  Chemotaxis is a fundamental mechanism of cells and organisms, which is
responsible for attracting microbes to food, embryonic cells into developing
tissues, or immune cells to infection sites. Mathematically chemotaxis is
described by the Patlak--Keller--Segel model. This macroscopic system of
equations is derived from the microscopic model when limiting behaviour is
studied. However, on taking the limit and passing from the microscopic
equations to the macroscopic equations, fluctuations are neglected. Perturbing
the system by a Gaussian random field restitutes the inherent randomness of the
system. This gives us the motivation to study the classical
Patlak--Keller--Segel system perturbed by random processes.
  We study a stochastic version of the classical Patlak--Keller--Segel system
under homogeneous Neumann boundary conditions on an interval
$\mathcal{O}=[0,1]$. In particular, let $\mathcal{W}_1$, $\mathcal{W}_2$ be two
time-homogeneous spatial Wiener processes over a filtered probability space
$\mathfrak{A}$. Let $u$ and $v$ denote the cell density and concentration of
the chemical signal. We investigate the coupled system \begin{align*} & d {u} -
( r_u\Delta u- \chi {\rm div }( u\nabla v) )\, dt =u\circ d\mathcal{W}_1, \\ &
d{v} -(r_v \Delta v -\alpha v)\, dt = \beta u \, dt+ v\circ d\mathcal{W}_2,
\end{align*} with initial conditions $(u(0),v(0))=(u_0,v_0)$. The positive
terms $r_u$ and $r_v$ are the diffusivity of the cells and chemoattractant,
respectively, the positive value $\chi$ is the chemotactic sensitivity,
$\alpha\ge0$ is the so-called damping constant. The noise is interpreted in the
Stratonovich sense. Given $T>0$, we will prove the existence of a martingale
solution on $[0,T]$.
