Abstract
The increasing frequency and severity of extreme climate events present significant challenges to microbial communities. These microorganisms play a pivotal role in shaping nutrient cycling, soil health, and the stability of ecosystems. However, changes in temperature patterns, precipitation cycles, and extreme weather events have direct consequences on microbial physiology, community structure, and overall ecosystem function. Consequently, the resilience of microbial communities becomes paramount for their persistence and effective functioning. Microbes exhibit plasticity at the cellular level, altering metabolic pathways, membrane composition, and stress response mechanisms in response to changing environmental conditions. This review explores microbial adaptations and responses to some important climate-induced stressors, such as drought, floods, heatwaves, and cold temperatures.
Introduction
The increase in the frequency and intensity of extreme climate events like prolonged droughts, catastrophic floods, heatwaves, cold waves and other climatic disturbances poses formidable challenges to microbial communities. Microbes are the unseen architects of life on earth, influencing nutrient cycling, soil health, and the overall stability of ecosystems. However, temperature alterations, shifts in precipitation patterns, and extreme weather events can directly influence microbial physiology, community composition, and ecosystem functioning. For instance, one of the primary impacts of climate change on microbes is the alterations in temperature regimes. Many microorganisms have specific temperature ranges at which they thrive, and even slight deviations can disrupt their metabolic processes. Warmer temperatures can accelerate microbial activities, such as nutrient cycling and decomposition, potentially leading to shifts in ecosystem dynamics. Conversely, cold-adapted microbes may face challenges as their habitats warm, impacting their ability to function optimally. Similarly, changes in precipitation patterns and the frequency of extreme weather events also have significant repercussions for microbial communities. Microbes in soil and water are particularly vulnerable to shifts in moisture levels, as their activities are often dependent on the availability of water (Shade, 2023). Increased drought conditions or more intense rainfall events can disrupt microbial habitats, affecting their abundance and diversity. Moreover, rising atmospheric carbon dioxide (CO2) levels, a hallmark of climate change, can directly influence microbial processes. Microbes are critical players in carbon cycling, and alterations in CO2 concentrations can impact their ability to decompose organic matter and affect greenhouse gas emissions. This, in turn, creates a feedback loop, where microbial responses to climate change contribute to further alterations in the Earth’s climate (Ibáñez et al., 2023).
Microbial resilience, in this context refers to the capacity of microorganisms to withstand and recover from environmental disturbances, ensuring the persistence and functionality of microbial communities. The concept of microbial resilience to climate change involves a variety of responses, ranging from individual physiological adaptations to community-level shifts in structure and function. At the cellular level, microbes may exhibit alterations in metabolic pathways, membrane composition, or stress response mechanisms in response to changing environmental conditions. This plasticity allows them to maintain functionality and, in some cases, enhance their performance in the face of adversity. This adaptability not only underscores the resilience of individual microbes but also highlights the dynamic nature of microbial ecosystems. Thus, understanding the mechanisms behind microbial resilience is not only critical for deciphering the intricacies of microbial life but also holds significance for predicting the overall resilience of ecosystems to climate change.
Impact of Climate Extremes on Microbial Communities
Microorganisms have existed since the beginning of Earth, at least 3.5 billion years ago (Knoll, 2015), and they will surely continue to exist long after any extinctions occur in the future. The biosphere depends on the abundance and diversity of these microorganisms to remain healthy (Cavicchioli et al., 2019). Microbes are essential to food security, agricultural output, environmental health, and nutritional cycles like those involving carbon and nitrogen. Therefore, it makes sense to think about a potential impact on microbial biodiversity and its subsequent effects (Cavicchioli et al., 2019; Griffth, 2012; Banerjee et al., 2020) given that climate change can exacerbate seasonal disturbances and increase the frequency of extreme events (Khursheed, 2016).
Global warming has an overwhelming impact on the variation in soil microbial diversity among all the environmental factors affected by climate change. By increasing the temperature in the surface soil and lowering its moisture content, global warming plays a significant part in shaping microbial diversity compared to other identified environmental drivers (Guo et al., 2018; Zhou et al., 2016).
Climate extremes, such as heatwaves, droughts, floods, and extreme precipitation events, can exert profound effects on microbial communities. These events alter environmental conditions, including temperature, moisture, and nutrient availability, leading to shifts in microbial diversity, abundance, and activity. Thus, understanding the effects of climate change on microbial diversity is a mandatory thing to maintain the ecosystem integrity.
Extremes in temperature have the potential to cause substantial and enduring changes in the abiotic characteristics of soil as well as the makeup and activity of soil microbial communities. In a study published in 2018 by MacFadden et al., temperature and population density were positively correlated for the common infections caused by bacterial species such as Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli. According to MacFadden et al., 2018 the average minimum temperature—which has been rising as a result of climate change—was linked to an increase in antibiotic resistance. As climate change intensifies, the combination of rising infection rates and growing antibiotic-resistant microorganisms will unavoidably result in an increasing number of antibiotic-resistant pathogens. In the same way, Salmonellosis, which is growing more resistant to antibiotics, is more common in areas with high heat and humidity. Climate change has the potential to dramatically increase the burden and morbidity from salmonellosis worldwide due to the millions of cases that the disease has reported globally and rising antibiotic resistance (Farag & Alagawany, 2018).
Microbial Responses to climate induced stressors
- Drought- Microbial communities demonstrate dynamic physiological and structural adaptations to cope with drought stress. These adaptations include osmoregulation, where microbes accumulate compatible solutes like trehalose, proline, and glycine betaine to counteract water loss. Additionally, morphological changes, such as transitioning to a dormant state, reduced metabolic activity, conserving energy and resources during drought (Malik et al., 2020). The metabolic flexibility of microbes allows them to switch between metabolic pathways and utilize alternative carbon and energy sources, thereby facilitating their survival in nutrient-poor environments. Biofilm formation emerges as a common strategy, providing resistance to desiccation, enhanced nutrient retention, and improved communication within microbial communities. Genetic adaptations, driven by natural selection and evolution, equip microbes with novel traits to withstand water scarcity. Symbiotic relationships with plants, like mycorrhizal associations and nitrogen-fixing bacteria, enhance water and nutrient uptake, promoting survival in arid environments (Trivedi et al., 2022). Collectively, these microbial strategies contribute significantly to nutrient cycling, organic matter decomposition, and soil structure maintenance, ensuring the stability and productivity of terrestrial and aquatic ecosystems (Evans et al., 2016).
- Floods- Flooding is a widespread and recurrent environmental challenge that significantly influences terrestrial and aquatic ecosystems. Microbes employ various physiological adaptations to thrive in flooded conditions. Some microorganisms exhibit morphological changes, such as altered cell shapes or the development of specialized structures, to navigate and survive in waterlogged environments. Additionally, the regulation of gas exchange mechanisms, including adaptations to oxygen availability, is crucial for microbial survival during flooding. Some microbes switch to anaerobic respiration or fermentation, utilizing alternative electron acceptors and metabolic pathways to generate energy in the absence of oxygen. This metabolic plasticity enables microbial communities to maintain essential functions even in oxygen-depleted conditions (Mishra et al., 2021). Similar to responses to drought, biofilm formation emerges as a common strategy for microbial adaptation to flooding. Microbes within biofilms create a protective matrix that enhances their resistance to water flow, facilitates nutrient retention, and promotes interspecies communication (Philippot et al., 2021). Mycorrhizal associations and nitrogen-fixing bacteria play essential roles in enhancing the flood tolerance of host plants, contributing to the overall resilience of ecosystems (Trivedi et al., 2022).
- Heatwaves-Microbes employ various thermotolerance mechanisms to survive high temperatures during heatwaves. One notable strategy involves the production of heat shock proteins (HSPs). These specialized proteins play a crucial role in safeguarding cellular structures, ensuring protein integrity, and mitigating the effects of heat stress. These proteins assist in refolding denatured proteins and preventing protein aggregation (Shekhawat et al., 2022). Additionally, microorganisms adapt to heatwaves by dynamically adjusting the composition of their cell membranes. This involves the incorporation of heat-resistant lipids, a mechanism that serves to maintain the structural integrity and optimal functioning of cell membranes even under extreme heat conditions (Koga, 2012). Furthermore, exposure to high temperatures can induce DNA damage in microorganisms. In response, these resilient microbes activate DNA repair mechanisms, addressing DNA lesions caused by the heat stress. Another noteworthy response involves the enhancement of antioxidant production by microbes. Elevated temperatures can lead to the generation of reactive oxygen species (ROS), which can be damaging to cellular components. Microbes counteract these detrimental effects by increasing the production of antioxidants, thereby mitigating oxidative stress and promoting cellular survival in the heatwave environment.In addition to these mechanisms, some microbes employ a more passive strategy by entering a dormant state or forming spores during adverse conditions, including heatwaves. This state of reduced metabolic activity serves as a protective measure, allowing the microbes to endure unfavorable conditions until more hospitable environments reemerge (Bérard et al., 2015).
- Cold and Freezing Temperatures- Microbial adaptations to cold and freezing temperatures are remarkable examples of how microorganisms have evolved to thrive in extreme environmental conditions. For instance, microorganisms have developed various strategies to adapt with sudden drops in temperature. One notable adaptation involves the production of cold shock proteins (CSPs), which play a vital role in maintaining membrane fluidity. CSPs prevent the formation of ice crystals and stabilize cellular structures, ensuring the integrity of the microorganisms in the face of temperature fluctuations. Additionally, microbes employ the accumulation of cryoprotectants and compatible solutes as a defense mechanism against the damage caused by ice formation. Substances like sugars and polyols serve to lower the freezing point of intracellular fluids, safeguarding the cells from the harmful effects of freezing (Phadtare & Inouye, 2008; Zhang & Gross, 2021). Furthermore, some cold-adapted microbes use quorum sensing mechanisms to regulate collective behaviors within their populations. This allows them to coordinate responses to environmental challenges, contributing to the overall resilience of the microbial community.
Beyond mere survival, microbial organisms engage in intricate relationships, ranging from competitive interactions to symbiotic collaborations. These connections not only influence the adaptability of microbial communities to environmental stressors but also play a fundamental role in shaping broader ecological processes.
Microbial interactions and synergies
Microbial interactions play a crucial role in the adaptability of ecosystems to environmental stressors. In the face of climate-induced challenges, microbial communities may undergo shifts in composition and function, driven by the intricate interplay of species responding to changing conditions. The resilience of ecosystems relies on the ability of microbial communities to adapt collectively through dynamic interactions and synergies. Figure 1 represents the different synergistic interactions among microbes in the context of climate extremes.
a. Metabolic Interactions
Microbes often engage in synergistic metabolic interactions, where the by-products of one microorganism serve as nutrients or energy sources for others. This cooperative metabolism can enhance overall community resilience to climate extremes by optimizing resource utilization. Conversely, microbial communities may also exhibit competitive interactions for limited resources. Climate extremes can alter resource availability, intensifying competition and influencing community composition.
b. Community-Level Responses
Climate extremes can lead to shifts in microbial community composition. Certain species may thrive or decline in response to changing environmental conditions, influencing the overall functioning of the microbial community. Moreover, Microbial communities undergo successional changes in response to climate extremes. Certain species may dominate during the initial stages of a disturbance, while others become more prevalent as the environment stabilizes.
c. Cross-feeding
Microbial cross-feeding during climate extremes involves the collaborative exchange of metabolites or by-products among different microbial species. This cooperative strategy is crucial in challenging context like climate extremes. For example, certain metabolite or enzyme produced by one microbe is beneficial for another microbe’s survival. Similarly, in nutrient-poor environments, one group of microbes break down complex organic compounds into simpler forms, providing a resource that is then utilized by other microbial groups.
d. Mutualism
Mutualistic interactions are characterized by reciprocal benefits, where each microbe provides something valuable for the other, contributing to overall community resilience. For example, in environments with high salinity or osmotic stress, microbes may engage in mutualistic relationships to share osmoprotective compounds. Similarly, in extreme environments (such as hot springs or deep-sea vents) microbial communities often form symbiotic relationships where different species work together to optimize resource utilization and survival.
e. Bio-control and pathogen suppression
These interactions are vital in maintaining ecological balance, especially when climate extremes may exacerbate the prevalence and impact of pathogens. For instance, Microbes engage in antagonistic interactions where they produce compounds that have inhibitory effects on the growth or virulence of pathogens. These compounds can include antibiotics, antifungal agents, or other bioactive molecules. Also, Microbes can induce systemic resistance in plants, making them more resistant to pathogenic attacks. This systemic response helps plants defend against pathogens even during climate extremes.
It is understood that microbial resilience and climate extremes are interconnected. Some microorganisms are extremely pathogenic and subtle changes exhibited by them due to extreme climates can have devastating effects on life. The unchecked advancement of climate change is a social justice issue that will disproportionately impact the health and well-being of people living in low- and middle-income nations worldwide. In order to put an end to the approaching climate catastrophe, we need to act now. We should stop the development of antibiotic resistance caused by climate change now rather than attempting to mitigate it later. In order to safeguard the health of the people as well as the environment, it is our responsibility to deal with the interconnected issues of microbial resilience, antibiotic resistance and climate change.
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