diff --git a/Cargo.toml b/Cargo.toml
index 94797d3..32b0248 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "frag_gene_scan_rs"
-version = "0.3.1"
+version = "0.3.2"
 authors = ["Felix Van der Jeugt <felix.vanderjeugt@ugent.be>"]
 edition = "2018"
 
diff --git a/src/bin/FragGeneScanRs.rs b/src/bin/FragGeneScanRs.rs
index 29b5f59..b513443 100644
--- a/src/bin/FragGeneScanRs.rs
+++ b/src/bin/FragGeneScanRs.rs
@@ -180,30 +180,74 @@ fn run<R: Read + Send, W: Write + Send>(
     let aastream = aastream.map(Mutex::new);
     let metastream = metastream.map(Mutex::new);
     let dnastream = dnastream.map(Mutex::new);
-    fasta::Reader::new(inputseqs)
-        .into_records()
+    Chunked::new(100, fasta::Reader::new(inputseqs).into_records())
         .par_bridge()
-        .map(|record| {
-            let fasta::OwnedRecord { mut head, seq } = record?;
-            head = head.into_iter().take_while(u8::is_ascii_graphic).collect();
-            let nseq: Vec<Nuc> = seq.into_iter().map(Nuc::from).collect();
-            let read_prediction = viterbi(
-                &global,
-                &locals[count_cg_content(&nseq)],
-                head,
-                nseq,
-                whole_genome,
-            );
+        .map(|recordvec| {
+            let mut metabuf = Vec::new();
+            let mut dnabuf = Vec::new();
+            let mut aabuf = Vec::new();
+            for record in recordvec {
+                let fasta::OwnedRecord { mut head, seq } = record?;
+                head = head.into_iter().take_while(u8::is_ascii_graphic).collect();
+                let nseq: Vec<Nuc> = seq.into_iter().map(Nuc::from).collect();
+                let read_prediction = viterbi(
+                    &global,
+                    &locals[count_cg_content(&nseq)],
+                    head,
+                    nseq,
+                    whole_genome,
+                );
+                if metastream.is_some() {
+                    read_prediction.meta(&mut metabuf)?;
+                }
+                if dnastream.is_some() {
+                    read_prediction.dna(&mut dnabuf, formatted)?;
+                }
+                if aastream.is_some() {
+                    read_prediction.protein(&mut aabuf, whole_genome)?;
+                }
+            }
             if let Some(metastream) = &metastream {
-                read_prediction.print_meta(&mut *metastream.lock().unwrap())?; // TODO lock together content
+                metastream.lock().unwrap().write_all(&metabuf)?;
             }
             if let Some(dnastream) = &dnastream {
-                read_prediction.print_dna(&mut *dnastream.lock().unwrap(), formatted)?;
+                dnastream.lock().unwrap().write_all(&dnabuf)?;
             }
             if let Some(aastream) = &aastream {
-                read_prediction.print_protein(whole_genome, &mut *aastream.lock().unwrap())?;
+                aastream.lock().unwrap().write_all(&aabuf)?;
             }
             Ok(())
         })
         .collect()
 }
+
+struct Chunked<I: Iterator> {
+    size: usize,
+    iterator: I,
+}
+
+impl<I: Iterator> Chunked<I> {
+    fn new(size: usize, iterator: I) -> Self {
+        Chunked { size, iterator }
+    }
+}
+
+impl<I: Iterator> Iterator for Chunked<I> {
+    type Item = Vec<I::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut items = Vec::with_capacity(self.size);
+        for _ in 0..self.size {
+            if let Some(item) = self.iterator.next() {
+                items.push(item);
+            } else {
+                break;
+            }
+        }
+        if items.is_empty() {
+            None
+        } else {
+            Some(items)
+        }
+    }
+}
diff --git a/src/gene.rs b/src/gene.rs
index a00cd87..972c9bb 100644
--- a/src/gene.rs
+++ b/src/gene.rs
@@ -1,7 +1,3 @@
-use std::fs::File;
-use std::io;
-use std::io::Write;
-
 extern crate thiserror;
 use thiserror::Error;
 
@@ -21,30 +17,26 @@ impl ReadPrediction {
         }
     }
 
-    pub fn print_meta(&self, file: &mut File) -> Result<(), GeneError> {
+    pub fn meta(&self, buf: &mut Vec<u8>) -> Result<(), GeneError> {
         if !self.genes.is_empty() {
-            file.write_all(&format!(">{}\n", std::str::from_utf8(&self.head)?).into_bytes())?;
+            buf.append(&mut format!(">{}\n", std::str::from_utf8(&self.head)?).into_bytes())
         }
         for gene in &self.genes {
-            gene.print_meta(file)?;
+            gene.meta(buf);
         }
         Ok(())
     }
 
-    pub fn print_dna(&self, file: &mut File, formatted: bool) -> Result<(), GeneError> {
+    pub fn dna(&self, buf: &mut Vec<u8>, formatted: bool) -> Result<(), GeneError> {
         for gene in &self.genes {
-            gene.print_dna(file, &self.head, formatted)?;
+            gene.dna(buf, &self.head, formatted)?;
         }
         Ok(())
     }
 
-    pub fn print_protein<W: Write>(
-        &self,
-        whole_genome: bool,
-        file: &mut W,
-    ) -> Result<(), GeneError> {
+    pub fn protein(&self, buf: &mut Vec<u8>, whole_genome: bool) -> Result<(), GeneError> {
         for gene in &self.genes {
-            gene.print_protein(file, &self.head, whole_genome)?;
+            gene.protein(buf, &self.head, whole_genome)?;
         }
         Ok(())
     }
@@ -63,9 +55,9 @@ pub struct Gene {
 }
 
 impl Gene {
-    pub fn print_meta(&self, file: &mut File) -> Result<(), GeneError> {
-        file.write_all(
-            &format!(
+    pub fn meta(&self, buf: &mut Vec<u8>) {
+        buf.append(
+            &mut format!(
                 "{}\t{}\t{}\t{}\t{:.6}\tI:{}\tD:{}\n",
                 self.metastart,
                 self.end,
@@ -82,16 +74,10 @@ impl Gene {
                     .collect::<String>()
             )
             .into_bytes(),
-        )?;
-        Ok(())
+        );
     }
 
-    pub fn print_dna(
-        &self,
-        file: &mut File,
-        head: &Vec<u8>,
-        formatted: bool,
-    ) -> Result<(), GeneError> {
+    pub fn dna(&self, buf: &mut Vec<u8>, head: &Vec<u8>, formatted: bool) -> Result<(), GeneError> {
         let dna: Vec<u8> = match (self.forward_strand, formatted) {
             (true, true) => self.dna.iter().map(|&n| u8::from(n)).collect(),
             (true, false) => self
@@ -110,8 +96,8 @@ impl Gene {
                 .collect(),
         };
 
-        file.write_all(
-            &format!(
+        buf.append(
+            &mut format!(
                 ">{}_{}_{}_{}\n{}\n",
                 std::str::from_utf8(head)?,
                 self.start,
@@ -120,14 +106,14 @@ impl Gene {
                 std::str::from_utf8(&dna)?,
             )
             .into_bytes(),
-        )?;
+        );
 
         Ok(())
     }
 
-    pub fn print_protein<W: Write>(
+    pub fn protein(
         &self,
-        file: &mut W,
+        buf: &mut Vec<u8>,
         head: &Vec<u8>,
         whole_genome: bool,
     ) -> Result<(), GeneError> {
@@ -167,8 +153,8 @@ impl Gene {
             }
         }
 
-        file.write_all(
-            &format!(
+        buf.append(
+            &mut format!(
                 ">{}_{}_{}_{}\n{}\n",
                 std::str::from_utf8(head)?,
                 self.start,
@@ -177,15 +163,13 @@ impl Gene {
                 std::str::from_utf8(&protein)?,
             )
             .into_bytes(),
-        )?;
+        );
         Ok(())
     }
 }
 
 #[derive(Error, Debug)]
 pub enum GeneError {
-    #[error("could not write to file")]
-    IoError(#[from] io::Error),
     #[error("could not convert header back to UTF-8")]
     Utf8Error(#[from] std::str::Utf8Error),
 }