Chitin primary production

Smucker, Richard A.

doi:10.1016/0305-1978(91)90052-2

Cited by 31 publications

(27 citation statements)

References 25 publications

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“…Chitin is the most abundant polymer in the ocean and serves as an enormous reservoir of organic carbon and nitrogen. Diatoms have traditionally been excluded from considerations of chitin production (27,59). Our work suggests that diatoms are likely larger contributors to this organic reservoir than previously thought.…”

Section: Discussionmentioning

confidence: 64%

Chitin in Diatoms and Its Association with the Cell Wall

2009

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Chitin is a globally abundant polymer widely distributed throughout eukaryotes that has been well characterized in only a few lineages. Diatoms are members of the eukaryotic lineage of stramenopiles. Of the hundreds of diatom genera, two produce long fibers of chitin that extrude through their cell walls of silica. We identify and describe here genes encoding putative chitin synthases in a variety of additional diatom genera, indicating that the ability to produce chitin is more widespread and likely plays a more central role in diatom biology than previously considered. Diatom chitin synthases fall into four phylogenetic clades. Protein domain predictions and differential gene expression patterns provide evidence that chitin synthases have multiple functions within a diatom cell. Thalassiosira pseudonana possesses six genes encoding three types of chitin synthases. Transcript abundance of the gene encoding one of these chitin synthase types increases when cells resume division after short-term silicic acid starvation and during short-term limitation by silicic acid or iron, two nutrient conditions connected in the environment and known to affect the cell wall. During long-term silicic acid starvation transcript abundance of this gene and one additional chitin synthase gene increased at the same time a chitin-binding lectin localized to the girdle band region of the cell wall. Together, these results suggest that the ability to produce chitin is more widespread in diatoms than previously thought and that a subset of the chitin produced by diatoms is associated with the cell wall.Chitin is the most abundant polymer in the ocean and the second most abundant polymer on earth, exceeded only by cellulose (see, for example, references 1, 16, and 27). The pervasiveness of chitin is attributed to its use by diverse eukaryotic organisms, including fungi, insects, mollusks, crustaceans, algae, and protists. These diverged lineages commonly use chitin to strengthen their cell walls or skeletons. Chitin synthase is used by all chitin-producing organisms to generate the ␤-(134)-linked N-acetylglucosamine polymers. The universality of this enzyme suggests an ancient eukaryotic origin (54). Chitin synthases are identified by the conserved amino acid motifs QXXEY, EDR, QXRRW, and additional lineage specific motifs that together are responsible for substrate specificity and reaction catalysis (38,54). Chitin synthases are embedded across the cell membrane, and it is at the membrane junction that N-acetylglucosamine monomers are added to a growing polymer while it is transported across the membrane (55). While maintaining these general features, chitin synthases have also diverged and diversified within and between eukaryotic lineages. These enzymes have been most extensively studied within fungi where sequence phylogenies identify two major divisions of chitin synthases, with additional classes within these divisions. Phylogenetically distinct chitin synthases produce chitin at different cellular locations and for different biol...

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Section: Discussionmentioning

confidence: 64%

Chitin in Diatoms and Its Association with the Cell Wall

2009

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Section: Discussionmentioning

confidence: 99%

“…The diatoms are known to produce chitin (SMUCKER, 1991) and take up and incorporate a chitin precursor (NEDOMA et al, 1994). The enzymes may enable the diatoms to acquire N-acetylglucosamine from ambient amino sugars instead of by the de novo synthesis described by SMUCKER (1991). Considering the energy demands of chitin primary production by diatoms (SMUCKER, 1991), the ability to acquire N-acetylglucosamine from an ambient pool of dissolved organic carbon may be of great ecological advantage (VRBA et al, 1996a).…”

Section: Discussionmentioning

confidence: 99%

“…The enzymes may enable the diatoms to acquire N-acetylglucosamine from ambient amino sugars instead of by the de novo synthesis described by SMUCKER (1991). Considering the energy demands of chitin primary production by diatoms (SMUCKER, 1991), the ability to acquire N-acetylglucosamine from an ambient pool of dissolved organic carbon may be of great ecological advantage (VRBA et al, 1996a). On the other hand, peaks of low-affinity -N-acetylhexosaminidase in the metalimnion (VRBA 1992;VRBA et al, 1997) or during diatom bloom decay may also result from massive bacterial occupation of decaying diatom cells.…”

Section: Discussionmentioning

confidence: 99%

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Are Bacteria the Major Producers of Extracellular Glycolytic Enzymes in Aquatic Environments?

Vrba

Callieri

Bittl

et al. 2004

International Review of Hydrobiology

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In aquatic microbial ecology, it has been considered that most extracellular enzymes except phosphatases are of bacterial origin. We tested this paradigm by evaluating the relationship between bacterial cell number and the activity of three glycolytic enzymes from 17 fresh waters and also from a laboratory experiment. Our large sets of pooled data do not seem to support such a simple explanation, because we found only a weak correlation of bacterial number with activity of α-glucosidase (r s = 0.63), -glucosidase (r s = 0.45), and -N-acetylhexosaminidase (r s = 0.44). We also tested relations of the enzymatic activities to potential sources of natural substrates: dissolved organic carbon (DOC) and phytoplankton (as chlorophyll a). Their correlations with the enzymatic activities tested were very weak or insignificant. On the other hand, we found evidence for distinct producers of extracellular enzymes by analysing enzyme kinetics. The kinetics usually did not follow the simple Michaelis-Menten model but a more complex one, indicating a mixture of two enzymes with distinct affinity to a substrate. In combination with size fractionation, we could sometimes even distinguish three or more different enzymes. During diatom blooms, the diatom biomass tightly correlated with -N-acetylhexosaminidase activity (> 4 µm fraction). We also documented very tight relationships between activity of both glucosidases and dry weight of Daphnia longispina (r s = 1.0 and 0.60 for α-and -glucosidases, respectively) in an alpine clear-water lake. Our data and evidence from other studies indicate that extracellular glycosidic activities in aquatic ecosystems cannot generally be assigned only to bacteria. Also invertebrate animals and other eukaryotes (fungi, diatoms, protozoa etc.) should be considered as potentially very important enzyme producers.

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“…They both contain a phytoplankton component as indicated Mid-Atlantic Bight Small-particle POM "Detritus" and "Phytoplankton" by the presence of chlorophyll and the fatty acid distributions (Wakeham and Canuel, 1988 and sources therein). The presence of chitin in both large and small particles may indicate a grazer population existing in both size classes, though it must be mentioned that chitin also exists in certain phytoplankton Smucker, 1991) and, as chitan, has been found to compose up to 34% of the cell biomass in Thalassiosira weissflogii (Smucker, 1991, and references therein). Inspection of the average spectra (Fig.…”

Section: Discussionmentioning

confidence: 99%

Compositional heterogeneity within oceanic POM : a study using flow cytometry and mass spectrometry

Minor¹

1998

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This thesis applied direct temperature-resolved mass spectrometry (DT-MS), flow cytometry, and multivariate statistics to the study of marine particulate organic matter (POM) collected from the North Atlantic.DT-MS is an important asset to marine organic geochemistry as a single two minute analysis (with 16 eV, EI* ionization) provides information on polysaccharides, proteins, and lipids within concentrated and desalted samples. Although the molecularlevel information obtained with DT-MS is less detailed than traditional analyses of specific compound classes, DT-MS can act as a useful molecular-level screening technique (as illustrated in this thesis), indicating what samples and compound classes to investigate more thoroughly.In addition to its rapidity, DT-MS only reqires microgram quantities of sample. This sensitivity permits the coupling of DT-MS and preparative flow cytometry. In this thesis, preparative flow cytometry was used to isolate "phytoplankton" and "detritus" (i.e., non-phytoplankton particles) in 2-+53 gm POM. The molecular-level differences between and within small-particle POM (<53 gm), large-particle POM (>53 pm), "phytoplankton" and "detritus" were explored using DT-MS and discriminant analysis. For POM collected from the Mid-Atlantic Bight and from Great Harbor, Woods Hole, MA, small-particle POM contained more phytoplankton chemical characteristics than large-particle POM. In Great Harbor, the molecular-level characteristics of large-particle POM indicated a significant grazer biomass component. On the MAB (in March 1996), the large-particle POM appeared more phytodetrital. "Phytoplankton" was enriched in protein, chlorophyll and lipids as compared to "detritus," which was enriched in selected polysaccharides.As the polysaccharide composition of POM subclasses was a major source of variation, polysaccharides in selected samples were further studied using ammonia and deuterated ammonia CI*DT-MS. Principal component analysis of the resulting NH 3 -CI* spectra indicated that the majority of polysaccharide variation in the selected samples could be explained by a component that appeared related to the degree of degradation of the organic matter.The results from this thesis, coupled with existing work on particulate and dissolved organic matter, were used to support a modified "size-reactivity continuum model" of organic matter cycling. Thesis Supervisor: Timothy EglintonTo my parents, "Uncle Ben," and the old Venture AknowledgementsThis thesis would never have been finished without the help of a great many people. I would like to thank my advisor Tim Eglinton for introducing me to the field, giving me free reign with lots of instruments, and convincing me to do more than I thought I could. Thanks to my committe members are also in order. Without Rob Olson's expertise, the flow cytometer might be in even more pieces today than it was when I started. Jaap Boon's perspective as a mass spectrometrist helped greatly in the interpretation of DT-MS data. Phil Gschwend's inciteful questions ha...

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Chitin primary production

Cited by 31 publications

References 25 publications

Chitin in Diatoms and Its Association with the Cell Wall

Chitin in Diatoms and Its Association with the Cell Wall

Are Bacteria the Major Producers of Extracellular Glycolytic Enzymes in Aquatic Environments?

Compositional heterogeneity within oceanic POM : a study using flow cytometry and mass spectrometry

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