial colonies growing on hard agar.

The physical interactions of growing bacterial cells with each other and with their surroundings significantly affect the structure and dynamics of biofilms. Here a 3D agent-based model is formulated to describe the establishment of simple bacterial colonies expanding by the physical force of their growth. With a single set of parameters, the model captures key dynamical features of colony growth by non-motile, non EPS-producing E. coli cells on hard agar. The model, supported by experiment on colony growth in different types and concentrations of nutrients, suggests that radial colony expansion is not limited by nutrients as commonly believed, but by mechanical forces. Nutrient penetration instead governs vertical colony growth, through thin layers of vertically oriented cells lifting up their ancestors from the bottom. Overall, the model provides a versatile platform to investigate the influences of metabolic and environmental factors on the growth and morphology of bacterial colonies.

Novel neural network application for bacterial colony classification

BackgroundBacterial colony morphology is the first step of classifying the bacterial species before sending them to subsequent identification process with devices, such as VITEK 2 automated system and mass spectrometry microbial identification system. It is essential as a pre-screening process because it can greatly reduce the scope of possible bacterial species and will make the subsequent identification more specific and increase work efficiency in clinical bacteriology. But this work needs adequate clinical laboratory expertise of bacterial colony morphology, which is especially difficult for beginners to handle properly. This study presents automatic programs for bacterial colony classification task, by applying the deep convolutional neural networks (CNN), which has a widespread use of digital imaging data analysis in hospitals. The most common 18 bacterial colony classes from Peking University First Hospital were used to train this framework, and other images out of these training dataset were utilized to test the performance of this classifier.ResultsThe feasibility of this framework was verified by the comparison between predicted result and standard bacterial category. The classification accuracy of all 18 bacteria can reach 73%, and the accuracy and specificity of each kind of bacteria can reach as high as 90%.ConclusionsThe supervised neural networks we use can have more promising classification characteristics for bacterial colony pre-screening process, and the unsupervised network should have more advantages in revealing novel characteristics from pictures, which can provide some practical indications to our clinical staffs.

H-NS is an activator of exopolysaccharide biosynthesis genes transcription in Vibrio parahaemolyticus

Vibrio parahaemolyticus is capable of surviving in biofilm communities attached to biotic and abiotic surfaces. The exopolysaccharide (EPS) plays a key role in the maturing of the biofilm. The VPA1403-1412 (cpsA-J) operon is responsible for EPS production in V. parahaemolyticus. The expression of cpsA-J is controlled by ScrABC, intracellular concentration of c-di-GMP, CpsS-CpsR-CpsQ regulatory cascade, and quorum sensing. The data presented here showed that H-NS activates the EPS-dependent bacterial colony morphology and the transcription of cpsQ and cpsA-J. H-NS has negative regulatory activity on scrABC transcription, and thereby may result in enhancing the intracellular concentration of c-di-GMP. Thus, a regulatory circuit involved in regulating cpsA-J/EPS production by H-NS, ScrABC and CpsQ was identified in V. parahaemolyticus.

ISOLASI DAN IDENTIFIKASI BAKTERI Aeromonas sp. DARI LELE DUMBO (Clarias sp.) DI KABUPATEN NGAWI

African catfish (Clarias sp.) is one of important freshwater fish which prefer consumed by people due to many advantages. Aeromonas sp. bacteria are dangerous patogen for freshwater fishes. This objective of the research was to isolate, identify and determine pathogenicity of Aeromonas sp. bacteria from African catfish from District Ngawi. The samples of catfish with 20 - 25 cm length showing clinical signs disease were obtained from three sub districts. Bacteria were isolated from kidney and inoculated into GSP medium. Characterization and identification through morphology of bacterial colonies, cells and biochemical test. Postulate Koch was conducted to verify abaility to couse disease. Pathogenicity was analyzed by determination of value of Lethal Dosage-50 on catfish on 7 - 9 cm length. The result showed that the disease symptoms of fish infected by the bacteria were skin ulcer, abdominal swelling and kidney damage. Fifteen bacterial isolates were collected which five, six and four isolates were from Kecamatan Karang Jati, Geneng dan Paron.sub-district respectively. The result showed 12 isolates (GKJ1, GKJ3, GKJ4, GGN1, GGN2, GGN3, GGN4, GGN5, GGN6, GPR2, GPR3 and GPR4) were identified as Aeromonas hydrophila. Three isolates (GKJ2, GKJ5 and GPR1) were identified as A. salmonicida. Isolate of A. hydrophila GKJ1, GKJ4, GGN2, GGN5, GPR2 and GPR4 were virulent to African catfish with LD50 values of 1,55 x 105, 3,89 x 105, 7,24 x 105, 2,39 x 105, 6,61 x 104 and 1,95 x 104 cfu/fish.

88 Prevalence and characterization of unusual Staphylococcus aureus strains with a mucoid phenotype recovered from the airways of cystic fibrosis patients

Objectives Staphylococcus aureus is frequently isolated from the respiratory tract already in early childhood and often persists for extended periods. Mucoid bacterial colony morphology has been described for Pseudomonas aeruginosa, the most prominent pathogen in CF, but not for S. aureus. Recently, we identified mucoid isolates also for S. aureus. To determine the prevalence and the underlying mechanism of mucoid S. aureus isolates we used S. aureus isolates collected during two independent studies including 371 CF patients. Methods To determine the underlying mechanism of mucoidy, the ica promoter region of all isolates and the entire ica operon of selected strains were sequenced. Biofilm formation was determined by a microtiter plate assay. Mucoid and normal isolates of one patient were characterized in terms of capsule expression and phagocytosis by neutrophils. Results From the respiratory specimens of 8 patients (prevalence of 2.2%) mucoid S. aureus isolates were recovered. M ucoid isolates were strong biofilm producers. Mucoidy was associated with a 5-bp deletion in the ica promoter region. Subsequent non-mucoid isolates, which also carried a 5-bp deletion, harbored compensatory mutations . Transformation of 5-bp deletion carrying normal strains with a vector expressing intact ica restored mucoidy. In contrast to the normal phenotype, mucoid strains were protected against phagocytosis by neutrophils. Conclusion Although mucoid S. aureus strains are rarely identified during chronic airway infection in CF, biofilm hyper-production seems to be an effective strategy for protection against phagocytosis by neutrophils.

CpsA, a LytR-CpsA-Psr Family Protein in Mycobacterium marinum, Is Required for Cell Wall Integrity and Virulence.

LytR-CpsA-Psr family proteins play an important role in bacterial cell wall integrity. Although the pathogenic relevance of LytR-CpsA-Psr family proteins has been studied in a few bacterial pathogens, their function in mycobacteria remains uncharacterized. In this work, a transposon insertion mutant (cpsA::Tn) of Mycobacterium marinum was studied. We found that inactivation of CpsA altered bacterial colony morphology, sliding motility, cell surface hydrophobicity, and cell wall permeability. Besides, the cpsA mutant exhibited a decreased arabinogalactan content, indicating that CpsA plays a role in cell wall assembly. Moreover, the mutant shows impaired growth within macrophage cell lines and is severely attenuated in zebrafish larvae and adult zebrafish. Taken together, our results indicated that CpsA, a previously uncharacterized protein, is important for mycobacterial cell wall integrity and is required for mycobacterial virulence.

MorphoCol: An ontology-based knowledgebase for the characterisation of clinically significant bacterial colony morphologies

BackgroundOne of the major concerns of the biomedical community is the increasing prevalence of antimicrobial resistant microorganisms. Recent findings show that the diversification of colony morphology may be indicative of the expression of virulence factors and increased resistance to antibiotic therapeutics. To transform these findings, and upcoming results, into a valuable clinical decision making tool, colony morphology characterisation should be standardised. Notably, it is important to establish the minimum experimental information necessary to contextualise the environment that originated the colony morphology, and describe the main morphological features associated unambiguously. ResultsThis paper presents MorphoCol, a new ontology-based tool for the standardised, consistent and machine-interpretable description of the morphology of colonies formed by human pathogenic bacteria. The Colony Morphology Ontology (CMO) is the first controlled vocabulary addressing the specificities of the morphology of clinically significant bacteria, whereas the MorphoCol publicly Web-accessible knowledgebase is an end-user means to search and compare CMO annotated colony morphotypes. Its ultimate aim is to help correlate the morphological alterations manifested by colony-forming bacteria during infection with their response to the antimicrobial treatments administered. ConclusionsMorphoCol is the first tool to address bacterial colony morphotyping systematically and deliver a free of charge resource to the community. Hopefully, it may introduce interesting features of analysis on pathogenic behaviour and play a significant role in clinical decision making. Database URLhttp://morphocol.org.

Two approaches to form antibacterial surface: Doping with bactericidal element and drug loading

Two approaches (surface doping with bactericidal element and loading of antibiotic into specially formed surface microcontainers) to the fabrication of antibacterial yet biocompatible and bioactive surfaces are described. A network structure with square-shaped blind pores of 2.6±0.6×10−3mm3 for drug loading was obtained by selective laser sintering (SLS). The SLS-fabricated samples were loaded with 0.03, 0.3, 2.4, and 4mg/cm2 of co-amoxiclav (amoxicillin and clavulanic acid). Ag-doped TiCaPCON films with 0.4, 1.2, and 4.0at.% of Ag were obtained by co-sputtering of composite TiC0.5-Ca3(PO4)2 and metallic Ag targets. The surface structure of SLS-prepared samples and cross-sectional morphology of TiCaPCON-Ag films were studied by scanning electron microscopy. The through-thickness of Ag distribution in the TiCaPCON-Ag films was obtained by glow discharge optical emission spectroscopy. The kinetics of Ag ion release in normal saline solution was studied using inductively coupled plasma mass spectrometry. Bacterial activity of the samples was evaluated against S. epidermidis, S. aureus, and K. pneum. ozaenae using the agar diffusion test and photometric method by controlling the variation of optical density of the bacterial suspension over time. Cytocompatibility of the Ag-doped TiCaPCON films was observed in vitro using chondrocytic and MC3T3-E1 osteoblastic cells. The viability and proliferation of chondrocytic cells were determined using the MTS assay and PicoGreen assay tests, respectively. The alkaline phosphatase (ALP) activity of the SLS-fabricated samples loaded with co-amoxiclav was also studied. The obtained results showed that the moderate bacteriostatic effect of the Ag-doped TiCaPCON films is mainly manifested in the change of bacterial colony morphology and optical densities of bacteria suspensions. In contrast, the SLS-prepared samples showed a very rapid initial drug release resulting in strong bactericidal effect just from the start of the test and for as long as several days. Cytocompatibility and ALP activity tests demonstrated that it is possible to achieve a pronounced antibacterial effect compatible or even higher than that in the control sample (standard disk loaded with the amoxicillin/clavulanic acid mixture (30μg)) without compromising the material biocompatibility and bioactivity.

First Report of Bacterial Root Rot of Ginseng Caused by Pseudomonas aeruginosa in China.

Ginseng (Panax ginseng) is an economically valuable medicinal herb mainly planted in Jilin Province, China. In September 2013, during harvest, suspected bacterial rots were observed on ginseng roots with about 10% incidence in Fusong County, Jilin Province, China (127°29.48' N, 42°11.12' E). Rotted roots completely lost their economic value. Symptoms on roots began as water-soaked lesions, and developed rapidly into a soft, watery, decayed mass within 3 to 5 days. Three diseased root tissues were surface-sterilized in 70% ethanol for 30 s, rinsed 3 times in sterilized water and cut into small pieces (2 to 3 mm). Tissues were then macerated for 5 min in sterilized water, streaked onto nutrient agar (NA) medium, and incubated at 28°C for 2 days. Representative colonies were selected from each plate and further purified by sub-culturing onto NA medium. Five strains of the bacteria were gram-negative, short straight rods, 0.5 to 1.0 × 1.5 to 3.0 μm with a single, polar flagellum. Colonies were round, smooth, translucent, and yellowish green on NA medium. The bacteria were identified based on physiological and biochemical tests as follows (3): They were levan and potato rot negative, oxidase, aerobic, and arginine dihydrolase positive, converted nitrate to N2, hydrolyzed gelatin, produced nitrites from nitrates, produced pyocyanin, and grew at 41°C. Bacterial identity was further confirmed by amplifying the 16S rRNA (1,461 bp), gyrB (1,134 bp), and 16S-23S ITS genes (523 bp) with 27F/1492R, UP1/UP2, and L1/L2 primer sets, respectively. The 16S rRNA gene sequence (NCBI Accession No. KJ156527), gyrB gene sequence (KJ748373), and 16S-23S ITS gene sequence (KJ748374) had 99% identity to that of Pseudomons aeruginosa strain BS01 (JQ229778), ATCC25011 (FJ652721), and ATCC15522 (AB547908), respectively. The strains were also identified by using BD Phoenix-100 Automated Microbiology System (BD Ltd., New Jersey) as P. aeruginosa with 99% confidence. A pathogenicity test was conducted by spraying a suspension of five strains individually (108 CFU/ml) onto 4-year-old ginseng roots (cv. Damaya) wounded with a sterilized needle. Five ginseng roots were inoculated with each strain and five ginseng roots were inoculated with sterilized water as controls. All inoculated plants were maintained at 28°C with 80 to 85% relative humidity. Soft, watery tissue rot symptoms developed 3 to 5 days after inoculation, and were similar to those observed on the diseased plants under natural conditions. In contrast, no symptoms developed on control plants. The bacteria were readily re-isolated from inoculated plants and identified as P. aeruginosa using bacterial colony morphology, physiological and biochemical tests, as well as sequence analysis of the 16S rRNA gene, fulfiling Koch's postulates. The bacterium was not isolated from control plants. P. aeruginosa has been reported to cause diseases in a variety of plants including onion (1,2), arabidopsis, and sweet basil (4). To our knowledge, this is the first report of P. aeruginosa causing ginseng root rot in China.

Evaluation of biofilm formation in the presence of saliva on poly(ethylene glycol)deposited titanium.

Titanium (Ti) is widely used for oral cavity biomedical devices. However, because it penetrates the mucosa and exists partially external to the tissue, it sometimes induces tissue inflammation, minor infection, or peri-implantitis due to oral bacteria after implantation and causes serious consequences. We have previously shown that poly(ethylene glycol) (PEG)- electrodeposited Ti inhibits bacterial adhesion and biofilm formation. However, the effect of the PEG coating in body fluid is still unclear. In this study, we investigated bacterial colony morphology and biofilm formation on PEG-electrodeposited Ti in comparison with untreated Ti in the presence of saliva. After 48 h incubation, Streptococcus mutans biofilms adhered on the untreated Ti were rigid and cohesive, while those on the PEG-electrodeposited were loose and were easily washed off. These results indicate electrodeposited-PEG layers inhibit the biofilm formation on Ti in the presence of saliva.

Improvements on colony morphology identification towards bacterial profiling

Colony morphology may be an indicator of phenotypic variation, this being an important adaptive process adopted by bacteria to overcome environmental stressors. Furthermore, alterations in colony traits may reflect increased virulence and antimicrobial resistance. Despite the potential relevance of using colony morphological traits, the influence of experimental conditions on colony morphogenesis has been scarcely studied in detail. This study aims to clearly and systematically demonstrate the impact of some variables, such as colony growth time, plate colony density, culture medium, planktonic or biofilm mode of growth and strain genetic background, on bacterial colony morphology features using two Pseudomonas aeruginosa strains. Results, based on 5-replicate experiments, demonstrated that all variables influenced colony morphogenesis and 18 different morphotypes were identified, showing different sizes, forms, colours, textures and margins. Colony growth time and composition of the medium were the variables that caused the highest impact on colony differentiation both derived from planktonic and biofilm cultures. Colony morphology characterization before 45h of incubation was considered inadequate and TSA, a non-selective medium, provided more colony diversity in contrast to P. aeruginosa selective media. In conclusion, data obtained emphasized the need to perform comparisons between colony morphologies in equivalent experimental conditions to avoid misinterpretation of microbial diagnostics and biomedical studies. Since colony morphotyping showed to be a reliable method to evaluate phenotypic switching and also to infer about bacterial diversity in biofilms, these unambiguous comparisons between morphotypes may offer a quite valuable input to clinical diagnosis, aiding the decision-making towards the selection of the most suitable antibiotic and supportive treatments.

Coevolving parasites enhance the diversity-decreasing effect of dispersal

High dispersal rates between patches in spatially structured populations can impede diversification and homogenize diversity. These homogenizing effects of dispersal are likely to be enhanced by coevolving parasites that impose strong selection on hosts for resistance. However, the interactive effects of dispersal and parasites on host diversification have never been tested. We used spatially structured, experimental populations of the bacterium Pseudomonas fluorescens, cultured with or without the phage SBW25Ф2 under three levels of dispersal (none, localized or global), and quantified diversity in terms of evolved bacterial colony morphologies after approximately 100 bacterial generations. We demonstrate that higher levels of colony morphology richness evolved in the presence of phage, and that dispersal reduced diversity most strongly in the presence of phage. Thus, our results suggest that, while parasites can drive host diversification, host populations coevolving with parasites are more prone to homogenization through dispersal.

Identification of Buffaloes hemorrhagic septicemia in southern Iraq marshland-2008

A satisfactory investigation of buffaloes hemorrhagic septicemia was obtained in the marshes of Dhi Qar governorate in southern Iraq. Has described the clinical and pathological symptoms and exterior morphology of bacterial colonies and biochemical behavior of Pasterulla multocida. Gross and histopathological changes were recorded also in 13 samples collected from infected and dead animals.

Effect of a Chemical Modified Urea Fertilizer on Soil Quality: Soil Microbial Populations Around Corn Roots

Slow‐release nitrogen (N) fertilizers are used to increase N‐use efficiency and extend N availability over a plant‐growing season. One formula of this fertilizer commonly used in turf and horticultural crops is methylene–urea–triazone. After this compound is applied in the soil, it is subject to bacterial degradation and becomes available for uptake by plants. The objective of this work is to elucidate the application of methylene–urea–triazone in the soil microbial population as well as effects on soil quality. Zea mays was planted in a silty loam soil. Urea and methylene–urea–triazone were incorporated into the soil. Two weeks and 6 weeks after inoculation, soil samples were collected and used to inoculate agar plates and for DNA extraction. Bacterial colony morphology was examined. Denaturing gradient gel electrophoresis (DGGE) was performed with the polymerase chain reaction (PCR) amplicons from the internal transcribed spacer (ITS) of the rRNA gene cluster. The Shannon Wiener index was determined for colony morphology and DGGE bands. There was a difference between urea and the slow‐release fertilizer on both plant responses and bacterial diversity. Although for the first 2 weeks DGGE did not show any difference in bacterial diversity, after 6 weeks, differences in the composition of the bacterial community were observed. There were concomitant effects on plant growth and microorganism population and diversity, probably reflecting changes in the richness and in the eveness of the bacterial population in the rhizosphere caused by the fertilizers. Therefore, both soil microorganisms and plant growth respond to environmental changes over time.

A simple model for the early events of quorum sensing in Pseudomonas aeruginosa: modeling bacterial swarming as the movement of an "activation zone"

BackgroundQuorum sensing (QS) is a form of gene regulation based on cell-density that depends on inter-cellular communication. While there are a variety of models for bacterial colony morphology, there is little work linking QS genes to movement in an open system.ResultsThe onset of swarming in environmental P. aeruginosa PUPa3 was described with a simplified computational model in which cells in random motion communicate via a diffusible signal (representing N-acyl homoserine lactones, AHL) as well as diffusible, secreted factors (enzymes, biosurfactans, i.e. "public goods") that regulate the intensity of movement and metabolism in a threshold-dependent manner. As a result, an "activation zone" emerges in which nutrients and other public goods are present in sufficient quantities, and swarming is the spontaneous displacement of this high cell-density zone towards nutrients and/or exogenous signals. The model correctly predicts the behaviour of genomic knockout mutants in which the QS genes responsible either for the synthesis (lasI, rhlI) or the sensing (lasR, rhlR) of AHL signals were inactivated. For wild type cells the model predicts sustained colony growth that can however be collapsed by the overconsumption of nutrients.ConclusionWhile in more complex models include self-orienting abilities that allow cells to follow concentration gradients of nutrients and chemotactic agents, in this model, displacement towards nutrients or environmental signals is an emergent property of the community that results from the action of a few, well-defined QS genes and their products. Still the model qualitatively describes the salient properties of QS bacteria, i.e. the density-dependent onset of swarming as well as the response to exogenous signals or cues.ReviewersThis paper was reviewed by Gáspár Jékely, L. Aravind, Eugene V. Koonin and Artem Novozhilov (nominated by Eugene V. Koonin).

Short‐term rates of parasite evolution predict the evolution of host diversity

Coevolution with parasites has been implicated as an important factor driving the evolution of host diversity. Studies to date have focussed on gross effects of parasites: how host diversity differs in the presence vs. absence of parasites. But parasite-imposed selection is likely to show rapid variation through time. It is unclear whether short-term fluctuations in the strength of parasite-imposed selection tend to affect host diversity, because increases in host diversity are likely to be constrained by both the supply of genetic variation and ecological processes. We followed replicate populations of coevolving, initially isogenic, bacteria and phages through time, measuring host diversity (with respect to bacterial colony morphologies), host density and rates of parasite evolution. Both host density and time-lagged rates of parasite evolution were good independent predictors of the magnitude of bacterial within- and between-population diversities. Rapid parasite evolution and low host density decreased host within-population diversity, but increased between-population diversity. This study demonstrates that short-term changes in the rate of parasite evolution can predictably drive patterns of host diversity.

Constructal pattern formation in stony corals, bacterial colonies and plant roots under different hydrodynamics conditions

This paper explores a new application of the constructal theory, namely in describing and predicting the formation of dissimilar patterns inside elements of the same species under different hydrodynamics conditions. Our study proposes an explanation for the differences found in morphology of stony corals, bacterial colonies and plant roots. It specially provides an answer to the following question: have their shapes (architecture) been developed by chance, or do they represent the optimum structure serving their ultimate purpose? We show that in order to persist in time, these systems must evolve in such a way that an easy access to nutrients is ensured: their shapes develop in such a way as to minimize the time to reach the nutrient source. Moreover, it is also shown that it is the combination of a dispersive (diffusive) and a convective mechanism that allows for the maximization of nutrient transfer through use of the best of these mechanisms at a specific time. In the light of this outcome, it is straightforward to conclude why the existence of an optimal architecture makes sense: it is because there is an overriding natural tendency and because the system has the freedom to morph its shape in the search for an optimal attainment of this goal within a set of constraints imposed by the situation.