Trade-off between competition ability and invulnerability to predation in marine microbes; protist grazing versus viral lysis effects

Trade-offs between competition ability and invulnerability to predation are important mechanisms explaining how predation promotes bacterial diversity. However, existence of these trade-offs has apparently not been investigated in natural marine bacterial communities. Here, we address this question with growth-based measurements for each marine bacterial taxon by conducting on-board dilution experiments to manipulate predation pressure and using high-throughput sequencing to assess the response of bacterial communities. We determined that bacterial taxa with a higher predation-free growth rate were accompanied with higher predation-caused mortality, supporting existence of competitiveness-invulnerability trade-off. This trade-off was stronger and more consistent under viral lysis than protist grazing. In addition, predation generally flattened out the rank-abundance distribution and increased the evenness and richness of the bacterial community. These findings supported the 'Kill-the-Winner' hypothesis. All experiments supported a significant competitiveness-invulnerability trade-off, but there was substantial variation among bacterial communities in response to predation across experiments conducted in various sites and seasons. Therefore, we inferred that the Kill-the-Winner hypothesis is important but likely not the only deterministic mechanism explaining how predation shapes bacterial assemblages in natural marine systems.

Global Stability of a Lotka-Volterra Competition-Diffusion-Advection System with Different Positive Diffusion Distributions

In this paper, the problem of a Lotka–Volterra competition–diffusion–advection system between two competing biological organisms in a spatially heterogeneous environments is investigated. When two biological organisms are competing for different fundamental resources, and their advection and diffusion strategies follow different positive diffusion distributions, the functions of specific competition ability are variable. By virtue of the Lyapunov functional method, we discuss the global stability of a non-homogeneous steady-state. Furthermore, the global stability result is also obtained when one of the two organisms has no diffusion ability and is not affected by advection.

Enhancing the Efficiency of Soybean Inoculant for Nodulation under Multi-Environmental Stress Conditions

The development of rhizobial inoculants with increased resistance to abiotic stress is critical to mitigating the challenges related to climate change. This study aims at developing a soybean stress-tolerant Bradyrhizobium inoculant to be used under the mixed stress conditions of acidity, high temperature, and drought. Six isolates of Bradyrhizobium with high symbiotic performance on soybean were tested to determine their growth or survival abilities under in vitro conditions. The representative stress-tolerant Bradyrhizobium isolates 184, 188, and 194 were selected to test their ability to promote soybean growth under stress conditions compared to the type strain Bradyrhizobium diazoefficiens USDA110. The plant experiment indicated that isolate 194 performed better in symbiosis with soybean than other Bradyrhizobium strains under stress conditions. Based on the stress tolerance index, soybeans inoculated with isolate 194 showed a high growth performance and significantly better nodulation competition ability than USDA110 under several stress conditions. Interestingly, supplementation of sucrose in the culture medium significantly enhances the survival of the isolate and leads to improved plant biomass under various stress conditions. Analysis of the intra-cellular sugars of isolate 194 supplemented with sucrose showed the accumulation of compatible solutes, such as trehalose and glycerol, that may act as osmoprotectants. This study indicates that inoculation of stress-tolerant Bradyrhizobium together with sucrose supplementation in a medium could enhance bacterial survival and symbiosis efficiency under stress conditions. Although it can be applied for inoculant production, this strategy requires validation of its performance in field conditions before adopting this technology.

Emergence of ciprofloxacin heteroresistance in foodborne Salmonella enterica serovar Agona

Background Bacterial heteroresistance has been increasingly identified as an important phenomenon for many antibiotic/bacterium combinations. Objectives To investigate ciprofloxacin heteroresistance in Salmonella and characterize mechanisms contributing to ciprofloxacin heteroresistance. Methods Ciprofloxacin-heteroresistant Salmonella were identified by population analysis profiling (PAP). Target mutations and the presence of PMQR genes were detected using PCR and sequencing. Expression of acrB, acrF and qnrS was conducted by quantitative RT–PCR. Competition ability and virulence were also compared using pyrosequencing, blue/white screening, adhesion and invasion assays and a Galleria model. Two subpopulations were whole-genome sequenced using Oxford Nanopore and Illumina platforms. Results PAP identified one Salmonella from food that yielded a subpopulation demonstrating heteroresistance to ciprofloxacin at a low frequency (10−9 to 10−7). WGS and PFGE analyses confirmed that the two subpopulations were isogenic, with six SNPs and two small deletions distinguishing the resistant from the susceptible. Both subpopulations possessed a T57S substitution in ParC and carried qnrS. The resistant subpopulation was distinguished by overexpression of acrB and acrF, a deletion within rsxC and altered expression of soxS. The resistant population had a competitive advantage against the parental population when grown in the presence of bile salts but was attenuated in the adhesion and invasion of human intestinal cells. Conclusions We determined that heteroresistance resulted from a combination of mutations in fluoroquinolone target genes and overexpression of efflux pumps associated with a deletion in rsxC. This study warns that ciprofloxacin heteroresistance exists in Salmonella in the food chain and highlights the necessity for careful interpretation of antibiotic susceptibility.

POSISI STRATEGI BERSAING BISNIS PEMBENIHAN UDANG VANAME DENGAN PENDEKATAN COMPETITIVE PROFIL MATRIX

The business competition of vannamei shrimp seed has strongly expanded by the increasing of Indonesian shrimp export. The businessman competesin preparing vannamei shrimp seed for Indonesian fisherman. The ability of competition has influenced in company competitive strategy. Thisresearch aimed to identify the position of competitive strategy and to know the strong and low point of critical success factor (CSF) in the businessof vannamei shrimp seed. This research used descriptive qulaititative research by using phenomenology. The technic of data collecting usedinterview and direct observation to the research subject. The research result by using Competitive Profile Matrix (CPM) showed that the positionof competitive strategy in PT Semar Emas is not strong enough yet as its competitor, PT Dewa Ndaru. The competition ability of PT Semar Emascan be showed in critical success factor (CSF) with the low point in the old company management, the traditional marketing management, thegovernment policy and unstable economic condition. The strong point is in the product location of vannamei shrimp seed and the quality of humanresource.

Studies on tolerance of chickpea to some pre and post-emergence herbicides

Herbicides application is an integral part of farmer’s crop management in modern agricultural systems. Weeds always cause serious losses in legumes due to poor competition ability. In order to quantify the tolerance of chickpea against some pre and post-emergence herbicides, a pot study was carried out in the department of Weed science, The University of Agriculture, Peshawar Pakistan during 2012-13 and 2013-14. The pre emergence herbicides includes pendimethalin and s-metolachlor while, the post emergence herbicides comprised of Clodinafop-propargyl, fenoxaprop-p-ethyl and di-methyl urea. The chickpea variety Karak-I was sown in the pots and the trial was arranged in CR Design repeated three times. During the investigation data were recorded on different growth parameters of chickpea plants including both aerial and underground parts. The results revealed the all treatments had a significant effect on all the examined parameters of chickpea except nodule fresh and dry biomasses. However, the toxic effect of pre emergence herbicides on chickpea was significantly higher as compared to post emergence herbicides. The minimum number of nodule plant-1 (17.83), plant height (50.50cm), and seed protein (14.13%) was recorded in Pendimethalin treated pots. However, the highest seed protein content of 21.75 and 21.15 % were recorded for control and fenoxaprop-p-ethyl treatments respectively. Thus, it is concluded from the present data that chickpea has less tolerance for pre emergence herbicides pendimethalin and S-metolachlor as compared to post-emergence herbicides so farmers are advised to give preference to post emergence herbicides instead of a pre emergence while controlling weeds in chickpea through chemicals.

Posisi Strategi Bersaing Bisnis Pembenihan Udang Vaname Dengan Pendekatan Competitive Profil Matrix (Studi Pada PT. Semar Emas Situbondo, Jawa Timur)

The business competition of vannamei shrimp seed has strongly expanded by the increasing of Indonesian shrimp export. The businessman competes in preparing vannamei shrimp seed for Indonesian fisherman. The ability of competition has influenced in company competitive strategy. This research aimed to identify the position of competitive strategy and to know the strong and low point of critical success factor (CSF) in the business of vannamei shrimp seed. This research used descriptive qulaititative research by using phenomenology. The technic of data collecting used interview and direct observation to the research subject. The research result by using Competitive Profile Matrix (CPM) showed that the position of competitive strategy in PT Semar Emas is not strong enough yet as its competitor, PT Dewa Ndaru. The competition ability of PT Semar Emas can be showed in critical success factor (CSF) with the low point in the old company management, the traditional marketing management, the government policy and unstable economic condition. The strong point is in the product location of vannamei shrimp seed and the quality of humanresource.