Blakeslea trispora is a mould and member of the division Zygomycota. This species has been well studied for its ability to produce carotenoids, particularly, β-carotene and lycopene. β-carotene is a vitamin A precursor and both of β-carotene and lycopene play a significant role in the inhibition of oxidative stress. Blakeslea trispora is commonly isolated from soil samples throughout the Southern United States and Southern Asia. B. trispora is a pathogen of tropical plants. In vivo pathogenicity testing using animal models suggests this fungus is not a cause of animal or human disease.
History
The genus Blakeslea was named in honor of American botanist Albert Francis Blakeslee based on B. trispora. While A.F. Blakeslee was studying another fungus called Botrytis rileyi, he collaborated with Roland Thaxter to further study this fungus. In 1914, while Thaxter was doing further research on Botrytis rileyi, Blakeslea trispora was accidentally isolated from a contaminated caterpillar infected with Botrytis rileyi. Blakeslea trispora was first identified from the larvae of the caterpillar, which was growing on the cowpea plant. The caterpillar was infected by the fungus Botrytis rileyi; however, Blakeslea trispora was thought to be incidentally transferred to the diseased caterpillar feeding on a cowpea flower. When Thaxter first identified B. trispora, he considered B. trispora to be very closely related to the genus Choanephora because of highly similar sporangiospore morphology. Both have a distinctive brown colour with faint, longitudinal striations on the sporangiole wall. The shape of the large spherical heads of their sporangiola are also similar. However, Choanephora and Blakeslea are considered to be distinct genera and can be distinguishable by the spore wall and its separation from the sporangiole wall. Species of Choanephora have highly adherent sporangiole wall in contrast to Blakeslea species where the sporangiole wall is readily separable from the underlying spore at maturity.
Growth and morphology
Blakeslea trispora undergoes both sexual and asexual reproduction. The asexual reproductive phase of Blakeslea trispora involves the production of sporangiospores produced in sporangia. Once released, they can germinate in the presence of free water. Colonies of B. trispora grow rapidly on the agar growth media at 25 °C. They are white at first but become yellow to pale brown and very dark brown as they mature. The hyphae of B. trispora are aseptate, very dense, and highly branched. Sexual reproduction is by the formation of zygospores, which contain high concentrations of triglycerol-rich lipids and phosphatidylcholine. Zygospores can persist for long periods of time, and their germination is dependent on a cytoplasmic regulatory system that sustains dormancy and forestalls germination in the presence of unfavorable growth conditions. Zygospores range in size from 40-80μm. They are spherical or slightly flattened in shape. Blakeslea trispora has a heterothallic mating system, having (+) and (-) mating types. Contact and interchange between the opposite mating types is a necessary precursor to induce sexual reproduction and development of zygospores. Extensions called gametangia are formed from each of the compatible haploid mycelia. Following anastomosis, a fertile heterokaryotic zygosporangium is formed within which the zygospores develop. During sexual reproduction, carotenoid pigments are produced by both of mating type. Carotenoids are precursors of many apocarotenoids that contain very important sex-specific precursors, trisporic acid (TSA) for the sexual reproduction of Blakeslea trispora. Carotenes produced from carotenoids are further processed by carotene oxygenase to synthesize trisporic acid (TSA). TSA produced from carotene stimulates both sexually complementary cells to make contact with each other. TSA is considered an important signalling molecule for the initiation and control sexual reproduction.