The marine phosphorus cycle driven by an unlikely microbe – Nature

Report on the Role of Alteromonas in the Marine Phosphorus Cycle and its Implications for Sustainable Development Goals

Executive Summary

A comprehensive analysis combining global seawater sample data and laboratory experiments has identified the bacterium Alteromonas as a primary regulator of the marine phosphorus cycle. Despite its relatively low abundance, this microbe dominates the production of alkaline phosphatase (APase), an essential enzyme for making phosphorus bioavailable. The research reveals that Alteromonas expresses APase constitutively, challenging the conventional view that the enzyme is only produced under phosphorus-deficient conditions. This finding provides a solution to the long-standing “APase paradox” of high enzyme activity in phosphorus-rich deep ocean waters. This new understanding of marine biogeochemistry has profound implications for achieving several Sustainable Development Goals (SDGs), particularly SDG 14 (Life Below Water), SDG 13 (Climate Action), and SDG 2 (Zero Hunger).

Phosphorus Cycling: A Foundation for Marine Sustainability

The Importance of Phosphorus in Ocean Ecosystems

Phosphorus is an indispensable element for all life, forming critical components of cell membranes, proteins, and nucleic acids. In marine environments, the availability of dissolved inorganic phosphorus often limits the growth of phytoplankton and bacteria, which form the base of the oceanic food web. The cycling of this nutrient is therefore fundamental to the health, productivity, and biodiversity of marine ecosystems.

Relevance to United Nations Sustainable Development Goals (SDGs)

• SDG 14 (Life Below Water): The health of marine ecosystems is directly dependent on nutrient cycles. Understanding the key microbial drivers of phosphorus availability is essential for the conservation and sustainable use of oceans, seas, and marine resources.
• SDG 13 (Climate Action): The phosphorus cycle is intrinsically linked to the marine carbon cycle. Phytoplankton, whose growth is often phosphorus-limited, play a major role in absorbing atmospheric carbon dioxide. Accurate modeling of these interconnected cycles is vital for climate science and policy.
• SDG 2 (Zero Hunger): Marine primary productivity, fueled by nutrients like phosphorus, underpins global fisheries. A stable and predictable phosphorus cycle is necessary to support the marine food webs that provide a critical source of protein for billions of people.

Key Research Findings on Alteromonas and APase Activity

Dominant Contribution of a Low-Abundance Microbe

The study reveals a counterintuitive ecological dynamic: the bacterial group Alteromonas is the dominant producer of APase transcripts and proteins in the global ocean. This is significant because Alteromonas is hundreds of times less abundant than other key microbes like Prochlorococcus and Peliagibacter. This suggests that Alteromonas possesses an exceptionally high rate of APase synthesis and activity, making it a disproportionately influential player in marine biogeochemistry.

Resolution of the “APase Paradox”

A key finding is that APase expression in Alteromonas is constitutive, meaning it occurs continuously regardless of ambient phosphate concentrations. This discovery explains the long-observed “APase paradox”—the high prevalence of APase activity in the deep ocean where phosphorus is not limited. The continuous release of bioavailable phosphorus by Alteromonas in deep waters can subsequently be transported by upwelling to support phytoplankton in surface waters, thereby linking deep-ocean microbial activity to surface productivity.

Implications for Achieving SDG Targets

Advancing Marine Ecosystem Management (SDG 14)

This research fundamentally alters the scientific understanding of marine nutrient regulation. Key implications include:

1. The need to recognize that ecologically critical functions may be driven by less abundant, highly active microbial groups.
2. The potential for revising biogeochemical models to more accurately reflect the role of Alteromonas.
3. Providing a new basis for assessing ecosystem health and the impacts of pollution on natural nutrient cycles.

Informing Climate Action and Food Security (SDG 13 & SDG 2)

The role of Alteromonas has direct relevance to global climate and food systems:

• Climate Models: By clarifying a key mechanism in the phosphorus cycle, the research helps refine models of the ocean’s biological carbon pump, improving our ability to predict responses to climate change.
• Fisheries Productivity: The continuous supply of phosphorus from deep-ocean processes, driven by Alteromonas, is a crucial factor supporting the phytoplankton blooms that sustain fisheries. Understanding this process is vital for sustainable fisheries management.
• Harmful Algal Blooms: The study suggests that models for predicting harmful algal blooms, which are often linked to nutrient availability, may need to be revised to account for the dominant sources of APase activity.

Future Research and Policy Directions

Priority Scientific Questions

The findings prompt further investigation into several critical areas:

1. How will climate change, particularly ocean warming and increased stratification, affect the distribution and activity of Alteromonas and, consequently, the global phosphorus cycle?
2. What are the specific roles and dominant producers of APase among phytoplankton communities in the euphotic zone?
3. How do changes in trace metal availability, which act as cofactors for different APase types, impact the overall landscape of phosphorus and carbon cycling?

Recommendations for Sustainable Ocean Governance

• Integrate these findings into Earth system models to improve projections of climate change and its impact on marine ecosystems.
• Support targeted research into keystone microbial species to develop more effective strategies for marine conservation and resource management under SDG 14.
• Enhance monitoring programs to track changes in microbial community composition and function as key indicators of ocean health in a changing climate.

Analysis of Sustainable Development Goals (SDGs) in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 14: Life Below Water

  This is the primary SDG addressed. The article focuses entirely on the health and functioning of marine ecosystems by examining the marine phosphorus cycle. It discusses how phosphorus availability is “vital to ocean ecosystem functioning” and influences key marine organisms like “bacteria and phytoplankton.” The research into the role of Alteromonas bacteria directly contributes to understanding the fundamental biogeochemical processes that sustain life in the oceans. The potential connection between phosphorus cycling, phytoplankton, and “harmful algal blooms” further reinforces the link to marine ecosystem health and pollution.

• SDG 13: Climate Action

  This SDG is connected through the article’s discussion of the future impacts of climate change on marine environments. It explicitly states that “Changes in ocean chemistry and stratification with global warming may affect the distribution, cycling, and transport of phosphorus.” This highlights the vulnerability of fundamental marine biogeochemical cycles to climate change, linking the article’s scientific focus to the broader need for climate action and understanding its consequences.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. SDG 14: Life Below Water

   • Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution.
     
     Explanation: The article’s focus on the phosphorus cycle is directly related to nutrient dynamics in the ocean. It mentions that an imbalance in these cycles can lead to “harmful algal blooms that spit out environmental toxins,” which is a form of nutrient-related marine pollution. Understanding the natural regulation of phosphorus is critical to identifying and mitigating disruptions that cause such pollution.
   • Target 14.2: By 2020, sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration in order to achieve healthy and productive oceans.
     
     Explanation: The discovery that Alteromonas is a “powerhouse in phosphorus cycling” provides crucial knowledge for managing and protecting marine ecosystems. Understanding such “key forces in global biogeochemical processes” is fundamental to assessing ecosystem health and resilience, especially in the face of environmental changes.
   • Target 14.a: Increase scientific knowledge, develop research capacity and transfer marine technology… in order to improve ocean health and to enhance the contribution of marine biodiversity to the development of developing countries.
     
     Explanation: The entire article is a testament to this target. It describes new scientific findings from an “extensive global assessment of microbial sequences” and “laboratory experiments.” Furthermore, it calls for “Additional focused systematic studies,” directly advocating for the increase of scientific knowledge to better understand and model ocean health.

2. SDG 13: Climate Action

   • Target 13.3: Improve education, awareness-raising and human and institutional capacity on climate change mitigation, adaptation, impact reduction and early warning.
     
     Explanation: The article contributes to this target by raising awareness of the complex and often overlooked impacts of global warming. By explaining how climate change can alter “ocean chemistry and stratification” and subsequently affect the fundamental “cycling, and transport of phosphorus,” it educates on the cascading effects of climate change on marine life, thereby building scientific and public capacity to understand these impacts.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

The article, being a scientific publication, does not mention official SDG indicators but implies several measurable metrics that can serve as indicators of ocean health and scientific progress.

• Concentration of bioavailable phosphorus: The article repeatedly refers to “dissolved inorganic phosphorus (Pi)” and its limitation in the ocean. Monitoring the concentration of different forms of phosphorus is a direct indicator of nutrient status and potential pollution (relevant to Target 14.1).
• Alkaline Phosphatase (APase) activity: APase is presented as a “critical enzyme in the marine phosphorus cycle.” The article details how researchers measured “microbial APase activity in the global ocean.” Therefore, measuring the rate and distribution of APase activity serves as a direct indicator of the functioning of the phosphorus cycle and ecosystem health (relevant to Target 14.2).
• Abundance of key microbial groups: The study quantifies the “relative abundance” of bacteria like Alteromonas, Prochlorococcus, and Peliagibacter. Monitoring the abundance and distribution of these key functional groups can indicate the state and resilience of marine microbial ecosystems (relevant to Target 14.2).
• Volume and scope of genomic and transcriptomic data: The research is based on an “extensive global assessment of microbial sequences” and analysis of “APase transcripts.” The growth of such datasets is an indicator of increasing scientific knowledge and research capacity as called for in Target 14.a.
• Frequency and extent of harmful algal blooms: The article links phosphorus dynamics to phytoplankton groups “responsible for harmful algal blooms.” Tracking the occurrence of these blooms serves as an indicator of marine pollution and ecosystem distress (relevant to Target 14.1).

4. Summary Table of SDGs, Targets, and Indicators

Source: nature.com