Culture-to-culture physical interactions causes the alteration in red and infrared light stimulation of Escherichia coli growth rate.

Escherichia coli MC1061 cells were irradiated at 660 and 900 nm, incubated in M9 and LB media with the use of a specially constructed device, and assayed for growth rate. There was a reduction of growth rate stimulation when the irradiated culture was cultivated jointly with the non-irradiated one. In the same time, the irradiated culture extended the invigorate effect on the non-irradiated one. It is proposed that the effects observed were mediated by culture-to-culture physical interactions.