I found some popular articles (e.g. nbcnews and iflscience) that bacteria can "see," but I highly doubt it's in the same way as people do just from looking at the limitations in the vision of small animals like insects. So what exactly are bacteria capable of "seeing" or what are the limitations of their vision?
Simple answer is that many simple organisms, including bacteria, carry light-sensitive molecules. One example is halorhodopsin (not bacterial but archaeic). This is a molecule, light-gated ion pump, that reacts to light, thus allowing organism to react to photons by changing concentration of certain ions inside the cell.
Study from Stanford described similar molecule found in bacteria.
In conclusion, if by "vision" you understand ability to react to light in the visible part of the spectrum, then a lot of organisms possess such ability. However, they lack other crutial parts of human vision.
Because bacteria are extremely small, the principles of optics prevent them from having lenses or other organs capable of determining the direction from which light is incident. On the other hand, an entire spherical bacterium can potentially act as a lens, concentrating light from a given direction onto a corresponding position on the opposite side of the bacterium, and thus forming a very crude image. Bacteria are certainly capable of responding to the frequency of incident light, if they contain molecules that selectively absorb light in specific frequency ranges. And, they should be able to respond to the brightness or intensity of incident light, if those molecules return to their normal state shortly after absorbing a photon. Of course, additional molecular machinery would need to be present in a bacterium to translate absorption of a photon into any sort of meaningful response.
I'm surprised at the focus on light in all these answers! To my knowledge, light is absolutely not the way that some 'bacteria' may be able to see.
Try looking on youtube for a macrophage (white blood cell) chasing down a bacteria.
You can see it actually following the bacteria - it's crazy. How on earth does it know where it is?
Chemical signalling, of course!! Sort of like a neurotransmitter. They secrete chemicals and follow the trail - it could be really simple, such as, the transmitter converts to something else once it comes into contact with a phospholipid (of course indicating a cell membrane). I haven't researched that bit, but I hope it will allow you to direct your own train of thought/research.
Macrophages also have things called 'Toll-Like Receptor' proteins on their membranes, and they produce these things called 'pseudopods' that are essentially feelers/protrusions of the cell membrane. The Toll Like Receptor proteins recognise antigens by detecting Pathogen Associated Molecular Patterns that are common on the surface of pathogens/non-self objects (funnily enough). This is how your most basic innate immune system works- if the TLR protein on the pseudopod (wavy, baddie-finding arms) comes into contact with something it recognises as 'bad', it binds to it and draws it in for the white blood cell to engulf.
But it doesn't actually destroy/digest it at that point, because the TLR protein isn't perfect and sometimes there's some friendly-fire. A T Cell (I think T-Helper) comes along and 'double checks' that the macrophage hasn't picked up a friendly object. If it HAS picked up a friendly object, the T Cell will actually kill the macrophage for its mistake (usually).
OMG FRED, WHAT HAVE YOU DONE
Or at least that's how I like to imagine it goes down.