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A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. Possible combinations areare photo- and chemotrophy, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic. They can take advantage of different environmental conditions. If a trophic mode is obligate, then it is always necessary for sustaining growth and maintenance; if facultative, it can be used as a supplemental source.〔 Some organisms have incomplete Calvin cycles, so they are incapable of fixing carbon dioxide and must use organic carbon sources. ==Types of Mixotrophy== Organisms may employ mixotrophy obligately or facultatively. *Obligate mixotrophy: in order to support growth and maintenance, an organism must utilize both heterotrophic and autotrophic means. *Obligate autotrophy with facultative heterotrophy: Autotrophy alone is sufficient for growth and maintenance, but heterotrophy may be used as a supplementary strategy when autotrophic energy is not enough, for example, when light intensity is low. *Facultative autotrophy with obligate heterotrophy: Heterotrophy is sufficient for growth and maintenance, but autotrophy may be used to supplement, for example, when prey availability is very low. *Facultative mixotrophy: Maintenance and growth may be obtained by heterotrophic or autotrophic means alone, and mixotrophy is used only when necessary. In order to characterize the sub-domains within mixotrophy, several very similar categorization schemes have been suggested. Consider the example of a marine protist with heterotrophic and photosynthetic capabilities: In the breakdown put forward by Jones, there are four mixotrophic groups based on relative roles of phagotrophy and phototrophy. *A: Heterotrophy (phagotrophy) is the norm, and phototrophy is only used when prey concentrations are limiting. *B: Phototrophy is the dominant strategy, and phagotrophy is employed as a supplement when light is limiting. *C: Phototrophy results in substances for both growth and ingestion, phagotrophy is employed when light is limiting. *D: Phototrophy is most common nutrition type, phagotrophy only used during prolonged dark periods, when light is extremely limiting. An alternative scheme by Stoeker also takes into account the role of nutrients and growth factors, and includes mixotrophs who have a photosynthetic symbiont or who retain chloroplasts from their prey. This scheme characterizes mixotrophs by their efficiency. * Type 1: "Ideal Mixotrophs" who utilize prey and sunlight equally well * Type 2: Supplement phototrophic activity with food consumption * Type 3: Primarily heterotrophic, use phototrophic activity during times of very low prey abundance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mixotroph」の詳細全文を読む スポンサード リンク
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