Competitive Stress Research Articles

The effect of stress on the sportsman’s body and training activities

In the modern conditions of the development of sports, a great place is given to the impact of stress on the athlete's body. During preparation for competitions of various levels, the Olympic Games, world championships, continental championships, city competitions, athletes are "accompanied" by mental and emotional tension. Accordingly, when being in a given state of stress, corresponding negative disturbances appear in the performed sports activity. In general, stress is a fairly common and common phenomenon. Minor stresses are inevitable and harmless, but excessive stress creates problems for both individuals and organizations in accomplishing tasks. Psychologists believe that a person suffers more and more often from insults inflicted on him, a sense of his own insecurity, uncertainty about the future. There are two main groups of stress factors that most significantly affect the results of sports activities and are most often encountered: pre-competitive and competitive. Competitive stressors are stressors related directly to the sporting situation the athlete finds themselves in. Essentially, they are the most obvious stressors and are most directly linked to what happens during training or in a game. Organizational stressors can be attributed to, and therefore solved by, the coaching and organizational set up surrounding a team. The athlete needs to be helped to identify actions aimed at improving performance. Success in reaching sports peaks depends on the individual psychological characteristics of the athlete, and certain types of sports make demands and at the same time form personal qualities that are necessary for successful competitive activities. Each athlete is different, and their response to these competitive stressors will vary too. Finding the sweet spot where these stressors are contributing to an engaged, locked-in mindset can be the difference come crunch time. Knowing when a competitive stressor is overwhelming an athlete and having a detrimental affect can be an important preventative measure to avoid further issues down the road.

Ergotherapeutic means for the prevention of cardiovascular diseases in martial arts athletes

The article deals with the use of ergotherapeutic means of prevention of cardiovascular diseases in martial arts athletes. The purpose of the work was to substantiate the ergotherapeutic means’ effectiveness of cardiovascular diseases’ prevention of athletes in martial arts. The research methods were the analysis of literary sources, occupational therapy observation, questionnaires and interviews with martial arts athletes who have or had problems with the cardiovascular system, analysis of the obtained results. The novelty of the study consisted in substantiating the effectiveness of ergotherapeutic means of prevention of cardiovascular diseases in martial arts athletes. The causes of pathological and pre-pathological changes in the state of the cardiovascular system in athletes during training and competition were determined. These include excessive physical exertion, competitive stress, abuse of pharmacological agents, lack of knowledge of elementary rules of self-control of functional state, planning of workload and recovery after training and competitive processes. To prevent these reasons, we have developed ergotherapeutic means of preventing cardiovascular diseases in martial arts athletes. They included: regular medical examination with diagnostic examination, self-monitoring of the functional state and activity of the cardiovascular system, training load planning, rational balanced nutrition, psychological means of combating stress. When introducing agrotherapeutic means, the main emphasis was placed on various types of physical activity, which was appropriate for the age and individual capabilities of the athletes. The use of ergotherapeutic means of prevention of cardiovascular diseases of martial arts athletes in practical activities will help to avoid pathological and pre-pathological changes in the state of the cardiovascular system during the training and competitive activities of athletes.

Stress Management Mechanisms in Younger Athletes

Background/Purpose: Physiological responses to stress are associated with tension in the autonomic nervous system. One of the physiological reactions to stress is the tension of the autonomic nervous system. Intense physical activity and emotional stress can provoke mental stress in young athletes. Purpose - to study the features of the mechanisms of stress management in young athletes.
 Method: Method: 30 younger athletes were examined (Greco-Roman wrestlers, 13-16 years old). Young athletes represented the Kremenchug sports club. Heart rate variability (HRV) was assessed using a Fazagraph computer electrocardiograph (Ukraine). The characteristics of the statistical and frequency analysis of heart rate were evaluated. HRV indicators were recorded before and after the competition. The study of statistically significant difference between the obtained results carry out with help Wilcoxon rank sum test.
 Results: During the competition the meaning of LF increases with simultaneous a decrease in HF oscillation. This fact is associated with a high level of tension in the regulatory mechanisms of HRV in younger athletes in a competitive state. At the same time, the parasympathetic activity of autonomic regulation is decline. Result shows the development of stress during psycho-emotional strain in competition condition. The stress caused by competitive situation in younger athletes is characterized by an increase in the tension of the autonomic regulation of HRV with deterioration in sympathetic and parasympathetic activity. The stress caused by competitive situation in younger athletes is characterized by an increase in the tension of the autonomic regulation of HRV with deterioration in sympathetic and parasympathetic activity.
 Conclusion: It was revealed that the conditions of competition among young athletes provoke a stress reaction with a predominance of sympathetic regulation. The mechanism of prevention of competitive stress in younger athletes is associated with a change in the ratio of autonomic regulation of the heart rate.

Native Wolbachia infection and larval competition stress shape fitness and West Nile virus infection in Culex quinquefasciatus mosquitoes.

Wolbachia transinfections established in key mosquito vectors, including Aedes aegypti are typically associated with pathogen blocking-reduced susceptibility to infection with key pathogens and reduced likelihood those pathogens are transmitted to new hosts. Host-symbiont-virus interactions are less well understood in mosquitoes like Culex quinquefasciatus, which naturally harbor Wolbachia, with pathogen blocking observed in some populations but not others, potentially due to innate differences in their Wolbachia load. In nature, mosquito larvae are often subject to developmental stresses associated with larval competition, which can lead to reduced body size and differential susceptibility to arbovirus infection. In this study, we sought to understand whether competition stress and Wolbachia infection in Cx. quinquefasciatus combine to impact host fitness and susceptibility to infection with West Nile virus. We reared Wolbachia-infected and uninfected Cx. quinquefasciatus larvae under three competition stress levels, increasing larval density without increasing the amount of food supplied. We then monitored larval development and survival, measured wing length and quantified Wolbachia density in adults, and then challenged mosquitoes from each treatment group orally with West Nile virus. We observed that high competition stress extended development time, decreased the likelihood of eclosion, decreased body size, and increased susceptibility to West Nile virus (WNV) infection. We also observed that Wolbachia infection reduced WNV load under low competition stress, and significantly improved the rate of survival for larval reared under higher competition stress. Consequently, our data suggest that native Wolbachia infection in Cx. quinquefasciatus has differential consequences for host fitness and susceptibility to WNV infection depending on competition stress.

Interactive Visualization of Deep Neural Networks for Feature Positioning and Biomedical Monitoring in Physical Education

Visualization is primarily utilized as a training method to enhance athletic movement quality, increase concentration power, and minimize competition stress on the player while building firm confidence. Physical literacy (PL) provides a valuable lens for analyzing physical activity (PA) movement in more significant social and affective learning processes. This paper presents an Interactive Visualization positioning in physical education (IVPPE) to deal with the signal fluctuations and positioning techniques in visualizing Deep Neural Network (DNN). To ensure the success of their game, athletes are always looking for new ways to improve their health and performance. Using sensors to keep tabs on training and recovery has become more popular among athletes. Currently, sports teams are using sensors to track both the players’ internal and external workloads. It illustrates the multilayer localizer (MLL) based on transfer learning to improve the positioning accuracy and physical literacy positioning model (PLPM) as a health determinant. A variety of data augmentation techniques are used to combat signal fluctuations. As a result, the combined effects of motivation-promoting physical activity-based visualization improve the accuracy ratio to 96.7%, prediction ratio to 96.2%, efficiency ratio to 96.8%, and reduce the error rate to 18.7%, stress level (52.8%) compared to other conventional models and have a positive impact on the localizer and positioning, making a difference in physical activity (PA) levels.

Modulation of social behavior by distinct vasopressin sources.

The neuropeptide arginine-vasopressin (AVP) is well known for its peripheral effects on blood pressure and antidiuresis. However, AVP also modulates various social and anxiety-related behaviors by its actions in the brain, often sex-specifically, with effects typically being stronger in males than in females. AVP in the nervous system originates from several distinct sources which are, in turn, regulated by different inputs and regulatory factors. Based on both direct and indirect evidence, we can begin to define the specific role of AVP cell populations in social behavior, such as, social recognition, affiliation, pair bonding, parental behavior, mate competition, aggression, and social stress. Sex differences in function may be apparent in both sexually-dimorphic structures as well as ones without prominent structural differences within the hypothalamus. The understanding of how AVP systems are organized and function may ultimately lead to better therapeutic interventions for psychiatric disorders characterized by social deficits.

Oxidative Stress Response in the Seaweed Padina pavonica Associated with the Invasive Halimeda incrassata and Penicillus capitatus

The western Mediterranean Sea is one of the most affected areas by the introduction of alien seaweed. Penicillus capitatus Lam. and the recently introduced Halimeda incrassata (J.Ellis) J.V.Lamour are tropical algae that invade native algae assemblies in the shallow sandy beds of Mallorca (Balearic Islands, western Mediterranean) where they are already settled. The aim of this study was to evaluate the effect of a potential competition between the invasive P. capitatus and H. incrassata and the native Padina pavonica (L.) Thivy, by means of biomarkers. P. pavonica samples were collected in their habitat without invasive species and areas where P. capitatus and H. incrassata cohabitated. P. pavonica densities were measured in the three investigated areas. The coexistence of the invasive algae and P. pavonica was related to a significant decrease in the densities of native algae when compared to the area without the invaders. Antioxidant enzymes, catalase and superoxide dismutase, and the reduced glutathione and polyphenols levels were significantly increased in P. pavonica in the presence of both invasive algae. Malondialdehyde, a marker of oxidative damage, and the reactive oxygen species production tended to increase in the presence of the alien species, but without significant differences. The obtained results show that the presence of P. capitatus and H. incrassata altered the normal vegetative growth of P. pavonica and caused an antioxidant response that led to a context of stress, but without evidence of oxidative damage. In conclusion, the presence of the alien H. incrassata and P. capitatus can be considered a source of competitive stress for P. pavonica, although further research regarding the increased water temperature is required.

Predicting ecosystem productivity based on plant community traits.

With the rapid accumulation of plant trait data, major opportunities have arisen for the integration of these data into predicting ecosystem primary productivity across a range of spatial extents. Traditionally, traits have been used to explain physiological productivity at cell, organ, or plant scales, but scaling up to the ecosystem scale has remained challenging. Here, we show the need to combine measures of community-level traits and environmental factors to predict ecosystem productivity at landscape or biogeographic scales. We show how theory can extend the production ecology equation to enormous potential for integrating traits into ecological models that estimate productivity-related ecosystem functions across ecological scales and to anticipate the response of terrestrial ecosystems to global change.

Effect of ThymoQuin Black Cumin Seed Oil as a Natural Immune Modulator of Upper-Respiratory Tract Complaints and Psychological Mood State.

We conducted a randomized, double blind, placebo-controlled study to evaluate the effects of dietary supplementation with black cumin seed oil (Nigella sativa) on upper-respiratory tract complaints (URTCs) and psychological mood state. Thirty-seven runners (13.1-mile half-marathon and 26.2-mile marathon distance) consumed 500mg of black cumin seed oil extract (commercial name ThymoQuin®3%) or placebo daily during the 4 week supplementation period (3 weeks before and 1 week following a marathon or half-marathon competition). We collected subjective and objective measures before and after supplementation. Before and after supplementation, each subject completed two subjective surveys; (1) the profile of mood state (POMS) psychological assessment and (2) a standardized health log assessing health status and URTCs, as well as provided saliva samples and fecal samples for objective measurement of cortisol and microbiome balance, respectively. Compared to placebo, subjects in the ThymoQuin supplementation group reported significantly fewer upper-respiratory tract complaints (URTCs such as cough, sore throat, sinus congestion, etc) and better overall well-being (e.g. lower stress, increased energy), as well as lower stress hormones (cortisol) and superior microbiome diversity (S. thermophilus). These results suggest that ThymoQuin black cumin seed oil extract may improve immune system vigilance and overall well-being following the stress of endurance training and competition, and that these immune-mood benefits may be mediated through the Gut-Immune-Axis.

Resilience of Pinus durangensis Martínez in Extreme Drought Periods: Vertical and Horizontal Response of Tree Rings

Extreme drought events reduce the productivity of forest ecosystems. One approach for estimating the effects of drought on forests is by assessing their resilience. The objective of this study was to estimate resilience rates at different heights along the tree stem of Pinus durangensis Martínez. The radial growth of 200 cross sections extracted at four heights of tree stems (0.07–0.15, 1.3, 6.3, and 11.0–12.0 m) was analyzed and subsequently transformed into ring-width indices (RWI). These indices were correlated with the Standardized Precipitation-Evapotranspiration Index on a six-month time scale (accumulated drought of six months in the period February–May; SPEI06FM). Seven extreme drought events were identified (1890, 1902, 1956, 1974, 1999, 2006, 2011), and radial growth before, during, and after each event was determined. Based on ring-width index values, resistance, recovery, and resilience indices were calculated. The results indicated a significant correlation (p ≤ 0.05) between annual radial increment and climate indices along the stem (0.56 to 0.80). Climatic sensitivity was higher in the lower part of the stem, with mean sensitivity (MS) and expressed population signal (EPS) values of 0.38 and 0.97, respectively. Resistance index values ranged from 0.44 to 0.76 and were better expressed in higher sections of the stem. Resilience indices changed over time. Regardless of the height of the tree stem, the latest extreme drought events (1999, 2006, and 2011) have led to a lower resilience of trees, indicating that their recovery capacity has decreased. Therefore, forestry practices in the study area may consider managing tree density as a strategy to regulate the stress in competition and to increase the tolerance of trees to drought.

Can decentralized science help tackle the deterioration in working conditions in academia?

Academic staff’s working conditions have been deteriorating for years. In particular, the reduced availability of both research funding and permanent research positions has continuously led to insidious competition and intense stress among academics. Whereas governing bodies have made significant attempts to narrow pervasive social inequalities in the distribution of research funding within the scientific community, they have not truly taken into account the importance of the academics’ overall well-being in the development of more sustainable financing of academic researchers. This originates not only from the complexity to develop comprehensive models reflecting staff’s overall well-being in the academic environment, but also from the limited access to reliable and immutable data that transparently account for the staff’s direct experience. In this context, blockchain technology can push further the use of more transparent survey data collection and record-keeping that can help mitigate the systematic bias inherent to the centralized nature of traditional auditing. We discuss how research institutions and governing bodies can build on blockchain technology and the early momentum generated by the decentralized science (DeSci) movement to implement the future-proof research funding chain that values overall well-being across academia in a transparent and coordinated way.

A cross-sectional study on the mental toughness of female basketball players of different age groups

Introduction: Mental toughness is one of the abilities that is known to be important components of athlete performance. In light of this information, the aim of this study was to investigate mental toughness among basketball players of age range of 18-20 years and 21-23 years groups. Aim of Study: The focus of the present study was to conduct a cross-sectional study on the mental toughness among female basketball players of age range of 18-20 years and 21-23 years groups. Material and Methods: For this study the researcher selects thirty (30) female basketball players. In which 15 female Basketball players of 18 to 20 years and 15 Basketball players of under 21 to 23 years were randomly selected from LNIPE, Gwalior (M.P.) and LNIPE (NERC), Guwahati (Assam). Results: The results obtained from age range of 18-20 years and 21-23 years female basketball players groups revealed that Reboundability, Handling Pressure, Concentration, Confidence and Motivation were found higher in the age range of 21-23 years female basketball players. And total mental toughness that consist all the categories like Reboundability, Handling Pressure, Concentration, Confidence and Motivation also was found higher in the age range of 21-23 years female basketball players. At last significant difference was found between both the age range of 18-20 years and 21-23 years on total mental toughness of female basketball players at 0.05 level of significance. Conclusions: On the basis of finding concluded that 21-23 years players had exhibited higher mental toughness score might be because they could manage the competition stress in a better maimer and were more capable of handling the challenges and pressure more efficiently than 18-20 years group.

Repeated survey along the foreland of a receding Norwegian glacier reveals shifts in succession of beetles and spiders

Glacier forelands provide important sites to study climate-forced ecological succession because a chronosequence is apparent along a single valley. However, most studies of invertebrate succession in forelands provide a single snapshot of community assemblage patterns. With glaciers retreating rapidly worldwide, it is important to begin re-surveying community composition and assessing changes in relation to new terrain revealed by the retreating ice. In this study, we repeat a survey of spiders and beetles along the glacier foreland of the sub-alpine glacier Austerdalsbreen in western Norway, 15 years after an initial assessment in 2004, during which time the glacier has retreated 400 m. Invertebrates were sampled in 18 sites that represent a terrain age gradient of approximately 10–250 years since glacier recession. Forty spider species and 70 beetle species were identified, constituting the richest record in Nordic glacier forelands for these two taxonomic groups. Furthermore, three distinctive stages of succession were determined using TWINSPAN and NMDS: (1) a pioneer colonizer stage; (2) an intermediate successional stage; and (3) two late colonizer stages. Additionally, a species group of omnipresent species was identified. The transition from pioneer stage to early succession was characterized by a high degree of taxonomic replacement. Compared to the findings in 2004, we found that the composition of species groups on relatively old terrain is becoming more similar, while the differences between the species groups on the younger terrain are widening. This discrepancy is discussed in relation to climate warming, which potentially facilitates faster establishment of vegetation and early successional invertebrates and may therefore increase competition stress for cold-adapted pioneer species.

FORMATION OF WEEDINESS OF THE WINTER WHEAT DEPENDING ON THE FERTILIZER SYSTEM UNDER THE EXPERIENCE FIELD OF VNAU

The article reflects the results of studying the features of the formation of the level of weediness of winter wheat agrocenosis with gradually increasing rates of nitrogen nutrition against the background of the recommended rates of phosphorus and potassium fertilizers. A literature review of scientific sources on the impact of the level of mineral nutrition on the formation of segetal vegetation in winter wheat is carried out. The species and generic composition of weeds was determined taking into account various fertilizer options in quantitative and percentage values, on the basis of which a generalization with respect to the specifics of additional mineral nutrition from the standpoint of influencing the growth in the number of the most dominant species and genera of weeds was made. The effect of fertilizers on the indicators of quantitatively weighted weediness, which ultimately made it possible to formulate a useful interval for reducing the level of weediness by a certain interval for increasing the fertilizer rate is estimated. Based on the conducted studies, the specifics of the effect of fertilizers on ensuring the corresponding levels of competitive stress between winter wheat plants and weed plants are formulated. The nature of the species distribution of agrophytocenoses of winter wheat and weeds in the context of individual species by biological characteristics is determined. Fertilizer rate of 60 kg/ha d.r. in the conditions of our research, the Podolyanka variety can be marked as a landmark in the system of ensuring a sufficient level of cenotic tension, which determines the subsequent reduction of the weediness indicator with an increase in the rate of nitrogen mineral nutrition. Prospects for further research on the effect of mineral fertilizers on the options for modern fractional application to the main critical periods of winter wheat on the formation of weed levels against this background are outlined.

Impacts of stand density on tree crown structure and biomass: A global meta-analysis

Stand density is a critical factor in the variation of crown structure and biomass, and can significantly change the growing space and resource acquisition of trees. However, an understanding of the interactive mechanisms of this effect with stand characteristics and environmental conditions is still lacking. In this study, our goal was to quantify the responses of crown structure and biomass to stand density and explore how shade tolerance, tree species functional group, tree age and climate affect these responses. We synthesized the outcomes of 356 observations from 60 studies published since 2000 using a meta-analysis approach. The results showed that stand density did not change the ratio of branch plus leaf biomass to aboveground biomass (CB:TB) but did have a significant effect on the crown structure and the branch and leaf biomass. This indicates that in the face of density stress, trees are generally less able to adjust biomass allocation among different organs than they are to alter the morphology of organs. The effect of stand density on crowns varied greatly among different shade-tolerant species, tree species functional groups and tree age, while climatic gradients had no significant effect on the response of crowns to stand density, which reflected the change in tree growth strategies in response to the combined effect of many factors. Overall, our meta-analysis indicates that crown growth can be regulated by changing stand density but that the interaction of stand characteristics and environmental conditions with stand density results in different tree growth strategies. This meta-analysis helps to deepen the understanding of the adaptation strategies of trees in response to competition and environmental stress and serves to promote sustainable management of forest ecosystems.

The Influence of Academic Stress on Academic Burnout among Middle School Students in Guangdong

Objective To explore the characteristic of academic stress and academic burnout, and analyze the impact of academic stress on academic burnout among middle school students in Guangdong Province, China. Methods A stratified cluster sampling method was used to select 1011 students from 6 middle schools in Guangdong province. Academic Stress Scale for Middle School Students (ASSMSS) and Academic Burnout Scale for Middle School Students (ABSMSS) were used to investigate them. Results ⑴ The total scores of ASSMSS and ABSMSS were (60.86±9.31) and (231.43±37.54), respectively. ⑵ The students with rather serious, serious, general, light academic burnout accounted for 13.60%, 20.53%, 24.43% and 41.44%, respectively. The students with serious, general and light academic stress accounted for 66.32%, 3.81% and 29.87%, respectively. ⑶ the result of multivariate stepwise linear regression showed that the scores of competitive stress, task requirement stress, frustration stress and expectation stress were positively correlated with the total score of ABSMSS (β=.258-.459，all P <.001). Conclusions The academic stress and academic burnout of middle school students in Guangdong are rather serious. Academic stress may be an important influenced factor of academic burnout.

Competition Stress Prolongs Exercise Recovery In Collegiate Soccer Players

Athlete conditioning is vital to success in collegiate soccer. Effective conditioning programs incorporate adequate rest between exercise sessions. The duration of an athlete's recovery may be sensitive to variables beyond training load, including emotional and psychological factors. PURPOSE: To determine the effect of competition stress on recovery time in female collegiate soccer players. METHODS: We monitored 30 Division 1 female soccer players for 35 consecutive days. All athletes wore Polar Team Pro devices (Polar Electro Inc., Bethpage, NY), which recorded duration of exercise, total distance covered, kcals burned, number of sprints performed, average and maximum speed achieved, average and maximum heart rate (HR), and Polar calculations of training load, cardio load, and recovery duration in hours. Data were captured for 20 practices and 7 games, resulting in 858 observations. Linear regression tested the effect of formal competition on recovery duration holding constant time of day and all significant workload variables. RESULTS: Players were 20.1 ± 1.1 years of age. Across all practice and competition sessions, the mean duration of exercise was 59.0 ± 38.8 min, total distance covered was 2,518.9 ± 2,074.5 m, and estimated energy consumption was 381.7 ± 284.8 kcals. Athletes performed 5.9 ± 7.9 sprints per session, maintained an average speed of 2.8 ± 1.2 km/h, and achieved a maximum speed of 20.7 ± 7.3 km/h. Average HR was 131.9 ± 24.3 bpm, maximum HR was 177.4 ± 32.7 bpm, training load was 70.1 ± 59.3, and cardio load was 76.0 ± 62.2. Recovery duration was 12.8 ± 15.7 hr following practice sessions and 51.3 ± 59.6 hr following competitions (p < 0.001). Holding constant all significant predictors (time of day, exercise duration, total distance covered, estimated kcals, number of sprints, average speed, average HR, training load, and cardio load), formal competition corresponded to 33.8 additional hours of recovery (p < 0.001; 95% CI of β = 27.7 to 39.9; model r2 = 0.691; adjusted r2 = 0.687). CONCLUSION: Sufficient recovery is a crucial component of optimal performance in collegiate athletics. Our data indicate prolonged recovery duration following formal competition settings, which could not be explained by workload. Further research on psychological contribution to allostatic load is warranted.

Adaptation to stress in football athletes: The importance of cognitive appraisal.

This study analysed the adaptation of football athletes to competitive stressors regarding the upcoming match. For that, the study adopted a cross-sectional methodology using a critical incident approach. The participants were 352 young male football athletes, aged between 15 and 19 years (M = 16.91, SD = 0.99), who were competing in the national football championship. The results indicated that cognitive appraisal partially mediated the relationship between competitive stressors and emotions: athletes who perceived stressors as a challenge, tended to feel more control over the situation and more resourceful (coping perception), leading to a more positive emotional experience, while those perceiving the stressors as a threat were more prone to experience less control and more negative emotions. This mediation model was moderated by athletes’ competitive level (U17 or U19), as the role of challenge perception was more pronounced in the U19 team, while the relationship between threat perception and less control was only observed for the U17 team. In sum, the data reveals the importance of cognitive appraisal in young football athletes’ adaptation to competitive stressors, bolstering the theoretical models in this area and the importance of psychologists to consider these variables during intervention, particularly cognitive appraisal.

Nutritional stress induced intraspecies competition revealed by transcriptome analysis in Sphingomonas melonis TY.

Bacteria have developed various mechanisms by which they can compete or cooperate with other bacteria. This study showed that in the cocultures of wild-type Sphingomonas melonis TY and its isogenic mutant TYΔndpD grow with nicotine, the former can outcompete the latter. TYΔndpD undergoes growth arrest after four days when cocultured with wild-type TY, whereas the coculture has just entered a stationary phase and the substrate was nearly depleted, and the interaction between the two related strains was revealed by transcriptomic analysis. Analysis of the differential expression genes indicated that wild-type TY inhibited the growth of TYΔndpD mainly through toxin-antitoxin (TA) systems. The four upregulated antitoxin coding genes belong to type II TA systems in which the bactericidal effect of the cognate toxin was mainly through inhibition of translation or DNA replication, whereas wild-type TY with upregulated antitoxin genes can regenerate cognate immunity protein continuously and thus prevent the lethal action of toxin to itself. In addition, colicin-mediated antibacterial activity against closely related species may also be involved in the competition between wild-type TY and TYΔndpD under nutritional stress. Moreover, upregulation of carbon and nitrogen catabolism related-, stress response related-, DNA repair related-, and DNA replication-related genes in wild-type TY showed that it triggered a series of response mechanisms when facing dual stress of competition from isogenic mutant cells and nutritional limitation. Thus, we proposed that S. melonis TY employed the TA systems and colicin to compete with TYΔndpD under nutritional stress, thereby maximally acquiring and exploiting finite resources. KEY POINTS: • Cross-feeding between isogenic mutants and the wild-type strain. • Nutrition stress caused a shift from cooperation to competition. • TYΔndpD undergo growth arrest by exogenous and endogenous toxins.

Adverse role of colonial morphology and favorable function of microcystins for Microcystis to compete with Scenedesmus

In eutrophic freshwaters, Microcystis usually becomes dominant in phytoplankton communities due to the synergistic effects of its special eco-physiological traits and environmental factors. Colonial morphology can protect Microcystis from zooplankton grazing, which indirectly favors Microcystis to outcompete other phytoplankton, although the colonial form is not conducive to the absorption of nutrients. Moreover, unicellular Microcystis usually has competitive advantages over other phytoplankton due to its efficient absorption capacity for nutrients and releasing microcystins. However, the consequence of direct competition between toxic colonial Microcystis and green algae without external grazing pressure still remained unknown. In this study, the competition between toxic colonial Microcystis aeruginosa and a common green alga Scenedesmus obliquus was explored. Results showed that: (1) colonial M. aeruginosa had a higher requirement for key macro-nutrient phosphorus than S. obliquus, and thus its population declined and was replaced by S. obliquus eventually; (2) microcystins released by colonial M. aeruginosa inhibited the photosynthetic activity and growth of S. obliquus at early stage of the competition; (3) the photosynthetic potential of colonial M. aeruginosa was stimulated in response to the competitive stress from S. obliquus, although the population of colonial M. aeruginosa declined eventually; (4) microcystin production of colonial M. aeruginosa was enhanced by phosphorus limitation due to S. obliquus competition and was positively related to photosynthetic potential of colonial M. aeruginosa. These results indicated that, in the absence of complex natural environment, colonial Microcystis cannot outcompete Scenedesmus in a pure competition, although microcystins can play a favorable role in the competition, which clarified the opposite role of colonies and microcystins in the competition of colonial Microcystis against other phytoplankton.