Drilling fluids or muds are provided for the drilling of a borehole into an earth formation. The drilling fluid or mud may be used for drilling oil and/or natural gas wells in subterranean reservoirs. In some embodiments, the fluid is formed from an additive comprising lignin and at least one biosurfactant produced by at least one strain of bacteria capable of biosurfactant production.

The present invention relates to the field of industrial fermentation. In particular, it relates to method for producing a protein of interest from a Bacillus host cell comprising the steps of inoculating a fermentation medium with a Bacillus host cell comprising an expression construct for a gene encoding a protein of interest, cultivating the Bacillus host cell in said fermentation medium under conditions conducive for the growth of the Bacillus host cell and the expression of the protein of interest for a cultivation phase, wherein the cultivation of the Bacillus host cell during said cultivation phase comprises the addition of at least one feed solution and wherein the at least one feed solution provides a carbon source, and separating portions from said Bacillus host cell culture during the cultivation phase at different time points and obtaining the protein of interest from said portions.