Vitzilaiou Eirini, Aunsbjerg Stina D, Mahyudin N A, Knøchel Susanne
Laboratory of Microbiology and Fermentation, Department of Food Science, University of Copenhagen, Copenhagen, Denmark.
Department of Food Service and Management, Faculty of Food Science and Technology, Universiti Putra Malaysia, Serdang, Malaysia.
Front Microbiol. 2020 May 5;11:816. doi: 10.3389/fmicb.2020.00816. eCollection 2020.
Filamentous yeast species belonging to the closely related and were recently found to dominate biofilm communities on the retentate and permeate surface of Reverse Osmosis (RO) membranes used in a whey water treatment system after CIP (Cleaning-In-Place). Microscopy revealed that the two filamentous yeast species can cover extensive areas due to their large cell size and long hyphae formation. Representative strains from these species were here further characterized and displayed similar physiological and biochemical characteristics. Both strains tested were able to grow in twice RO-filtrated permeate water and metabolize the urea present. Little is known about the survival characteristics of these strains. Here, their tolerance toward heat (60, 70, and 80°C) and Ultraviolet light (UV-C) treatment at 255 nm using UV-LED was assessed as well as their ability to form biofilm and withstand cleaning associated stress. According to the heat tolerance experiments, the D°C of and is 16.37 min and 7.24 min, respectively, while a reduction of 3.5 to >4.5 log (CFU/mL) was ensured within 5 min at 70°C. UV-C light at a dose level 10 mJ/cm had little effect, while doses of 40 mJ/cm and upward ensured a ≥4log reduction in a static laboratory scale set-up. The biofilm forming potential of one filamentous yeast and one budding yeast, , both isolated from the same biofilm, was compared in assays employing flat-bottomed polystyrene microwells and peg lids, respectively. In these systems, employing both nutrient rich as well as nutrient poor media, only the filamentous yeast was able to create biofilm. However, on RO membrane coupons in static systems, both the budding yeast and a filamentous yeast were capable of forming single strain biofilms and when these coupons were exposed to different simulations of CIP treatments both the filamentous and budding yeast survived these. The dominance of these yeasts in some filter systems tested, their capacity to adhere and their tolerance toward relevant stresses as demonstrated here, suggest that these slow growing yeasts are well suited to initiate microbial biofouling on surfaces in low nutrient environments.
最近发现，属于密切相关的丝状酵母物种在就地清洗（CIP）后的乳清水处理系统中使用的反渗透（RO）膜的截留物和渗透物表面上主导生物膜群落。显微镜检查显示，这两种丝状酵母物种由于其大的细胞尺寸和长的菌丝形成，可以覆盖广泛的区域。来自这些物种的代表性菌株在此进一步表征，并显示出相似的生理和生化特征。测试的两种菌株都能够在经过两次RO过滤的渗透水中生长并代谢其中存在的尿素。关于这些菌株的存活特性知之甚少。在此，评估了它们对热（60、70和80°C）和使用UV-LED在255nm处的紫外线（UV-C）处理的耐受性，以及它们形成生物膜和承受与清洗相关的压力的能力。根据耐热性实验，[具体物种1]和[具体物种2]的D°C分别为16.37分钟和7.24分钟，而在70°C下5分钟内可确保减少3.5至＞4.5 log（CFU/mL）。剂量水平为10 mJ/cm²的UV-C光影响很小，而40 mJ/cm²及以上的剂量在静态实验室规模设置中可确保减少≥4log。分别在使用平底聚苯乙烯微孔板和栓盖的试验中比较了从同一生物膜中分离出的一种丝状酵母和一种出芽酵母[具体出芽酵母物种]的生物膜形成潜力。在这些系统中，使用营养丰富和营养贫乏的培养基，只有丝状酵母能够形成生物膜。然而，在静态系统中的RO膜试片上，出芽酵母和丝状酵母都能够形成单菌株生物膜，并且当这些试片暴露于不同的CIP处理模拟时，丝状酵母和出芽酵母都能在这些处理中存活下来。如在此所证明的，这些酵母在一些测试的过滤系统中的优势、它们的粘附能力以及它们对相关压力的耐受性表明，这些生长缓慢的酵母非常适合在低营养环境中的表面上引发微生物生物污垢。
