Abstract: Recombinant microorganisms which produce non-adaptive proteins in a mixed, microbiologically competitive environment and which utilize a selective substrate are disclosed as field application vectors.

Abstract: Liquid (13, 13a) within a vessel (12, 12a) which receives an inflow is maintained at a predetermined level (43) by discharging liquid as necessary to compensate for the inflow. Discharge flow is drawn from below the surface (18) of the liquid to avoid clogging from scum or from other undesirable effects of surface draw off. Intake structure (34) for the discharge pump (33, 33a) has a branched flow path (47) that includes a first inlet (48) situated above the predetermined level, a second inlet (49) situated below the predetermined level and a flow junction (51) through which both inlets are communicated with the discharge pump, the junction being at the predetermined liquid level. If the liquid rises above the flow junction, the pump draws liquid through the second, subsurface inlet. If the liquid surface recedes below the flow junction, the pump aspirates air or other gas through the first inlet. Consequently liquid level is stabilized at the elevation of the flow junction.