facultative

Similarly the saphrophytes are classed as obligatory saphrophytes and facultative parasites.

If a parasite cannot exist outside animal tissues, it is an obligatory parasite; if it can, it is a facultative saphrophyte.

I have seen this particularly in those cases where facultative divergence also was greater than usual.

Moreover, the extent of the "facultative" divergence attainable by prisms shows a considerable latitude.

(b) Both saprophytic and facultative parasitic bacteria agree in requiring non-concentrated food.