Active systems, ensembles of active particles capable of expending energy at the individual level to produce motion or other forms of mechanical work, are present at all scales in biology. Bacteria are a paradigmatic example of such out-of-equilibrium systems, as they can convert chemical energy into motion through structures such as pili or flagella. Active turbulence is one possible state of collective motion exhibited by species of elongated and flagellated bacteria. Their rod-shaped bodies promote nematic alignment, leading to a so-called active nematics where nematic order is disrupted by the turbulent motion of topological defects. A crucial ingredient to produce such collective motion is the effect of the fluid surrounding the bacteria.