Seasonal Dynamics ofBacterial Colonization ofCottonFiber andEffects ofMoisture on GrowthofBacteria within theCotton Boll

A highly replicated 3-year field study was conducted todetermine theseasonal patterns ofbacterial colonization ofcotton fiber fromthetimeofdehiscence ofthebolls (the point atwhichthebolls justbegin to open)through harvest andcommercial ginning. Bacterial numberson fibersamples from16plots were determined by dilution pour plating withtryptic soy agarcontaining cycloheximide, and numbersof gram-negative bacteria were determined byplating on tryptic soyagarcontaining vancomycin andcycloheximide. Populations ofbacteria varied fromyeartoyear,butinallthree seasonsthepattern ofcolonization was generally apattern consisting ofarapid increase following opening ofthebolls anda more orlessstable number thereafter throughout thegrowing season.Gram-negative bacteria accountedfor50% or more ofthe recoverable bacterial population. We hypothesized thattheluxuriant bacterial flora developed asaresult ofthe availability ofsufficient freewaterinthebollstoallowbacterial proliferation withthecarbonsources remaining afterfibermaturation. Therefore, laboratory experiments were conducted todetermine the threshold moisture level allowing growth ofbacteria onfiber inthebolls. Bacterial proliferation occurred when aslittle as2% moisture was addedtoair-dried fiber. Using simulated bolls, we demonstrated bacterial growth resulting fromdewformation on fiber heldincontrolled-humidity chambers.