The importance of the interactions between plants and bacteria is well known for plant development and success of agriculture. A number of succeeded examples are reported in the literature for the improvement of plant yields and protection against pathogens and pests. However, some specific niches where these interactions are essential are still unexplored, like the environments where the agriculture is not practiced due to the harsh conditions found; mangroves and the Brazilian semiarid caatinga. Digging into the bacterial diversity associates to plant growth promotion in such spots can help on the description of new species and features related to the plant growth-promoting rhizobacteria character under harsh tropical conditions. This chapter gives an overview of examples of such niches, where the bacterial community must be adapted to survive and support the plant development. Possible bacterial characteristics related to this ability will be discussed, as the production of biofilms and exopolysaccharides. Furthermore, the application of these biotechnological products will be evaluated and discussed allowing the reader to have a snapshot on this yet nonexplored biodiversity.