Nutrient-Rich Microhabitats within Biofilms Are Synchronized with the External Environment

Abstract

The nutrient ion concentrations in the interstitial waters of biofilms (BFs) formed on reed and stone surfaces were investigated in the northern and southern basins of Lake Biwa over several years. The following were observed for both types of BF: 1) Concentrations of ammonium, nitrate, nitrite, and phosphate ions were much (hundreds to thousands of times) higher in the BFs than in the surrounding lake water; 2) the concentration of ions, especially nitrate ions, in the BFs changed seasonally, being higher from winter to spring and lower from summer to autumn, synchronizing with the changes in the lake water; 3) dissolved-form N:P ratios were higher in the lake water than BFs; and 4) the bacterial flora of the BFs differed from that of the lake water, with smaller seasonal variations. The present study reveals for the first time that the inside of BFs in a natural environment is rich in nutrient ions and shows similar seasonal changes as the lake water. The BFs in an aquatic environment provide a microenvironment capable of sustaining a specific bacterial flora different from that in the surrounding lake water.Key words: biofilm, nutrient ions, bacterial flora, Lake Biwa Microbial biofilms (BFs) are ubiquitous in aquatic environments and perform important environmental functions, including nutrient recycling (2, 5, 27) and purification of pollutants (8,14,15). Natural BFs are generally composed of a variety of microbes and their secretory products, such as extracellular polymeric substances (EPS). The EPS-containing matrix confers on the constituent microbes certain advantages over their free-living counterparts (16,17). An important advantage is the ability to trap and retain dissolved nutrients through an entrapment mechanism that has been proposed (4, 7, 11) and proven (9) to depend on ion exchange processes.However, few studies have been conducted on the nutrient conditions inside BFs formed in natural environments over a long period of observation. Therefore, the present study was designed to compare over several years the concentrations of various nutrient ions in the interstitial waters of BFs and the surrounding lake water. An additional aim was to examine the relationship between the nutrient conditions and bacterial flora inside the BFs. Moreover, the BFs formed on reed and stone surfaces were compared, to clarify the influences of the substratum surfaces.Here, we report for the first time that the nutrient conditions in a BF and in the surrounding water are significantly different with respect to concentrations of ions, particularly nitrate ions, while exhibiting similar seasonal variations. The relationships among the nutrient conditions, bacterial flora constitution, and the physicochemical properties of the BFs are discussed. Materials and Methods Study area and samplingLake Biwa is located in the central part of the Japanese Archipelago (Lat. 35°15' N, Long. 136°05' E). The lake has a surface area of 670 km 2 and a total storage volume of 2.75×10 10 m 3 , consisting of two basins that differ in wa...

Response of heterotrophic stream biofilm ­communities to a gradient of resources

“…The dramatic in crease in EEA may also be linked to differential rates of enzyme expression related to changes in bacterial community composition (Martinez et al 1996). Thus, although the present study lacked the resolution to differentiate between several possible underlying mechanisms, heterotrophic biofilm development is highly responsive to the availability of resources, effectively storing (Tsuchiya et al 2009) and cycling available resources. Ultimate limits are probably imposed by physicochemical constraints such as shear strength and diffusion gradients (Battin et al 2003, Besemer et al 2007) -conditions likely to be found in biofilms in later successional stages rather than in the communities, described in the present study, that developed in 3 wk.…”

“…These results suggest that turnover in biofilms is a result of internal cycling supported by biofilm structural and community responses to enrichment. Structurally, increased biofilm thickness protects extracellular enzymes from being washed out of the system by downstream flow, and it allows biofilms to concentrate nutrients (Tsuchiya et al 2009) and energy-yielding materials (Battin et al 1999) -which are dispersed in planktonic communities. This protection probably also encourages the production of extracellular enzymes by quorum sensing (DeAngelis et al 2008, Decho et al 2010, diffusion sensing (Redfield 2002), or efficiency sensing (Hense et al 2007), which occur when concentrations of small, energy-inexpensive signal molecules reach threshold levels, inducing the transcription of large, energy-expensive extracellular enzymes.…”

Electric Charge Characteristics of Biofilms Formed on Various Surfaces

“…Biofilm is generally defined as an aggregate of microbes that formed on the surfaces [1][2][3][4]. These microbial aggregates have been found almost in all aquatic ecosystems from fresh water until ocean.…”

“…The matrix of biofilms was indicated as a highly hydrated matrix (interstitial water content up to 98%) [9,10]. The previous study showed that the concentrations of nutrient ions in the interstitial water of biofilms are hundreds to thousands of times greater than surrounding water [2,4]. These particular nutrient-rich environments inside the biofilm matrices are established from a very early stage of biofilm formation [7].…”

“…These particular nutrient-rich environments inside the biofilm matrices are established from a very early stage of biofilm formation [7]. The adsorption of nutrient ions from the surroundings to the biofilm is suggested to form this nutrient-rich environment [2,4]. …”