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Microbial Ecosystems - Major marine phototrophs

10 important questions on Microbial Ecosystems - Major marine phototrophs

How does Ostreococcus differ from Prochlorococcus? What do they have in common?

  • Differences: Ostreococcus and Prochlorococcus differ in their genomic characteristics. Ostreococcus has a larger genome (12.6 Mbp) compared to Prochlorococcus, which has a smaller genome size (around 2 Mbp). The Ostreococcus genome is gene-dense, containing about 8000 genes, whereas Prochlorococcus has approximately 2000 genes. Ostreococcus is a eukaryotic organism, while Prochlorococcus is a cyanobacterial prokaryote.
    • Commonalities: Both Ostreococcus and Prochlorococcus are oxygenic phototrophs, meaning they perform photosynthesis to produce oxygen. Despite their differences in genome size and structure, they share the common feature of being major marine phototrophs, contributing to primary productivity in marine ecosystems.

How does the organism Prochlorococcus contribute to both the carbon and oxygen cycles in the oceans?

Prochlorococcus contributes to both the carbon and oxygen cycles in the oceans through photosynthesis. As a primary producer, Prochlorococcus utilizes sunlight to convert carbon dioxide into organic carbon, releasing oxygen as a byproduct. This process is a fundamental part of the carbon cycle as it fixes carbon into organic molecules, supporting the marine food web. Additionally, the oxygen produced during photosynthesis by Prochlorococcus contributes to oxygen levels in marine environments, impacting aerobic processes and sustaining marine life.

How does Roseobacter differ from Prochlorococcus?

  • Taxonomy: Roseobacter and Prochlorococcus belong to different taxonomic groups. Roseobacter is a genus of Alphaproteobacteria, while Prochlorococcus is a cyanobacterial genus.
  • Metabolism: Roseobacter is an aerobic anoxygenic phototroph, meaning it carries out photosynthetic light reactions only under oxic (oxygenated) conditions. In contrast, Prochlorococcus is an oxygenic phototroph, performing photosynthesis under both oxic and anoxic conditions.
  • Carbon Source: Roseobacter relies on organic carbon for its carbon sources, exhibiting photoheterotrophy. On the other hand, Prochlorococcus is primarily autotrophic, using inorganic carbon sources for carbon fixation during photosynthesis.
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What distinguishes Prochlorococcus from most cyanobacteria in terms of pigments, and how does this distinction impact its appearance?

Prochlorococcus differs from most cyanobacteria in that it lacks phycobilins, the accessory pigments typically found in cyanobacteria. This absence of phycobilins results in Prochlorococcus cells appearing olive green, unlike the blue-green color associated with cyanobacteria.

What role does Prochlorococcus play in the primary productivity of the tropical and subtropical regions of the world's oceans?

Prochlorococcus is a major contributor to the primary productivity in the tropical and subtropical regions of the world's oceans. It accounts for up to half of the photosynthetic biomass and primary production in these regions, reaching cell densities of 10^5 cells per milliliter. Prochlorococcus conducts photosynthesis, converting light energy into organic carbon, and thus plays a crucial role in supporting marine food webs and the carbon cycle.

Describe the concept of Prochlorococcus ecotypes and provide an example of an ecological difference between different ecotypes.

Prochlorococcus ecotypes are distinct genetic variants of the species that differ physiologically, occupying slightly different ecological niches. For example, different Prochlorococcus ecotypes exhibit variations in their photosynthetic responses to light intensities (high-light versus low-light ecotypes) and utilize different inorganic and organic nitrogen and phosphorus sources. These ecological differences allow different ecotypes to thrive in specific environmental conditions, contributing to the overall success of Prochlorococcus in diverse marine habitats.

How does genetic diversity within Prochlorococcus populations contribute to its adaptive response to changing environmental conditions?

Genetic diversity within Prochlorococcus populations, revealed through single-cell genomics, plays a crucial role in the adaptive response to changing environmental conditions. Each Prochlorococcus ecotype is composed of hundreds of subpopulations, sharing a common set of core genes controlling interactions with the environment. Additionally, each subpopulation contains flexible genes that vary, contributing to high microdiversity. This genetic versatility allows Prochlorococcus to adapt to new niche opportunities, as demonstrated by seasonal shifts in different genotypes in response to changing light intensity, nutrient availability, and predator populations.

What distinguishes Trichodesmium from Prochlorococcus, and what role does Trichodesmium play in the marine nitrogen cycle?

Trichodesmium is a planktonic filamentous marine cyanobacterium that differs from Prochlorococcus in its colonial filamentous structure and the presence of phycobilins. Trichodesmium is a nitrogen-fixing cyanobacterium, contributing to the marine nitrogen cycle by converting atmospheric nitrogen into fixed nitrogen compounds. This process is crucial for providing an essential nutrient to marine ecosystems.

Compare the genome characteristics of Ostreococcus and Prochlorococcus, highlighting their differences in genome size, gene density, and number of genes.

Ostreococcus and Prochlorococcus, despite both being oxygenic phototrophs, differ in genome characteristics. The genome of Ostreococcus is larger, with a size of 12.6 Mbp distributed over 20 chromosomes, whereas Prochlorococcus has a smaller genome size of around 2 Mbp. The Ostreococcus genome is gene-dense, containing about 8000 genes, while the Prochlorococcus genome is smaller, containing around 2000 genes. This emphasizes the genomic diversity between eukaryotic and prokaryotic marine phototrophs.

Explain the concept of aerobic anoxygenic phototrophs and provide examples of bacteria belonging to this group. How do they synthesize ATP in illuminated and oxic pelagic waters?

Aerobic anoxygenic phototrophs are bacteria that perform photosynthetic light reactions only under oxic (oxygenated) conditions. Examples of bacteria in this group include Erythrobacter, Roseobacter, and Citromicrobium, all of which belong to the Alphaproteobacteria. These organisms synthesize ATP by photophosphorylation when oxygen is present in illuminated and oxic pelagic waters. However, they cannot grow autotrophically and rely on organic carbon for their carbon sources, a nutritional condition known as photoheterotrophy.

The question on the page originate from the summary of the following study material:

Brock Biology of Microorganisms, Global Edition | 9781292235103 | Michael T Madigan, et al

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