Chapter 6 Key Concepts Marine Viruses Viral Characteristics Biodiversity and Distribution of Marine Viruses

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1 Chapter 6 Key Concepts Microbial life in the sea is extremely diverse, including members of all three domains of life as well as viruses. Marine virology is an emerging field of study, due to recognition of the critical role that viruses may play in population control of other microbes, in nutrient cycling, and in marine pathology. Photosynthetic and chemosynthetic bacteria and archaeons are important primary producers in marine ecosystems. Heterotrophic bacteria, archaeons, and fungi play essential roles in recycling nutrients in the marine environment. Marine eukaryotic microbes are primary producers, decomposers, and consumers, and some contribute significantly to the accumulation of deep-sea sediments. Populations of several kinds of photosynthetic marine microbes may form harmful blooms that affect other marine and maritime organisms directly and indirectly. Marine Viruses Virology Marine Viruses are diverse and abundant Significant source of food and diseases of Marine viruses first reported in the 1970s Reliable counts made in the 1980s Viral Characteristics Is a virus alive? DNA or RNA surrounded by protein Rely entirely on host to reproduce themselves Origin of viruses: two hypotheses highly reduced prokaryotic parasites renegade genes Viral structure Virion- virus outside the host cell viral shapes: icosahedral viruses helical viruses binal viruses some virions have filaments and other attachment parts Viral life cycles lytic cycle lysogenic cycle Biodiversity and Distribution of Marine Viruses 10 times more abundant than prokaryotes Estimated 100 to 10,000 genotypes Most are icosahedral or binal bacteriophages with lytic life cycles Sediment viruses are typically helical and lysogenic

2 Ecology of Marine Viruses Viruses control populations of microbes Cause chronic infection and mortality of animals Viral populations are probably controlled by several biotic and abiotic factors Marine Bacteria General characteristics prokaryotic organization reproduce asexually by binary fission Nutritional Types Cyanobacteria (blue-green bacteria) photosynthetic Cyanophycean chlorophyll a and chlorophyll b carotenoids and phycobilins chromatic adaptation Single cells or mats Other photosynthetic bacteria anaerobic green and purple sulfur bacteria bacteriochlorophylls obligate anaerobes facultative anaerobes Chemosynthetic bacteria Heterotrophic bacteria decomposers respiration and fermentation mucilage (glue-like substance) Heterotrophic aids with: consolidation lithification sedimentation marine snow Nitrogen Fixation and Nitrification Nitrogen fixation: process that converts molecular nitrogen dissolved in seawater to ammonium ion major process that adds new usable nitrogen to the sea only some cyanobacteria and a few archaeons with nitrogenase (enzyme) are capable of fixing nitrogen Symbiotic Bacteria Endosymbiotic theory Chemosynthetic bacteria within tube worms and clams bioluminescent bacteria

3 photophores embedded in the ink sacs of squid Archaea General characteristics small (0.1 to 15 micrometers) prokaryotic extreme conditions formerly considered bacteria differences from bacteria cell walls lack special sugar-amino acid compounds cell membranes contain different lipids Nutritional Types photosynthesizers, chemosynthesizers and heterotrophs most are methanogens Halobacteria bacteriorhodopsins, purple proteins Hyperthermophiles Eukarya plants animals fungi algae protozoa Fungi History of marine mycology marine fungi first discovered in 1849 ecological role is difficult to evaluate important in marine ecosystems eukaryotes with cell walls of chitin Hyphae can branch to produce mycelium heterotrophic decomposers store energy as glycogen 4 phyla: Chytridiomycota Zygomycota Basidiomycota Ascomycota ascomycotes are the most diverse and abundant Ecology and physiology of marine fungi obligately marine or facultatively marine salinity is toxic to fungi most marine fungi live on wood

4 others live on grass, algae, mangroves or sand fungi decompose the chitinous remains of dead crustaceans Reproduction of Marine Fungi Marine yeasts reproduce asexually by budding Filamentous marine fungi reproduce asexually by production of conidiospores on the tips of hyphae Filamentous marine ascomycotes can reproduce sexually by forming an ascocarp Maritime Lichens Lichens: mutualistic associations between a fungus and an alga Stramenopiles A diverse group of eukaryotic organisms unified by the nature of their cells 2 flagella Heterokont Ochrophytes Diatoms Extremely diverse Diatom structure frustule valve 2 basic diatom shapes: radially symmetrical bilaterally symmetrical Diatomaceous sediments Frustules sink and form siliceous oozes accumulations form sedimentary rock diatomaceous earth siliceous oozes account for most of the worlds petroleum reserves Other Ochrophytes Silicoflagellates abundant in cold marine waters skeleton appears internal Pelagophyceans Labyrinthomorphs Labyrinthulids Thraustochytrids Alveolates Recent re-grouping Have alveoli beneath their cell membranes Examples:

5 dinoflagellates ciliates apicomplexans Dinoflagellates globular, unicellular, 2 heterokont flagella Dinosporin unarmored dinoflagellates vs. armored dinoflagellates plates are used to identify different species Alveolates (Dinoflagellates) Dinoflagellate nutrition photosynthetic ones have chlorophylls a and c, beta-carotene and peridinin (a xanthophyll which imparts a golden-brown color) mixotrophic photosynthetic ones supplement photosynthesis by osmotrophy (absorbing nutrients) or phagotrophy (engulfing nutrients) Reproduction in dinoflagellates asexual reproduction by fission sexual reproduction by fusion and meiosis often have dormant stages (cyst formation) Ecological roles of dinoflagellates major component of phytoplankton some are parasites of copepods zooxanthellae photosynthetic zooxanthellae Harmful Algal Blooms (HABs) photosynthetic dinoflagellate population explosion dinoflagellates that cause HABs produce toxins oxygen content of the water may be reduced Alveolates (Ciliates) Ciliates protozoans with cilia Membranelles cytostome planktonic and benthic major links in marine food chains form symbiotic and parasitic relationships Reproduce by binary fission and by conjugation Types of marine ciliates scuticociliates oligotrichs tintinnids Ecological roles most are heterotrophs; some harbor autotrophic symbionts or chloroplasts link hetero- and autotrophic blue-green bacteria to higher levels in the food chain

6 Choanoflagellates Closely related to animals Unicellular or colonial Highly efficient consumers of bacteria Amoeboid Protozoans Pseudopod heterotrophs Most have a test an externally secreted organic membrane often covered with foreign particles or strengthened by mineral secretions Two major phyla: Foraminiferans actinopods radiolarians acantharians heliozoans Foraminiferans branched pseudopods that form reticulopods consume bacteria and diatoms some harbor symbiotic green and red algae and zooxanthellae Foraminiferan test elaborate, multi-chambered tests globigerina ooze Foraminiferans and zooxanthellae zooxanthellae live symbiotically within the cytoplasm of many forams photosynthetic zooxanthellae use foram waste products as nutrients