| Abstract
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Greenhouse evaporative cooling pads are frequently attacked by the growth of diverse microorganisms. Those microorganisms which are composed of cyanobacteria or diatoms form biological film layer entities known as biofilms. The degradation and blocking effects wrought on the pads by these biofilms markedly reduce their efficiency, lifespan and increase maintenance cost on the stakeholders. Samples of biofilms from evaporative cooling pads were collected from different locations in Saudi Arabia: King Fahd University of Petroleum & Minerals (KFUPM) Greenhouse, Dhahran, Al-Rasheed Farm in Dhurma, Sara Farm in Al-Kharj, Riyad and Municipality Greenhouse (DMG), Dammam. Evaporative cooling water from the various greenhouses was assessed for pH and Conductivity using PS-2102 and PS-2116 Sensors respectively. Water quality examination revealed elevated total dissolved solids (TDS) for all the greenhouses with the exception of Dhahran greenhouse. The origin of the elevated TDS is due to hardness of the ground water used for evaporative cooling in those greenhouses. The TDS values of 2641 ppm (conductivity, 5282 μS/cm) for Al-Rasheed, 2327.5 ppm (conductivity, 4655 μS/cm) for Sara and 3352 ppm (conductivity, 6704 μS/cm) for DMG at 25°C were recorded. Light Microscopy, Scanning Electron Microscopy (SEM) and QWIN software were used to reveal different morphometric parameters for the characterization of cyanobacteria and diatoms within the biofilm samples collected from those greenhouses. Molecular analysis for sample collected from KFUPM was carried out using PCR amplification of 16S rRNA gene sequences; CYA359F and CYA781R were used as cyanobacteria-specific primers while GM5F in combination with the reverse primer 907R were used for the domain bacteria. Cyanobacterial phylogenetic tree was constructed using the nearest neighbor alignment method embedded in the RDP software. Our results indicate the occurrence of various genera of cyanobacteria and diatom including; Phormidium, Oscillatoria, Lyngbya, Navicula, Melosira and Gomphonema. However, we observed limited occurrence and distribution of diatoms on evaporated pads compared to cyanobacteria. This may be ascribed to the water quality and the extent of light exposure of the various sites, and the ability of cyanobacteria to grow under low light intensity and elevated TDS. Phylogenetic analysis of nucleic acid sequences of sample taken from KFUPM greenhouse No. 3 has revealed 14 novel sequences of cyanobacteria which hitherto have never been identified before. This finding further stresses the importance of exploring the existence of novel species of cyanobacteria that are restricted in their living to such unique niche.
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