HISTOPHILUS SOMNI CAUSES RESPIRATORY AND MANY OTHER DISEASES IN CATTLE. HOWEVER, THESE BACTERIA ALSO LIVE NORMALLY IN HOST MUCOSAL SITES, SUCH AS THE UPPER RESPIRATORY TRACT OR GENITAL TRACT, WITHOUT CAUSING DISEASE. H. SOMNI IS KNOWN AS AN OPPORTUNISTIC PATHOGEN, OR ONE THAT CAUSES DISEASE WHEN THE HOST IS STRESSED, WEAKENED, OR IS SUFFERING FROM ANOTHER INFECTION. BACTERIAL FACTORS THAT CONTRIBUTE TO DISEASE (VIRULENCE FACTORS) ENABLE H. SOMNI TO RESIST HOST DEFENSES, AND MOST OR ALL OF THESE FACTORS HAVE BEEN IDENTIFIED. FORMATION OF AN H. SOMNI BIOFILM, A LARGE COMMUNITY OF BACTERIA LIVING WITHIN A MATRIX OF MATERIAL COMPOSED OF POLYSACCHARIDES, DNA, AND PROTEINS, IS KNOWN TO OCCUR IN HOST TISSUES. THE GENES THAT ARE RESPONSIBLE FOR MAKING THESE VIRULENCE FACTORS HAVE ALSO BEEN IDENTIFIED. HOWEVER, IT IS NOW WELL ESTABLISHED THAT DIFFERENT FACTORS ARE PRODUCED ON THE BACTERIA DEPENDING ON WHERE IN THE HOST THE BACTERIA ARE RESIDING: THE LOWER RESPIRATORY TRACT, THE UPPER RESPIRATORY TRACT, THE BLOODSTREAM, JOINTS, ETC. SELECTIVE EXPRESSION OF DIFFERENT FACTORS AT DIFFERENT TIMES OR IN DIFFERENT HOST SITES INDICATES THAT EXPRESSION OF THE GENES FOR THESE VIRULENCE FACTORS IS HIGHLY REGULATED; IN OTHER WORDS THE EXPRESSION (MANUFACTURING) OF THESE FACTORS CA BE TURNED ON OR OFF. HOWEVER, NO WORK HAS BEEN REPORTED ON GENE REGULATION IN H. SOMNI. SMALL, NON-CODING (DO NOT PRODUCE A FUNCTIONAL PROTEIN) RNAS (SRNA) AND THE SRNA CHAPERONE HFQ (MUST BIN TO SRNA TO MAKE THEM FUNCTION) ARE GLOBAL REGULATORS; H. SOMNI HAS AT LEAST 94 SRNA AND HFQ. OUR HYPOTHESIS IS THAT SRNA AND HFQ REGULATE EXPRESSION OF MANY CRITICAL VIRULENCE FACTORS IN H. SOMNI. IDENTIFYING THESE SRNA, THE GENES THEY REGULATE, AND GENERATING MUTANT STRAINS LACKING OR OVER-EXPRESSING ONE OR MORE OF THESE FACTORS WILL ENABLE THE DESIGN OF IMPROVED VACCINES AND THERAPEUTICS. OUR AIMS ARE TO: 1) IDENTIFY H. SOMNI SRNA THAT BIND TO HFQ BY CAPTURING HFQ WITH ANTIBODIES TO HFQ AND DETERMINING WHICH SRNA ARE PRESENT BY SEQUENCING; 2) MUTATE HFQ IN A VIRULENT STRAIN OF H. SOMNI AND DETERMINE HOW THE VIRULENCE FACTORS HAVE CHANGED, AND IF THE MUTANT IS NO LONGER ABLE TO CAUSE DISEASE IN A BOVINE MODEL OF RESPIRATORY DISEASE; 3) OVER-EXPRESS SRNAS IN A VIRULENT H. SOMNI STRAIN TO DETERMINE WHETHER THIS MUTANT MAKES MORE OR LESS OF SEVERAL VIRULENCE FACTORS, INCLUDING BIOFILM, AND IF THEY CAN CAUSE MORE OR LESS DISEASE IN CATTLE. THIS PROJECT IS HIGHLY RELEVANT BECAUSE THE RESULTING INFORMATION AND/OR MUTANTS GENERATED MAY RESULT IN AN IMPROVED VACCINE OR THERAPEUTICS, WHICH CAN PREVENT PRODUCTION OF IMPORTANT VIRULENCE FACTORS RATHER THAN USE OF ANTIBIOTICS.