Comparing extracellular enzymatic hydrolysis between plain peptides and their corresponding analogs in the northern Gulf of Mexico Mississippi River plume

Abstract

Peptide analogs, such as leucine-methylcoumarinylamide (Leu-MCA) and Lucifer yellow anhydride-tetraalanine (LYA-Ala4), are often used as proxies to quantify extracellular peptidase activities, but how accurately these analogs represent natural peptides remains unclear. Here we compared hydrolysis rates of tetrapeptides alanine-valine-phenylalanine-alanine (AVFA) and tetraalanine (Ala4) with their corresponding LYA analogs along a salinity gradient in the northern Gulf of Mexico Mississippi River plume. Hydrolysis rates were generally similar, but not always, between natural peptides and their analogs in the plume water. For example, hydrolysis rates were similar between LYA-AVFA and AVFA at all stations except one. In contrast, hydrolysis rates of LYA-Ala4 were significantly higher than those of Ala4 at lowsalinity (18-19) stations, but significantly lower at one high-salinity (36) station. These results suggest that relative activities of different types of peptidases, measured by the analogs or peptides, depended on biological and chemical properties at each station, such as abundance of certain "opportuni-trophic" bacteria, including Flavobacterium, Ruegeria and Roseobacter. The produced fragments and amino acids from peptide hydrolysis implied further that the hydrolysis pathway depended on specific peptide substrate, and that the LYA tag affected the hydrolysis pathway. Taken together, this study validates the technique of using LYA analogs to study extracellular enzymatic activities, particularly the overall hydrolysis rate, and provides insights into the patterns of extracellular enzymatic activities in estuarine environments.

Linking Heterotrophic Microbial Activities with Particle Characteristics in Waters of the Mississippi River Delta in the Aftermath of Hurricane Isaac

“…Compared to previous reports from near-shore sites in the Gulf of Mexico, peak peptidase activities at Stn. TE were more than double those measured in Mississippi River plumes in the Atchafalaya Bay (Ammerman and Glover, 2000), and were more than an order of magnitude higher than at other nearby sites affected by Mississippi River plumes (Liu and Liu, 2015). In Pensacola Bay, northwestern Florida, peptidase and glucosidase activity averaged over different times of a year were 165 and 10 nM L −1 , respectively (Murrell, 2003), and thus also considerably lower than peak activities at Station TE.…”

“…Factors that may drive differences in bacterial community structure and activities at the investigated sites include differences in freshwater influence due to the location of the three sites relative to the river mouth (Liu and Liu, 2015). It is also possible that bacterial community structure and function is influenced by the chronic oil leakage from the sunken Taylor Energy platform near Stn.…”

Differentiating the role of different-sized microorganisms in peptide decomposition during incubations using size-fractioned coastal seawater

“…In addition, peptide analogs with large fluorophores cannot be taken up directly by microbes, so the measured rates do not include uptake, which may be significant in certain scenarios (Liu et al, 2013). In contrast, studies with small peptides without fluorogenic tags can provide information on their hydrolysis and microbial decomposition rates in a more realistic way, and the hydrolyzed fragments of small peptides can also be used to pinpoint the hydrolysis pathway (Kirchman and Hodson, 1984;Liu et al, 2013;Liu et al, 2010;Liu and Liu, 2015;Liu and Liu, 2014;Mulholland and Lee, 2009). The decomposition pathways of small peptides include both extracellular hydrolysis with subsequent uptake for further metabolism and direct uptake for intracellular hydrolysis (Cunha, 2010;Payne and Smith, 1994;Weiss et al, 1991).…”

A streamlined method to quantify the fates of 15N in seawater samples amended with 15N‐labeled organic nitrogen

“…15 N‐tetrapeptide alanine‐valine‐phenylalanine‐alanine ( 15 N‐AVFA; C 20 H 30 15 N 4 O 5 ; synthesized by CS Bio Co.) was used for the 2016 incubation experiment. AVFA is a fragment of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO), and decomposition and hydrolysis of AVFA in coastal waters have been well studied (e.g., Liu et al ; Liu and Liu , , ). This study quantifies uniquely the fate of amino acid‐N and peptide‐N incubation in incubation experiments.…”