Marine Microbiology and Aquatic Plankton Dynamics

Plankton Classification and Composition

Plankton is categorized into zoo, plant, and bacterioplankton (peak at 0.2–2 µm, nano at 2–20 µm, which includes cyanomicroalgae). Samples from profound deep-sea zones are contaminated if water from upper KPAS layers mixes in. The sampling bottle is securely closed, airtight, and sterilized.

Medium Composition and Biomass Analysis

Culture media include magnesium sulfate (0.7%), potassium chloride (0.075%), and sodium chloride (2.4%). Direct methods count total bacterial numbers, while molecular methods assess bacterial biomass.

• Bacterial Biomass: Influenced by temperature, salinity, and nutrients.
• Bacterial Activity: Influenced by nutrients (for organic matter acquisition), oxygen (respiration), and nitrogen.

Particulate Organic Matter and Marine Snow

Particulate organic matter (POM) colonizes millimeters-forming particles in suspension. Their vertical displacement results from activity, size, and new colonizations driven by chemotaxis. These aggregates consist of animals, plants, protists, fecal matter, inorganic particles, and marine snow formed when particles bind tightly via transparent exopolymer and mucous products originating from bacteria and plant degradation. These particles are typically 100–200 µm in size, sink at 100 m/day, and exhibit a high metabolism.

Adenosine Triphosphate and Lipopolysaccharides (LPS)

Adenosine triphosphate (ATP) quantities are measured via LPS (lipopolysaccharide, exclusive to Gram-negative bacteria) using radioactive isotopes. Assuming cellular LPS content remains constant across all cells, the methodology relies on turbidimetric analysis of LPS using horse erythrocytes. Turbidity is measured at 360 nm with a conversion factor of 2.78 ± feritograms of LPS per cell.

Microbial Domains and Phototrophy

Bacteria represent the first branch, while archaea divide into other archaea and Eukarya. The first two groups are exclusively microbial, whereas the third is not.

Primary phototrophs fix carbon in the oceans, possessing pigments such as chlorophyll b and phycoerythrin. They cannot live below 200 m in the euphotic zone due to a lack of proper light penetration, though they contain chlorophyll a, b, and alpha-carotenes.

Metabolic Pathways in Aquatic Environments

Organotrophs rely on fermentation or anaerobic respiration in darkness, and aerobic life or photoheterotrophy in illuminated aquatic environments. In sulfide-rich environments, sulfur acts as the primary electron donor for primitive organisms, permitting the reduction of NADP to NADPH.

Bergey's Manual and Gram-Negative Groups

Gram-negative groups include:

• Phylum Chloroflexi: Green sulfur bacteria.
• Chlorobi: Green sulfur bacteria, including the family Chromatiaceae, which accumulate purple sulfur bacteria.
• Ectothiorhodospiraceae: Sulfur bacteria that accumulate sulfur outside the cell, unlike previous groups.

Cellular Activity and Adaptive Processes

Cells can be visualized using INT for respiratory activity. Tetrazolium salts are colorless inside normal cells but form colored formazan precipitates when reduced by electron transport chain intermediates.

Cells adapt to variable, unfavorable conditions by shrinking into ultramicrocells through continuous degradation of endogenous reduction material. An increased surface-to-volume ratio allows for more efficient nutrient sequestration in oligotrophic environments. This size reduction also protects bacterioplankton from herbivorous predators.

Adaptive structural changes include:

• Transition to coccoid forms with reduced cell size.
• Increased surface-to-volume ratio.
• Changes in murein cross-linking.
• Reduction of lipoteichoic acid in the cell wall.
• Cytoplasmic densification and content reduction.

Specific Bacterial Genera and Morphologies

Gram-negative bacilli, thermophiles, inhabit hot springs, submarine vents, and geochemical activity zones.

Spiral-shaped or non-filamentous bacteria lack an axial filament. FS-K strains utilize carbohydrates, amino acids, and fatty acids as carbon and energy sources.

Non-FS-K bacteria are classified under:

• Domain: Bacteria
• Phylum: Proteobacteria
• Class: Gamma-proteobacteria
• Order: Pseudomonadales
• Family: Pseudomonadaceae
• Genus: Pseudomonas (e.g., P. elongata, P. nautica)

Cellular Appendages and Prosthecae

Cell walls can extend to form cytoplasmic extensions:

• Appendages (small)
• Hyphae (large), which serve a reproductive function (e.g., Hyphomonas) or increase surface area for nutrient uptake (e.g., Caulobacter).

Gram-negative bacteria with stalks or prosthecae reproduce via binary fission or budding at one cell pole or at the tip of hyphae extensions.

Filamentous Sulfur Bacteria and Rice Paddies

Notable filamentous genera include Beggiatoa, Thiothrix, Thioploca, Leucothrix, and Thiobacillus. In rice paddies, anaerobic root zones produce hydrogen sulfide ($H_2S$), which is toxic to rice plants. Beggiatoa helps mitigate this toxicity in the rhizosphere. Plant roots release oxygen, creating microaerophilic conditions preferred by Beggiatoa.

Iron Limitation and Marine Pathogens

Iron is often a limiting factor in marine environments. Gram-negative curved bacteria with polar or lateral flagella inhabit fresh and salt water and include aquatic animal pathogens and bioluminescent bacteria. They are oxidase-positive and include human pathogens such as those causing cholera.

Bacteriological Assays and Microbial Control

Cultures are incubated for 24 hours in lactose medium at 35 °C as part of group differential testing and bioassays. In deep thermal springs and sediments lacking oxygen, bacteria fulfill roles as microbial predators and organic matter mineralizers, oxidizing carbon compounds to carbon dioxide ($CO_2$).

Anoxygenic Photosynthesis and Nitrification

Some bacteria possess bacteriochlorophyll and a single photosystem. Electrons move from the reaction center to cytochrome bc1 via quinone, generating a proton gradient necessary for ATP synthesis. Some transfer electrons to NAD+ to produce NADH, similar to water oxidation in higher plants.

Chemoautotrophic aerobic bacteria (requiring $O_2$) act as nitrite-oxidizing nitrifiers, utilizing reduced nitrogen compounds as electron sources.

Quorum Sensing and Bioluminescence

Bioluminescent bacteria regulate luciferase production through quorum sensing using an autoinducer. When bacterial population density drops, luminescence ceases.

Fluorescence In Situ Hybridization (FISH)

FISH is a molecular technique used to track specific organisms or groups based on probe specificity. Cells are permeabilized and treated with fluorochrome-labeled probes to track specific bacterial genes and species.