Colony Appearance Color

When growing on agar substrate, yeast isolates typically appear as larger opaque ( creamy ) colonies compared with smaller ( pinpoint ) transparent bacterial colonies. Additionally, color development (chromogenesis) provide immediate diagnostic information. For example, Rhodotorula sp. produces a salmon-pink-colored colony on laboratory media. The yeast is believed to be part of native vineyard flora and is occasionally encountered during routine platings. 

Budding represents the most frequendy encountered form of reproduction and, in the case of wet mounts from juice or fermenting wine, the only form that will be seen. Budding of the mother cell initially yields a bud and after separation, the daughter cell. Under ideal conditions for growth (as would be found in commercial yeast production facilities), a single mother cell may bud many times during the cultivation period. However, 

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Sodium molybdate and other molybdenum compounds in toxic baits have potential for termite control (Brill et al. 1987). Baits containing 1000 mg Mo/kg were fatal to 99% of the termite Reticu-litermes flavipes in 48 days. After 8 to 10 days, termites became steel-gray in color, but appeared otherwise normal. Mortality began only after day 16. Termites did not avoid the poisoned bait, even at concentrations of 5000 mg Mo/kg. Yoshimura et al. (1987) reported similar results with another species of termite sodium molybdate killed 100% of the workers in a colony of Copotermes formo-sanus within 24 h after eating filter paper treated with a 5% solution. Some other species of insects — including fire ants (Solenopsis sp.) and various species of beetles and cockroaches — were not affected when exposed to baits containing 5000 mg Mo/kg for 48 days (Brill et al. 1987). 

Many fungi can precipitate reduced forms of metals and metalloids (e.g. elemental silver, selenium, tellurium) within and around fungal cells (Gadd, 2004). The reductive ability of fungi is manifest by the appearance of black coloration of fungal colonies precipitating elemental silver or tellurium, and a red coloration for precipitation of elemental selenium (Gharieb et al., 1999). 

Morphological properties, although crucial in identification, depend (as was the case with yeast) on substrate and other conditions of growth. For example, some molds may appear yeastlike when growing under mi-croaerophilic conditions as would be found in bottled juice. The color of the mold colony is frequently used for preliminary field identification of molds. 

The various types of media used for the presumptive and confirmatory tests for fecal streptococci along with the respective characteristic colors and appearances of the colonies are presented in Table 4.12. However, the two media most commonly used for presumptive fecal streptococci tests are membrane enterococcus (mE) agar and the Kenner Fecal (KF) streptococcus agar, although the mE agar is more selective than the KF streptococcus agar [152]. 

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