Determinative Factors of Competitive Advantage between Aerobic Bacteria for Niches at the Air-Liquid Interface

Abstract

We focused on bacterial interspecies relationships at the air-liquid interface where the formation of pellicles by aerobes was observed. Although an obligate aerobe (Brevibacillus sp. M1-5) was initially dominant in the pellicle population, a facultative aerobe (Pseudoxanthomonas sp. M1-3) emerged and the viability of M1-5 rapidly decreased due to severe competition for oxygen. Supplementation of the medium with carbohydrates allowed the two species to coexist at the air-liquid interface. These results indicate that the population dynamics within pellicles are primarily governed by oxygen utilization which was affected by a combination of carbon sources.Key words: multispecies interaction, resource competition, air-liquid interface, pellicleIt has been widely recognized that most microorganisms have lifestyles specifically adapted to heterogeneous environments, such as solid surfaces and air-liquid interfaces. At these interfacial surfaces, various substances accumulate or are concentrated and consequently serve as biologicallyactive sites where microorganisms are thought to actively compete for space and resources (16,18,21,23). Interspecies relationships within biofilms on solid surfaces have been reported (3,11,15). Although the ubiquity of the airliquid surface in both natural and artificial environments is also well recognized (22), microbiological studies on the airliquid interface have been limited. Microbial aggregation at the air-liquid interface forms what is known as a pellicle, which is a strategy displayed by various aerobic microorganisms as it enables them to acquire oxygen effectively. Therefore, pellicles are considered advantageous to aerobic bacteria for acquiring niches at the air-liquid interface. Pellicles of acetic acid bacteria (2), Bacillus sp. (1, 10), and Pseudomonas sp. (17, 19) have been studied morphologically and physiologically under pure culture conditions. However, microbiological analyses of pellicles composed of multiple bacterial species have not been reported.We have previously demonstrated the stable co-culture of four bacterial species grown under static aerobic conditions in which pellicles were observed (6, 8). Among the members, an obligate aerobe, Brevibacillus sp. strain M1-5 and a facultative aerobe, Pseudoxanthomonas sp. strain M1-3, were both pellicle-forming species and stably coexisted in the four-species mixed culture. However, the growth of M1-5 was inhibited by M1-3 in two-species co-cultures (9). Since the pellicle is the sole niche for M1-5, it is expected that these interspecies interactions at the air-liquid interface determined the microbial population of the pellicle. In this study, we attempted to clarify the competitive relationships for niches at the air-liquid interface. Effects of the composition of the gaseous phase and growth medium on the interaction between the obligate aerobe M1-5 and facultative aerobe M1-3 were investigated by viability testing and microscopic analysis.The two species used in this study were isolated from a cellulose-degradin...

Interspecies Interaction between <i>Pseudomonas aeruginosa</i> and Other Microorganisms

“…Pellicles are known as microbial aggregations at the interface between air and liquid, and various aerobic microorganisms form pellicles to acquire oxygen effectively (142, 144). This kind of aggregation enables several bacterial species to coexist (40, 53–55, 144). According to these reports, an anaerobic cellulolytic bacterium Clostridium straminisolvens CSK1 could coexist in a multispecies culture including two pellicle-forming bacteria, obligate aerobe Brevibacillus sp.…”

Motility, Chemotaxis and Aerotaxis Contribute to Competitiveness during Bacterial Pellicle Biofilm Development

“…and Pseudoxanthomonas sp. at the air-liquid interface [22]. In P. aeruginosa , decreased availability of oxygen in the atmosphere has been shown to be detrimental to pellicle integrity, and provision of an alternative electron acceptor in the medium promoted growth in the liquid phase below the pellicle [23].…”

Laboratory Evolution of Microbial Interactions in Bacterial Biofilms

“…However, biofilm formation may also be triggered as a competitive or defensive response against other strains or species (13). In addition, the structured environment of biofilms creates gradients of nutrients that potentiate the competition for limiting resources, resulting in exploitative competition between cohabiting species (14).…”