There are concerns that it will decrease the biodiversity within a species. people are also worried that because the genome of a species undergoes such rapid alteration, the outcomes, including health issues, ability to transfer between species/organisms and mutation rate, are undiscovered-unknown territory. There are fears that transgenic bacteria may be able to acquire antibiotic resistance, or that tolerance that is transferred to one species could be passed on to others. This is a great concern for the health and safety of humans and the environment. Despite these concerns, it is mainly all just theoretical risks, nothing is proven, and until Genetic engineering is tried and tested- it will be impossible to tell if these concerns will eventuate.