Can Proteobacteria and Burkholderiales being Gram-negative (thin cell wall) be easily destroyed by antimicrobial producing Gram-positive genera for instance Actinobacteria and Salinospora in soil?
The scarcity of nutrition often leads to the competitive growth among microbes. Production of antibiotics to kill other food competitors is a well-known strategy for bacterial survival. However, soil is enriched with vast nutrients and solid-semisolid-brittle in nature with controlled moisture. So, complete eradication of gram negatives may not be possible due to un-uniformed nutrient/antibiotic transport into the microbe cells present throughout the soil.
"Thin" cell wall is largely irrelevant. Gram negative bacteria - esp. the many of the Burkholderia spp.- are highly resistant to antimicrobials, synthetic and antibiotic, via biofilm, efflux pumps etc.