The Metabolism of Streptomyces avermitilis Isolated from Agricultural Soils During the Four Seasons of the Year

Streptomyces avermitilis is a soil actinobacterium and has a complex metabolism in its natural habitat. Because of this, the environmental fluctuations present in the seasons can activate or silence the biosynthetic pathways involved in its metabolism. The objective of this research was to analyze the morphological characteristics of the metabolism of Streptomyces avermitilis, isolated during the four seasons of the year and from four types of soil. Isolation was performed on oat agar ISP-3 and nystatin as an antifungal agent. The planting methods were rod drag and cross striations. The Petri dishes were incubated for 10 days at 30 °C in complete darkness. For 10 days, a colony count was performed to analyze the growth curves, as was an evaluation of the diffusible pigments in each Petri dish. The isolates presented the diffusible pigments white, yellow, orange, red and pink with a higher proportion in spring and summer compared to in autumn and winter. Under laboratory conditions, the isolates in summer presented the three phases of bacterial growth: lag (24 h), exponential (48–96 h) and stationary (120–168 h). A doubling time of 35.30–62.92 h was obtained. The morphological characteristics of the metabolism of Streptomyces avermitilis show differences according to the climatic conditions of each season of the year.