  An optimal control problem associated to the Keller-Segel with logistic
reaction system will be studied in $2D$ domains. The control acts in a bilinear
form only in the chemical equation. The existence of optimal control and a
necessary optimality system are deduced.
  The main novelty is that control can be rather singular and the state (cell
density $u$ and the chemical concentration $v$) remains only in a weak setting,
which is not usual in the literature to solve optimal control problems subject
to chemotaxis models (see e.g. Guill\'en-Gonz\'alez et al. ESAIM Control Optim.
Calc. Var. 26 (2020), Paper No. 29, 21 pp).
